easy chemical energy experiments

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Science project, chemical energy in a bottle.

Grade Level: Elementary Type: Physical Science

To demonstrate chemical energy.

Questions Research:

What are some examples of chemical changes?

Chemical energy is a form of potential energy stored in matter when atoms join together to form chemical compounds. It can be released when matter undergoes a chemical change. The food that you eat provides your body with chemical potential energy and helps your body function. What else can chemical energy do?

• 1 liter bottle
• Plastic spoon
• 4 spoonfuls of vinegar
• 1 level spoonful of baking soda

Experimental Procedure:

• After putting on your goggles, carefully pour the vinegar into the bottle.
• Using the funnel, carefully pour the baking soda into the balloon.
• Without spilling any of the baking soda into the bottle, put the balloon neck around the bottle neck.
• Once the balloon is in place, lift the balloon up and shake the baking soda into the vinegar. Observe what happens. What kind of energy was released?

Now that you know how baking soda and vinegar react, make a Ziplock Bag Explosion !

Terms/Concepts: Energy; Potential energy; Chemical energy

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72 Easy Science Experiments Using Materials You Already Have On Hand

Because science doesn’t have to be complicated.

If there is one thing that is guaranteed to get your students excited, it’s a good science experiment! While some experiments require expensive lab equipment or dangerous chemicals, there are plenty of cool projects you can do with regular household items. We’ve rounded up a big collection of easy science experiments that anybody can try, and kids are going to love them!

Easy Chemistry Science Experiments

Easy physics science experiments, easy biology and environmental science experiments, easy engineering experiments and stem challenges.

1. Taste the Rainbow

Teach your students about diffusion while creating a beautiful and tasty rainbow! Tip: Have extra Skittles on hand so your class can eat a few!

Learn more: Skittles Diffusion

2. Crystallize sweet treats

Crystal science experiments teach kids about supersaturated solutions. This one is easy to do at home, and the results are absolutely delicious!

Learn more: Candy Crystals

3. Make a volcano erupt

This classic experiment demonstrates a chemical reaction between baking soda (sodium bicarbonate) and vinegar (acetic acid), which produces carbon dioxide gas, water, and sodium acetate.

Learn more: Best Volcano Experiments

4. Make elephant toothpaste

This fun project uses yeast and a hydrogen peroxide solution to create overflowing “elephant toothpaste.” Tip: Add an extra fun layer by having kids create toothpaste wrappers for plastic bottles.

5. Blow the biggest bubbles you can

Add a few simple ingredients to dish soap solution to create the largest bubbles you’ve ever seen! Kids learn about surface tension as they engineer these bubble-blowing wands.

Learn more: Giant Soap Bubbles

6. Demonstrate the “magic” leakproof bag

All you need is a zip-top plastic bag, sharp pencils, and water to blow your kids’ minds. Once they’re suitably impressed, teach them how the “trick” works by explaining the chemistry of polymers.

Learn more: Leakproof Bag

7. Use apple slices to learn about oxidation

Have students make predictions about what will happen to apple slices when immersed in different liquids, then put those predictions to the test. Have them record their observations.

Learn more: Apple Oxidation

8. Float a marker man

Their eyes will pop out of their heads when you “levitate” a stick figure right off the table! This experiment works due to the insolubility of dry-erase marker ink in water, combined with the lighter density of the ink.

Learn more: Floating Marker Man

9. Discover density with hot and cold water

There are a lot of easy science experiments you can do with density. This one is extremely simple, involving only hot and cold water and food coloring, but the visuals make it appealing and fun.

Learn more: Layered Water

10. Layer more liquids

This density demo is a little more complicated, but the effects are spectacular. Slowly layer liquids like honey, dish soap, water, and rubbing alcohol in a glass. Kids will be amazed when the liquids float one on top of the other like magic (except it is really science).

Learn more: Layered Liquids

11. Grow a carbon sugar snake

Easy science experiments can still have impressive results! This eye-popping chemical reaction demonstration only requires simple supplies like sugar, baking soda, and sand.

Learn more: Carbon Sugar Snake

12. Mix up some slime

Tell kids you’re going to make slime at home, and watch their eyes light up! There are a variety of ways to make slime, so try a few different recipes to find the one you like best.

13. Make homemade bouncy balls

These homemade bouncy balls are easy to make since all you need is glue, food coloring, borax powder, cornstarch, and warm water. You’ll want to store them inside a container like a plastic egg because they will flatten out over time.

Learn more: Make Your Own Bouncy Balls

14. Create eggshell chalk

Eggshells contain calcium, the same material that makes chalk. Grind them up and mix them with flour, water, and food coloring to make your very own sidewalk chalk.

Learn more: Eggshell Chalk

15. Make naked eggs

This is so cool! Use vinegar to dissolve the calcium carbonate in an eggshell to discover the membrane underneath that holds the egg together. Then, use the “naked” egg for another easy science experiment that demonstrates osmosis .

Learn more: Naked Egg Experiment

16. Turn milk into plastic

This sounds a lot more complicated than it is, but don’t be afraid to give it a try. Use simple kitchen supplies to create plastic polymers from plain old milk. Sculpt them into cool shapes when you’re done!

17. Test pH using cabbage

Teach kids about acids and bases without needing pH test strips! Simply boil some red cabbage and use the resulting water to test various substances—acids turn red and bases turn green.

Learn more: Cabbage pH

18. Clean some old coins

Use common household items to make old oxidized coins clean and shiny again in this simple chemistry experiment. Ask kids to predict (hypothesize) which will work best, then expand the learning by doing some research to explain the results.

Learn more: Cleaning Coins

19. Pull an egg into a bottle

This classic easy science experiment never fails to delight. Use the power of air pressure to suck a hard-boiled egg into a jar, no hands required.

Learn more: Egg in a Bottle

20. Blow up a balloon (without blowing)

Chances are good you probably did easy science experiments like this when you were in school. The baking soda and vinegar balloon experiment demonstrates the reactions between acids and bases when you fill a bottle with vinegar and a balloon with baking soda.

21 Assemble a DIY lava lamp

This 1970s trend is back—as an easy science experiment! This activity combines acid-base reactions with density for a totally groovy result.

22. Explore how sugary drinks affect teeth

The calcium content of eggshells makes them a great stand-in for teeth. Use eggs to explore how soda and juice can stain teeth and wear down the enamel. Expand your learning by trying different toothpaste-and-toothbrush combinations to see how effective they are.

Learn more: Sugar and Teeth Experiment

23. Mummify a hot dog

If your kids are fascinated by the Egyptians, they’ll love learning to mummify a hot dog! No need for canopic jars , just grab some baking soda and get started.

24. Extinguish flames with carbon dioxide

This is a fiery twist on acid-base experiments. Light a candle and talk about what fire needs in order to survive. Then, create an acid-base reaction and “pour” the carbon dioxide to extinguish the flame. The CO2 gas acts like a liquid, suffocating the fire.

25. Send secret messages with invisible ink

Turn your kids into secret agents! Write messages with a paintbrush dipped in lemon juice, then hold the paper over a heat source and watch the invisible become visible as oxidation goes to work.

Learn more: Invisible Ink

26. Create dancing popcorn

This is a fun version of the classic baking soda and vinegar experiment, perfect for the younger crowd. The bubbly mixture causes popcorn to dance around in the water.

27. Shoot a soda geyser sky-high

You’ve always wondered if this really works, so it’s time to find out for yourself! Kids will marvel at the chemical reaction that sends diet soda shooting high in the air when Mentos are added.

Learn more: Soda Explosion

28. Send a teabag flying

Hot air rises, and this experiment can prove it! You’ll want to supervise kids with fire, of course. For more safety, try this one outside.

Learn more: Flying Tea Bags

29. Create magic milk

This fun and easy science experiment demonstrates principles related to surface tension, molecular interactions, and fluid dynamics.

Learn more: Magic Milk Experiment

30. Watch the water rise

Learn about Charles’s Law with this simple experiment. As the candle burns, using up oxygen and heating the air in the glass, the water rises as if by magic.

Learn more: Rising Water

31. Learn about capillary action

Kids will be amazed as they watch the colored water move from glass to glass, and you’ll love the easy and inexpensive setup. Gather some water, paper towels, and food coloring to teach the scientific magic of capillary action.

Learn more: Capillary Action

32. Give a balloon a beard

Equally educational and fun, this experiment will teach kids about static electricity using everyday materials. Kids will undoubtedly get a kick out of creating beards on their balloon person!

Learn more: Static Electricity

33. Find your way with a DIY compass

Here’s an old classic that never fails to impress. Magnetize a needle, float it on the water’s surface, and it will always point north.

Learn more: DIY Compass

34. Crush a can using air pressure

Sure, it’s easy to crush a soda can with your bare hands, but what if you could do it without touching it at all? That’s the power of air pressure!

35. Tell time using the sun

While people use clocks or even phones to tell time today, there was a time when a sundial was the best means to do that. Kids will certainly get a kick out of creating their own sundials using everyday materials like cardboard and pencils.

Learn more: Make Your Own Sundial

36. Launch a balloon rocket

Grab balloons, string, straws, and tape, and launch rockets to learn about the laws of motion.

37. Make sparks with steel wool

All you need is steel wool and a 9-volt battery to perform this science demo that’s bound to make their eyes light up! Kids learn about chain reactions, chemical changes, and more.

Learn more: Steel Wool Electricity

38. Levitate a Ping-Pong ball

Kids will get a kick out of this experiment, which is really all about Bernoulli’s principle. You only need plastic bottles, bendy straws, and Ping-Pong balls to make the science magic happen.

39. Whip up a tornado in a bottle

There are plenty of versions of this classic experiment out there, but we love this one because it sparkles! Kids learn about a vortex and what it takes to create one.

Learn more: Tornado in a Bottle

40. Monitor air pressure with a DIY barometer

This simple but effective DIY science project teaches kids about air pressure and meteorology. They’ll have fun tracking and predicting the weather with their very own barometer.

Learn more: DIY Barometer

41. Peer through an ice magnifying glass

Students will certainly get a thrill out of seeing how an everyday object like a piece of ice can be used as a magnifying glass. Be sure to use purified or distilled water since tap water will have impurities in it that will cause distortion.

Learn more: Ice Magnifying Glass

42. String up some sticky ice

Can you lift an ice cube using just a piece of string? This quick experiment teaches you how. Use a little salt to melt the ice and then refreeze the ice with the string attached.

Learn more: Sticky Ice

43. “Flip” a drawing with water

Light refraction causes some really cool effects, and there are multiple easy science experiments you can do with it. This one uses refraction to “flip” a drawing; you can also try the famous “disappearing penny” trick .

Learn more: Light Refraction With Water

44. Color some flowers

We love how simple this project is to re-create since all you’ll need are some white carnations, food coloring, glasses, and water. The end result is just so beautiful!

45. Use glitter to fight germs

Everyone knows that glitter is just like germs—it gets everywhere and is so hard to get rid of! Use that to your advantage and show kids how soap fights glitter and germs.

Learn more: Glitter Germs

46. Re-create the water cycle in a bag

You can do so many easy science experiments with a simple zip-top bag. Fill one partway with water and set it on a sunny windowsill to see how the water evaporates up and eventually “rains” down.

Learn more: Water Cycle

47. Learn about plant transpiration

Your backyard is a terrific place for easy science experiments. Grab a plastic bag and rubber band to learn how plants get rid of excess water they don’t need, a process known as transpiration.

Learn more: Plant Transpiration

48. Clean up an oil spill

Before conducting this experiment, teach your students about engineers who solve environmental problems like oil spills. Then, have your students use provided materials to clean the oil spill from their oceans.

Learn more: Oil Spill

49. Construct a pair of model lungs

Kids get a better understanding of the respiratory system when they build model lungs using a plastic water bottle and some balloons. You can modify the experiment to demonstrate the effects of smoking too.

Learn more: Model Lungs

50. Experiment with limestone rocks

Kids  love to collect rocks, and there are plenty of easy science experiments you can do with them. In this one, pour vinegar over a rock to see if it bubbles. If it does, you’ve found limestone!

Learn more: Limestone Experiments

51. Turn a bottle into a rain gauge

All you need is a plastic bottle, a ruler, and a permanent marker to make your own rain gauge. Monitor your measurements and see how they stack up against meteorology reports in your area.

Learn more: DIY Rain Gauge

52. Build up towel mountains

This clever demonstration helps kids understand how some landforms are created. Use layers of towels to represent rock layers and boxes for continents. Then pu-u-u-sh and see what happens!

Learn more: Towel Mountains

53. Take a play dough core sample

Learn about the layers of the earth by building them out of Play-Doh, then take a core sample with a straw. ( Love Play-Doh? Get more learning ideas here. )

Learn more: Play Dough Core Sampling

54. Project the stars on your ceiling

Use the video lesson in the link below to learn why stars are only visible at night. Then create a DIY star projector to explore the concept hands-on.

Learn more: DIY Star Projector

55. Make it rain

Use shaving cream and food coloring to simulate clouds and rain. This is an easy science experiment little ones will beg to do over and over.

Learn more: Shaving Cream Rain

56. Blow up your fingerprint

This is such a cool (and easy!) way to look at fingerprint patterns. Inflate a balloon a bit, use some ink to put a fingerprint on it, then blow it up big to see your fingerprint in detail.

57. Snack on a DNA model

Twizzlers, gumdrops, and a few toothpicks are all you need to make this super-fun (and yummy!) DNA model.

Learn more: Edible DNA Model

58. Dissect a flower

Take a nature walk and find a flower or two. Then bring them home and take them apart to discover all the different parts of flowers.

59. Craft smartphone speakers

No Bluetooth speaker? No problem! Put together your own from paper cups and toilet paper tubes.

Learn more: Smartphone Speakers

60. Race a balloon-powered car

Kids will be amazed when they learn they can put together this awesome racer using cardboard and bottle-cap wheels. The balloon-powered “engine” is so much fun too.

Learn more: Balloon-Powered Car

61. Build a Ferris wheel

You’ve probably ridden on a Ferris wheel, but can you build one? Stock up on wood craft sticks and find out! Play around with different designs to see which one works best.

Learn more: Craft Stick Ferris Wheel

62. Design a phone stand

There are lots of ways to craft a DIY phone stand, which makes this a perfect creative-thinking STEM challenge.

63. Conduct an egg drop

Put all their engineering skills to the test with an egg drop! Challenge kids to build a container from stuff they find around the house that will protect an egg from a long fall (this is especially fun to do from upper-story windows).

Learn more: Egg Drop Challenge Ideas

64. Engineer a drinking-straw roller coaster

STEM challenges are always a hit with kids. We love this one, which only requires basic supplies like drinking straws.

Learn more: Straw Roller Coaster

65. Build a solar oven

Explore the power of the sun when you build your own solar ovens and use them to cook some yummy treats. This experiment takes a little more time and effort, but the results are always impressive. The link below has complete instructions.

Learn more: Solar Oven

66. Build a Da Vinci bridge

There are plenty of bridge-building experiments out there, but this one is unique. It’s inspired by Leonardo da Vinci’s 500-year-old self-supporting wooden bridge. Learn how to build it at the link, and expand your learning by exploring more about Da Vinci himself.

Learn more: Da Vinci Bridge

67. Step through an index card

This is one easy science experiment that never fails to astonish. With carefully placed scissor cuts on an index card, you can make a loop large enough to fit a (small) human body through! Kids will be wowed as they learn about surface area.

68. Stand on a pile of paper cups

Combine physics and engineering and challenge kids to create a paper cup structure that can support their weight. This is a cool project for aspiring architects.

Learn more: Paper Cup Stack

69. Test out parachutes

Gather a variety of materials (try tissues, handkerchiefs, plastic bags, etc.) and see which ones make the best parachutes. You can also find out how they’re affected by windy days or find out which ones work in the rain.

Learn more: Parachute Drop

70. Recycle newspapers into an engineering challenge

It’s amazing how a stack of newspapers can spark such creative engineering. Challenge kids to build a tower, support a book, or even build a chair using only newspaper and tape!

Learn more: Newspaper STEM Challenge

71. Use rubber bands to sound out acoustics

Explore the ways that sound waves are affected by what’s around them using a simple rubber band “guitar.” (Kids absolutely love playing with these!)

Learn more: Rubber Band Guitar

72. Assemble a better umbrella

Challenge students to engineer the best possible umbrella from various household supplies. Encourage them to plan, draw blueprints, and test their creations using the scientific method.

Learn more: Umbrella STEM Challenge

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• Heat Experiments
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• 150 Science Experiments

Carbon sugar snake

Create a growing carbon sugar snake with simple ingredients. A science activity for the adults to try that demonstrates combustion & chemistry for kids.

Make a cloud in a jar

Learn how to make a cloud in a jar with easy to get materials. An effective demonstration of why clouds form and simple to do!

Hot air expands demonstration

A classic demonstration of hot air rising! Easy to do and highly visual.

Rising water experiment

Learn about air pressure with the classic rising water experiment! You just need a candle, some water, a glass and a plate to do this activity

Colourful currents

A colourful density experiment

It's all about heat!

Science and cooking via Baked Alaska

Learn about insulation by cooking!

Yummy science :)

What Freezes first… Hot or Cold Water?

Experiment with a weird result

Learn about energy within a liquid

Endothermic reaction

Use only pantry ingredients!

Reactions that get colder!

Make honeycomb

Heat can break bonds

Science you can eat!

Pizza box solar oven

Control the Sun's rays

Get cooking!

Lemon juice Christmas cards

Just add heat!

Christmas chemistry

Make A Simple Thermometer

Uses household materials

Thermal expansion of liquids

Microwave soap

Why does this happen?

Get adult help please!

Dry ice + spoons

Good vibrations

Adult help please

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68 Best Chemistry Experiments: Learn About Chemical Reactions

Whether you’re a student eager to explore the wonders of chemical reactions or a teacher seeking to inspire and engage your students, we’ve compiled a curated list of the top 68 chemistry experiments so you can learn about chemical reactions.

While the theories and laws governing chemistry can sometimes feel abstract, experiments bridge the gap between these concepts and their tangible manifestations. These experiments provide hands-on experiences illuminating the intricacies of chemical reactions, molecular structures, and elemental properties.

1. Covalent Bonds

By engaging in activities that demonstrate the formation and properties of covalent bonds, students can grasp the significance of these bonds in holding atoms together and shaping the world around us.

Learn more: Covalent Bonds

2. Sulfuric Acid and Sugar Demonstration

Through this experiment, students can develop a deeper understanding of chemical properties, appreciate the power of chemical reactions, and ignite their passion for scientific exploration.

3. Make Hot Ice at Home

Making hot ice at home is a fascinating chemistry experiment that allows students to witness the captivating transformation of a liquid into a solid with a surprising twist.

4. Make a Bouncing Polymer Ball

This hands-on activity not only allows students to explore the fascinating properties of polymers but also encourages experimentation and creativity.

Learn more: Thought Co

5. Diffusion Watercolor Art

This experiment offers a wonderful opportunity for students to explore the properties of pigments, observe how they interact with water, and discover the mesmerizing patterns and textures that emerge.

Learn more: Diffusion Watercolor Art

6. Exploding Baggie

The exploding baggie experiment is a captivating and dynamic demonstration that students should engage in with caution and under the supervision of a qualified instructor.

Learn more: Exploding Baggie

7. Color Changing Chemistry Clock

This experiment not only engages students in the world of chemical kinetics but also introduces them to the concept of a chemical clock, where the color change acts as a timekeeping mechanism.

Learn more: Color Changing Chemistry Clock

8. Pipe Cleaner Crystal Trees

By adjusting the concentration of the Borax solution or experimenting with different pipe cleaner arrangements, students can customize their crystal trees and observe how it affects the growth patterns.

Learn more: Pipe Cleaner Crystal Trees

9. How To Make Ice Sculptures

Through this experiment, students gain a deeper understanding of the physical and chemical changes that occur when water freezes and melts.

Learn more: Ice Sculpture

10. How to Make Paper

Through this hands-on activity, students gain a deeper understanding of the properties of cellulose fibers and the transformative power of chemical reactions.

Learn more: How to Make Paper

11. Color Changing Chemistry

Color changing chemistry is an enchanting experiment that offers a captivating blend of science and art. Students should embark on this colorful journey to witness the mesmerizing transformations of chemicals and explore the principles of chemical reactions.

12. Gassy Banana

The gassy banana experiment is a fun and interactive way for students to explore the principles of chemical reactions and gas production.

Learn more: Gassy Banana

13. Gingerbread Man Chemistry Experiment

This hands-on activity not only introduces students to the concepts of chemical leavening and heat-induced reactions but also allows for creativity in decorating and personalizing their gingerbread creations.

Learn more: Gingerbread Man Chemistry Experiment

14. Make Amortentia Potion

While the love potion is fictional, this activity offers a chance to explore the art of potion-making and the chemistry behind it.

Learn more: How to Make Amortentia Potion

15. Strawberry DNA Extraction

This hands-on experiment offers a unique opportunity to observe DNA, the building blocks of life, up close and learn about its structure and properties.

16. Melting Snowman

The melting snowman experiment is a fun and whimsical activity that allows students to explore the principles of heat transfer and phase changes.

Learn more: Melting Snowman

17. Acid Base Cabbage Juice

The acid-base cabbage juice experiment is an engaging and colorful activity that allows students to explore the pH scale and the properties of acids and bases.

By extracting the purple pigment from red cabbage leaves and creating cabbage juice, students can use this natural indicator to identify and differentiate between acidic and basic substances.

Learn more: Acid Base Cabbage Juice

18. Magic Milk

The magic milk experiment is a mesmerizing and educational activity that allows students to explore the concepts of surface tension and chemical reactions.

By adding drops of different food colors to a dish of milk and then introducing a small amount of dish soap, students can witness a captivating display of swirling colors and patterns.

Learn more: Magic Milk

19. Melting Ice with Salt and Water

Through this hands-on activity, students can gain a deeper understanding of the science behind de-icing and how different substances can influence the physical properties of water.

Learn more: Melting Ice with Salt and Water

20. Barking Dog Chemistry Demonstration

The barking dog chemistry demonstration is an exciting and visually captivating experiment that showcases the principles of combustion and gas production.

21. How to Make Egg Geodes

Making egg geodes is a fascinating and creative chemistry experiment that students should try. By using common materials like eggshells, salt, and food coloring, students can create their own beautiful geode-like crystals.

Learn more: How to Make Egg Geodes

22. Make Sherbet

This experiment not only engages the taste buds but also introduces concepts of acidity, solubility, and the chemical reactions that occur when the sherbet comes into contact with moisture.

Learn more: Make Sherbet

23. Hatch a Baking Soda Dinosaur Egg

As the baking soda dries and hardens around the toy, it forms a “shell” resembling a dinosaur egg. To hatch the egg, students can pour vinegar onto the shell, causing a chemical reaction that produces carbon dioxide gas.

Learn more: Steam Powered Family

24. Chromatography Flowers

By analyzing the resulting patterns, students can gain insights into the different pigments present in flowers and the science behind their colors.

Learn more: Chromatography Flowers

25. Turn Juice Into Solid

Turning juice into a solid through gelification is an engaging and educational chemistry experiment that students should try. By exploring the transformation of a liquid into a solid, students can gain insights of chemical reactions and molecular interactions.

Learn more: Turn Juice into Solid

26. Bouncy Balls

Making bouncy balls allows students to explore the fascinating properties of polymers, such as their ability to stretch and rebound.

 27. Make a Lemon Battery

Creating a lemon battery is a captivating and hands-on experiment that allows students to explore the fundamentals of electricity and chemical reactions.

28. Mentos and Soda Project

The Mentos and soda project is a thrilling and explosive experiment that students should try. By dropping Mentos candies into a bottle of carbonated soda, an exciting eruption occurs.

29. Alkali Metal in Water

The reaction of alkali metals with water is a fascinating and visually captivating chemistry demonstration.

30. Rainbow Flame

The rainbow flame experiment is a captivating and visually stunning chemistry demonstration that students should explore.

31. Sugar Yeast Experiment

This experiment not only introduces students to the concept of fermentation but also allows them to witness the effects of a living organism, yeast, on the sugar substrate.

32. The Thermite Reaction

The thermite reaction is a highly energetic and visually striking chemical reaction that students can explore with caution and under proper supervision.

This experiment showcases the principles of exothermic reactions, oxidation-reduction, and the high temperatures that can be achieved through chemical reactions.

33. Polishing Pennies

Polishing pennies is a simple and enjoyable chemistry experiment that allows students to explore the concepts of oxidation and cleaning methods.

34. Elephant Toothpaste

The elephant toothpaste experiment is a thrilling and visually captivating chemistry demonstration that students should try with caution and under the guidance of a knowledgeable instructor.

35. Magic Potion

Creating a magic potion is an exciting and imaginative activity that allows students to explore their creativity while learning about the principles of chemistry.

36. Color Changing Acid-Base Experiment

Through the color changing acid-base experiment, students can gain a deeper understanding of chemical reactions and the role of pH in our daily lives.

Learn more: Color Changing Acid-Base Experiment

37. Fill up a Balloon

Filling up a balloon is a simple and enjoyable physics experiment that demonstrates the properties of air pressure. By blowing air into a balloon, you can observe how the balloon expands and becomes inflated.

38. Jello and Vinegar

The combination of Jello and vinegar is a fascinating and tasty chemistry experiment that demonstrates the effects of acid on a gelatin-based substance.

Learn more: Jello and Vinegar

39. Vinegar and Steel Wool Reaction

This experiment not only provides a visual demonstration of the oxidation process but also introduces students to the concept of corrosion and the role of acids in accelerating the process.

Learn more: Vinegar and Steel Wool Reaction

40. Dancing Rice

The dancing rice experiment is a captivating and educational demonstration that showcases the principles of density and buoyancy.

By pouring a small amount of uncooked rice into a clear container filled with water, students can witness the rice grains moving and “dancing” in the water.

Learn more: Dancing Rice

41. Soil Testing Garden Science

Soil testing is a valuable and informative experiment that allows students to assess the composition and properties of soil.

By collecting soil samples from different locations and analyzing them, students can gain insights into the nutrient content, pH level, and texture of the soil.

Learn more: Soil Testing Garden Science

42. Heat Sensitive Color Changing Slime

Creating heat-sensitive color-changing slime is a captivating and playful chemistry experiment that students should try.

Learn more: Left Brain Craft Brain

43. Experimenting with Viscosity

Experimenting with viscosity is an engaging and hands-on activity that allows students to explore the flow properties of liquids.

Viscosity refers to a liquid’s resistance to flow, and this experiment enables students to investigate how different factors affect viscosity.

Learn more: Experimenting with Viscosity

44. Rock Candy Science

Rock candy science is a delightful and educational chemistry experiment that students should try. By growing their own rock candy crystals, students can learn about crystal formation and explore the principles of solubility and saturation.

Learn more: Rock Candy Science

45. Baking Soda vs Baking Powder

Baking soda and baking powder have distinct properties that influence the leavening process in different ways.

This hands-on experiment provides a practical understanding of how these ingredients interact with acids and moisture to create carbon dioxide gas.

46. Endothermic and Exothermic Reactions Experiment

The endothermic and exothermic reactions experiment is an exciting and informative chemistry exploration that students should try.

By observing and comparing the heat changes in different reactions, students can gain a deeper understanding of energy transfer and the concepts of endothermic and exothermic processes.

Learn more: Education.com

47. Diaper Chemistry

By dissecting a diaper and examining its components, students can uncover the chemical processes that make diapers so effective at absorbing and retaining liquids.

Learn more: Diaper Chemistry

48. Candle Chemical Reaction

The “Flame out” experiment is an intriguing and educational chemistry demonstration that students should try. By exploring the effects of a chemical reaction on a burning candle, students can witness the captivating moment when the flame is extinguished.

49. Make Curds and Whey

This experiment not only introduces students to the concept of acid-base reactions but also offers an opportunity to explore the science behind cheese-making.

Learn more: Tinkerlab

50. Grow Crystals Overnight

By creating a supersaturated solution using substances like epsom salt, sugar, or borax, students can observe the fascinating process of crystal growth. This experiment allows students to explore the principles of solubility, saturation, and nucleation.

Learn more: Grow Crystals Overnight

51. Measure Electrolytes in Sports Drinks

The “Measure Electrolytes in Sports Drinks” experiment is an informative and practical chemistry activity that students should try.

By using simple tools like a multimeter or conductivity probe, students can measure the electrical conductivity of different sports drinks to determine their electrolyte content.

52. Oxygen and Fire Experiment

The oxygen and fire experiment is a captivating and educational chemistry demonstration that students should try. By observing the effects of oxygen on a controlled fire, students can witness the essential role of oxygen in supporting combustion.

53. Electrolysis Of Water

The electrolysis of water experiment is a captivating and educational chemistry demonstration that students should try.

Learn more: Electrolysis Of Water

54. Expanding Ivory Soap

The expanding Ivory Soap experiment is a fun and interactive chemistry activity that students should try. By placing a bar of Ivory soap in a microwave, students can witness the remarkable expansion of the soap as it heats up.

Learn more: Little Bins Little Hands

55. Glowing Fireworks

This experiment not only introduces students to the principles of pyrotechnics and combustion but also encourages observation, critical thinking, and an appreciation for the physics and chemistry behind.

Learn more: Glowing Fireworks

56. Colorful Polymer Chemistry

Colorful polymer chemistry is an exciting and vibrant experiment that students should try to explore polymers and colorants.

By combining different types of polymers with various colorants, such as food coloring or pigments, students can create a kaleidoscope of colors in their polymer creations.

Learn more: Colorful Polymer Chemistry

57. Sulfur Hexafluoride- Deep Voice Gas

This experiment provides a firsthand experience of how the density and composition of gases can influence sound transmission.

It encourages scientific curiosity, observation, and a sense of wonder as students witness the surprising transformation of their voices.

58. Liquid Nitrogen Ice Cream

Liquid nitrogen ice cream is a thrilling and delicious chemistry experiment that students should try. By combining cream, sugar, and flavorings with liquid nitrogen, students can create ice cream with a unique and creamy texture.

59. White Smoke Chemistry Demonstration

The White Smoke Chemistry Demonstration provides an engaging and visually captivating experience for students to explore chemical reactions and gases. By combining hydrochloric acid and ammonia solutions, students can witness the mesmerizing formation of white smoke.

60. Nitrogen Triiodide Chemistry Demonstration

The nitrogen triiodide chemistry demonstration is a remarkable and attention-grabbing experiment that students should try under the guidance of a knowledgeable instructor.

By reacting iodine crystals with concentrated ammonia, students can precipitate nitrogen triiodide (NI3), a highly sensitive compound.

61. Make a Plastic- Milk And Vinegar Reaction Experiment

Through the “Make a Plastic – Milk and Vinegar Reaction” experiment, students can gain a deeper understanding of the chemistry behind plastics, environmental sustainability, and the potential of biodegradable materials.

Learn more: Rookie Parenting

62. Eno and Water Experiment

This experiment not only introduces students to acid-base reactions but also engages their senses as they witness the visible and audible effects of the reaction.

63. The Eternal Kettle Experiment

By filling a kettle with alcohol and igniting it, students can investigate the behavior of the alcohol flame and its sustainability.

64. Coke and Chlorine Bombs

Engaging in this experiment allows students to experience the wonders of chemistry firsthand, making it an ideal choice to ignite their curiosity and passion for scientific exploration.

65. Set your Hand on Fire

This experiment showcases the fascinating nature of combustion and the science behind fire.

By carefully following proper procedures and safety guidelines, students can witness firsthand how the sanitizer’s high alcohol content interacts with an open flame, resulting in a brief but captivating display of controlled combustion.

66. Instant Ice Experiments

The Instant Ice Experiment offers an engaging and captivating opportunity for students to explore the wonders of chemistry and phase changes.

By using simple household ingredients, students can witness the fascinating phenomenon of rapid ice formation in just a matter of seconds.

67. Coke Cans in Acid and Base

Engaging in this experiment allows students to gain a deeper understanding of the chemical properties of substances and the importance of safety protocols in scientific investigations.

68. Color Changing Invisible Ink

The Color Changing Invisible Ink experiment offers an intriguing and fun opportunity for students to explore chemistry and learn about the concept of chemical reactions.

Learn more: Research Parent

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Energy Experiments for Kids

Simple Engineering Projects for High School

Energy exists in two forms, kinetic and potential. Potential energy sources include chemical, mechanical, nuclear and gravitational and are stored energy forms. Kinetic energy is considered "working" energy and includes sound, motion, light and heat and electricity, according to the U.S. Energy Information Administration. You can use experiments to show kids how energy works.

Lemon Power

Turn a lemon into an energy source known as a voltaic battery, which changes one energy form into another. The lemon contains chemical energy that converts into electrical energy when you add one copper wire and one steel wire to it. Use a small sheet of sandpaper to even out the edges of both the steel and copper wires. Keep the lemon whole and rub it gently between your hands before inserting the copper and steel wires. Get the wires as close together as possible, but do not allow them to touch each other. Once you have the wires poked into the lemon, place your wet tongue on the tips of both wires at the same time. You will feel a small tingle once your tongue touches the wires, as you have now completed the circuit.

Heat up a Balloon

Find out how warm air acts differently from cold air using an experiment that tests warm air's effects. Most people can blow up a balloon by mouth, but with a deflated balloon, a plastic bottle and a pan of hot water your kids can see how hot air makes things rise. Place the balloon over the bottle mouth and place the bottle in the pan. The experiment shows how warm air uses more space than cold air and illustrates how molecules move to inflate the balloon without adding additional air.

Water Purification

Use a simple outdoor experiment to demonstrate the sun's energy. Water purification is a process in which you remove impurities to create a drinkable product. In this experiment, fill a bowl with regular tap water but add strong spices like curry or garlic to "taint" the flavor of the water. Place a small cup in the center of the bowl, cover the bowl with plastic wrap and set a small rock on top. Once you place the experiment in a well-lit area outside, the sun's energy will cause water vapors to form, and over a period of time, create drinkable water. This simple steam distillation process works because the vapors cling to the plastic wrap, travel to the center where the rock is and drip down into the cup.

Potential Energy

Establish the concept of potential energy using several objects like pebbles, empty cans and wooden blocks. The experiment's purpose reveals how height and weight affect potential energy. Some of the items will demonstrate gravitational energy and others will identify a moving object's energy. There are several factors to consider when calculating the height and weight of an object and its potential energy; increasing or decreasing the weight or height of an object affects its energy. Some of the experimental items can be dropped, swung or moved side-to-side to determine their potential energy.

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Ideas for projects on energy in the fifth grade, can fruits make electricity, how to calculate a change in potential energy, why is styrofoam a good insulator, how to make a potato lightbulb for a science project, project ideas for an egg drop with instructions, how to make a buzz wire game, how to mix calcium chloride and water, convection experiments for kids, how to build a clorox bleach battery, simple explanation of electromagnets, endothermic science projects, what is renewable energy create clean energy with..., fun science experiments with potatoes, how to measure the voltage in fruits, heat and energy transfer experiments, how to light a lightbulb with saltwater.

• US Energy Administration: What is Energy?
• Science Kids: What Happens to Air as it Heats Up?
• Green Planet Solar Energy: Water Science Experiments: Water Purification
• Illinios Institute of Technology: Potential Energy

About the Author

Annabeth Kaine began writing in 2010 with work appearing on various websites. She has successfully run two businesses, held chairmanship positions on two fund-raising committees and received excellence-in-service awards for both. Kaine is completing her Bachelor of Arts in psychology.

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Forms of Energy – Science Experiments for Kids

Updated:  01 Jul 2024

Investigate mechanical, electrical, light, thermal, and sound energy with this set of science activities for kids.

Editable:  Google Slides

Non-Editable:  PDF

Pages:  6 Pages

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Science 4.2(A)

Plan and implement descriptive investigations, including asking well defined questions, making inferences, and selecting and using appropriate equipment or technology to answer his/her questions;

Science 4.2(B)

Collect and record data by observing and measuring, using the metric system, and using descriptive words and numerals such as labeled drawings, writing, and concept maps;

Science 4.2(C)

Construct simple tables, charts, bar graphs, and maps using tools and current technology to organize, examine, and evaluate data;

Science 4.2(D)

Analyze data and interpret patterns to construct reasonable explanations from data that can be observed and measured;

Science 4.2(F)

Communicate valid oral and written results supported by data.

Science 4.4

Scientific investigation and reasoning. The student knows how to use a variety of tools, materials, equipment, and models to conduct science inquiry. The student is expected to collect, record, and analyze information using tools, including c...

Science 4.6(A)

Differentiate among forms of energy, including mechanical, sound, electrical, light, and thermal;

What Are the Different Types of Energy? – For Kids!

Are your students starting to dive into the different energy types found in our world? Let’s take a look at the common times of energy. To help you remember the different forms, all you have to do is remember the acronym MELTS. It stands for mechanical, electrical, light, thermal, and sound energy.

• Mechanical energy is the energy that is possessed by an object due to its motion or position. It is the energy that is involved in the movement of objects and can be transferred from one object to another.
• Electrical energy is the energy that is associated with the movement of electric charges. It is a type of energy that can be transferred through wires and other conductive materials. Electrical energy can be produced from a variety of sources, including batteries, generators, and solar panels.
• Light energy is a type of energy that is emitted by hot objects and can be seen by the human eye. It travels in waves and allows us to see things around us. Light energy is also important for plants to make food through photosynthesis and is used in a variety of technologies.
• Thermal energy is the energy associated with an object’s temperature. The more thermal energy an object or system has, the higher its temperature will be. 
• Sound energy is a type of energy that is produced by the vibration of matter. When an object vibrates, sound waves travel through the air or other media, such as water or solids.

Investigate Different Forms of Energy

Teach Starter has created a set of science station cards to use in your classroom when students learn about the different energy types. Each station card includes the materials needed as well as the steps to complete the experiment. With your download, there is also a printable tri-fold where students will record their findings.

Students will investigate different types of energy by:

• Dropping a ball from different heights
• Creating a playdough circuit (Check out a great Playdough recipe from  Squishy Circuits ™)
• Shining a flashlight on different objects
• Dissolving sugar in cups of water with different temperatures
• Creating a string telephone

Easily Prepare This Resource for Your Students

Use the dropdown icon on the Download button to choose between the PDF or editable Google Slides version of this resource.

Print the station cards on cardstock for added durability and longevity. Place all pieces in a folder or large envelope for easy access. 

This resource was created by Kaylyn Chupp, a teacher in Florida and a Teach Starter Collaborator. 

Don’t stop there! We’ve got more activities and resources that cut down on lesson planning time:  

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Forms of energy poster pack.

Display information about mechanical, electrical, light, thermal and sound energy with this poster pack.

Energy and Electricity Vocabulary Cards

Reinforce science vocabulary in your classroom with this set of word wall cards that focus on forms of energy and electricity.

Forms of Energy & Electricity Vocabulary Worksheets

Review forms of energy and electricity terms with this science vocabulary worksheet pack.

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Easy Chemistry Experiments to Do at Home

These 12 projects use materials you probably already have

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Looking for fun, educational activities to do at home? This list of easy chemistry experiments and science activities will allow you to perform experiments with materials you likely already have in your kitchen cupboards .

You don't need esoteric chemicals and a lab to have a good time with chemistry. Your average fourth-grader can make slime , and it doesn't get any less fun when you're older, so this is a good at-home experiment for kids and adults alike.

Borax Snowflake

Anne Helmenstine

Making a sparkly borax snowflake is a crystal-growing project that's safe and easy enough for kids. You can make shapes other than snowflakes, and you can color the crystals. If you use these as Christmas decorations and store them, the borax is a natural insecticide and will help keep your long-term storage area pest-free. If they develop a white precipitant, lightly rinse them but don't dissolve too much crystal.

Mentos and Diet Soda Fountain

This is a backyard activity best accompanied  by a garden hose . The Mentos fountain  is more spectacular than a baking soda volcano . If you make the volcano and find the eruption to be disappointing, substitute these ingredients.

Penny Chemistry

You can clean pennies, coat them with verdigris, and plate them with copper. This project demonstrates several chemical processes , yet the materials are easy to find and the science is safe enough for kids.

Invisible Ink

Invisible inks either react with another chemical to become visible or else weaken the structure of the paper so the message appears if you hold it over a heat source. But we're not talking about fire here; the heat of a normal light bulb is all that's required to darken the lettering. This baking soda recipe is nice because if you don't want to use a light bulb to reveal the message, you can just swab the paper with grape juice instead.

Colored Fire

Fire is fun. Colored fire is even better. These additives are safe. They won't, in general, produce smoke that is any better or worse for you than normal wood smoke. Depending on what you add, the ashes will have a different elemental composition from a normal wood fire, but if you're burning trash or printed material, you have a similar result. This is suitable for a home fire or campfire, plus most chemicals are found around the house (even of non-chemists).

Seven-Layer Density Column

Make a  density column with many liquid layers . Heavier liquids sink to the bottom, while lighter (less dense) liquids float on top. This is an easy, fun, colorful science project that illustrates the concepts of density and miscibility.

Homemade Ice Cream in a Plastic Bag

Science experiments can taste good! Whether you're learning about  freezing point depression or not, the ice cream is a delicious result either way. This cooking chemistry project potentially uses no dishes, so cleanup can be very easy.

Hot Ice (Sodium Acetate)

Got vinegar and  baking soda ? If so, you can make " hot ice ," or sodium  acetate , and then cause it to instantly crystallize from a liquid into "ice." The reaction generates heat, so the ice is hot. It happens so quickly that you can form crystal towers as you pour the liquid into a dish.

Burning Money

The " burning money trick " is a  magic trick   using chemistry . You can set a bill on fire, yet it won't burn. Are you brave enough to try it? All you need is a real bill.

Coffee Filter Chromatography

Exploring separation chemistry with coffee filter chromatography is a snap. A coffee filter works well, though if you don't drink coffee you can substitute a paper towel. You can also devise a project comparing the separation you get using different brands of paper towels. Leaves from outdoors can provide pigments. Frozen spinach is another good choice.

Baking Soda and Vinegar Foam Fight

The foam fight is a natural extension of the baking soda volcano . This easy chemistry experiment is a lot of fun and a little messy, but quick enough to clean up as long as you don't add food coloring to the foam.

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Easy Chemistry Experiments for Kids

October 19, 2021 By Emma Vanstone 1 Comment

When I think back to my own childhood and school days, I don’t remember any chemistry experiments until secondary school, which is a shame because there are so many wonderfully visual easy chemistry experiments for kids that can be done at home or in school with young children.

I’ve put together a collection of my favourite examples, do let us know if you try any.

  Please remember young children should be supervised at all times.

Chemistry Experiments for Kids in the Kitchen

Exploding sandwich bags .

I did struggle a little when we tried this as the reaction happens so fast, but  Steve Spangler has a nifty method where he traps the vinegar in a second smaller bag, which you then have to burst to get the reaction started.

Inspiration laboratories add a twist by adding some colour and making  firework pictures at the same time.

Blow Up a Balloon

This is a super simple demonstration or experiment that has never failed me, and all you need is a container with a small neck, a balloon and either an alka seltzer or an effervescent vitamin tablet. The alka seltzer or vitamin tablet reacts with water to release bubbles of carbon dioxide filling the jar and then blowing up the balloon.

Blow up a balloon with alka seltzer

Find out how to blow up a balloon with lemon juice and baking soda.

Colourful Milk

Make a lovely, colourful display using milk, food colouring and vinegar.

Oil, Food Colouring and Water Exploration Table

My oil, water and food colouring exploration table is brilliant for even very young children. For older children, try a more structured approach, they could measure the amount of vinegar and baking soda needed to make the reaction spill over the top of the beaker or try dropping tiny amounts of coloured water into the oil.

Density Rainbow Jar

Learn about the tricky concept of density and make a beautiful demonstration density jar .

Simple Density Jar

If you don’t want to make as many layers as we have, why not try this smaller version and try to find an object to float on each layer?

Lemon Volcanoes

This lemon volcano from Babble Dabble Do is a great alternative to the traditional volcano and is handy as the lemon already contains acid.

Clean coins

Did you know you can clean coins with vinegar ?

Colourful Chemistry Experiments

Make your own ph indicator.

Test the pH of vinegar and baking soda with a red cabbage indicator . What do you think might happen if you blow into the indicator?

Dissolving Skittles

Watching the colour dissolve from skittles or M & Ms dissolve into water is a lovely, quick, visual activity.

Chemistry Experiments for Kids Outside

Giant bubbles.

Who doesn’t love a giant bubble ? Red Ted Art makes bubble making look easy in this great video. Remember, the mixture gets better the longer you leave it, so allow plenty of time.

Make a Square Bubble

All you need to make a square bubble is a square frame. If you don’t have plastic pieces to use, pipe cleaners also work well.

Coke and Mento Reaction

The infamous coke and mento reaction is super easy and very impressive to watch. Try comparing the size of the geyser using diet and full sugar cola or using different types of fizzy drinks.

Can you design something which allows the mentos to drop in as soon as you remove the lid?

Elephants Toothpaste

Fun at Home with Kids makes elephants toothpaste   look super simple, but do be careful with the hydrogen peroxide and take appropriate precautions.

Film Canister Rockets

Film canister rockets are easy, inexpensive and great fun. All you need is a film canister, an effervescent vitamin tablet and some water. Experiment with different amounts of water and tablets to find the most explosive combination.

Make a Volcano

Find out how to make a volcano erupt with sand, snow or papier mache. A baking soda volcano is a brilliant classic chemistry experiment every kid should try at least once!

Chemistry Separation Methods

Bicycle centrifuge.

Did you know you can use bike wheels as a very basic centrifuge ?

Stone and Gravel Filter

Learn about filters by making a filter with stones , gravel and sand.

Filter Paper Chromatography

Take on the role of a detective with some fun filter paper chromatography .

Can you think of any more amazing chemistry experiments for kids?

Last Updated on April 13, 2023 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

Reader Interactions

June 15, 2021 at 5:04 pm

these ideas are great i picked two to do at my moms house the skittles in water and coke with mentos my mom might not let me do the coke bootle and mentos but she might let me do the skittles i will let you know if it works if it does i give this website a 10/10

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37 Cool Science Experiments for Kids to Do at Home

General Education

Are you looking for cool science experiments for kids at home or for class? We've got you covered! We've compiled a list of 37 of the best science experiments for kids that cover areas of science ranging from outer space to dinosaurs to chemical reactions. By doing these easy science experiments, kids will make their own blubber and see how polar bears stay warm, make a rain cloud in a jar to observe how weather changes, create a potato battery that'll really power a lightbulb, and more.

Below are 37 of the best science projects for kids to try. For each one we include a description of the experiment, which area(s) of science it teaches kids about, how difficult it is (easy/medium/hard), how messy it is (low/medium/high), and the materials you need to do the project. Note that experiments labelled "hard" are definitely still doable; they just require more materials or time than most of these other science experiments for kids.

#1: Insect Hotels

• Teaches Kids About: Zoology
• Difficulty Level: Medium
• Messiness Level: Medium

Insect hotels can be as simple (just a few sticks wrapped in a bundle) or as elaborate as you'd like, and they're a great way for kids to get creative making the hotel and then get rewarded by seeing who has moved into the home they built. After creating a hotel with hiding places for bugs, place it outside (near a garden is often a good spot), wait a few days, then check it to see who has occupied the "rooms." You can also use a bug ID book or app to try and identify the visitors.

• Materials Needed
• Shadow box or other box with multiple compartments
• Hot glue gun with glue
• Sticks, bark, small rocks, dried leaves, bits of yarn/wool, etc.

#2: DIY Lava Lamp

• Teaches Kids About: Chemical reactions
• Difficulty Level: Easy

In this quick and fun science experiment, kids will mix water, oil, food coloring, and antacid tablets to create their own (temporary) lava lamp . Oil and water don't mix easily, and the antacid tablets will cause the oil to form little globules that are dyed by the food coloring. Just add the ingredients together and you'll end up with a homemade lava lamp!

• Vegetable oil
• Food coloring
• Antacid tablets

#3: Magnetic Slime

• Teaches Kids About: Magnets
• Messiness Level: High (The slime is black and will slightly dye your fingers when you play with it, but it washes off easily.)

A step up from silly putty and Play-Doh, magnetic slime is fun to play with but also teaches kids about magnets and how they attract and repel each other. Some of the ingredients you aren't likely to have around the house, but they can all be purchased online. After mixing the ingredients together, you can use the neodymium magnet (regular magnets won't be strong enough) to make the magnetic slime move without touching it!

• Liquid starch
• Adhesive glue
• Iron oxide powder
• Neodymium (rare earth) magnet

#4: Baking Soda Volcanoes

• Teaches Kids About: Chemical reactions, earth science
• Difficulty Level: Easy-medium
• Messiness Level: High

Baking soda volcanoes are one of the classic science projects for kids, and they're also one of the most popular. It's hard to top the excitement of a volcano erupting inside your home. This experiment can also be as simple or in-depth as you like. For the eruption, all you need is baking soda and vinegar (dishwashing detergent adds some extra power to the eruption), but you can make the "volcano" as elaborate and lifelike as you wish.

• Baking soda
• Dishwashing detergent
• Large mason jar or soda bottle
• Playdough or aluminum foil to make the "volcano"
• Additional items to place around the volcano (optional)
• Food coloring (optional)

#5: Tornado in a Jar

• Teaches Kids About: Weather
• Messiness Level: Low

This is one of the quick and easy and science experiments for kids to teach them about weather. It only takes about five minutes and a few materials to set up, but once you have it ready you and your kids can create your own miniature tornado whose vortex you can see and the strength of which you can change depending on how quickly you swirl the jar.

• Glitter (optional)

#6: Colored Celery Experiment

• Teaches Kids About: Plants

This celery science experiment is another classic science experiment that parents and teachers like because it's easy to do and gives kids a great visual understanding of how transpiration works and how plants get water and nutrients. Just place celery stalks in cups of colored water, wait at least a day, and you'll see the celery leaves take on the color of the water. This happens because celery stalks (like other plants) contain small capillaries that they use to transport water and nutrients throughout the plant.

• Celery stalks (can also use white flowers or pale-colored cabbage)

#7: Rain Cloud in a Jar

This experiment teaches kids about weather and lets them learn how clouds form by making their own rain cloud . This is definitely a science project that requires adult supervision since it uses boiling water as one of the ingredients, but once you pour the water into a glass jar, the experiment is fast and easy, and you'll be rewarded with a little cloud forming in the jar due to condensation.

• Glass jar with a lid
• Boiling water
• Aerosol hairspray

#8: Edible Rock Candy

• Teaches Kids About: Crystal formation

It takes about a week for the crystals of this rock candy experiment to form, but once they have you'll be able to eat the results! After creating a sugar solution, you'll fill jars with it and dangle strings in them that'll slowly become covered with the crystals. This experiment involves heating and pouring boiling water, so adult supervision is necessary, once that step is complete, even very young kids will be excited to watch crystals slowly form.

• Large saucepan
• Clothespins
• String or small skewers
• Candy flavoring (optional)

#9: Water Xylophone

• Teaches Kids About: Sound waves

With just some basic materials you can create your own musical instrument to teach kids about sound waves. In this water xylophone experiment , you'll fill glass jars with varying levels of water. Once they're all lined up, kids can hit the sides with wooden sticks and see how the itch differs depending on how much water is in the jar (more water=lower pitch, less water=higher pitch). This is because sound waves travel differently depending on how full the jars are with water.

• Wooden sticks/skewers

#10: Blood Model in a Jar

• Teaches Kids About: Human biology

This blood model experiment is a great way to get kids to visual what their blood looks like and how complicated it really is. Each ingredient represents a different component of blood (plasma, platelets, red blood cells, etc.), so you just add a certain amount of each to the jar, swirl it around a bit, and you have a model of what your blood looks like.

• Empty jar or bottle
• Red cinnamon candies
• Marshmallows or dry white lima beans
• White sprinkles

#11: Potato Battery

• Teaches Kids About: Electricity
• Difficulty Level: Hard

Did you know that a simple potato can produce enough energy to keep a light bulb lit for over a month? You can create a simple potato battery to show kids. There are kits that provide all the necessary materials and how to set it up, but if you don't purchase one of these it can be a bit trickier to gather everything you need and assemble it correctly. Once it's set though, you'll have your own farm grown battery!

• Fresh potato
• Galvanized nail
• Copper coin

#12: Homemade Pulley

• Teaches Kids About: Simple machines

This science activity requires some materials you may not already have, but once you've gotten them, the homemade pulley takes only a few minutes to set up, and you can leave the pulley up for your kids to play with all year round. This pulley is best set up outside, but can also be done indoors.

• Clothesline
• 2 clothesline pulleys

#13: Light Refraction

• Teaches Kids About: Light

This light refraction experiment takes only a few minutes to set up and uses basic materials, but it's a great way to show kids how light travels. You'll draw two arrows on a sticky note, stick it to the wall, then fill a clear water bottle with water. As you move the water bottle in front of the arrows, the arrows will appear to change the direction they're pointing. This is because of the refraction that occurs when light passes through materials like water and plastic.

• Sticky note
• Transparent water bottle

#14: Nature Journaling

• Teaches Kids About: Ecology, scientific observation

A nature journal is a great way to encourage kids to be creative and really pay attention to what's going on around them. All you need is a blank journal (you can buy one or make your own) along with something to write with. Then just go outside and encourage your children to write or draw what they notice. This could include descriptions of animals they see, tracings of leaves, a drawing of a beautiful flower, etc. Encourage your kids to ask questions about what they observe (Why do birds need to build nests? Why is this flower so brightly colored?) and explain to them that scientists collect research by doing exactly what they're doing now.

• Blank journal or notebook
• Pens/pencils/crayons/markers
• Tape or glue for adding items to the journal

#15: DIY Solar Oven

• Teaches Kids About: Solar energy

This homemade solar oven definitely requires some adult help to set up, but after it's ready you'll have your own mini oven that uses energy from the sun to make s'mores or melt cheese on pizza. While the food is cooking, you can explain to kids how the oven uses the sun's rays to heat the food.

• Aluminum foil
• Knife or box cutter
• Permanent marker
• Plastic cling wrap
• Black construction paper

#16: Animal Blubber Simulation

• Teaches Kids About: Ecology, zoology

If your kids are curious about how animals like polar bears and seals stay warm in polar climates, you can go beyond just explaining it to them; you can actually have them make some of their own blubber and test it out. After you've filled up a large bowl with ice water and let it sit for a few minutes to get really cold, have your kids dip a bare hand in and see how many seconds they can last before their hand gets too cold. Next, coat one of their fingers in shortening and repeat the experiment. Your child will notice that, with the shortening acting like a protective layer of blubber, they don't feel the cold water nearly as much.

• Bowl of ice water

#17: Static Electricity Butterfly

This experiment is a great way for young kids to learn about static electricity, and it's more fun and visual than just having them rub balloons against their heads. First you'll create a butterfly, using thick paper (such as cardstock) for the body and tissue paper for the wings. Then, blow up the balloon, have the kids rub it against their head for a few seconds, then move the balloon to just above the butterfly's wings. The wings will move towards the balloon due to static electricity, and it'll look like the butterfly is flying.

• Tissue paper
• Thick paper
• Glue stick/glue

#18: Edible Double Helix

• Teaches Kids About: Genetics

If your kids are learning about genetics, you can do this edible double helix craft to show them how DNA is formed, what its different parts are, and what it looks like. The licorice will form the sides or backbone of the DNA and each color of marshmallow will represent one of the four chemical bases. Kids will be able to see that only certain chemical bases pair with each other.

• 2 pieces of licorice
• 12 toothpicks
• Small marshmallows in 4 colors (9 of each color)
• 5 paperclips

#19: Leak-Proof Bag

• Teaches Kids About: Molecules, plastics

This is an easy experiment that'll appeal to kids of a variety of ages. Just take a zip-lock bag, fill it about ⅔ of the way with water, and close the top. Next, poke a few sharp objects (like bamboo skewers or sharp pencils) through one end and out the other. At this point you may want to dangle the bag above your child's head, but no need to worry about spills because the bag won't leak? Why not? It's because the plastic used to make zip-lock bags is made of polymers, or long chains of molecules that'll quickly join back together when they're forced apart.

• Zip-lock bags
• Objects with sharp ends (pencils, bamboo skewers, etc.)

#20: How Do Leaves Breathe?

• Teaches Kids About: Plant science

It takes a few hours to see the results of this leaf experiment , but it couldn't be easier to set up, and kids will love to see a leaf actually "breathing." Just get a large-ish leaf, place it in a bowl (glass works best so you can see everything) filled with water, place a small rock on the leaf to weigh it down, and leave it somewhere sunny. Come back in a few hours and you'll see little bubbles in the water created when the leaf releases the oxygen it created during photosynthesis.

• Large bowl (preferably glass)
• Magnifying glass (optional)

#21: Popsicle Stick Catapults

Kids will love shooting pom poms out of these homemade popsicle stick catapults . After assembling the catapults out of popsicle sticks, rubber bands, and plastic spoons, they're ready to launch pom poms or other lightweight objects. To teach kids about simple machines, you can ask them about how they think the catapults work, what they should do to make the pom poms go a farther/shorter distance, and how the catapult could be made more powerful.

• Popsicle sticks
• Rubber bands
• Plastic spoons
• Paint (optional)

#22: Elephant Toothpaste

You won't want to do this experiment near anything that's difficult to clean (outside may be best), but kids will love seeing this " elephant toothpaste " crazily overflowing the bottle and oozing everywhere. Pour the hydrogen peroxide, food coloring, and dishwashing soap into the bottle, and in the cup mix the yeast packet with some warm water for about 30 seconds. Then, add the yeast mixture to the bottle, stand back, and watch the solution become a massive foamy mixture that pours out of the bottle! The "toothpaste" is formed when the yeast removed the oxygen bubbles from the hydrogen peroxide which created foam. This is an exothermic reaction, and it creates heat as well as foam (you can have kids notice that the bottle became warm as the reaction occurred).

• Clean 16-oz soda bottle
• 6% solution of hydrogen peroxide
• 1 packet of dry yeast
• Dishwashing soap

#23: How Do Penguins Stay Dry?

Penguins, and many other birds, have special oil-producing glands that coat their feathers with a protective layer that causes water to slide right off them, keeping them warm and dry. You can demonstrate this to kids with this penguin craft by having them color a picture of a penguin with crayons, then spraying the picture with water. The wax from the crayons will have created a protective layer like the oil actual birds coat themselves with, and the paper won't absorb the water.

• Penguin image (included in link)
• Spray bottle
• Blue food coloring (optional)

#24: Rock Weathering Experiment

• Teaches Kids About: Geology

This mechanical weathering experiment teaches kids why and how rocks break down or erode. Take two pieces of clay, form them into balls, and wrap them in plastic wrap. Then, leave one out while placing the other in the freezer overnight. The next day, unwrap and compare them. You can repeat freezing the one piece of clay every night for several days to see how much more cracked and weathered it gets than the piece of clay that wasn't frozen. It may even begin to crumble. This weathering also happens to rocks when they are subjected to extreme temperatures, and it's one of the causes of erosion.

• Plastic wrap

#25: Saltwater Density

• Teaches Kids About: Water density

For this saltwater density experiment , you'll fill four clear glasses with water, then add salt to one glass, sugar to one glass, and baking soda to one glass, leaving one glass with just water. Then, float small plastic pieces or grapes in each of the glasses and observe whether they float or not. Saltwater is denser than freshwater, which means some objects may float in saltwater that would sink in freshwater. You can use this experiment to teach kids about the ocean and other bodies of saltwater, such as the Dead Sea, which is so salty people can easily float on top of it.

• Four clear glasses
• Lightweight plastic objects or small grapes

#26: Starburst Rock Cycle

With just a package of Starbursts and a few other materials, you can create models of each of the three rock types: igneous, sedimentary, and metamorphic. Sedimentary "rocks" will be created by pressing thin layers of Starbursts together, metamorphic by heating and pressing Starbursts, and igneous by applying high levels of heat to the Starbursts. Kids will learn how different types of rocks are forms and how the three rock types look different from each other.

• Toaster oven

#27: Inertia Wagon Experiment

• Teaches Kids About: Inertia

This simple experiment teaches kids about inertia (as well as the importance of seatbelts!). Take a small wagon, fill it with a tall stack of books, then have one of your children pull it around then stop abruptly. They won't be able to suddenly stop the wagon without the stack of books falling. You can have the kids predict which direction they think the books will fall and explain that this happens because of inertia, or Newton's first law.

• Stack of books

#28: Dinosaur Tracks

• Teaches Kids About: Paleontology

How are some dinosaur tracks still visible millions of years later? By mixing together several ingredients, you'll get a claylike mixture you can press your hands/feet or dinosaur models into to make dinosaur track imprints . The mixture will harden and the imprints will remain, showing kids how dinosaur (and early human) tracks can stay in rock for such a long period of time.

• Used coffee grounds
• Wooden spoon
• Rolling pin

#29: Sidewalk Constellations

• Teaches Kids About: Astronomy

If you do this sidewalk constellation craft , you'll be able to see the Big Dipper and Orion's Belt in the daylight. On the sidewalk, have kids draw the lines of constellations (using constellation diagrams for guidance) and place stones where the stars are. You can then look at astronomy charts to see where the constellations they drew will be in the sky.

• Sidewalk chalk
• Small stones
• Diagrams of constellations

#30: Lung Model

By building a lung model , you can teach kids about respiration and how their lungs work. After cutting off the bottom of a plastic bottle, you'll stretch a balloon around the opened end and insert another balloon through the mouth of the bottle. You'll then push a straw through the neck of the bottle and secure it with a rubber band and play dough. By blowing into the straw, the balloons will inflate then deflate, similar to how our lungs work.

• Plastic bottle
• Rubber band

#31: Homemade Dinosaur Bones

By mixing just flour, salt, and water, you'll create a basic salt dough that'll harden when baked. You can use this dough to make homemade dinosaur bones and teach kids about paleontology. You can use books or diagrams to learn how different dinosaur bones were shaped, and you can even bury the bones in a sandpit or something similar and then excavate them the way real paleontologists do.

• Images of dinosaur bones

#32: Clay and Toothpick Molecules

There are many variations on homemade molecule science crafts . This one uses clay and toothpicks, although gumdrops or even small pieces of fruit like grapes can be used in place of clay. Roll the clay into balls and use molecule diagrams to attach the clay to toothpicks in the shape of the molecules. Kids can make numerous types of molecules and learn how atoms bond together to form molecules.

• Clay or gumdrops (in four colors)
• Diagrams of molecules

#33: Articulated Hand Model

By creating an articulated hand model , you can teach kids about bones, joints, and how our hands are able to move in many ways and accomplish so many different tasks. After creating a hand out of thin foam, kids will cut straws to represent the different bones in the hand and glue them to the fingers of the hand models. You'll then thread yarn (which represents tendons) through the straws, stabilize the model with a chopstick or other small stick, and end up with a hand model that moves and bends the way actual human hands do.

• Straws (paper work best)
• Twine or yarn

#34: Solar Energy Experiment

• Teaches Kids About: Solar energy, light rays

This solar energy science experiment will teach kids about solar energy and how different colors absorb different amounts of energy. In a sunny spot outside, place six colored pieces of paper next to each other, and place an ice cube in the middle of each paper. Then, observe how quickly each of the ice cubes melt. The ice cube on the black piece of paper will melt fastest since black absorbs the most light (all the light ray colors), while the ice cube on the white paper will melt slowest since white absorbs the least light (it instead reflects light). You can then explain why certain colors look the way they do. (Colors besides black and white absorb all light except for the one ray color they reflect; this is the color they appear to us.)

• 6 squares of differently colored paper/cardstock (must include black paper and white paper)

#35: How to Make Lightning

• Teaches Kids About: Electricity, weather

You don't need a storm to see lightning; you can actually create your own lightning at home . For younger kids this experiment requires adult help and supervision. You'll stick a thumbtack through the bottom of an aluminum tray, then stick the pencil eraser to the pushpin. You'll then rub the piece of wool over the aluminum tray, and then set the tray on the Styrofoam, where it'll create a small spark/tiny bolt of lightning!

• Pencil with eraser
• Aluminum tray or pie tin
• Styrofoam tray

#36: Tie-Dyed Milk

• Teaches Kids About: Surface tension

For this magic milk experiment , partly fill a shallow dish with milk, then add a one drop of each food coloring color to different parts of the milk. The food coloring will mostly stay where you placed it. Next, carefully add one drop of dish soap to the middle of the milk. It'll cause the food coloring to stream through the milk and away from the dish soap. This is because the dish soap breaks up the surface tension of the milk by dissolving the milk's fat molecules.

• Shallow dish
• Milk (high-fat works best)

#37: How Do Stalactites Form?

Have you ever gone into a cave and seen huge stalactites hanging from the top of the cave? Stalactites are formed by dripping water. The water is filled with particles which slowly accumulate and harden over the years, forming stalactites. You can recreate that process with this stalactite experiment . By mixing a baking soda solution, dipping a piece of wool yarn in the jar and running it to another jar, you'll be able to observe baking soda particles forming and hardening along the yarn, similar to how stalactites grow.

• Safety pins
• 2 glass jars

Summary: Cool Science Experiments for Kids

Any one of these simple science experiments for kids can get children learning and excited about science. You can choose a science experiment based on your child's specific interest or what they're currently learning about, or you can do an experiment on an entirely new topic to expand their learning and teach them about a new area of science. From easy science experiments for kids to the more challenging ones, these will all help kids have fun and learn more about science.

What's Next?

Are you also interested in pipe cleaner crafts for kids? We have a guide to some of the best pipe cleaner crafts to try!

Looking for multiple different slime recipes? We tell you how to make slimes without borax and without glue as well as how to craft the ultimate super slime .

Want to learn more about clouds? Learn how to identify every cloud in the sky with our guide to the 10 types of clouds .

Want to know the fastest and easiest ways to convert between Fahrenheit and Celsius? We've got you covered! Check out our guide to the best ways to convert Celsius to Fahrenheit (or vice versa) .

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Energy Activities For Elementary Students: Ideas, Crafts, And Experiments For All Types Of Energy

December 20, 2023 //  by  Florence Florah

Are you studying the scientific ideas behind various forms of energy in your classes? Do you want to conduct hands-on activities with your kids to bring your energy lessons to life? Why not consider including some Energy Science Experiments in your lesson plan? Using experiments, you may genuinely involve your kids in understanding various types of energy. It allows learners to engage and participate in the course, adding an interactive component.

Potential and Elastic Energy

1. rubber band stretching.

Rubber bands are great illustrators of elastic energy because of their extensibility. Students participate in this exercise by stretching and releasing rubber bands to observe the correlation between the amount of strain and the subsequent distance traveled by the band.

Learn more: The University of British Columbia

2. Rubber Band Car

In this elementary grade level project, students construct a vehicle propelled by a rubber band's force. Winding the car's axle stretches the rubber band, storing potential energy. The car's potential energy turns into kinetic energy when the rubber band is released.

Learn more: Scientific American

3. Paper Airplane Launcher

Students will create a rubber band-powered launcher for paper airplanes that will use the elastic energy of a rubber band to send them soaring. The youngsters learn how using the hand and arm to launch an aircraft is different from using a rubber band launcher.

Learn more: My Baba

4. Catapult made on popsicle sticks

Elementary grade level kids construct a basic catapult in this exercise using recyclable materials, craft sticks, and rubber bands. When you push down on the launching stick, it stores up potential energy, much like an elastic band would do when you stretch it. The energy stored in the stick is transformed into kinetic energy when it is released.

Learn more: Little Bins for Little Hands

5. Chain Reaction of Popsicle Sticks

Learners gently weave wooden sticks together in this project, ensuring each piece flexes. The twisted sticks are maintained in position and store potential energy. The free stick snaps back to its usual shape when the first stick is released, converting elastic energy to kinetic energy.

Learn more: Clearway Community Solar

Gravitational Energy

6. acceleration and gravity.

Using cardboard tubes, students study the link between drop height and object speed in this assignment. Gravity increases an object's speed by 9.8 meters per second (m/s) when it is in free fall. Students test the effects of gravity by timing how far a marble slides down a cardboard tube in one second, two seconds, etc.

Learn more: Science Sparks

7. Gravity modeling

In this activity, students study how gravity functions in the solar system using a broadsheet, a pool ball, and marbles. Using a pool ball for the Sun and marbles for the planets, students test the gravitational force of the Sun's mass and attraction.

Learn more: Science Learning Hub

8. Maneuvers Using Gravity Assist

This lesson explores how a gravity assist or "slingshot" maneuver might help rockets reach faraway planets. Students study the elements contributing to a successful slingshot movement while simulating a planetary encounter using magnets and ball bearings.

Learn more: Science Learn

Chemical Energy

9. colors of fireworks.

In this chemical energy lesson, students test how fireworks colors relate to chemicals and metal salts. Because of the chemical energy they generate, various chemicals and metal salts burn with varying light hues.

Learn more: ThoughtCo.

Light Energy

10. reflecting light off a cd.

Ever wonder why CD light reflects a rainbow? Your kids probably have too. This project explains to kids why and how light energy works. It's a wonderful way to bring science outdoors.

Learn more: Twinkl

Nuclear Energy

11. observing nuclear energy in a cloud chamber.

This energy activity aims for students to construct and test a cloud chamber. A water- or alcohol-supersaturated vapor is present in a cloud chamber. Particles enter the cloud chamber as the atom's nucleus releases nuclear energy upon disintegration.

Learn more: Jefferson Lab

Kinetic Energy and Motion Energy

12. car safety during a crash.

Students explore techniques to prevent a toy automobile from crashing while studying Newton's law of conservation of energy. In order to design and construct an effective bumper, students must consider the toy car's speed and direction of motion energy just before impact.

Learn more: STEM Inventions

13. Creating a device for dropping eggs

This motion energy activity aims to have students create a mechanism to cushion the impact of an egg being dropped from various heights. Although the egg drop experiment may teach potential & kinetic types of energy, and the law of conservation of energy, this lesson focuses on preventing the egg from shattering.

Learn more: Get Smart about STEAM

Solar Energy

14. solar pizza box oven.

In this activity, kids use pizza boxes and plastic wrap to build a simple solar oven. By capturing the Sun's rays and transforming them into heat, a solar oven is able to prepare meals.

Learn more: Blendspace

15. Solar Updraft Tower

This project has students create a solar updraft tower out of paper and look into its potential for converting solar energy into motion. The top propeller will rotate when the device's air warms up.

Learn more: Walk with Easha!!

16. Do Different Colors Absorb Heat Better?

In this classic physics experiment, students investigate if the color of a substance impacts its thermal conductivity. White, yellow, red, and black paper boxes are used, and the order in which the ice cubes melt in the sun is predicted. In this way, they can determine the sequence of events that caused the ice cubes to melt.

Learn more: Teach Engineering

Heat Energy

17. homemade thermometer.

Students create basic liquid thermometers in this classic physics experiment to examine how a thermometer is made using the thermal expansion of liquids.

Learn more: Yuri Ostr

18. Heat-curling metal

Within the context of this activity, students investigate the relationship between temperature and the expansion of various metals. Students will see that strips produced from two materials behave differently when set over a lit candle.

Learn more: Science Buddies

19. Hot air in a balloon

This experiment is the best way to show how thermal energy affects air. A tiny glass bottle, a balloon, a big plastic beaker, and access to hot water are required for this. Pulling the balloon over the bottle's rim should be your first step. After inserting the bottle into the beaker, fill it with hot water so that it surrounds the bottle. The balloon begins to expand as the water gets hotter.

Learn more: Go Science Girls

20. Heat conduction experiment

Which substances are most effective in transferring thermal energy? In this experiment, you will compare how different materials can carry heat. You'll need a cup, butter, some sequins, a metal spoon, a wooden spoon, a plastic spoon, these materials, and access to boiling water to complete this experiment.

Learn more: STEM Little Explorers

Sound Energy

21. rubber band guitar.

In this lesson, students construct a basic guitar from a recyclable box and elastic bands and investigate how vibrations produce sound energy. When a rubber band string is pulled, it vibrates, causing air molecules to move. This generates sound energy, which is heard by the ear and recognized as sound by the brain.

Learn more: Wiki How

22. Dancing Sprinkles

Students learn in this lesson that sound energy may cause vibrations. Using a plastic-covered dish and candy sprinkles, students will hum and observe what happens to the sprinkles. After conducting this investigation, they can explain why sprinkles react to sound by jumping and bouncing.

23. Paper cup and string

Your kids should be accustomed to engaging in activities like this sound experiment. It's a great, entertaining, and straightforward scientific idea showing how sound waves may pass through things. You only need some twine and some paper cups.

Learn more: Global Call Forwarding

Electrical Energy

24. coin-powered battery.

Can a pile of coins generate electrical energy? Within the context of this activity, students make their own batteries using a few pennies, and vinegar. They get to study electrodes as well as the movement of charged particles from one metal to another through electrolytes.

Learn more: Generation Genius

25. Electric Play Dough

Students gain background knowledge on circuits in this lesson using conductive dough and insulating dough. Kids build basic "squishy" circuits using the two types of dough that light an LED so they can observe firsthand what occurs when a circuit is open or closed.

Learn more: The Dad Lab

26. Conductors and insulators

Your kids will love using this worksheet on conductors and insulators to explore how electrical energy may travel through various materials. The document includes a list of several materials, all of which you should be able to acquire quickly. Your pupils must guess whether each of these substances will be an insulator that doesn't carry an electric form of energy or a conductor of electricity.

Learn more: Science Notes

Potential and Kinetic Energy Combined

27. paper roller coaster.

In this lesson, students construct paper roller coasters and try out adding loops to see if they can. The marble in the roller coaster contains potential energy and kinetic energy at different locations, such as at the summit of a slope. The stone rolls down a slope with kinetic energy.

Learn more: Instructables

28. Bouncing a Basketball

Basketballs have potential energy when they are first dribbled, which is transformed into kinetic energy once the ball hits the ground. When the ball collides with anything, part of the kinetic energy is lost; as a result, when the ball bounces back up, it is unable to achieve the height it had reached before.

Learn more: Research Gate

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Experiments

Try these with your students

Acid–base back titration | 16–18 years

Write balanced equations and calculate reacting masses and moles to find the limiting reagent

‘Gold’ coins on a microscale | 14–16 years

Practical experiment where learners produce ‘gold’ coins by electroplating a copper coin with zinc, includes follow-up worksheet

Toothpaste investigation: neutralisation reactions

Test the basicity of toothpastes and give context to neutralisation reactions

Qualitative tests for organic functional groups | practical videos | 16–18 students

Video and supporting resources to support a practical investigation to identify organic functional groups using a range of qualitative tests

Preparation of an organic liquid | practical videos | 16–18 students

Video and supporting resources to support practical work based on synthesis of an organic liquid, the experiment includes the stages of preparation, separation and purification

Electrochemical cells | practical videos | 16–18 students

Video and supporting resources to support electrochemistry practical work, including two microscale experiments, animation and cell diagrams

Rates of reaction | practical videos | 16–18 students

Video and supporting resources, includes an initial rate (iodine clock reaction) and continuous monitoring method (volume of gas)

Practical potions microscale | 11–14 years

Observe chemical changes in this microscale experiment with a spooky twist.

Microscale neutralisation and precipitation reactions | 11–14 years

Hone your learners’ observation skills with two microscale reactions: neutralising citric acid and creating a lead iodide precipitate

Antibacterial properties of the halogens | 14–18 years

Use this practical to investigate how solutions of the halogens inhibit the growth of bacteria and which is most effective

Equilibrium and Le Chatelier’s principle

Investigate the effects of concentration, pressure and temperature on equilibrium and explore Le Chatelier’s principle in this series of demonstrations.

Microscale technicians in trouble! investigation

Some solutions have been mixed up – help the technicians work out which is which

Rates of hydrolysis – practical videos | 16–18 students

Video resources and associated questions on the topic of hydrolysis of halogenoalkanes.

Redox – practical videos | 16–18 students

Video resources to support the teaching of popular classroom-based redox titrations.

Practical videos | 16–18 years

Videos of key practical techniques and apparatus for revision, flipped learning or remote teaching

Electrolysis of brine

In association with Nuffield Foundation

Use this colourful practical to introduce students to the electrolysis of brine, or sodium chloride solution. Includes kit list and safety instructions.

The equilibrium between two coloured cobalt species

In this demonstration the equilibrium between two different coloured cobalt species is disturbed. Le Chatelier’s principle is used to predict a colour change.

Precipitation reactions of lead nitrate

Compare the colours of various lead compounds to identify which would be good pigments in this microscale practical. Includes kit list and safety instructions.

Some reactions of sulfur dioxide

Observe the reactions of sulfur dioxide with potassium manganate (IV), iodide/iodate mixture and indicator solution. Includes kit list and safety instructions. 

The determination of copper in brass

Try this microscale class practical to investigate how much copper there is in brass using nitric acid. Includes kit list and safety instructions.

Microscale reactions of hydrogen sulfide

Observe the reactions of hydrogen sulfide with lead nitrate, silver nitrate and potassium manganate(VII) in this microscale practical. Includes kit list and safety instructions.

Microscale reactions of ammonia

Try this practical to explore the reactions of ammonia with indicator solution, copper(II) sulfate solution and Nessler’s reagent. Includes kit list and safety instructions.

Measuring density

By measuring the relative mass of seawater and tap water, students will be able to discover the density of these liquids. Includes kit list and safety instructions. 

The chemistry of thiosulfate ions

Sodium thiosulfate has several interesting reactions with a variety of chemicals. This experiment will let students explore and record these reactions. Includes kit list and safety instructions.

Some reactions of nitrogen dioxide

Using a range of chemicals and solutions, students can create an experiment that will explore some of the reactions of nitrogen dioxide. Includes kit list and safety instructions.

Testing acids and bases on a microscale

Test various substances with indicator solution and look for colour changes in this microscale class practical. Includes kit list and safety instructions.

Mass changes in chemical reactions

Perform two chemical reactions to see whether any mass changes occur in this microscale class practical. Includes kit list and safety instructions.

The oxidation of cyclohexanol by nitric acid

Perform a ring opening oxidation using nitric acid to produce the dicarboxylic acid, 1,6-hexanedioic acid (adipic acid) – and then use the solid crystals that form to determine a melting point. Includes kit list and safety instructions.

Exploring the chemistry of chromium, molybdenum and tungsten

Discover how transition elements differ in aspects of colour, precipitate formation, changes in oxidation state and equilibria. Includes kit list and safety instructions.

Brady’s test for aldehydes and ketones

Identify aldehydes and ketones using Brady’s reagent (2,4-dinitrophenylhydrazine) in this microscale experiment. Includes kit list and safety instructions.

The chemical properties of phenol

Observe and interpret some of the chemical reactions of hydroxybenzene (phenol), by adding five different substances to a Petri dish, and noting down findings. Includes kit list and safety instructions.

Preparing ethyne on a microscale

Generate ethyne gas with calcium carbide and test its properties in this microscale class practical. Includes kit list and safety instructions.

Observing chemical changes

Try this microscale practical to explore the chemical changes in displacement, redox and precipitation reactions. Includes kit list and safety instructions.

Diffusion of gases on a microscale

Try this class practical to explore the diffusion of gases and how relative molecular mass affects rate of diffusion. Includes kit list and safety instructions.

Redox chemistry with dichromate ions

Observe the colour changes that occur with the reduction of dichromate ions by hydrogen peroxide. Includes kit list and safety instructions.

Oxidation states of iron

Compare the two main oxidation states of iron and consider explanations for differences in this microscale practical. Includes kit list and safety instructions.

Microscale reactions of metals with acids

Try this class practical to explore reactivity series with various metals as they react with acids on a microscale. Includes kit list and safety instructions.

Unsaturation test with potassium manganate(VII)

Use a solution of potassium manganate to test for unsaturation in organic compounds in this microscale practical. Includes kit list and safety instructions.

Properties of group 2 elements

Microscale experiment where various anion solutions are added to drops of group 2 element cations. Includes kit list and safety instructions.

Testing for unsaturation with bromine on a microscale

Try this class experiment to prepare elemental bromine and use it to test for unsaturation in organic compounds. Includes kit list and safety instructions.

Oxygen and methylene blue

Reacting hydrogen peroxide, and potassium manganate together will produce detectable oxygen so by using methylene blue solution, and a gas generating apparatus students can test for the presence of oxygen in this practical. Includes kit list and safety instruction.

Synthesis of aspirin on a microscale

Use this class practical to produce aspirin in a microscale esterification reaction using phosphoric acid as a catalyst. Includes kit list and safety instructions.

Energy changes in neutralisation

Study energy changes in two chemical reactions using thermometer strips to measure temperature in this experiment. Includes kit list and safety instructions.

Formation of TCP (2,4,6-trichlorohydroxybenzene)

Delve into preparing TCP by reacting hydroxybenzene (phenol) with chlorine gas, and create this distinctive smelling compound.

Investigating redox reactions on a microscale

Carry out two redox reactions and observe and interpret the results in this microscale class practical. Includes kit list and safety instructions.

The microscale synthesis of indigo dye

Carry out a microscale organic synthesis, the result of which will leave students with indigo dye. Includes kit list and safety instructions.

The treatment of oil spills

Tackle the real-life environment problem of oil spills in your classroom, by creating and then treating a micro version of an oil event. Includes kit list and safety instructions.

The microscale synthesis of azo dyes

Synthesise an azo dye, and use it to change the colour of cotton, with this class experiment. Includes kit list and safety instructions.

Sulfate and carbonate solubility of Groups 1 and 2

Try this microscale practical to explore the properties of elements in Groups 1 and 2 as they form various precipitates. Includes kit list and safety instructions.

Exploring the properties of the carvones

Test the smell of each enantiomer of carvone and detect the differences

Measuring the amount of vitamin C in fruit drinks

Explore ascorbic acid in fruit drinks through titration in this experiment, with specimen results and calculations, stock solutions, and detailed notes included. 

Displacement reactions of metals on a microscale

Examine the reactions between various metals and metal salt solutions in this microscale class practical. Includes kit list and safety instructions.

Electrolysis using a microscale Hoffman apparatus

Investigate the electrolysis of sodium sulfate solution using a microscale Hoffman apparatus in this class practical. Includes kit list and safety instructions.

The chemistry of silver

Discover the properties of silver compounds with redox reactions, complex formation and colour/state changes. Includes kit list and safety instructions.

Transition elements and complex compounds microscale experiment | 16–18 years

Try this microscale practical investigating the transition elements, complex formation and change in oxidation state. Includes kit list and safety instructions

Analysis of aspirin tablets on a microscale

Try this microscale class practical to analyse aspirin tablets and find out how much salicylic acid is present. Includes kit list and safety instructions.

The temperature changes induced by evaporation

Explore the rate of evaporation for a trio of liquids, using just a temperature strip, and our worksheet. Includes kit list and safety instructions.

Properties of stereoisomers

By soaking cotton wool in two limonene enantiomers, and adding a stereoisomer, students can explore the differences between each chemical and discuss how they each might react in different conditions. Includes kit list and safety instructions.

Turning copper coins into ‘silver’ and ‘gold’

Perform what looks like alchemy with ordinary copper coins in this teacher demonstration. Includes kit list and safety instructions.

The effect of temperature on solubility

Hot or cold, which water is better for soluble substances? Explore your finding from this practical into the effect of temperature on solubility. Includes kit list and safety instructions. 

Particles in motion?

Explore the movement of gas particles in this practical but reacting calcium carbonate with hydrochloric acid. Includes kit list and safety instructions. 

The reactivity of the group 2 metals

Compare group 1 and group 2 metals with this practical that shows their reactivity rates, where students can take control of their own observations and come to their own conclusions

Producing a foam

Explore foams and their properties in this experiment, so students learn how foam is produced and produce their own. Includes kit list and safety instructions.

Electricity from chemicals

Use various metals, in pairs, and n electrolyte to form a cell. Then observe the formation of ions around the reactive metal, and compare the speed with which they form around the less reactive metal. Includes kit list and safety instructions. 

The electrolysis of solutions

Electricity is passed through various solutions and the products are identified. Includes kit list and safety instructions

The volume of 1 mole of hydrogen gas

Understand the volume of one mole of hydrogen gas through a magnesium and acid reaction, taking note of the temperature and pressure. Includes kit list and safety instructions. 

The effect of temperature on reaction rate

Discover more about collision theory in this practical, where a sodium thiosulfate and hydrochloric acid mixture produce an interesting reaction. Includes kit list and safety instructions. 

The effect of concentration and temperature on reaction rate

Reaction rate can be altered by many things, in this practical students explore how temperature and concentration effect reaction in an closer look at kinetics. Includes kit list and safety instructions. 

Reacting elements with oxygen

Different members of the periodic table will exhibit different reactions when exposed to oxygen, often through heating. This practical supports students to understand the diversity of chemicals and their principles.

Creating an effervescent universal indicator ‘rainbow’

This quick practical uses existing chemicals in your learning space, for students to observe the effervescent reaction that causes universal indicator to create a ‘rainbow’ of colour. Kit list and safety instructions included.

The reaction of magnesium with steam

Plunge a burning magnesium ribbon into the steam above boiling water and allow the hydrogen that is formed to burn – or collect it over water and test it with a lighted spill.

Making a reaction tube

Guide students through this practical to create a reaction tube. Includes kit list and safety instructions.

Properties of the transition metals and their compounds

Student discover the diversity of transition metals in this practical that puts their knowledge of these common elements to the test. Includes kit list and safety instructions.

Disappearing ink

Explore the reaction between acids and bases as students create disappearing ink, in this favourite classroom practical.

Testing salts for anions and cations

A full range of chemicals will guide students into discovering how to identify the composition of unknown substances. Includes kit list and safry instructions. 

Rubber band experiment

A rubber band, a hairdryer, and a curious mind will see students discover the principles of heat based reactions. Includes kit list and safety instruction.

A Cartesian diver

An old favourite experiment, the Cartesian diver is easy for students to complete. Explore important ideas that build a foundation of knowledge. 

Chemistry and electricity

Create coloured writing from acids, alkali, and salt solution, all activated through electrolysis.

Compare the viscosity of thick and thin liquids in this experiment, which gets young learners exploring how viscosity alters the speed of an air bubble through the substances. Includes kit list and safety instructions.

The oxidation states of vanadium

Introduce your students to the idea that different oxidation states of transition metal ions often have different colours, and that electrode potentials can be used to predict the course of the redox reactions. Includes kit list and safety instructions. 

Burning milk powder

Gather a Bunsen burner, and some common powdered milk to help students grasp the ideas of surface area and reaction rates. Includes kit list and safety instructions. 

A visible activated complex

A simple demonstration of catalysis also introducing the idea of an activated complex and to allow discussion of the mechanism of catalysis. Includes kit list and safety instructions.

Hydrogen peroxide decomposition using different catalysts

Collect a range of catalysts to explore the decomposition of hydrogen peroxide, paying close attention to the varied reaction rates. Includes kit list and safety instructions.

Competition for oxygen | reacting metals with oxides

Explore the reactions of metals when exposed to the oxide of another metal. When reactions like these occur, the two metals compete for the oxygen. Includes kit list and safety instructions.

Electrolysis of potassium iodide solution

Find out how the electrolysis of a potassium iodide solution works with this practical. Includes kit list, and safety instructions. 

An alternative to using compressed gas cylinders

Getting gas under pressure allows exciting demonstrations such as igniting balloons filled with hydrogen gas. Includes kit list and safety instructions.

Flame tests (the wooden splint method)

Find a new method to perform flame tests using wooden splints soaked in chlorides. Includes kit list and safety instructions.

Making nylon: the ‘nylon rope trick’

The ‘nylon rope trick’ is a classic of chemistry classrooms, by mixing decanedioyl dichloride and in cyclohexane you can create a solution that will form nylon strings when floated on an aqueous solution of 1,6-diaminohexane. Kit list and safety instructions included.

Neutralisation circles

Support students to explore neutralisation circles in this experiment that can be performed with common chemistry classroom equipment. Kit list and safety instructions included. 

The methane rocket

Ignite methane with oxygen in a bottle, and amaze students with this methane rocket. Contains kit list and safety instructions.

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Latest works.

SCIENCE TOYS - Younger Kids

Anchoring Ni(II) bisacetylacetonate complex into CuS immobilized MOF for enhanced removal of tinidazole and metronidazole

• Saptarshi Roy 1 ,
• Soumya Ranjan Mishra 1 ,
• Vishal Gadore 1 ,
• Ankur Kanti Guha 2 &
• Md. Ahmaruzzaman   ORCID: orcid.org/0000-0002-6805-5409 1  

npj Clean Water volume  7 , Article number:  83 ( 2024 ) Cite this article

Metrics details

• Nanoscale materials
• Pollution remediation

Here in this study, a novel ternary CuS/HKUST‒1/Ni(acac) 2 nano photocatalyst (CSHK‒Ni) was developed through a facile modification of HKUST‒1 MOF with Ni(acac) 2 metal complex and by immobilizing CuS into the metal-organic framework (MOF). The incorporation of CuS, a narrow bandgap semiconductor, is anticipated to allow easy excitation by visible-light and improve the photocatalytic potential of the formulated catalyst which is validated by the decrease in the bandgap energy from 3.10 eV of pristine MOF to 2.19 eV. Moreover, the anchoring of the metal complex improves the light harvesting behavior by increased conjugation. Photoluminescence studies provided evidence of the effective separation of the photoinduced charge-carriers, reducing the rate of recombination and enhancing the photocatalytic potential of the CSHK‒Ni nanocomposite. The engineered catalyst displayed remarkable efficiency in the degradation of nitroimidazole containing antibiotics, Tinidazole (TNZ) and Metronidazole (MTZ), via H 2 O 2 assisted AOP achieving a maximum photocatalytic efficiency of 95.87 ± 1.64% and 97.95 ± 1.33% in just 30 min under irradiation of visible light at optimum reaction conditions. The possible degradation pathway was elucidated based on the identification of ROS and degradation intermediates via HR‒LCMS and quenching experiments. Meanwhile, the chemical oxygen demand (COD) and total organic carbon (TOC) removal were also examined, encompassing the discussing of various aspects including reaction conditions, influence of various oxidizing agents, competing species and dissolved organic substrates present in the wastewater, marking the novelty of the study. This research elucidated the role of the CSHK‒Ni nanocomposite as an interesting photocatalyst in the elimination of emerging nitroimidazole containing pharmaceutical pollutant under visible-light exposure, presenting an exciting novel avenue for a cleaner and greener environment in the days to come.

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Introduction.

One of the main reasons for the deterioration of our environment is the rapid and increased industrialization brought about by the Industrial Revolution. Furthermore, the amount of untreated wastewater released into aquatic bodies has significantly expanded due to the manufacturing industries’ large-scale output, contributing to the global water and environmental pollution issue 1 . The scarcity of clean drinking water has now become a global issue. Most developing countries like India, Bangladesh, Pakistan, and Nepal are adversely affected by water pollution 2 . Discharging water-soluble and non-biodegradable pollutants, such as textile dyes, pesticides, pharmaceuticals, heavy metals, personal care products, nitro compounds, and phenols, contaminates most freshwater bodies 3 .

Personal care products and pharmaceuticals (PPCP) have been classified as emerging pollutants because of their potentially harmful environmental impacts. Antibiotics represent a prominent category of pharmaceuticals frequently found in aqueous systems, originating from the discharge of hospital effluents and industries engaged in drug and pesticide manufacturing. Since antibiotics are highly persistent and resilient to biological breakdown, they are categorized as emerging contaminants. Antibiotic resistance in bacteria may result from a genetic mutation brought on by prolonged antibiotic treatment 4 . Studies have indicated that the continued presence of antibiotics in aquatic environments may negatively affect both human health and the ecosystem. Tinidazole (TNZ) and metronidazole (MTZ) are antibiotics belonging to the nitroimidazole class, are mainly used to treat parasite and bacterial infections, skin ailments and gum infections. Previous literatures have suggested that antibiotics, featuring a nitroimidazole framework, have the potential to induce gene mutations and may possess carcinogenic properties. Thirty percent of the medication is eliminated and enters the aquatic environment unaltered tending to accumulate with time 5 . Due to their widespread distribution in a range of aquatic settings, tinidazole and metronidazole were designated as drugs of significant environmental concern.

Conventional wastewater treatment approaches are ineffective for eliminating nitroimidazoles from wastewater effluent owing to their complex molecular structure and high solubility 6 . Photodegradation is widely used to remove harmful pollutants because of its primary process, affordable nature, and easy operating circumstances, which also prevent the risk of secondary pollution. Photocatalysis, which converts hazardous organic pollutants in wastewater into safe molecules solely using solar light, is a promising environmentally friendly solution to reduce environmental pollution. Advanced oxidation process (AOP) is a novel approach by which reactive oxygen species (ROS) like hydroxyl radicals (OH • ), superoxide radicals (O 2 −• ) and sulfate radicals (SO 4 −• ) are generated by the decomposition of an oxidizing agent like hydrogen peroxide (H 2 O 2 ), ozone (O 3 ), persulfate (S 2 O 8 2− ), etc., by a heterogeneous catalyst under mild conditions and the ROS generated then attack the pollutant molecules and bring their degradation 7 .

Heterogenous AOP is a surface phenomenon occurring over the surface of a semiconductor photocatalyst and is a facile method for degrading organic pollutants in wastewater. Here, a photocatalyst is excited under light irradiation, generating electron-hole pairs that decompose the oxidizing agent, resulting in the formation of ROS. The separation of the electrons and holes is necessary to utilize them for generating ROS before their recombination. The synergistic attack of the ROS allows the degradation of the target pollutant into less harmful products like CO 2 and H 2 O. Recently, a photo-Fenton like AOP has been gaining broad attention owing to its ease of operation, cost-effectiveness, and higher efficiency. Hydrogen peroxide is used as a green oxidizing agent in a photo-Fenton-like AOP for generating OH • and O 2 −• radicals to degrade target pollutants under light irradiation 8 .

Since nanomaterials possess a large surface area, are highly reactive, and have more exposed active sites than other materials, they are widely desired for photocatalysis 9 . Various nanoscale metal oxide-based photocatalysts have been extensively explored for the photodegradation of organic pollutants from aqueous streams owing to their low cost, high abundance, higher light absorption properties, and high stability. Titanium dioxide (TiO 2 ) has remained a milestone in photocatalysis due to its excellent stability, resistance to photocorrosion, non-toxicity, and low cost 10 . Despite its significant advantages, some limitations, such as low specific surface area, a faster rate of charge recombination, and a higher bandgap of 3.2 eV, force researchers to develop new materials with multifunctional properties to cope with the limitations of TiO 2 . Additionally, the agglomeration of nanoparticles during synthesis limits their light absorption and decreases the photocatalytic activity. Copper sulfide (CuS) is a non-toxic, low-cost p-type semiconductor photocatalyst with a suitable bandgap of 1.8 eV and outstanding light-harvesting properties 11 , 12 . Interestingly, the photocatalytic properties of CuS can be tailored based on its morphology and synthesis techniques. Different morphologies of CuS, such as spheres 13 , hollow spheres 13 , nanotubes 14 , hexagonal sheets 15 , and flower-like 16 , have been previously reported in the literature. Recently, Abdullah et al. 17 fabricated a ternary CuO/CuS/MnO 2 nanocomposite to photodegrade methylene blue dye with 98% efficiency. Mertah et al. 18 investigated the degradation of sulfamethoxazole using Cu-CuS@TiO 2 nanocomposite. CuFeS 2 /CuS heterojunction showed enhanced photodegradation of organophosphate insecticides, as reported by Gholami et al. 19 . The literature suggests that the photocatalytic properties of CuS could be improved by forming its nanocomposites.

Various porous materials such as activated carbon, biochar, zeolites, and clays have been explored as support for nanomaterials to prevent their agglomeration. However, the shortcomings of irregular pore size, low surface area, and negligible light absorption still need to be resolved. Metal-organic frameworks (MOFs) are a novel category of porous and crystalline supports that can be constructed in one, two, or three dimensions using organic linkers to connect a metal center with an organic ligand 20 . The ability of MOFs to easily adjust their pore size from meso to micro scale by modifying their organic ligand and inorganic metal ions is one of its most remarkable features 21 . Additionally, they have a large surface area, strong chemical reactivity, tunable pore diameter, and a variety of structural types that facilitates them to be used in a diverse range of applications 22 . MOF-based semiconductor nanocomposites exhibit novel and remarkable capabilities due to their synergistic effect. With copper as its inorganic metal center and benzene-1,3,5-tricarboxylate (H 3 BTC) as its organic ligand, HKUST-1 is one of the most commonly mentioned MOFs 23 . A vacancy in the framework structure is created by Cu ions coordinating with oxygen atoms from BTC moieties and H 2 O molecules 24 . This MOF has extensive uses in various industries, including hazardous gas purification, liquid phase separation, sensing, CO 2 adsorption, environmental remediation, hydrogen storage, photocatalysis, drug delivery, etc 25 . A novel ternary nanocomposite of CuS supported over zeolite and ZIF-8 showed 87% removal of methylene blue from the aqueous phase 26 . Recently, CuS/HKUST-polydopamine nanocomposite showed enhanced photo-antimicrobial properties under visible light irradiation with an efficiency of up to 99% 27 . Despite all these developments, the creation of CuS heterojunctions with metal complexes was not given much attention. The synergistic benefits of heterojunctions of CuS and metal complexes include a conjugated structure for effective charge transfers, a decreased charge recombination rate at very low metal concentrations, and metal centers for redox reactions. Complexes of Ni (II) with acetylacetone are increasingly attracting interest in fields of material science due to their diverse utility as molecular separation, catalysis, solar energy storage, and light-emitting diode materials. The remarkable thermal stability and the chelating behavior of acetylacetone, allows it to be an excellent supporting moiety for harvesting of light, and then subsequently transfers energy to the metal ion, serving as a photosensitizer 28 . Ouedraogo et al. 29 synthesized g-C 3 N 4 /copper octacarboxyphthalocyanine heterojunction, which showed 98% degradation of methylene blue under optimum conditions. Das et al. 30 studied the photocatalytic hydrogen evolution and chromium reduction using Copper tetraphenylporphyrin tetrasulfonic acid decorated g-C 3 N 4 . Recently, g-C 3 N 4 /Mn(acac) 3 nanocomposite showed 99.59% degradation of rhodamine B dye within 55 min of visible light irradiation.

Continuing this vein, we aim to present a novel ternary CuS/HKUST-1/Ni(acac) 2 (CSHK‒Ni) nanocomposite by anchoring a transition metal Ni(II) Bis-acetylacetonate complex into CuS immobilized Metal-Organic Framework via a facile approach for the degradation of nitroimidazole antibiotics. There is no mention of such examples obtained by coupling HKUST‒1 MOF with Ni(acac) 2 complex as a photocatalyst in previous literatures as per the best knowledge of the author, and this work is first of its kind. The designed photocatalyst was investigated for the elimination of two nitroimidazole framework containing pharmaceutical, tinidazole (TNZ) and metronidazole (MTZ), using H 2 O 2 -assisted AOP under visible light in a very short duration of 30 min. Also, theoretical and computational studies using Gaussian 16 suit program have been provided to validate the bandgap of the synthesized materials. The possible degradation pathway of the breakdown of TNZ and MTZ was elucidated based on the identification of degradation intermediates via HR‒LCMS. Quenching experiments using different scavenging agents and EPR studies were conducted for the assessment of the ROS responsible for the breakdown of the model contaminants. Meanwhile, COD and TOC removal were also examined, encompassing the discussing of various aspects including reaction conditions, influence of various oxidizing agents, competing species and dissolved organic substrates present in the wastewater, marking the novelty of the study. Furthermore, the performance of the fabricated CSHK‒Ni nanocomposite under practical water conditions and the removal of other toxic pharmaceutical contaminants was comprehensively analyzed. From the commercial perspective the designed catalyst displays significant potential for large-scale industrial applications owing to its cost-effectiveness compared to previously reported catalysts. Besides, several strategies have been outlined as future prospects to enhance the catalytic recycling of the synthesized CSHK–Ni nanocomposite via structural modifications focusing on improving the stability, durability, and reusability of the nanomaterial. This research elucidated the role of the CSHK‒Ni nanocomposite as an interesting photocatalyst in the elimination of emerging nitroimidazole containing pharmaceutical pollutant under visible light exposure for a cleaner and greener environment in the days to come.

Cupric nitrate trihydrate extrapure (Cu (NO 3 ) 2 .3H 2 O), thioacetamide (CH 3 CSNH 2 ), trimesic acid extrapure and nickel (II) nitrate hexahydrate (Ni (NO 3 ) 2 .6H 2 O) were acquired from SRL chemicals, India. Solvents and reagents such as ethanol, NaOH, acetylacetone and chloroform were obtained from Sigma‒Aldrich. Further purification steps were avoided as the chemicals utilized were of analytical grade, and deionized water was consistently employed throughout the experiments.

The preparation of Ni(acac) 2 complex is carried out by slowly adding 4.5 ml of acetylacetone (0.044 moles) into an aqueous solution of NaOH (1.6 g in 15 ml water, 0.04 moles) while stirring, maintaining the temperature below 40 °C. The reaction mixture should be stirred thoroughly to ensure that any white precipitate formed at this point is completely dissolved. The yellow‒colored solution prepared above is added dropwise with vigorous stirring over 15 min into a 25 ml aqueous solution of Ni (NO 3 ) 2 .6H 2 O (5.81 g, 0.02 moles). The resulting bluish‒green precipitate is filtered, washed with distilled water, and subsequently dissolved in a hot solution mixture of 39 mL of 95% ethanol and 26 mL chloroform in a fume hood. Prolonged boiling should be avoided. Finally, the green solution is allowed to cool to ambient temperature, and then chilled in ice to obtain turquoise‒colored needles of pure Ni(acac) 2 . These crystals are then washed with cold ethanol, dried in air and stored for further use.

Typically, for the synthesis of CuS/HKUST‒1, 0.50 g of HKUST‒1 MOF support is dispersed in ethanol under ultrasonication for 20 min. Then, aqueous solution of 1.2 g of Cu (NO 3 ) 2 .3H 2 O is added into the former mother solution, followed by the addition of 0.75 g of thioacetamide (CH 3 CSNH 2 ) under stirring at room temperature. The resulting reaction mixture was then taken into a 100 ml stainless steel reactor with lined with Teflon and heated in an electric oven at 160 °C for 8 h. The obtained bluish-black precipitate of CuS/HKUST‒1 was subsequently collected via centrifugation, subjected to multiple times washing with distilled water and ethanol, and finally dried overnight at 80 °C.

The CuS/HK (0.20 g), so obtained, was dispersed in 95% ethanol and then slowly added in drops with constant stirring into another solution containing Ni(acac) 2 dissolved in 39 mL of 95% ethanol and 26 mL chloroform. The resulting reaction mixture was then kept under sonication for 1 h and subsequently cooled in an ice bath, to form precipitates of CSHK‒Ni. The obtained greenish‒black CSHK‒Ni composite was subjected to filtration and multiple rounds of washing with 95% ethanol, and then finally dried in an electric oven maintained at 80 °C overnight. Figure 1 portrays the schematic illustration of the fabrication of the CSHK‒Ni composite.

Schematic representation of the fabrication of CuS/HK and CSHK‒Ni nanocomposite.

Analytical experiments

The entire photodegradation tests were performed in glass beakers of 100 mL capacity, subjected to irradiation under a Philips LED bulb of 23 W with an illuminance of 11,790 lx and the measured intensity of radiation was found to be 51.25 W/m 2 to assess the photodegradation efficacy of the CSHK‒Ni nanocomposite. The experimental arrangement was established inside a wooden compartment with the LED bulb positioned overhead and the glass beaker was placed at a distance of 10 cm from the LED source. Typically, the batch degradation experiments were performed with an optimized amount of the synthesized nanocomposite in 50 mL TNZ/MTZ solution of 20 mg/L initial concentration as the standard model contaminant, and then followed by the introduction of an optimized amount of H 2 O 2 . Subsequently, the reaction mixture was allowed to attain the adsorption-desorption equilibrium by stirring in the dark for 20 min, prior to 30 min irradiation of visible light for photodegradation to occur. The photodegradation of TNZ and MTZ was tracked by monitoring a decrease in the maximum absorbance at 277 nm and 321 nm, respectively by employing a UV‒vis spectrophotometer. Moreover, no significant decline in the intensity of absorption (<5%) was noted after allowing the contaminant solution to agitate in the absence of light with the photocatalyst (HKUST‒1, CuS/ HKUST‒1 and CSHK‒Ni) and H 2 O 2 alone, eliminating the possibility of subsequent degradation by H 2 O 2 alone. Additionally, no significant change in the intensity of absorption (<3%) was observed after the irradiation of the TNZ/MTZ solution with visible light in the absence of any oxidizing agent and the photocatalyst, indicating that the pollutant solution exhibited resistance to self-degradation under visible light. The percentage degradation efficiency of the photocatalytic process can be determined by the following reaction:

In this equation, C o denotes the initial concentration of the contaminant, while C t signifies the contaminant concentration after specified time t, in mg/L.

Again, the degradation kinetics of the TNZ/MTZ solution was computed employing the pseudo-first order kinetics model, employing the equation outlined below:

Herein, k refers to the pseudo-first order rate constant of the degradation reaction. The graphs involving the error bars depict the degradation profile and the reaction kinetics plot with negligible standard deviations, suggesting reasonable reproducibility of the experiments for atleast three times under consistent reaction conditions.

While in most of the literatures, the photocatalytic degradation reactions were typically performed in pure water, however, the influence of practical water samples on the photodegradation of hazardous organic contaminants have not been extensively investigated. Hence, this study primarily revolves around the practical utility of the synthesized CSHK‒Ni photocatalyst in practical wastewater conditions by considering the consequence of various inorganic ions and dissolved organic compounds on the photodegradation mechanism. To access the performance of the photocatalyst in real‒water matrices, photodegradation experiments were conducted using mineral water purchased from a local grocery store, waters from Barak river, lake water collected from a lake in the NIT Silchar campus with a pH of 8.17, rain water and tap water from municipal water systems. The standard method for determining chemical oxygen demand (COD) was employed in which samples containing H 2 O 2 were first subjected to an excess of 10% Na 2 SO 3 to eliminate the influence of H 2 O 2 in COD measurement 31 . This is followed by heating the solution under air to oxidize the unreacted excess Na 2 SO 3 . Furthermore, the mineralization of TNZ and MTZ was assessed via total organic carbon (TOC) analysis under optimized reaction conditions, as outlined in Eq. ( 3 ).

In this equation, TOC o represent the initial TOC concentration and TOC t denotes the final TOC concentration at reaction time t.

The structural stability of the engineered CSHK–Ni catalyst was established through a reusability assessment. After centrifugal recovery, the catalyst underwent multiple cycles of washing in ethanol and water. It was then oven–dried at 80 °C before being utilized for the subsequent catalytic cycle.

Material characterization

PXRD analysis of the as-synthesized samples were conducted on Phillips X’PERT Pro X-ray diffractometer using Cu-K α at a measured wavelength of 1.5418 Å for the assessment of the crystallographic evidence. The microstructure and surface morphology, SAED patterns and the size of the particles of the prepared composite were studied using HR−TEM analyzed via a JEOL, model JEM 2100 F 200 kV instrument. FTIR spectra was obtained by Bruker Hyperion 3000 Spectrometer for the detection of functional groups. For the structural and compositional determination, SEM images and EDAX were analyzed using Gemini 500 FE−SEM instrument accelerated at a range of 0.2 to 30 kV. The determination of the elemental composition of CSHK–Ni nanocomposite was conducted via XPS utilizing a PHI 5000 versaprobe II FEI Inc. Varian Cary eclipse fluorescence spectrophotometer was utilized for recording photoluminescence (PL) spectra. Cary 5000 UV–vis–NIR, Agilent Inc. spectrophotometer instrument was employed for UV-DRS analysis to estimate the band gap energy. Genesys 10S UV-vis spectrophotometer equipped with a 1 cm cuvette, covering wavelengths from 200–800 nm was utilized for measuring the absorbance of the liquid samples.

Results and discussion

XRD analysis was employed to investigate the variation in the crystal structure of the fabricated materials i.e., HKUST‒1, CuS, CuS/HK and CSHK‒Ni as displayed in Supplementary Fig. 1 , Fig. 2a–c . The XRD spectrum of the pristine HKUST‒1 in Supplementary Fig. 1 showed distinct peaks at 7.08°, 9.51°, 11.91°, 13.39°, 16.24°, 17.36°, 19.26°, 20.46°, 22.95°, 25.27°, 29.35°, 35.79° and 39.14° are consistent to our previous reports and can be associated to the lattice planes (200), (220), (222), (400), (422), (511), (440), (600), (551), (731), (751), (773) and (882), respectively 23 , 24 . Moreover, as portrayed in Fig. 2b , the XRD spectrum of CuS/HK reveals some additional distinct characteristic peaks at 27.98°, 29.34°, 31.91°, 32.60°, 46.95°, 47.98°, 52.62° and 59.1°, which can be indexed to (101), (102), (103), (006), (107), (110), (108) and (116) crystal facets of CuS (JCPDS No. 06‒0464) 27 , 32 . This confirms the presence of the hexagonal phase of CuS in the synthesized CuS/HK composite. However, compared with the XRD spectrum of the pristine HKUST‒1, the spectrum of CuS/HK composite exhibited a slightly broader pattern, with the appearance of small peaks. This occurrence can be attributed to the in‒situ sulfuration process, wherein the synthesized CuS nanoparticles compressed the 3D structure of the MOF which contributed to the disorder and the observed small peaks in the XRD spectrum 33 . In Fig. 2c , the XRD patterns of the synthesized ternary CSHK‒Ni nanocomposite portray all the above-mentioned peaks of CuS and HKUST‒1, including some distinct peaks that perfectly agree with the previously reported literatures of Ni(acac) 2 following the JCPDS No. 19‒1524. The peaks situated at 2θ values of 8.14°, 19.14°, 26.28°, 29.68°, 36.18°, 41.32°, 42.17° and 49.52° assigned to the lattice planes (100), (111), (300), (113), (114), (123), (204) and (106), respectively are of the monoclinic phase of Ni(acac) 2 . Hence, the presence of all the mentioned distinct peaks of CuS, HKUST‒1 and Ni(acac) 2 in Fig. 2c , agreeing with their respective JCPDS No. signifies the successful fabrication of the designed ternary CSHK‒Ni nanocomposite.

X–ray diffraction patterns of the fabricated a CuS, b CuS/HK, b CSHK‒Ni nanocomposite, and; FT–IR spectra of d HKUST MOF, e Ni(acac) 2 , and f CSHK‒Ni nanocomposite.

The existence of surface functional groups and chemical bonds of the fabricated HKUST-1, Ni(acac) 2 and CSHK‒Ni nanocomposite was analyzed by FT−IR as illustrated in Fig. 2d–f . Figure 2d portrays the FTIR spectrum of pristine HKUST-1 where the characteristic distinct peaks at 1625 cm −1 , 1441 cm −1 and 1366 cm −1 were produced because of the stretching vibrations of C=O and C–O and bending vibrations of O–H of bidentate coordination mode of carboxylic acid moiety that coincide with the previous literatures 23 , 24 . Furthermore, the distinctive peak at 875 cm −1 , especially reflects the tri-substitution of benzene, originating from the bending vibrations of C–H. Again, the distinctive peak for Cu−O stretching vibration positioned at 727 cm −1 signifies that copper has been successfully coordinated with the BTC linker. The Ni(acac) 2 complex displayed prominent stretching vibrations at 1590 cm ‒1 and 1477 cm ‒1 , attributed to the C=O moiety and the allylic fragment of acetylacetonate, respectively 28 in Fig. 2e . Moreover, the peak at 1372 cm ‒1 , 1046 cm ‒1 and 1005 cm ‒1 can be ascribed to the stretching vibrations of C=C, C‒O and C–C, respectively. Vibration peaks at 603 cm ‒1 and 650 cm ‒1 confirms the existence of Ni–O bonds. Additionally, in Fig. 2f , the distinct peak observed at 476 cm ‒1 , responsible for the vibrational stretching of the Cu–S bond, validated the presence of CuS in the CSHK‒Ni nanocomposite 27 , 34 . Thus, it is evident from Fig. 2f that peaks ascribed to pristine HKUST-1, CuS and Ni(acac) 2 can be clearly observed in the FT-IR spectrum of CSHK‒Ni composite, suggesting the successful synthesis of the nanocomposite.

The XPS analysis serves to examine the purity and the chemical states of the elements present in the synthesized sample. Figure 3 depicts the XPS spectrum of the synthesized CSHK‒Ni conducted within the binding energy ranging from 0‒1400 eV. The wide spectrum analysis revealed the presence of five elements including copper, sulfur, nickel, oxygen and carbon as portrayed in the survey spectrum (Fig. 3a ). The Ni 2p deconvoluted spectra in Fig. 3b displays two characteristic Ni 2+ peaks with a spin‒orbit separation of 18 eV. Two intense strong peaks at binding energy values of 854.41 eV and 872.31 eV, correspond to Ni 2p 3/2 and Ni 2p 1/2 states respectively which validates the +2 oxidation state of Ni in Ni(acac) 2 . Moreover, two satellite peaks were also observed of Ni 2p situated at B.E values of 860.02 eV and 878.06 eV 35 . The short scan HR‒XPS Cu 2p spectrum, depicted in Fig. 3c , exhibits two prominent peaks at 934.05 eV and 954.01 eV, characteristic of the Cu 2p 3/2 and Cu 2p 1/2 states of Cu 2p respectively. The binding energies of these peaks, with a spin–orbit separation of 19.9 eV, signifies the +2-oxidation state of Cu +2 . Besides these, additional vibrational satellite peaks were observed at 939.90 eV and 944.61 eV which clearly identifies the Cu 2+ state 36 , 37 . The high-resolution S 2p spectrum shown in Fig. 3d depicts two characteristic peaks situated at energies 163.90 eV and 161.60 eV, attributable to S 2p 1/2 and S 2p 3/2 spin‒orbit states of S 2p respectively. The appearance of these peaks indicates the presence of S 2‒ state in transition metal sulfides, thus confirming the formation of CuS in the CSHK‒Ni composite 38 . The short scan deconvoluted spectrum of C 1 s offers insights into the type of carbon species present in the fabricated composite (Fig. 3e ). The existence of the sp 3 C‒C/C=C in the alkyl group of the acetylacetonate and the BTC linker of the MOF, was depicted by the peak at binding energy of 284.80 eV, whereas the peak at 286.76 eV can be attributable to the C‒O bond 37 . The high binding energy shoulder at 288.87 eV can be assigned to the C=O bond present in the organic linker molecules and is a characteristic of the acetylacetone ligand cycle in the synthesized composite 35 , 39 . The O 1 s spectrum can be deconvoluted as shown in Fig. 3f portraying different chemical environments of the O element. The peak at binding energies of 530.22 eV shows the existence of O‒Cu bond, while the presence of the carboxylate ‒C=O/‒OH bond can be associated to the peak position at 531.96 eV 36 , 40 . The existence of the Ni‒O bond gets overlapped with the O 1 s peak at 531.22 eV. These characteristic peaks are in good correlation with the previous studies.

a XPS survey spectrum of fabricated CSHK–Ni nanocomposite; b Ni 2p, c Cu 2p, d S 2p, e C 1s, f O 1s.

The optical characteristics are crucial in assessing the photocatalytic performance of the synthesized composites. To evaluate the light-harvesting abilities of HKUST‒1, CuS, Ni(acac) 2 and CSHK‒Ni nanocomposite, the UV‒DRS spectra of these samples were studied as depicted in Fig. 4a . Two broad peaks of absorption are noticed in the Cu-BTC UV–vis spectrum. The wide absorption peak observed around the wavelength 600–800 nm may be associated to Cu 2+ d–d spin allowed transitions, whereas the peak observed at approximately 300 nm can be associated to π-π transitions of the linker molecules 23 . The spectrum of the as‒synthesized CuS exhibits a wide absorption in the visible region ranging from 270‒800 nm, which suggests a potentially higher utilization and conversion efficiency of visible light after its incorporation in the CSHK‒Ni nanocomposite 32 , 41 . On the other hand, Ni(acac) 2 spectrum features two distinct peaks at 324 nm and 636 nm, corresponding to the 3 T 2g (D) → 3 A 2g (F) and 3 T 1g (F) → 3 A 2g (F) spin‒allowed transitions of Ni 2+ 28 . Additionally, the appearance of a shoulder at 307 nm signifies a strong MLCT interaction between the Ni d‒orbitals and the acetylacetonate ligand π‒orbitals 42 . The peak at 260 nm reflects the delocalized π‒π* transitions of the ligand. The absorption peaks in the designed CSHK‒Ni nanocomposite is observed to be red shifted, indicating a strong interaction between the individual components. Notably, the fabricated CSHK–Ni nanocomposite displayed a strong and broad UV and visible light response than pristine HKUST‒1 and Ni(acac) 2 , contributing to an improved light harvesting characteristics and enhanced photodegradation efficiency of the nanocomposite.

a UV-vis spectrum; b Tauc’s plot showing optical bandgap energies of MOF, CuS, Ni(acac) 2 and the prepared CSHK–Ni nanocomposite; c PL spectrum; and d N 2 adsorption/desorption isotherm of CSHK‒Ni.

The bandgap of the synthesized samples was determined via the absorption edge using the Tauc’s plot, which involves the equation outlined below:

Here, in the above equation, the value of n depends on the type of optical transition involved in the semiconductor, and is usually considered as ½ for indirect and 2 for direct transition, α designates the co-efficient of absorption, h \({\rm{\nu }}\) signifies the incident light energy, A represents the energy–dependent constant, and E g is the energy of the optical band gap. The band gap of the samples was estimated from the plot of (αh \({\rm{\nu }}\) ) 2 vs Energy (h \({\rm{\nu }}\) ) as displayed in Fig. 4b . It can be observed that pristine HKUST-1, CuS and Ni(acac) 2 presents a direct band gap energy (E g ) of 3.10 eV, 1.86 eV and 3.61 eV, respectively 42 . The low bandgap energy of CuS is in accordance with its broad absorption peak as observed in Fig. 4a 11 , 32 , 41 . However, after the incorporation of CuS and Ni(acac) 2 into the HKUST‒1 framework, the bandgap of the synthesized CSHK‒Ni nanocomposite was considerably reduced to 2.19 eV. This sudden decline in the bandgap energy, falling in the visible light region, is anticipated to improve the photocatalytic performance of the CSHK‒Ni nanocomposite compared to its individual counterparts. Meanwhile, the narrow bandgap allows easy excitation and higher utilization of visible light.

Furthermore, in addition to the effective separation of photoinduced charges, minimizing the probability of recombination of the e − ‒ h + pair is crucial for designing visible light active photocatalysts. The photoluminescence (PL) studies provide useful insights into the recombination and separation of charges in nanomaterials. Figure 4c depicts a comparative examination of the PL spectra of the designed CSHK‒Ni photocatalyst with that of pristine HKUST‒1, with an excitation wavelength of 300 nm. The prominent emission peak in the PL spectra of pristine HKUST‒1, at about 340 nm, is indicative of rapid recombination of photoinduced charge carriers 43 . However, the decline in the PL emission intensity at 340 nm in the designed CSHK‒Ni photocatalyst, suggests effective suppression of the charge recombination rate, leading to a reduction in the PL intensity 44 . Upon formation of the nanocomposite, the photoexcited electrons gets transferred facilitating effective delocalization of the charges over the surface of the photocatalyst, while diminishing the recombination rate and improving the photocatalytic performance 6 . This suggests the availability of more time for the photogenerated charges to generate increased ROS before undergoing recombination, promoting the overall photocatalytic performance of the designed catalyst.

The BET data offers detailed insights into the surface characteristics and structural porosity of the fabricated nanocomposite. A detailed analysis of the relationship between the relative pressure (P/P 0 ) and adsorption volume, as depicted in Fig. 4d , allows us to identify the specific type of isotherm and hysteresis loop present. According to IUPAC recommendations, the N 2 adsorption-desorption isotherm constructed from the BET data exhibits a typical Type IV curve. This type of isotherm is characterized by an initial behavior similar to Type II isotherm, indicating monolayer-multilayer adsorption, followed by a significant increase in adsorption at higher relative pressures owing to capillary condensation in mesopores. The substantial increase in adsorption volume at high relative pressures aligns closely with the typical features of a Type IV isotherm, commonly associated with mesoporous materials.

Moreover, the findings demonstrate the presence of a hysteresis loop, a characteristic often observed in Type IV isotherms, suggesting mesoporosity of the photocatalyst 45 . The shape and presence of this hysteresis loop unveils valuable insights into the pore structure of the nanomaterial. The notable increase in adsorption volume at higher relative pressures, along with the clear distinction between the adsorption and desorption branches, suggests the presence of an H1 hysteresis loop. This pattern is indicative of homogeneous mesopores within the material. The specific surface area of the material was observed to be 44.94 m²/g and a micropore volume of 0.15 cm³/g, suggesting the presence of micropores with diameters smaller than 2 nm. The combination of a substantial micropore volume, and the presence of a Type IV isotherm with an H1 hysteresis loop suggests a complex pore structure within the material. This structure includes both micropores, which dominate the surface area, and mesopores responsible for capillary condensation and the observed hysteresis. Such a hierarchical pore arrangement, including micropores and mesopores, makes it well-suited for enhanced pollutant degradation. In summary, single-layer adsorption of gas followed by pore condensation in mesoporous materials results in a type IV isotherm, with H1 hysteresis loop indicating the mesoporous structure with cylindrical pore channels of the prepared material. The pore volume of 0.15 cm 3 /g provides active sites for pollutant interaction and improves the photocatalytic activity of the overall nanocomposite 46 , 47 . However, the overall photocatalytic efficiency of a material hinges not solely on its specific surface area, but also on several other critical factors. These include the rate of charge transfer minimizing electron-hole recombination, adequate porosity, and reduced band gap of the photocatalyst 48 .

FE-SEM analysis was employed to study the surface morphology of the synthesized CSHK‒Ni nanocomposite. As can be observed from Fig. 5a, b , that the octahedral HKUST‒1 framework exhibit a rough surface texture with structural distortion upon formation of the composite 49 . Upon closer inspection in the magnified SEM micrographs, it becomes apparent that the surface of the octahedral HKUST‒1 is adorned with numerous CuS nanoparticles, making the surface irregular and relatively rougher with misty edges 27 . The surface irregularity of the fabricated CSHK‒Ni composite is advantageous for enhancing the interaction between the contaminant molecules and the photocatalyst, thereby improving the photocatalytic efficiency of the prepared composite 50 . The EDS results revealed the presence of sulfur and nickel, besides the existence of copper, carbon and oxygen, indicating the successful synthesis of CSHK‒Ni nanocomposite (Supplementary Fig. 2 ). Moreover, elemental mapping demonstrated uniform dispersion of all the elements over the CSHK‒Ni nanocomposite (Fig. 5c–h )

FESEM micrographs of a , b CSHK–Ni nanocomposite; elemental mapping of c Carbon, d Nickel, e Oxygen, f Copper, g Sulfur, h overall CSHK–Ni nanocomposite.

Additionally, the TEM and HR‒TEM micrographs were acquired to examine the morphological, structural, shape and size characteristics of the synthesized CSHK‒Ni nanocomposite as displayed in Fig. 6 . The representative HR‒TEM image in Fig. 6b, c of the synthesized nanocomposites allows us to clearly distinguish the octahedral geometry of HKUST‒1 with distinct boundary. Meanwhile, careful examination of Fig. 6d reveals the existence of interplanar lattice spacing of 0.26 nm and 0.34 nm, associated to the (773) and (300) lattice planes of HKUST‒1 and Ni(acac) 2 (JCPDS No. 19‒1524) respectively, confirming the existence of these components in the fabricated nanocomposite. The interplanar lattice spacing correlated well with the most intense peak observed in the XRD spectrum. Furthermore, the presence of CuS in the CSHK‒Ni nanocomposite can be confirmed from the lattice spacing of 0.18 nm, corresponding to the (110) plane of CuS (JCPDS No. 06‒0464). The SAED patterns were also analyzed, as shown in Fig. 6e , that confirms the polycrystalline nature of the synthesized CSHK‒Ni nanocomposite. The observed bright concentric rings indicated high crystallinity of the fabricated nanocomposite. Quantitative analysis of the TEM images involved fitting the particle size histogram with the Lorentzian function, revealing an average particle size of 14.97 nm of the synthesized CSHK‒Ni nanocomposite (Fig. 6f ).

HR-TEM images of CSHK–Ni nanocomposite at different resolution of a 50 nm, b 20 nm, c 20 nm, d 5 nm e SAED patterns, and f size distribution histogram.

Computational Studies of the bandgap energies

Structures of Ni(II) Bis-acetylacetonate complex, HKUST-1 Metal-Organic framework and copper sulfide were fully optimized at M06-2X/def2-TZVP level 51 . Harmonic frequency calculations were also performed at the same level of theory to understand the nature of stationary point on the potential energy surface. All the structures were found to be at their local minima with all real values of the Hessian matrix. All these calculations were performed using Gaussian 16 suite of program 52 . Figure 7 shows the optimized geometries of the complexes.

Optimized geometries of the complexes.

The band gap or the HOMO-LUMO gaps of these complexes were also evaluated at the same level of theory. There is a very good agreement between the experimental optical band gap and the calculated values. The HOMO-LUMO gap for Ni(II) Bis-acetylacetonate, Copper BTC/HKUST-1 MOF and copper sulfide monolayer are 3.78, 3.21 and 1.92 eV respectively which are very close to that observed experimentally. Figure 8 shows the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the respective complexes as well as their orbital eigen values. The HOMO and LUMO of Ni(II) Bis-acetylacetonate represent the π and π* orbitals of acetylacetonate ligands respectively. The HOMO of Copper BTC/HKUST-1 MOF represents the d-orbital on one of the Cu metal while LUMO represents the π* orbitals of the aromatic phenyl ring. The HOMO of copper sulfide layer represents the lone pair at the S atom along with Cu–S bonding while LUMO represents Cu–S antibonding orbital.

Occupied frontier orbitals (HOMO and LUMO) of the complexes along with their energies in eV.

Photocatalytic performance

To evaluate the photodegradation capabilities of the synthesized CuS, HKUST‒1, CuS/HK and CSHK‒Ni catalysts, the photodegradation of TNZ and MTZ was initially investigated as illustrated in Fig. 9a, c , conducted in 50 mL of the pollutant solution having initial concentration of 20 mg/L. A loading of 0.20 g/L of each prepared catalyst was utilized for each of the experiments under exposure to visible light irradiation for 30 min. The experimental data of the degradation process of the various synthesized catalysts in different systems is tabulated in Supplementary Table 1 . Initially, there was only a negligible decline in the intensity of absorption of the model contaminants after 30 min of irradiation of visible light in the blank condition, indicating the high stability of the drug molecules which makes it resistant to self-degradation under irradiation of visible light 6 . Similarly, pure HKUST‒1 and CuS/HK exhibited limited photocatalytic activity towards TNZ and MTZ degradation. Pristine HKUST‒1 achieved only 6.52±1.23% degradation of TNZ and 5.99 ± 1.21% degradation of MTZ after 30 min of irradiation, likely due to the wider bandgap of HKUST‒1, which surpasses the theoretical minimum energy required for excitation by visible light (3 eV) 53 . Conversely, the binary CuS/HK catalyst resulted in attaining an efficacy of 31.80 ± 1.34% TNZ and 37.90 ± 1.46% MTZ degradation, attributed to its comparatively narrower bandgap than the pristine MOF, enhanced light absorption properties, and delayed delocalization of charges facilitated by CuS incorporation into the MOF (Fig. 9b, d ). Notably, the photodegradation efficiency significantly increased to 50.67 ± 1.87%% for the TNZ + CSHK‒Ni+visible light system having a pseudo‒first order rate constant of 0.02771 min −1 . Interestingly, upon addition of H 2 O 2 , the efficacy of the system to eliminate TNZ drastically increased to 84.76 ± 1.16% with a pseudo‒first order rate constant of 0.06965 min −1 . Similarly, the maximum catalytic efficiency of the MTZ + CSHK‒Ni+H 2 O 2 +visible light system reached was 88.19 ± 1.22% and the rate constant was calculated to be 0.07836 min −1 . This unusual behavior could be accredited to the increased number of ROS, such as •OH species, produced in the system which facilitates the degradation of the targeted TNZ molecules. Consequently, the synthesized ternary CSHK‒Ni emerged as a superior photocatalyst compared to pristine HKUST‒1 and CuS/HK under visible light exposure. The improved performance of the CSHK‒Ni photocatalyst can be stemmed from its enhanced delocalization of photogenerated charges and increased light harvesting properties, which contributed towards the generation of ROS, responsible for boosting TNZ/MTZ degradation. The combination of MOFs with chelating metal complexes provides significant advantages, such as the availability of metal centers for redox reactions, and a lower rate of recombination even at very low metal concentrations. Additionally, acetylacetone, with its two oxygen atoms possessing lone pairs of electrons, plays a crucial role in binding metal cations effectively. The conjugated structure of the chelating acetylacetone ligand facilitates the delocalization of photogenerated charges across the surface of the photocatalyst, promoting efficient charge transfer. This results in diminishing the recombination rates, promoting photocatalytic performance.

a , c Photocatalytic performance of TNZ and MTZ; and the degradation kinetics of b TNZ and d MTZ of the various fabricated catalysts under different reaction systems.

In heterogeneous AOP, molecular O 2 serves as an electron scavenger, generating •O 2 ‒ species. The deficiency of O 2 resulting from sluggish O 2 consumption or mass transfer can be compensated by typical inorganic oxidants, namely H 2 O 2 , BrO 3 − , IO 4 − and ClO 3 − in which they serve a dual function, acting both as electron scavengers and potent oxidants. The influence of the above‒mentioned inorganic oxidants on the TNZ and MTZ degradation by the photocatalyst CSHK‒Ni was investigated as shown in Supplementary Table 2 . The study was performed under exposure to visible light for 30 min with a pollutant concentration of 20 mg/L, catalyst dosage of 0.20 g/L at neutral pH using various oxidizing agents. Visible light irradiation combined with these oxidizing agents accelerated the photodegradation of TNZ and MTZ as shown in Fig. 10a, c . After 30 min of exposure, degradation rates of 79.41 ± 1.23%, 84.76 ± 1.16, 86.34 ± 1.46% and 87.11 ± 1.22% were achieved for TNZ solution with ClO 3 − , H 2 O 2 , BrO 3 − and IO 4 − , respectively. On the other hand, 83.42 ± 1.86%, 88.19 ± 1.22, 89.01 ± 1.56% and 90.41 ± 1.46% were achieved for MTZ solution with ClO 3 − , H 2 O 2 , BrO 3 − and IO 4 − , respectively. Interestingly, the photocatalytic efficiency of the photocatalyst was found to be 50.67 ± 1.87% for TNZ and 52.78 ± 1.38% for MTZ, in the absence of any oxidizing agent. This can be explained by the fact that the efficacy of the entire catalytic system hinges on photons, which must possess sufficient energy for the excitation of the photocatalyst, to produce e − and h + . Nonetheless, without an oxidizing agent, the catalytic system lacks e − and h + scavengers, leading to rapid recombination probability and ultimately yielding poor degradation efficiency. The below equations (Eqs. ( 5 –12 )) outline the degradation mechanism and emphasize the generation of photoinduced charge carriers, alongside the production of •OH and •O 2 − radicals responsible for the breakdown of the pollutant molecules.

Profiles of degradation of a TNZ and c MTZ (reaction conditions: catalyst dosage 0.20 g/L, pollutant conc. 20 mg/L, pH 7); degradation kinetics of b TNZ and d MTZ using various oxidizing agents.

The addition of H 2 O 2 leads to the generation of increased •OH radicals under exposure to visible light, as explained above in Eqs. ( 13–15 ), which is the primary reason for the enhanced performance of the catalyst towards the degradation of the target contaminants. Moreover, the scavenging effect of the photogenerated e − and the h + , thereby generating •OH radicals and prolonging the recombination time is also responsible for the observed inference.

Again, the results from Fig. 10b, d demonstrate IO 4 − as the most effective oxidant towards the photodegradation of TNZ and MTZ which can be attributed to the formation of highly reactive IO 3 •, IO 4 • and OH• radicals in the reaction system as shown below 54 :

Additionally, BrO 3 − emerged as the second most effective oxidant by acting as scavengers of electrons, and producing BrO 2 • radical. Also the BrO 3 − ion reduces the recombination of photogenerated charge carriers by reacting with e − , thereby enhancing the degradation of TNZ and MTZ in the reaction system, as depicted by the below mentioned reactions 55 :

In addition, the TNZ degradation performance in the absence of the photocatalyst, was determined to be 8.23±1.19%, 10.63±1.47%, 16.11±1.44% and 25.91±1.86% for ClO 3 − , H 2 O 2, BrO 3 − and IO 4 − , respectively. Notably, the negligible degradation efficiency in the visible+ClO 3 − system towards TNZ and MTZ might be because of its limited ability for UV light absorption. Conversely, the improved degradation performance noted in the presence of IO 4 − can be attributed to the generation of highly reactive free radicals, thereby facilitating the degradation of TNZ and MTZ. Although IO 4 − and BrO 3 − demonstrated superior degradation performance in contrast to H 2 O 2 , further photodegradation experiments were conducted in H 2 O 2 as oxidant due to concerns related to environmental pollution and the high toxicity associated with other oxidants.

Hydrogen peroxide is well known for its oxidizing ability in a photo-Fenton-like AOP to increase the efficiency of a photocatalytic reaction. Thus, the influence of H 2 O 2 on the photocatalytic degradation of TNZ and MTZ (20 mg/L) using 0.20 g/L of the prepared photocatalyst was investigated by varying its concentration from 0 mL to 0.5 mL (Fig. 11a, c ). Initially, it was observed that the degradation of both TNZ and MTZ increases with increasing H 2 O 2 concentration and then starts to decline at higher concentrations. The initial increase in the degradation performance can be associated to the increased concentration of OH • due to the decomposition of H 2 O 2 on exposure to visible light, according to the Eqs. ( 13–15 ) 6 :

Profiles of degradation of a TNZ and c MTZ (reaction conditions: catalyst dosage 0.20 g/L, pollutant conc. 20 mg/L, H 2 O 2 dosage 0‒0.5 mL, pH 7); degradation kinetics of b TNZ and d MTZ at varying H 2 O 2 dosage.

The OH • initiates an attack on the target pollutants and increases the degradation efficiency. A decrease in the photocatalytic efficiency at higher H 2 O 2 dosage is due to the self‒quenching of •OH radicals by H 2 O 2 , generating less reactive hydroperoxyl radicals (HO 2 • ), as shown by the following Eq. ( 21 ):

The kinetics of the photodegradation of TNZ and MTZ at varying H 2 O 2 concentrations is displayed in Fig. 11b, d . Maximum degradation of 90.64 ± 1.86% of TNZ and 92.78 ± 2.16% of MTZ was observed at 0.2 mL and 0.3 mL H 2 O 2 dosages, with a maximum pseudo-first-order rate constant of 0.07986 min −1 and 0.08906 min −1 , respectively (Supplementary Table 3 ). Thus 0.2 mL and 0.3 mL of H 2 O 2 concentration were fixed for other photodegradation tests of TNZ and MTZ. Moreover, it is worth mentioning that without H 2 O 2 the photocatalyst could degrade 50.67 ± 1.87% of TNZ and 52.78 ± 1.38% MTZ, signifying the role of H 2 O 2 in this photocatalytic reaction.

The pH of the solution substantially influences the surface charge of the fabricated CSHK‒Ni catalyst, that ultimately affects the efficiency of the photocatalyst. Hence, it is essential to determine the initial optimal pH at which the targeted contaminant attains maximum decomposition from the aqueous medium. Dynamic Light Scattering (DLS) method was employed to determine the pH of the Zero Point Charge (P ZPC ) with 0.1 M NaOH and HCl, using 0.01 M KNO 3 solution as the electrolyte, and it was found to be 6.18 from Supplementary Fig. 3 .

The consequence of pH on the degradation of the model pollutants TNZ and MTZ was studied by conducting batch experiments by the fabricated CSHK‒Ni photocatalyst in a 20 mg/L pollutant solution at pH ranging between 3–11. The entire reactions were performed at optimal conditions under 30 min exposure of visible light. As illustrated in Fig. 12a, c , the maximum degradation efficiency peaked at pH = 3 for both TNZ and MTZ reaching 93.02 ± 1.42% and 95.78 ± 1.86% with a rate constant of 0.09378 min −1 and 0.10681 min −1 respectively (Fig. 12b, d ). With the gradual rise in the pH towards neutral conditions, a slight decline in the photocatalytic efficiency was observed which can be accounted to the decrease in the oxidation potential of •OH radicals that subsequently lowers the rate of degradation. However, a drastic decrease in the efficiency occurred at higher values of pH, slumping its efficiency to 58.90 ± 1.89% for TNZ and 64.33 ± 1.66% for MTZ, which signifies that the increase in the solution pH does not favor TNZ/MTZ degradation (Supplementary Table 4 ). This observation can be explained by the fact that at alkaline pH conditions, OH − ions of the medium tends to interact with the •OH radicals, resulting in the formation of weakly oxidizing hydroperoxyl radicals (HO 2 •) which are in agreement with previous reports 56 . These radicals further react with additional •OH radicals, resulting in the reduction of the removal efficiency 57 . Additionally, the lower efficiency observed for TNZ and MTZ at higher pH values stemmed not only from quenching effects, but also from the repulsive interaction arising between the anionic contaminant molecules and the surface of the synthesized CSHK‒Ni photocatalyst that is negatively charged at alkaline conditions 58 .

Profiles of degradation of a TNZ (reaction conditions: H 2 O 2 dosage 0.2 mL, catalyst loading 0.20 g/L, TNZ conc. 20 mg/L) and c MTZ (reaction conditions: H 2 O 2 dosage 0.3 mL, catalyst loading 0.20 g/L, MTZ conc. 20 mg/L); degradation kinetics of b TNZ and d MTZ at varying initial pH conditions.

The optimization of catalyst dosage is necessary to prevent the excess use of photocatalyst and to reduce the operation cost. The effect of photocatalyst loading on the photodegradation of TNZ and MTZ having initial concentration of 20 mg/L, was investigated by varying the photocatalyst concentration from 0.16 g/L to 0.32 g/L at optimum H 2 O 2 concentration. As seen in Fig. 13a, c , the photodegradation of target pollutants increases with increasing photocatalyst loading due to the increased number of surface-active sites and increased production of OH • radicals. However, a decline in the photodegradation efficiency was observed above 0.24 g/L for TNZ and 0.28 g/L for MTZ because excess photocatalysts in the solution hinder the path of photons from reaching the surface of the catalyst by increasing the opacity of the solution. The kinetics of the photodegradation of TNZ and MTZ are displayed in Fig. 13b, d . Maximum degradation of 95.87 ± 1.64% TNZ was observed at 0.24 g/L photocatalyst loading with a pseudo-first-order rate constant of 0.09591 min −1 (Supplementary Table 5 ). Similarly, a 97.95 ± 1.33% degradation of MTZ was observed with 0.28 g/L photocatalyst dosage having a rate constant of 0.11253 min −1 .

Profiles of degradation of a TNZ (reaction conditions: H 2 O 2 dosage 0.2 mL, TNZ conc. 20 mg/L, catalyst loading 0.16‒0.32 g/L, pH 3) and c MTZ (reaction conditions: H 2 O 2 dosage 0.3 mL, MTZ conc. 20 mg/L, catalyst loading 0.16‒0.32 g/L, pH 3); degradation kinetics of b TNZ and d MTZ at varying catalyst loading.

The initial concentration of the contaminants exerts a crucial role in determining the effectiveness of the photodegradation reaction. Therefore, it is essential to optimize the highest concentration of target pollutants, which could be degraded under optimum H 2 O 2 concentration and photocatalysts dosage. Figure 14a, c portrays the influence of initial concentration of TNZ and MTZ by varying the initial concentration in the range of 15 mg/L to 35 mg/L under the optimum concentration of H 2 O 2 and photocatalyst dosage. As can be observed, a maximum degradation of 95.87 ± 1.64% TNZ with a rate constant of 0.09591 min −1 was observed at a concentration of 20 ppm, and a 97.95 ± 1.33% degradation of MTZ with a rate constant of 0.11253 min −1 was observed at a similar concentration (Supplementary Table 6 ). The degradation efficiency started to decline at higher pollutant concentrations of 35 mg/L, possibly due to the hindrance in the path of photons at higher pollutant concentrations and narrowing of photon path lengths 59 (Fig. 14b, d ). Additionally, an increased concentration of the pollutant would necessitate a higher amount of photocatalyst, which will increase the opacity of the solution and consequently hindering photodegradation 60 . Again, higher concentration of the target pollutants enhances the probability of the contaminant molecules to occupy more surface active sites, displacing the surface adsorbed O 2 molecules and OH ‒ ions 4 . This phenomenon inevitably leads to the insufficient generation of the ROS, such as •OH and •O 2 ‒ radicals responsible for the photodegradation, thus reducing the overall efficiency of the photocatalyst. Therefore, 20 mg/L of TNZ and MTZ were fixed for further photocatalytic tests.

Profiles of degradation of a TNZ (reaction conditions: H 2 O 2 dosage 0.2 mL, catalyst loading 0.24 g/L, TNZ conc. 15‒35 mg/L, pH 3) and c MTZ (reaction conditions: H 2 O 2 dosage 0.3 mL, catalyst loading 0.28 g/L, MTZ conc. 15‒35 mg/L, pH 3); degradation kinetics of b TNZ and d MTZ at varying concentration of the target pollutant.

Possible TNZ and MTZ degradation mechanistic pathway

The reaction rate of the photodegradation process is significantly influenced by the concentration of ROS and the photoinduced charge carriers. To explore the impact of these radicals and charge carriers on the degradation process, various scavenging agents were added to the aqueous reaction medium to trap them and analyse their role in TNZ and MTZ degradation. For this purpose, 1 mM of 2‒butanol was added as quenching agent for •OH, ascorbic acid for •O 2 − , K 2 S 2 O 8 for e − and Na 2 EDTA as h + scavenging was employed. It can be observed from Fig. 15 that the introduction of 2-butanol resulted in the sudden decline in the photodegradation performance of TNZ and MTZ to 36.28 ± 1.32% and 42.19 ± 1.61%, respectively. Moreover, the degradation efficiency reduced to 49.27 ± 1.66% and 51.53 ± 1.23% for TNZ and MTZ in the presence of ascorbic acid, suggesting that •O 2 − radical contributed about 46.60% of the total degradation efficiency. These results indicate that both TNZ and MTZ underwent radical-based AOP. Furthermore, the role of other species such as e − and h + were also investigated. It was observed that the presence of K 2 S 2 O 8 and Na 2 EDTA had a relatively minor impact on the degradation performance, with removal percentages declining to 85.21 ± 1.47% and 89.51 ± 1.86% for TNZ and MTZ, respectively. Hence, it can be collectively summarized that the photocatalytic breakdown of the targeted contaminants is mainly controlled by both •OH and •O 2 − radicals, whereas the minor contribution of h + in the degradation process cannot be neglected, consistent with previous literature findings.

Consequence of radical scavengers on TNZ and MTZ degradation mechanism by CSHK‒Ni photocatalyst at optimum reaction conditions.

Furthermore, the ESR spin-trap technique was conducted for providing evidence of the generation of various reactive oxygen species in the photocatalytic system under visible light irradiation 61 . Typically, the intensity of a EPR signal is directly proportional to the amount of spin 62 . 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) served as a spin trapping agent to detect •OH radicals, which exhibit a characteristic quartet EPR signal with an intensity ratio of 1:2:2:1, corresponding to the typical DMPO–•OH adduct structure (Supplementary Fig. 4a ) 63 . Meanwhile, a strong quartet signal for DMPO–O 2 • − spin adduct with a peak intensity ratio of 1:1:1:1 reveals the existence of •O 2 − radical in the photocatalytic system (Supplementary Fig. 4b ) 64 .

In view of the aforesaid discussions, the mechanism of the photodegradation of TNZ and MTZ in the presence of CSHK‒Ni photocatalyst can be elucidated as illustrated in Fig. 16 . Meanwhile, the edge positions of conduction band (CB) and valence band (VB) can be estimated using the equations outlined below:

Suggested degradation mechanism of TNZ and MTZ by the designed CSHK‒Ni photocatalyst under irradiation of visible light.

In the above equations, E VB and E CB signifies the potentials of the VB and CB, \({\boldsymbol{\chi }}\) denotes the absolute electronegativity of the semiconductor, the value of 4.5 eV is considered for E e which represents the energy of the free electrons on the scale of hydrogen. Moreover, the optical bandgaps of the synthesized photocatalysts were calculated as explained in Fig. 4b .

The possible mechanistic pathway of the photodegradation process of TNZ and MTZ was proposed on the basis of the ROS identified from the scavenger experiments and the edge potentials determined from the VB‒XPS as shown in Fig. 17 . Initially, the degradation process involves the photoexcitation of e⎺ to the CB from the VB of the fabricated CSHK‒Ni photocatalyst, when irradiated with visible light, owing to its better light harvesting behavior leading to the creation of positively charged h + in the VB. As revealed by the PL analysis, the incorporation of the Ni(acac) 2 complex and CuS into the structural skeleton of the MOF significantly reduces the recombination of charges by facilitating effective delocalization of the charges, thereby improving the photocatalytic performance. Moreover, the potential of the CB (E CB ) of the CSHK‒Ni photocatalyst (−1.90 eV) is more negative compared to the O 2 /•O 2 − potential (−0.33 eV vs. NHE), allowing the dissolved O 2 in the reaction medium to interact with the photoexcited electrons present in the CB to generate free •O 2 − species (Eq. ( 25 )). On the other hand, the calculated VB edge potential (E VB ) (+0.29 eV) is less positive compared to the potential needed for the production of •OH radicals (H 2 O/OH• = +2.8 eV vs. NHE). This restricts the probability of the production of •OH radicals by the oxidation of the H 2 O molecules by the photogenerated h + present in the VB. The •O 2 − radicals engage with the H 2 O molecules, resulting in the generation of HO 2 • species, which subsequently interacts with additional water molecules to produce •OH radicals (Eqs. ( 26 ) and ( 27 )). These active radicals possess the ability to oxidize the targeted contaminants by initiating multiple reactions leading to the mineralization of the contaminants into smaller compounds. Also, the introduction of H 2 O 2 leads to the generation of •OH radicals, which can aid in the TNZ and MTZ degradation (Eqs. ( 28 ) and ( 29 )). This is in accordance with the scavenging experiments that validates that both •OH and •O 2 − radicals exert dominant role in the degradation of the targeted contaminants. Additionally, the Cu 2+ within the MOF undergoes reduction to Cu + by trapping the photogenerated e − , which subsequently undergoes further oxidation in the aqueous medium (Eqs. ( 30 ) and ( 31 )) 23 , 24 . This process results in the generation of more •OH radicals, indicating the availability of more time for the photogenerated charges to generate increased ROS before undergoing recombination, thereby promoting the overall photocatalytic performance of the designed catalyst.

Determination of VB edge potential of the synthesized CSHK‒Ni photocatalyst via VB‒XPS analysis.

HR‒LCMS was performed to analyze the degradation products of TNZ and MTZ at an intermediate stage, and the most probable pathway was elucidated based on the identified by‒products, as depicted in Supplementary Fig. 5a, b . The •OH and •O 2 − radicals were identified as the active ROS which initiate the breakdown of the C–C bond and the aromatic ring at C–N bond in TNZ under 30 min irradiation of visible light, thereby generating the reaction intermediates. The loss of an R‒NO 2 group due to the subsequent radical addition reactions, leads to the formation of the product with m/z = 178 56 . Subsequent bond rupture generates ‒CH 3 , yielding product at m/z = 149. Furthermore, the electrophilic attack of the •OH radicals produced in the system and the loss of the ‒NO 2 group results in the formation of the intermediates at m/z = 297 and 220, respectively. Moreover, the cleavage of the aromatic ring and the alkyl group after the attack of radicals, yields intermediates at m/z = 236, 108 and 164 as shown in the proposed degradation pathway (Fig. 18 ) 58 .

The Possible degradation pathway and the identified fragments of TNZ under irradiation of visible light.

Similarly, the photodegradation pathway of MTZ was elucidated by identifying the reaction intermediate products formed via the cleavage of the C‒N, C‒O and the aromatic ring at the C‒C bonds of the MTZ molecules. The proposed breakdown pathway based on the HR‒LCMS spectrum is illustrated in Fig. 19 , where the peak at m/z = 171.5 corresponds to the MTZ molecular ion 65 . The other observed intermediates include fragments at m/z = 188, formed by the electrophilic attack of the •OH radicals; whereas oxidation of the ‒OH group and reduction of the ‒NO 2 group yields fragments at m/z = 206 and 165, respectively 6 . Additionally, ring cleavage at the C‒N bond of the aromatic ring generates fragments at m/z = 149 and 188 as shown below 66 .

The Possible degradation pathway and the identified fragments of MTZ under irradiation of visible light.

Impact of different factors on the photodegradation of TNZ and MTZ

Studying the effect of the various inorganic salts typically found in the wastewater effluent or natural aquatic medium on the photodegradation performance of the catalyst is of crucial importance. Investigating how these ions influence the degradation of TNZ and MTZ in the presence of the CSHK‒Ni photocatalyst under visible light radiation is vital for deepening our comprehension of the degradation mechanism.

Wastewater effluent and natural aquatic resources harbor diverse inorganic metal cations, including Na + , Ca 2+ , Al 3+ and Fe 2+ , which due to their stable states of oxidation, do not exert a direct impact on the photocatalyst. For exploring the consequence of the specified cations on the elimination of TNZ and MTZ, aqueous solutions (0.01 M) of Na 2 SO 4 , CaSO 4 , Al 2 (SO 4 ) 3 and FeSO 4 were separately added in to 20 mg/L aqueous pollutant solutions with a catalyst concentration of 0.24 g/L and 0.28 g/L for TNZ and MTZ, respectively. It can be understood from Fig. 20a that the presence of these metal cations suppresses the photodegradation efficacy of the fabricated catalyst to variable extents, following the trend Al 3+ > Ca 2+ > Na + > Fe 2+ . The diminished performance may be attributed to the propensity of these cations to readily adsorb on the surface of the catalyst, thereby blocking the surface-active sites for ROS generation, causing a decline in the efficacy of the catalyst. Interestingly, the maximum inhibition of the photocatalytic efficiency was observed with Al 3+ ions, possibly due to the strong affinity of the metallic cation to be adsorbed on the photocatalyst surface, owing to its higher charge density. Notably, Ca 2+ exhibited a more pronounced effect in the degradation efficiency compared to Na + , likely due to its higher charge density. On the contrary, a change in the trend was witnessed for Fe 2+ ions which could be explained considering that Fe 2+ ion serves as an excellent Fenton reagent, augmenting the production of •OH radicals, consequently enhancing the photodegradation of TNZ and MTZ as highlighted by the following equation:

Degradation efficiency of the catalyst in presence of aqueous solutions (0.01 M) of varying a inorganic metal cations and b non-metallic anions on the removal of TNZ and MTZ.

Various studies have reported that the existence of different inorganic anions in effluent water can impede the degradation efficiency of the as–prepared catalyst by disrupting the generation of reactive oxygen species during the photodegradation mechanism. As previously mentioned, the consequence of the multiple inorganic anions was comprehensively examined by individually introducing aqueous solutions (0.01 M) of NaCl, Na 2 SO 4 , Na 2 CO 3 and NaNO 3 into 20 mg/L pollutant reaction. The observed decline in the photocatalytic efficiency can be explained by two major factors: firstly, the occupation of the active sites present on the catalyst surface by the inorganic anions, which inhibits the generation of ROS, and secondly, the scavenging behavior of the anions, contributing to the decline in the catalytic performance. The addition of these salts unmistakenly illustrates a substantial reduction in the degradation performance of the model contaminants in the order Cl − < CO 3 2− < SO 4 2− < F − , as displayed in Fig. 20b .

Compared to the other anions, the Cl − anions had a more noticeable inhibitory effect owing to their active participation as scavengers of h + and •OH radicals, which follow second order kinetics as further discussed below 67 , 68 :

The impact of Cl⎺ ions on the photodegradation performance surpasses that of other inorganic anions, primarily due to their significant quenching action. These ions interact with the photoinduced h + , leading to the generation of active radicals of chlorine. Moreover, they engage in reactions with •OH radicals, causing the oxidation of Cl⎺ ions and forming •Cl active radicals, which can subsequently revert to Cl⎺ ions by interacting with e⎺. As a result, these non-oxidizable metal anions compete with the pollutant molecules for reaction with •OH radicals, potentially hindering the degradation of TNZ and MTZ.

The influence of SO 4 2− and F − ions on the degradation performance is minimal, which may be explained by the formation of •SO 4 − active radicals as a result of their interaction with •OH radicals, which serve as highly potent oxidizing agent compared to •OH radicals 69 . These •SO 4 − radicals also aid in the decomposition of the contaminants as follows:

The relatively minor decrease in the degradation performance associated with CO 3 2⎺ ions in contrast to Cl⎺ indicates a weaker inhibitory effect of CO 3 2⎺ ions. Furthermore, they react with •OH species, yielding • CO 3 ⎺ free radicals as illustrated in the following reactions:

The F − ions are known for their stability and exhibit resistance to oxidation by h + 70 , 71 . Nevertheless, these inorganic ions are able to occupy the catalyst surface, thereby obstructing the formation of surface •OH active radicals. Furthermore, it can be summarized that the existence of inorganic ions did not significantly impair the degradation efficiency, highlighting the exceptional stability of the designed material in the wastewater system.

In addition to the inorganic impurities, the presence of several dissolved organic compounds of varying degrees in the wastewater effluent, competes with the target contaminant and influence the process of photodegradation. Hence, it becomes essential to explore the potential implications of these typical organic compounds, which includes urea, humic acid (HA), acetone, fulvic acid (FA), sodium dodecyl sulfate (SDS) and nitrobenzene (NB) on the functionality of the ternary photocatalyst in the degradation of TNZ and MTZ under optimal reaction conditions as shown in Fig. 21a . Urea is typically employed as a nitrogenous fertilizer, feed additive and is used as a raw ingredient in various industrial sectors dealing in polymers. Again, HA and FA are typically found as dissolved organic matter (DOM) in water bodies, whereas nitrobenzene is released by the petroleum refineries and chemical manufacturing industries. SDS functions as a surfactant and is commonly employed as a capping reagent in the synthesis of nanoparticles. It is also extensively utilized in detergents, toothpaste, shampoo and shaving cream. Acetone, on the other hand, serves as a highly effective solvent in numerous industrial processes and organic synthesis. The results demonstrate the inhibition of the photodegradation of the target pollutants by the above‒mentioned organic compounds in varying degrees owing to their scavenging properties. The maximum negative impact in the degradation effectiveness was exhibited by SDS, which could be due to the reduction in the visible light intensity reaching the surface of the catalyst and the generation of SO 4 2 − ions in the process of SDS photolysis. Again, the presence of FA and HA notably impeded the photocatalytic efficiency by hindering the penetration of light into the reaction medium for ROS generation, because of the increased opacity of the solution. Moreover, these organic substances competed with the targeted TNZ and MTZ molecules for their interaction with the •OH radicals, as outlined in Eqs. ( 43 – 49 ), thus, inhibiting TNZ and MTZ degradation.

The consequence of presence of varying a organic compounds of concentration 0.5M and b different water matrices on the degradation of TNZ and MTZ at optimum reaction conditions.

Since •OH radicals are highly electrophilic, they attack organic molecules that typically contain a variety of electron‒rich sites, leading to their degradation.

For acetone, the slight reduction in the degradation efficiency was recognized for its photosensitization and inhibitory phenomenon which can be described as follows:

Although the produced • OH species facilitated the degradation of TNZ and MTZ, however, the acetone molecules also compete with the contaminant molecules for the active sites of the photocatalyst for its decomposition, thereby diminishing the degradation efficiency. The photodegradation of TNZ and MTZ was inhibited by the presence of the dissolved organic compounds, indicating that these DOM were also undergoing degradation alongside the targeted TNZ and MTZ molecules in the solution. These results demonstrate the effectiveness of the prepared photocatalyst in the elimination of various dissolved organic compounds present in the wastewater effluent, highlighting its potential as a photocatalyst for wastewater remediation.

To evaluate the consequence of the different water matrices on the degradation performance of the catalyst, photocatalytic experiments were performed in five different water samples under optimum conditions as shown in Fig. 21b . As can be inferred, the degradation efficiency of the fabricated ternary CSHK‒Ni photocatalyst towards TNZ varied in different environmental conditions exhibiting 94.86 ± 1.31% for mineral water, 89.76 ± 1.37% for tap water, 83.42 ± 1.66% for lake water, 80.17 ± 1.73% for rain water and 76.49 ± 1.87% for river water. On the contrary, the maximum degradation efficiency towards MTZ obtained was 96.84 ± 1.25% for mineral water, 90.32 ± 1.44% for tap water, 85.19 ± 1.76% for lake water, 81.25 ± 1.82% for rain water and 78.89 ± 1.88% for river water. The presence of light attenuation and various organic compounds and inorganic ions that inhibit photocatalysis in these environmental water matrices, in varying concentrations, primarily contributed to the overall decrease in the photocatalytic efficiency. Mineral water, among all the experimental samples, exhibited the least reduction in the efficiency because of the lack of DOM and any impurities. The higher concentration of minerals and DOM in river water compared to lake and tap waters and their scavenging phenomenon could account for the comparatively poorer performance of the photocatalyst in the former matrix.

Elimination of other common pharmaceuticals

In order to mitigate environmental and human health risks, it is imperative to eliminate pharmaceutical residues from wastewater, which otherwise, infiltrates the aquatic bodies and pose threats to both the quality of the drinking water and the aquatic ecosystem at large. In this light, a study was conducted to assess the removal of various other commonly found pharmaceuticals, including Pantoprazole (PTZ), Ranitidine (RNT), Ofloxacin (OFL) and Amoxicillin (AMX) in wastewater effluent under optimized reaction conditions, as portrayed in Fig. 22 . Pantoprazole and Ranitidine, popularly employed as a protein pump inhibitor to treat issues related to the digestive system, were eliminated by 81.52 ± 1.26%, and 43.19 ± 1.52%, respectively at optimal conditions. Ofloxacin, an anti‒microbial drug, were observed to be eliminated with a maximum degradation efficiency of 75.98 ± 1.66%, whereas the degradation efficiency of Amoxicillin was found to be 69.54 ± 1.33%, respectively.

Removal of commonly found pharmaceuticals in water systems by CSHK‒Ni photocatalyst (reaction conditions: H 2 O 2 dosage 0.3 mL, catalyst loading 0.28 g/L, pollutant conc. 20 mg/L, irradiation time 30 min).

Assessment of TOC and COD removal

A comprehensive assessment of the TOC removal was conducted to evaluate the mineralization efficiency during the degradation of TNZ/MTZ using the synthesized CSHK‒Ni photocatalyst. Figure 23a demonstrates that initially pristine HKUST‒1 and CuS/HK exhibited poor mineralization efficiencies of 2.63% and 29.44%, respectively for TNZ. On the other hand, for MTZ, it was found to be 2.89% and 38.13% (Fig. 23b ). However, the TOC removal interestingly increased to 80.02% and 83.67% for TNZ and MTZ, respectively for the CSHK‒Ni photocatalyst, with a degradation efficiency of 95.87 ± 1.64% and 97.95± 1.33%.

COD and TOC removal of different catalysts for the degradation of a TNZ and b MTZ; and c reusability studies of the synthesized CSHK‒Ni photocatalyst.

Furthermore, the COD removal of the photodegradation of TNZ and MTZ was measured at various time intervals. Under optimized reaction conditions, a COD removal efficiency of 88.06% and 90.23% was achieved for TNZ and MTZ respectively. The high values of TOC and COD removal efficiencies suggested the facile breakdown of the targeted TNZ and MTZ molecules to CO 2 and H 2 O in the course of the degradation by the generated ROS. The intermediates produced during the degradation process was validated by HR‒LCMS analysis.

Comparison with other photocatalysts for TNZ/MTZ degradation

Several nanocomposites have been documented for the photodegradation of TNZ and MTZ from aqueous medium as described in Table 1 . However, the fabricated CSHK‒Ni photocatalyst reported in this study showcased exceptional efficiency even at low catalyst doses and short duration under visible light irradiation.

Reusability analysis

Recyclability is the most desired property of a photocatalyst to examine its stability and maximize its reusability potential. Hence, the recycling of the prepared CSHK‒Ni photocatalyst was investigated at optimum conditions over several runs, prior to its separation via centrifugation, repeatedly rinsing it with ethanol and distilled water and subsequently drying it at 80 °C overnight. As illustrated in Fig. 23c , the fabricated photocatalyst exhibited an impressively high (>78%) catalytic efficiency without any significant decline for up to four consecutive cycles. However, a minimal decrease in the catalytic performance may result from the potential blockage of the catalytic active sites and the pore channels of the CSHK‒Ni by the degradation intermediates. This leads to the decrease in the catalytic performance of the catalyst in subsequent runs. Furthermore, XRD analysis of the reused catalyst was conducted to assess the stability of the catalyst. As observed from the spectrum in Supplementary Fig. 6a , the XRD spectrum of the reused catalyst closely resembled with that of the fresh CSHK‒Ni catalyst, with the characteristic peaks of the HKUST‒1, CuS and Ni(acac) 2 remained intact. However, the intensity of the (511) lattice plane is observed to decrease, besides the disappearance of (551) and (773) plane of the MOF. During the course of the photocatalytic reaction, some of the reaction intermediates formed may get partially trapped over the surface and the pore channels of the CSHK‒Ni catalyst, obstructing the surface-active sites, despite being repeatedly rinsing with ethanol and distilled water. The accumulation of these species over the course of successive catalytic runs, can potentially contribute in the change in the intensity of the peak. This can be validated by the observed decrease in the photocatalytic efficiency to 63.09±1.46% and 68.72±1.82% of TNZ and MTZ respectively, during the fifth run. Additionally, the aggregation of the catalyst particles across multiple reaction cycles might induce changes in the peak areas in the XRD pattern which can be observed from the SEM image of the reused catalyst presented in Supplementary Fig. 6b . A comparative analysis of the SEM images of the CSHK–Ni catalyst prior to (Fig. 5b ) and after multiple catalytic runs (Supplementary Fig. 6b ) reveals that the catalyst nanoparticles have agglomerated. This is associated with the observed changes in the XRD peak areas of the reused catalyst and the decline in the efficiency of the photocatalyst. Furthermore, the adsorption of reactive species on the catalyst surface may also alter the lattice parameters.

Comparative cost analysis

The cost implication of a catalyst plays a critical role in evaluating its commercial viability, applicability, and scalability in real-world scenarios. The overall cost of a catalyst encompasses several components such as the cost of raw materials, expenses for drying, washing, chemical aggregation, energy consumption, labor and transportation charges and the recyclability of the catalyst 72 , 73 . The commercial feasibility of large-scale wastewater treatment is determined by the efficiency and cost-effectiveness of the fabricated catalyst. Table 2 provides a detailed cost analysis for the step-by-step preparation of 1 g of CSHK‒Ni catalyst, with all costs presented in US dollars ($).

The results unveiled that the estimated total cost for the synthesis of 1 g of CSHK‒Ni catalyst approximates to about $0.021, which was considerably lower than the estimated costs of other catalysts previously reported for wastewater treatment, such as hierarchical ZnS‒Ga 2 S 3 , 0.5 M-rGO-PEG, Fe3O4@MIL-101, NH2-MIL-88(Fe), and BUC–17. Additionally, the fabricated CSHK‒Ni nanocomposite in this study demonstrated superior cost-efficiency while offering significantly higher performance. Recently, a study performed by Qi et al. estimated that the cost of producing 1 g of hierarchical ZnS‒Ga 2 S 3 for Cr (VI) removal from wastewater effluent is about $0.0895 74 . In contrast, the estimated cost of manufacturing 0.5 M-rGO-PEG was significantly higher at approximately $2.88/g (54.068 ZAR) 75 . Therefore, MOFs are often viewed as frugal and cost-effective options for wastewater remediation. Biswal and his colleagues reported that BUC‒17 MOF is the most expensive at $5/gram, whereas Fe3O4@MIL-101 and NH2-MIL-88(Fe) cost around $1 and $0.5 per gram, respectively 76 . Given that these cost estimates are based on laboratory data and may fluctuate over time, they might not precisely represent the costs at an industrial scale. However, they provide a useful benchmark for evaluating the economic feasibility of the CSHK‒Ni catalyst. Therefore, from a commercial standpoint, the designed CSHK‒Ni catalyst appears to offer a promising and cost-effective solution for large-scale wastewater treatment.

The objective of this research is to explore the photocatalytic performance of a novel nano catalyst fabricated by anchoring a transition metal Nickel (II) bis-acetylacetonate complex into a MOF immobilized with a narrow band gap semiconductor. The proposed nano photocatalyst, with a particle size of 14.97 nm, was investigated for the enhanced visible light-driven removal of nitroimidazole framework antibiotics, Tinidazole (TNZ) and Metronidazole (MTZ), attaining a maximum photocatalytic efficiency of 95.87 ± 1.64% and 97.95 ± 1.33% respectively in just 30 min. The pseudo-first order rate constants were determined to be 0.09591 min −1 and 0.11253 min −1 with a catalyst dosage of 0.24 g/L and 0.28 g/L, for TNZ and MTZ respectively. The incorporation of CuS, which is a narrow bandgap semiconductor, is anticipated to allow easy excitation by visible light and improve the photocatalytic potential of the formulated catalyst. Moreover, the anchoring of the metal complex improves the light harvesting behavior by increased conjugation. The possible degradation pathway of the breakdown of TNZ and MTZ was elucidated based on the identification of degradation intermediates via HR‒LCMS. Quenching experiments confirmed that the •OH and •O 2 − radicals played a dominant role in the breakdown of the model contaminants. Meanwhile, the values of COD and TOC removal were 88.06% and 80.02% for TNZ, and 90.23% and 83.67% for MTZ respectively. A detailed discussing encompassing various aspects including reaction conditions, influence of various oxidizing agents, competing species and dissolved organic compounds present in the wastewater, are being performed marking the novelty of the study. Furthermore, the performance of the fabricated CSHK‒Ni composite under practical water conditions and the removal of other toxic pharmaceutical contaminants was comprehensively analyzed. The catalytic recycling of the fabricated nanocomposite can be enhanced through various structural modifications, such as incorporating magnetic metal oxide nanoparticles (MNPs), surface functionalization by tailoring auxochromic groups increases the stability of the nanocomposite, immobilization of the catalyst on polymer films such as carbon cloth, and designing yolk@shell structures. These strategies focus on improving the stability, durability, and reusability of the nanomaterial. Incorporating MNPs enhances the surface area, and catalytic activity while enabling efficient separation with an external magnetic field. Immobilizing nanocatalysts on supports like polymer films boosts recyclability and performance. Additionally, addressing metal leaching involves designing yolk@shell structures that prevent loss of the metal and enhances the stability and longevity of the catalyst. Surface functionalization, including modifications with electron-donating or electron-withdrawing groups, further improves the stability and photocatalytic efficiency of the MOF nanocomposites. The present research elucidated the role of the CSHK‒Ni nanocomposite as an impressive photocatalyst in the elimination of emerging nitroimidazole containing pharmaceutical pollutant under visible light exposure, even under challenging conditions of wastewater remediation, presenting an exciting novel avenue for a cleaner and sustainable environment in the days to come.

Data availability

Datasets used during this study will be made available by the corresponding author on reasonable request.

Code availability

For access to detailed code implementations, please contact the authors directly.

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The authors appreciatively acknowledge SAIF IIT Mumbai and Material Analysis & Research Center Bengaluru for characterization. Also, the authors acknowledge MHRD India for financing research fellowship.

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Establishing a process route for additive manufacturing of NiCu-based Alloy 400: an alignment of gas atomization, laser powder bed fusion, and design of experiments

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• Published: 03 September 2024

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• Jan-Philipp Roth   ORCID: orcid.org/0000-0003-4026-8012 1 ,
• Ivo Šulák 2 ,
• Tomáš Kruml 2 ,
• Wojciech Polkowski 3 ,
• Tomasz Dudziak 3 ,
• Peter Böhlke 4 ,
• Ulrich Krupp 5 &
• Katrin Jahns 1  

Alloy 400 is a corrosion-resistant, NiCu-based material which is used in numerous industrial applications, especially in marine environments and the high-temperature chemical industry. As conventional manufacturing limits geometrical complexity, additive manufacturing (AM) of the present alloy system promises great potential. For this purpose, a robust process chain, consisting of powder production via gas atomization and a design of experiment (DoE) approach for laser powder bed fusion (LPBF), was developed. With a narrow particle size distribution, powders were found to be spherical, flowable, consistent in chemical composition, and, hence, generally applicable to the LPBF process. Copper segregations at grain boundaries were clearly detected in powders. For printed parts instead, low-intensity micro-segregations at cell walls were discovered, being correlated with the iterative thermal stress applied to solidified melt-pool-near grains during layer-by-layer manufacturing. For the production of nearly defect-free LPBF structures, DoE suggested a single optimum parameter set instead of a broad energy density range. The latter key figure was found to be misleading in terms of part densities, making it an outdated tool in modern, software-based process parameter optimization. On the microscale, printed parts showed an orientation of melt pools along the build direction with a slight crystallographic [101] texture. Micro-dendritic structures were detected on the nanoscale being intersected by a high number of dislocations. Checked against hot-extruded reference material, the LPBF variant performed better in terms of strength while lacking in ductility, being attributed to a finer grain structure and residual porosity, respectively.

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1 Introduction

Alloy 400 is a NiCu-based alloy, consisting mainly of two-thirds nickel and one-third copper, respectively. Both, nickel and copper, crystallize in a face-centered cubic (fcc) structure and form a solid solution [ 1 , 2 , 3 ]. Thus, Alloy 400, also known as Monel 400, consists of one phase only and shows isomorphic characteristics [ 2 , 4 , 5 ]. Further alloying elements with marginal proportions are iron, silicon, manganese, aluminum, and carbon.

The alloy shows excellent corrosion resistance in various media, such as acids, bases, and sea water [ 1 , 4 , 6 , 7 , 8 ]. It finds its application in steam generator tubes as well as in gas- and liquid-carrying pipelines for power plants. In the field of shipbuilding and marine technology, impellers, pump shafts, and splash zone claddings on offshore platforms are made of Alloy 400. In pump construction, components are facing a combined stress resulting from abrasion, erosion, corrosion, and chemical resistance, which is why Alloy 400 can be considered indispensable within this field [ 9 ]. Generally speaking, products being manufactured out of Monel alloys are very long-lasting due to their long-term resistance to the environment [ 8 ]. Further benefits of Alloy 400 are its good ductility and easy cold formability, which opens up a wide variety of engineering systems [ 10 ]. It behaves ductile at temperatures below 0 °C, meaning that it does not show brittle properties in a cold state [ 5 ].

With nickel being the base material, the alloy has great potential in high-temperature environments as well [ 11 ]. Also, due to the high copper content within Alloy 400, heat exchangers for combustion engines can be considered a further area of application [ 12 ]. Most importantly, critical component failure due to metal dusting, as present in the aggressive environments of power plants, can be addressed by NiCu-based alloys. Caused by a combination of temperatures around 450–800 °C, a high carbon activity a c  > 1, and a low oxygen partial pressure p O2 , coke deposits both at the surface and inside the structure, eventually leading to the destruction of the entire component [ 13 , 14 ]. Monel alloys can counter this effect as a Cu content of at least 30% catalytically inhibits the sedimentation of C, and thus, no coke layer is formed [ 13 , 15 ].

Monel alloys have already been manufactured via conventional fabrication processes for more than a century [ 8 ]. But besides tool-bound technologies, additive manufacturing paves the way for products that cannot be manufactured in a classical manner and that allow complex undercuts as in extremely fine ribbed heat exchangers for instance. In contrast to conventional manufacturing processes, AM shows good applicability when it comes to low quantity but high complexity issues. Considering the physical state of the input material, AM technologies can generally be split up into the three different categories of powders, liquids, and solids, and against the background of metal materials, powder-based applications are of main interest [ 16 , 17 ]. According to DIN EN ISO/ASTM 52900, as one of seven process categories for additive manufacturing, powder bed fusion processes locally introduce thermal energy in order to fully melt loose powder particles. Thus, after rapid solidification of the melt, highly dense structures are created. Since a wide range of metal alloys show repeatable good processability, laser powder bed fusion, also known as selective laser melting (SLM), can be considered a promising technology for AM of Alloy 400 [ 18 ]. In this iterative process, a layer of powder is applied to a build plate and partly melted by a laser beam, resulting in complex structures with a higher degree of geometrical freedom than in conventional manufacturing.

For LPBF to be a powder bed–based process, suitable material has to be provided. Here, the atomization of bulk Alloy 400 to fine powder plays an essential part in the process route. There are existing several atomization processes within the field of metal additive manufacturing such as water atomization, electrode induction gas atomization (EIGA), the plasma rotating electrode process (PREP), plasma atomization (PA), and vacuum inert gas atomization (VIGA). Among these processes, VIGA leads to a high homogeneity of the melt and the alloying system, respectively. Vacuum and inert gas, such as argon, both prevent the melt from forming oxides with the ambient air, leading to very low oxygen contents of only a few ppm in the alloy. Moreover, an ideal particle size distribution (PSD) for LPBF such as high flowabilities and bulk densities of the powder can be achieved. Also, VIGA is well known for the processing of nonreactive metal alloys which is why, in summary, this atomization process is suited best for the production of Alloy 400 powders [ 19 , 20 ].

During atomization, when it comes to the exact place of the inert gas introduction, two different set-ups may be applied: free-fall atomization (FFA) or close-coupled atomization (CCA). The former method gives the melt a chance of falling out of the crucible nozzle into the atomization chamber. After a defined distance, the gas stream hits the melt stream, atomizing the alloy to spherical powder that reveals a log-normal PSD [ 21 ]. During the latter method, the powder is atomized just as it exits the crucible nozzle. The gas stream rapidly cools down the melt, resulting in a local low-pressure area that further increases the melt volume rate (MVR; MVR = cm 3 /10 min). High homogeneities and purities can be reached by application of CCA [ 21 , 22 ].

When setting up an experiment, there are several methods that can be applied. A classic approach would be the one-factor-at-a-time (OFAT) strategy. This approach, which dates back more than a century, is still used frequently in modern science although not being the most promising one as it is very time-consuming and only varies one parameter at a time. In contrast, a design of experiments approach has the ability to vary several parameters simultaneously, resulting in a more detailed overview of parameter interdependencies in less time. Here, on the basis of multiple input variables, a prediction of the system response can be carried out [ 23 ]. In general, DoE requires fewer resources, the prediction for a single parameter is more accurate, interconnections in between parameters cannot be determined with OFAT, and the optimal response of a system is located more precisely [ 24 ]. There are many DoE techniques that can be applied to different optimization cases, but they all require a design space as an input, which indicates the spectrum of the variability of one parameter. Conclusions from this input may explain alterations in the output data [ 25 ]. The full factorial method is a widely known one with the big advantage that it can clearly differentiate between single parameters, and therefore, clear conclusions of the respective effect of a parameter on the whole system can be drawn [ 25 , 26 , 27 ].

Developing usable material for AM in general and for LPBF in particular comes with some difficulties; the desired state and shape of the feedstock material have to be producible, key properties such as sufficient flowability and bulk density need to be ensured, and the chemical composition must be consistent and free of any impurities [ 28 ]. Moreover, defect formation of powders, e.g., in terms of satellite formation or lack of sphericity, has to be avoided as it negatively affects absorptivity and recoatability during printing [ 29 ]. Hence, finding a consistent procedure in powder and material development for any alloy to be used for LPBF is essential for the adaptation of the technology. Although numerous processes for gas atomization and laser powder bed fusion of metals are already known, there is no holistic approach for Alloy 400 at this point. The complexity of the atomization of high-melting alloys and the challenges associated with LPBF processing of conductive materials are the main reasons for this. Hence, this study aims to establish such an AM process routine to serve as a standard reference for the present alloy system. This includes material supply via gas atomization, parameter definition according to a design of experiments, and LPBF production of components. Throughout the whole process, powders and parts were analyzed on their microscale, including grain structure and chemical composition. Mechanical properties in terms of indentation hardness and tensile strength were quantified. Not least due to its wide applicability in industrial applications, there is an exigent need to qualify this alloy for the LPBF process. By putting a special focus on reproducibility and unambiguous comparability to hot-extruded reference material (provided by Cunova GmbH), this demand is intended to be satisfied. In order to reach this goal, an emphasis was put on the following novelties:

Development of a well-adjusted atomization routine, including extensive powder investigations for Alloy 400

Elaboration of a DoE approach tailored to the Alloy 400 LPBF process, reaching for the highest densities possible

First-time identification of material characteristics of the additively manufactured Alloy 400 and comparison to conventional fabrication

2 Experimental procedure

2.1 gas atomization.

For the production of metal powder prior to the AM process, an Indutherm Blue Power AU3000 gas atomizer was utilized. Due to its high atomization temperature of ~ 1600 °C (liquidus temperature: ~ 1350 °C), Alloy 400 can only be atomized using a high-temperature (HT) equipment setup; the bulk material got loaded into a ceramic crucible which itself was applied to a graphite susceptor as displayed in Fig.  1 . The heating was done via induction, and a close-coupled atomization setup was used with argon as inert gas. The CCA setup causes the formation of a low-pressure area beneath the nozzle and in combination with the low viscosity of the melt, achieved by considerable overheating, and high gas stream velocity; this leads to the formation of relatively fine particles [ 30 ]. During atomization, the Ar pressure was set to ~ 8 bar, and the gas flow was ~ 215 m 3 /h. In literature, the hereby resulting cooling rates vary from 10 2 to 10 8  K/s [ 30 , 31 ]. For a powder fraction from 20 to 63 µm, which matches approximately the desired range in this work, more precise cooling rates of 10 3 to 10 4  K/s are stated [ 32 , 33 ]. In order not to freeze the nozzle with Ar gas and to ensure a sufficient discharge of the liquid, the gas stream was activated with a delay of 1.5 s post to the release of the melt. To further homogenize the material, the liquid Alloy 400 was held at its atomization temperature for 15 min before releasing the melt into the atomization tower. Moreover, low viscosity and, thus, more effective mixing of the melt were ensured by overheating the system by ~ 250 °C above its liquidus temperature. This way, 10 kg of bulk material was atomized to powder during approx. 2 min.

High-temperature close-coupled atomization setup according to [ 34 ]

Considering LPBF fabrication capability, the powder being too coarse was sieved out, and particles being too fine were air-separated from the final fraction of 15–63 µm by using an automated sieve (EOS/Russell) and an AC1000 air classifier (Indutherm Blue Power), respectively. The final powder was analyzed by a Zeiss Auriga scanning electron microscope (SEM) in terms of particle size, microstructure, and porosity. By application of a focused ion beam (FIB), cross-sections of particles were analyzed for their grain structure, utilizing Ga + as the respective liquid metal ion source. Moreover, the existing elements were classified in greater detail via the application of energy-dispersive X-ray spectroscopy (EDS), using Aztec software (Oxford Instruments) for evaluation. The chemical composition of the powder used for LPBF was double-checked by wet chemical analysis (WCA, Agilent 5800 ICP-OES) and compared to the initial composition of the bulk material. Hall flow testing was performed in order to verify the flowability (DIN EN ISO 4490) and bulk density (DIN EN ISO 3923–1) of the powder. The measurements were extended by powder rheology investigations using a FT4 universal powder rheometer (Freeman Technology) according to ASTM D 7981 at the Research Institutes of Sweden (RISE). These shear cell investigations consisted of flow function, cohesion, Hausner ratio, and surface area. To quantify the particle size distribution with dynamic image analysis (ISO 13322–2), a Camsizer X2 (Retsch) was used.

2.2 Laser powder bed fusion

Throughout the whole laser powder bed fusion fabrication and optimization process, an EOS AMCM M290 customized machine was used. Special features of this machine are a heatable build plate (up to 500 °C), a reduced build space (diameter 100 mm, height 100 mm) for small batch investigations, and a green laser source (wavelength 532 nm). A brush was used as a recoater, and the build chamber was pressured with Ar inert gas. One layer had a thickness of 20 µm, the build plate was pre-heated at 80 °C, and a rotating scanning strategy of 67° was applied. Moreover, the travel of the laser was always directed against the inert gas stream. This way, ejections from the melt pool onto the unmolten powder bed, due to acceleration caused by the gas flow, were prevented. As a test geometry, cubes with an edge length of 8 × 8 × 8 mm 3 (1.5 mm of support beneath) were examined. In total, 24 cubes were fabricated within one build job. Support structures beneath the cubes allowed heat transferability from the part to the build plate and vice versa, as well as easy removal from the build plate by either band sawing or wire electrical discharge machining. The build plate was made of 1.0050 (E295) plain carbon steel and had a round shape with a diameter of 100 mm.

The resulting relative densities were obtained via buoyancy according to Archimedes and optically via light optical microscopy (LOM), respectively, as per VDI 3405–2. As stated in this standard, the first method leads to a quite accurate overview of the overall density of a part, while optical investigations provide more meaningful insights into the arrangement and form of pores in one specific layer. For this reason, densities measured according to both procedures were considered: buoyancy for a fast, approximate value and optical microscopy evaluations for the more accurate final value. Five areas of a single layer of DoE cubes were considered for the calculation of the average relative density within one specimen. Images of cross-sections parallel and perpendicular to the build plane were taken and compared. They showed no significant difference in terms of density in between each other, and thus, parallel preparation was chosen for the evaluation of optical density due to faster preparation. LOM images were taken by a digital microscope (Keyence), and the ImageJ software was used for the determination of density. Also, specimens were etched with ferric chloride in order to make visible the melt pool propagation in the build direction under the LOM.

For examinations via SEM, cubes were cut in half perpendicular to the build plane by a linear precision saw IsoMet 4000 (Buehler) and fixed in a conductive-filled phenolic mounting compound, using a warm embedding device SimpliMet 1000 (Buehler). Afterwards, parts were ground (down to 2500 grit SiC paper) and polished (down to 0.02 µm colloidal silica suspension) by an EcoMet 300 (Buehler). Chemical analysis was carried out by wet chemical analysis and double-checked by application of EDS. The grain structure was investigated by electron backscattered diffraction (EBSD). For more in-depth characterization of the nanoscale, a transmission electron microscope (TEM) JEOL JEM-2100F working at 200 kV was used. It was operated at the Institute of Physics of Materials, Brno, and it is equipped with a bright-field detector allowing observation in scanning mode (STEM) as well as an Oxford XMAX80 EDS detector for analysis of the local chemical composition.

2.3 Material properties

In order to obtain the mechanical properties of the LPBF-fabricated alloy, tensile tests according to VDI 3405–2 were performed. A universal electromechanical Zwick Z050 tensile testing machine was used with a strain rate of 8.0 × 10 −3 /s. The elongation was detected via sensor arm extensometers. Cylinders for tensile testing had a diameter of 10 mm and were reworked by machining, resulting in type B specimens as per DIN 50125 (diameter 6 mm, gauge length 30 mm). As recommended in the standard, blanks were built in three different orientations:

In a polar angle Θ of 90° to the build direction (horizontal orientation in build space)

In a polar angle Θ of 45° to the build direction (diagonal orientation in build space)

In a polar angle Θ of 0° to the build direction (vertical orientation in build space)

All blanks revealed an azimuth angle φ of 45° to the coater brush. This angle was chosen in order to ensure proper coverage of the melt pool with every new layer of powder. For hardness measurements, 8 × 8 × 8 mm 3 cubes were manufactured and ground on the test surfaces (parallel as well as perpendicular to the building plane). Hardness was then obtained according to Vickers as per DIN EN ISO 6507–1.

Tensile tests were also carried out at elevated temperatures at the Institute of Physics of Materials, Brno, in order to further investigate the behavior of the alloy in possible high-temperature fields of application. For this purpose, small cylindrical specimens (3 mm in diameter, 9 mm in gauge length) were used. The specimens were fabricated from a material block prepared by additive manufacturing; the specimen axis was perpendicular to the building direction (Θ = 90°). A universal electromechanical Zwick Z050 system was used in the regime of constant traverse speed (1 mm/min, which corresponds to a strain rate of 1.6 × 10 −3 /s). The ductility was measured by a clip-on extensometer with ceramic rods (MayTec), touching the specimen. The furnace was equipped with 3 thermocouples for controlling the temperature stability and keeping a low thermal gradient. Tests were performed in laboratory air.

2.4 Design of experiments

To be able to find a LPBF parameter set that exceeds high densities of 99.5%, a DoE approach using Minitab software was carried out and applied to the optical density data taken from cross-sections of specimens. As parameters, laser power p L in (W), scanning speed s S in (mm/s), and hatch distance d H in (µm) were investigated. They all affect the final density of the part in a significant way, and their interdependency can be described by a cube, consisting of a dark blue center point, orange corner points, and light blue star points (Fig.  2 ). The center point describes the input data, taken from previous studies and/or iterations. With the help of corner points, a space is built up around the center point which is likely to contain a better response in terms of density. Several combinations of input variables fluctuate in a positive and negative manner around the starting values of the center point. Ultimately, star points are reaching out of the cube, representing extreme values of one parameter only, while the other two stay at their center point levels. Single-parameter influences can be derived from this.

Laser power, scanning speed, and hatch distance within the design space

Three DoE iterations were carried out to narrow down further the parameter ranges needed to reach the goal of high density. However, before processing the first DoE iteration, the program needed initial information about the input–output interdependence. Therefore, the very first print job was carried out without the use of software but based on parameter sets that showed good processability for different yet comparable alloys, such as Alloy K500. By finding the correlations between parameter combinations and resulting densities, the computational simulation was filled with data. As a result, new parameter settings were calculated and interpreted, leading to higher densities throughout the first DoE iteration. The maximum attainable density rose from one iteration to another, but ultimately, the optimization would stagnate, revealing no significant improvement of a new parameter set when compared to the previous one. This indicated the end of the procedure.

3.1 Powder production and characterization

The chemical composition was determined for gas-atomized powders, LPBF-fabricated parts, and hot-extruded reference samples by wet chemical analysis and EDS, respectively. Results and face values according to DIN 17743 (material no. 2.4360, NiCu30Fe) are given in Table  1 . For carbon being a light element with a very low proportion in the present alloy, measurements were excluded due to unreliable detectability.

With respect to the chemical requirements of Alloy 400, no significant deviations were detected for LPBF-fabricated parts throughout the whole process. Moreover, when comparing powders and LPBF specimens, only small variations were measured. Due to this analytical evidence, the processing of gas-atomized powder was considered to fulfill the specification. Analyses on reference samples were to a great extent in line with the standard as well.

Further SEM investigations of the powder were carried out with a secondary electrons secondary ions (SESI) detector, and results are displayed in Fig.  3 a. Gas-atomized Alloy 400 reveals mostly spherical particles with only sporadic occurrence of satellites or coarse agglomerates, which would negatively influence powder processing properties, in particular its flowability [ 35 , 36 ]. The images clearly indicate the rapid cooling of the particles during atomization, resulting in very fine, dendritic grain growth and grain sizes of approx. 1 to 9 µm (mean 5.2 ± 3.2 µm). Small powder particles tend to evolve small grains of a few micrometers only, and larger particles show coarser grains of up to 15 µm. Figure  3 b shows a single powder particle that was cut with a focused Gallium ion beam. Having a more detailed look at single grains and grain boundaries with the in-lens detector, no precipitates of the associated elements were detected, being in line with the assumption of this alloy being a solid solution [ 1 ]. Nevertheless, having a closer look at EDS data, a special property of Alloy 400 was detected; the concentration of copper is higher at the grain boundaries than within the grains and vice versa, and the concentration of nickel is lower at the grain boundaries than within the grains. These local differences in concentration were classified as segregations, which are typical for NiCu-based alloys [ 37 , 38 , 39 ]. Segregations concerning the remaining five elements were not detected. Furthermore, no gas porosity or impurity was detected within the particles. Such defect-free particles with fine grains are considered favorable for production as stated in [ 31 , 40 ]. In general, the chemical distribution of elements can be described as homogeneous, both on the surface of and inside the particles, respectively.

a SEM micrograph of gas-atomized powder (overview and detail); b a FIB cross-section of a single particle, illustrating grain growth and, via application of EDS, Cu segregations at grain boundaries

On average, the volumetric sphericity measured by dynamic image analysis reached a normalized value of spht 3  = 0.766 (1.000 being perfectly spherical). Even though most particles appear spherical in SEM, a lower spht 3 was attributed to the few attached satellites, as documented in [ 41 ]. Volumetric symmetry (symm 3  = 0.916) and volumetric aspect ratio of width to length (w/l 3  = 0.821) correspond to this observation. This indicates that the powder is probably processable as key values close to 1.000 are linked to a high flowability of the powder and great energy absorption of the laser into the particles [ 42 , 43 ]. Powder being too coarse was sieved out by a sieve with a mesh size of 63 µm. The remaining fraction was then air-separated in order to remove particles being finer than 15 µm. This way and as displayed in Fig.  4 , the particle size distribution could be narrowed down to a Q 3 (10%) of 28.9 µm and a Q 3 (90%) of 61.5 µm; the Q 3 (50%) was 42.3 µm and in line with the qualitative findings via SEM. The bulk density of the final powder fraction was ρ b  = 4.38 g/cm 3 , indicating a relative density of ρ rel  =  ~ 50% when compared to the nominal density of Alloy 400 (ρ n  = 8.80 g/cm 3 ) [ 7 ]. With a Hall flowability of 15.22 s per 50 g powder, the particles showed a good mass flow; rat-holing phenomena were not observed, and the standard funnel did not have to be knocked at in order to initiate the flow. A good flowability was attributed to the high sphericity of the particles [ 44 ]. Shear cell investigations were performed after conditioning the powder with a pressure of 9 kPa. By twisting one layer of powder relative to another one, a flow function FF = σ M /σ C was calculated with σ M being the major principal stress and σ C the unconfined yield strength. A normalized flow function value of approx. 15 was detected, with values above 10 being considered as flowing well according to the specifications of the device manufacturer (Freeman Technology, 2023). This is underlined by the low degree of cohesion of ~ 0.25 kPa of the powder when being sheared. Moreover, the Hausner ratio as an indicator for the attrition in between particles was 1.09 for the present Alloy 400, which is desired in terms of processability [ 45 , 46 , 47 ]. On average, the surface area of the coarse powder measured 0.034 m 2 /g.

Particle size distribution of the final powder fraction used for LPBF printing

The above results led to the conclusion that the powder should behave as expected during LPBF, which meant that it could be applied properly to the powder bed and that processability was generally ensured.

3.2 Laser powder bed fusion and design of experiments

3.2.1 parameter optimization.

Throughout the LPBF process parameter optimization, the parameters were varied as follows:

Laser power p L : 60–120 W.

Scanning speed s S : 250–1350 mm/s.

Hatch distance d H : 30–120 µm.

Considering a single DoE iteration, the simulation needed to be interpreted against the background of input–output correlations, exemplary as displayed in Fig.  5 . This figure can be considered as a two-dimensional cut through the cube presented in Fig.  2 . The parameter setting revealed a constant value for the hatching distance (80 µm) and variations in the other two: scanning speed (600–1300 mm/s) and laser power (60–110 W), respectively. On the basis of density measurements and allocation to the set parameters (black dots), calculations were performed that predicted the occurrence of different, pre-defined density ranges (shades of green). In this particular case, no densities above 99.5% were predicted for a constant hatch distance of 80 µm, regardless of how much the other two parameters were adjusted. A hatching of 80 µm is therefore generally considered unsuitable in order to reach high densities. Hence, the investigated process window did not show sufficient measuring points at this stage and needed to be investigated for other hatch distances.

DoE contour diagram for varying laser powers and scanning speeds at a constant hatching distance of 80 µm, expected density ranges in shades of green

With density being the output variable of the regression equation, a Pareto diagram of standardized effects as in Fig.  6 was drawn from the parameters. For A being the laser power, B being the scanning speed, and C being the hatch distance, the diagram clearly indicates statistical significance for A and B as they cross the reference line of 2.228 in whatever combination (A, B, AA, AB, BB). The reference value varies from one iteration to another as it results from the respective regression equation of one iteration. The value is affected by the linear term, the quadratic term, the two-factor interaction, and the error term. The linear term illustrates the effect of a single parameter only, while the quadratic term acts as a balancing calculation (a more accurate replica of the answer term). For variable C, hatching, no statistically significant term was found with respect to the parameter combinations displayed in Fig.  5 . This underlines the need for further testing and evaluation of the influence of the hatch distance. The factors are statistically significant at the α = 0.05 level, which meant that the probability of the displayed results being not due to the investigated relationships is below 5%.

Pareto diagram of standardized effects revealing the statistical significance of the parameters laser power (A), scanning speed (B), hatch distance (C), and their combinations

According to [ 48 , 49 ], the nominal energy introduced into the part (neglecting reflection) can be described by

with e V being the volume energy density in (J/mm 3 ) and t L the thickness of a layer in (µm) with a constant value of 20 µm. In total, 72 parameter combinations were examined during three DoE iterations. Figure 7 gives an overview of the absolute positioning in the design space consisting of laser power, scanning speed, and hatch distance as well as relative positioning in between various parameter sets. While Fig 7 a indicates the resulting volume energy density, Fig 7 b shows the resulting optical relative density (ORD). Parameters leading to similar volume energy densities are colored equally with an e V of 210 J/mm 3 being the maximum tested one. It can clearly be observed that border areas like 0 to 55 J/mm 3 and 85 to 210 J/mm 3 are distributed widely throughout the design space, while an energy density of 60 to 80 J/mm 3 leads to a rather marginal distribution around the common core of the examined parameter sets. There are only two parameter combinations belonging to the category of 80 to 85 J/mm 3 , indicated by two green stars. The lower left star represents an e V of 80.95 J/mm 3 , originating from p L  = 85 W, s S  = 1050 mm/s, and d H  = 50 µm. For the upper right star, p L  = 100 W, s S  = 600 mm/s, and d H  = 100 µm were the parameters, resulting in an e V of 83.33 J/mm 3 . Both stars are highlighted concerning their ORD as well, once as a blue star with an ORD of 99.94% and once as a red star with an ORD of 97.26%.

a Parameter combinations within the design space, color-coded according to their resulting volume energy density in (J/mm 3 ); b same parameter combinations but in turn, color-coded according to their resulting optical relative density in (%)

3.2.2 Optical density

Representing the above-mentioned “red star,” Fig.  8 shows a cross-section perpendicular to the build direction. Since the parameters were not coordinated with each other, high porosity occurred, leading to multiple defect formation. According to [ 50 , 51 ], present defects were described as a profound lack of fusion and unmolten powder particles, both originating from low energy density, and fine keyhole formation, originating from high energy density.

Non-adjusted parameter set “red star,” leading to pronounced pore formation

For Fig.  9 instead, representing the “blue star,” very little pore formation occurred during LPBF. The existing pores were considered keyholes, resulting from fine shielding gas inclusions during re-solidification of the material and vaporization of the melt [ 50 , 51 , 52 ]. Comparing both the “red star” and the “blue star,” it was observed that highly similar volume energy densities led to highly different optical relative densities.

DoE-adjusted parameter set “blue star,” revealing a significant increase in part density

3.3 Part characterization

3.3.1 microstructural analysis.

Following the parameter optimization process, samples with the highest achievable densities were selected to be investigated for their microstructure, and comparisons to conventional materials were drawn. Having a look at the polished xy -plane of the LPBF specimen (view from the top, perpendicularly to the build direction) by operation of a backscattered electron detector (BSD), as displayed in Fig 10 a, small cellular grains with a maximum length of 50 µm were detected, while most of the grains were even finer (~ 16.5 µm on average). This particular layer revealed an orientation of the laser travel paths (yellow lines) of ~ 35° tilted against the nominal of the plane. Nevertheless, as a rotating scanning strategy was applied to other layers, different rotation angles have been found. The orientation within one single xy -layer varies along the z -axis throughout the whole part. When investigating the parts in parallel to the build direction (Fig 10b), fan-shell-shaped melt pools directed along the z -axis became observable, resulting from the iterative (re-)melting and solidification during LPBF in between layers, as described in [ 53 ]. An orientation along the build direction is a common phenomenon of LPBF-built parts that can be explained by the extreme temperature gradients occurring during fabrication and the resulting directed solidification [ 54 , 55 ]. Moreover, the width of the laser beam focus of approx. 50 µm was detected (yellow lines). The shell shape of single melt pools and the solidification orientated in the build direction were confirmed by an EBSD mapping (Fig 10 c). It also revealed a slight crystallographic < 101 > texture of the fcc unit cell parallel to the build direction. The corresponding inverse pole figure for the build direction (IPF Z) underlines this finding as the [101]-orientation is highlighted in red with a standardized maximum of 1.77. IPF Z was retrieved in the associated < 100 > pole figure (PF), highlighting the respective [101] texture uniformly around the [100] center at approximately 45°. In contrast to this, the texture of grains perpendicular to the build direction is randomly and evenly distributed; a clearly preferred orientation for IPF Z was not observed in the IPF X (Fig 10 d) and IPF Y (Fig 10 e) mappings.

a BSD of LPBF-printed specimen perpendicular to the build direction; b BSD parallel to the build direction; c Z EBSD mapping, IPF Z, PF for the build direction, color intensity bar and color code triangle; d X EBSD mapping and IPF X; e Y EBSD mapping and IPF Y

In comparison, the grain structure of the hot-extruded, recrystallized material was substantially coarser and reached grain sizes of up to 200 µm (Fig.  11 ). No directed solidification could be observed, and grains appeared in an equiaxed state. Hence, by a factor of approximately 10, LPBF-fabricated parts revealed a much finer grain structure.

Recrystallized reference material revealing a coarse, equiaxed grain structure, detected by SESI

Micro-dendritic structures as well as high dislocation densities are a common, well-studied phenomenon of LPBF-produced parts in as-built conditions, resulting from the high cooling-melting ratio [ 56 , 57 , 58 , 59 , 60 , 61 , 62 ]. Accordingly, these internal structures were also detected in this work as shown in Fig.  12 . Micro-dendritic cell structures, revealing a cell size of approx. 250–500 nm, accumulate in between grain and sub-grain boundaries and are intersected by a wide variety of dislocations. The dislocations, which to some extent compensate for the immense internal stresses due to rapid temperature changes during production, are mainly focused on the cell walls and to a lesser extent are also present inside these cells.

Bright-field STEM micrographs revealing grain and sub-grain boundaries and internal micro-dendritic structures with high dislocation density in wall segments and dislocation-free center

3.3.2 Mechanical properties

In order to quantify the mechanical properties of additively manufactured Alloy 400, tensile tests at room temperature were carried out on specimens that had been printed in different polar angles according to the DoE-optimized parameter set: perpendicular (90°), diagonal (45°), and parallel (0°) to the build direction. Tensile test specimens revealed an ORD of 99.56% on average. As displayed in Fig 13 a, for parts that were printed in horizontal orientation, ultimate tensile strength R m and yield strength R p 0.2 showed maximum values of 615 MPa and 556 MPa, respectively. Tensile specimens with a polar angle of 0° showed minimum values instead ( R m  = 592 MPa and R p 0.2  = 519 MPa, respectively). Therefore, tensile strength and yield strength decreased when the specimen axis approached the build direction (upright specimens). Young’s modulus E revealed a clear maximum of 159 GPa for 45° built geometries and lower values for the other two orientations (90°, 133 GPa; 0°, 135 GPa). In Fig 13 b, elongation at break A 5 , uniform elongation A g , and fracture necking Z are displayed. A g showed a certain tendency, the smaller the polar angle, the stronger the elongation (90°, 3.0%; 45°, 3.6%; 0°, 3.7%). Also, A 5  = 11.7% and Z  = 28.9% had their minima at 90°, respectively, leading to the observation that the ductility of the alloy increased with parts being printed more upright/vertically in the build space. These findings are in line with the above-described decline of R m and R p 0.2 from 90 to 0° oriented parts; the smaller the polar angle (speaking the more upright the part is orientated in the build space), the lower the strength and the higher the ductility within the part.

a Stress and Young’s modulus for LPBF Alloy 400, printed in different orientations; b strain and necking

Further tensile testing on specimens fabricated perpendicularly to the build direction was carried out at elevated temperatures, and a comparison to conventionally fabricated Alloy 400 was drawn. The resulting tensile curves are shown in Fig 14 a. LPBF parts were tested at room temperature, 400 °C, 550 °C, 650 °C, and 750 °C (red lines). For the hot-extruded, bulk parts, room temperature, 530 °C, and 936 °C were applied (blue lines). Fig 14 b shows the dependence of the yield strength on the testing temperature. The tensile strength and yield strength of the LPBF part were similar or higher in comparison to the bulk variant. However, the elongation at fracture of the LPBF variant was substantially lower with a tendency to decrease with rising temperature.

a Stress–strain-diagram for bulk (blue curves) and LPBF (red curves) Alloy 400 at various temperatures; b yield strength as a function of applied temperature

Concerning hardness, cubes were evaluated in parallel and perpendicular to the build direction; no difference was observed here. Moreover, results for micro- and macro-hardness were identical. On average, the samples showed a hardness according to Vickers of 194 HV1 and HV10, respectively. For conventionally fabricated material (annealed condition), a hardness of ~ 107–147 HV1 was stated, while hot-rolled and hot-finished parts may reach similar hardness values as the LPBF variant [ 1 , 7 ]. Hot-extruded material, as used throughout this study, shows an HBW 2.5/62.5 of 115–121. Higher hardness in the LPBF variant was traced back to the finer grain structure, as discussed in [ 2 ].

4 Discussion

4.1 powder suitability for lpbf.

The atomization process window was considered suitable in terms of an effective operation of the low-pressure area, leading to the desired rapid undercooling of the melt. Fine powders resulted, porosities and impurities were not detected which would be detrimental for the LPBF process [ 63 , 64 ]. It was possible to create spherical particles showing only a small number of satellites, resulting in high flowabilities and bulk densities needed for successful AM [ 64 , 65 ]. As a consequence, this eventually leads to higher build quality during LPBF [ 63 , 64 , 65 ]. The resulting fractal nature of the powder bed in the LPBF process was introduced by Estrada-Díaz et al., i.e., as per the fractal dimensions and lacunarity, accurately correlating both homogeneity and morphology with a sustainable, low-defect LPBF process [ 66 , 67 ]. No precipitates were found within the particles, which is in line with the assumption of this alloy being a one-phase solid solution [ 1 , 2 , 3 ]. Besides, Cu segregations were expected and also detected on grain boundaries [ 37 , 38 , 39 ]. A consistent chemical composition was found in both, powders and parts, and thus, the generated powder was generally considered appropriate for LPBF.

4.2 Melt pool geometry and resulting microstructure

NiCu-based Alloy 400 is a fcc alloy, and thus, it is expected that the preferred dendrite growth direction is along the [001] crystal direction [ 68 , 69 , 70 , 71 ]. In the case of LPBF, the thermal gradients are pointed normally to the melt pool boundary, and thus, grains with [001] directions parallel to the thermal gradients will preferentially grow from the melt pool boundary. Attributed to the Gaussian profile of the laser source, the core of the melt pool eventually exhibits higher temperatures than the border areas [ 68 , 71 , 72 , 73 ]. As frequently observed in other works like [ 55 , 71 , 74 , 75 ], due to the geometry of the melt pool, boundary-near grains grow transversely to the direction of the introduced laser power and build direction, respectively. In turn, nucleation near the melt pool core experiences undirected undercooling, leading to the formation of more equiaxed grains. Figure  15 shows the ideal melt pool that would result under these circumstances, consisting of dendrites near the melt pool boundary and of cross-sections of elongated grains resulting from the laser beam travel (here, out of the figure plane). The resulting growth mechanism gives reason for the [101] orientation with respect to the build direction that has been found for the present alloy and manufacturing routine, respectively; dendrites do not only grow along the build direction but deviate into the build plane as well. This type of process-induced deflection of grain growth toward < 011 > orientations was also found for a Ni-based IN718 by Pant et al. and for a NiTi-based alloy by Safaei et al. [ 71 , 76 ].

Schematic of an ideal melt pool, denoting different types of directed grain nucleation

Nevertheless, the texture was described as marginal only (Fig 10 ). This was found to be due to a wide variety of geometries, sizes, and growth directions of the grains, resulting in a very heterogeneous microstructure. In other words, the above-described ideal melt pool was hardly detected within the present LPBF manufactured parts as illustrated in Fig.  16 . Melt pool boundaries could be tracked down partially only, and equiaxed and columnar grains appeared randomly distributed over the cross-section. This can be related to the rotating scanning strategy; as stated by Serrano-Munoz et al., a rotation of 67° in between layers allows for the formation of both elongated grains along build direction and epitaxial growth [ 77 ]. According to Qin et al., this type of rotation lowers the overall texture [ 55 ].

SEM closeup of the melt pool intersections in between several layers

Etched with ferric chloride, the melt pool propagation in the build direction ( z -axis) was revealed in greater detail (Fig.  17 ). The pre-described fan-shell shape became even more observable, resulting from an overlapping of melt pools from one layer to another. The ratio of melt pool depth and layer height shows an effect here; with a width of 50 µm, approximately 80 µm was found to be the maximum melt pool depth, while the applied layer height measured 20 µm only. Hence, a melt pool of a considered level reached four layers deep into the part, meaning that the original melt pool geometry of one respective layer was dissolved by the impacts of further melt pools from overlying layers. This, in turn, results in a quadruple (re-)melting and solidification of the material with the heat-affected zone (HAZ) reaching even deeper. The HAZ may further significantly alter the microstructure [ 78 , 79 ]. These findings serve as another explanation for the above-found very different grain structures and nucleation mechanisms. Apart from that, a few remaining pores were observed on the etched samples, being classified as keyholes.

Light optical image of an etched slice parallel to the build direction, illustrating overlapping melt pools

Copper segregations on grain boundaries were clearly visible for the as-atomized powders (Fig 3 ). In contrast, using TEM for as-built LPBF parts, chemical micro-Cu-segregations became visible on the nanoscale, revealing a very low intensity at cell walls (Fig.  18 ). According to Bertsch et al., the occurrence of these micro-segregations can, in some cases, be correlated with the previously mentioned dislocations as these can act as traps for some elements [ 80 ]. Sabzi et al. showed that high cell-wall-near dislocation densities significantly enhance the strength performance of the respective alloy, while Kong et al. stated that high dislocation densities go along with nanosized cellular structures which, in turn, enable superior performance in comparison to conventional manufacturing [ 59 , 60 ]. These nanocell structures, revealing high dislocation occurrence, have been found for the present LPBF Alloy 400 as well as previously displayed in Fig.  12 .

Bright-field STEM micrograph and micro-segregation of Cu and Ni on the nanoscale as detected by EDS analysis in STEM

Compared to the one-time rapid undercooling of the melt during powder atomization, the thermal impact on LPBF parts is more complex and caused by an entire sequence of iterative laser melting and subsequent very high cooling rates [ 68 , 81 ]. As illustrated above (Fig.  18 ), the respective part layers experience several iterations of melting and solidifying before being additionally exposed to the HAZ during the fabrication of further layers. Also, non-molten powders aside may keep the heat locally concentrated near the melt pool [ 82 ]. Hence, an in situ, process-related heat treatment during manufacturing caused by the succession of several layers can be noted, inevitably benefitting diffusion processes based on a temperature gradient. From one layer to another, this eventually results in a decrease of locally different chemical concentrations, and ultimately, inhomogeneities almost dissolve completely into the preferred homogeneous solid solution. This serves as a further explanation for the copper segregations being only detectable on the nanoscale via TEM within LPBF parts compared to the strongly pronounced segregations in powders.

4.3 Building strategy and consequential material properties

Even though chemical imbalances are eliminated within the parts, structural irregularities do remain. Not only that no significant texture was found for the xy -plane but solely along the build direction, but there are also differences in mechanical properties concerning the orientations of fabricated specimens. As observed, the ultimate tensile strength and yield strength of tensile test specimens decrease with a falling polar angle from 90 to 0° to the build direction (Fig 13a). In other words, the more upright the cylinders were manufactured during LPBF, the less strength they showed. Keeping in mind the directed grain growth along the build direction, this leads to the assumption that the lateral overlap of melt pools (horizontally in the build space, primarily present in 90° oriented samples) results in a higher strength performance than the overlap of melt pools on top of each other (vertically in the build space, primarily present in 0° oriented samples). Here, the 45° oriented samples are equivalent to a combination of both, vertical and horizontal overlap, resulting in mechanical properties between them. The samples that were tested perpendicular to the build direction showed the lowest levels of elongation (Fig 13 b). Accordingly, higher ductility in the build direction was found by Wilson-Heid et al. for a Ti-6Al-4 V alloy, being correlated to the columnar grain growth along the z -axis and a consequent damage accumulation in the horizontal direction [ 83 ]. Also, Yu et al. found a higher ductility for upright-oriented Hastelloy X samples, mainly attributed to a considerable extent of texture and grain rotation in this direction [ 84 ]. These results are consistent with those shown here that the strength is inversely correlated with ductility. This is further underlined by the low fracture necking for 90° oriented samples. Thus, strength and ductility are evolving contrarily with the Young’s modulus being the highest for the diagonally oriented specimens. This anisotropic behavior of Young’s modulus in LPBF with accompanying varying stiffness values depending on the orientation of the specimen has been frequently discussed in literature like [ 84 , 85 , 86 ]. Ultimately, anisotropy along the z -axis was found, while for single xy -planes, isotropic behavior is present since it is not possible to differentiate between directions x and y . Still, due to the application of the rotating scanning strategy, anisotropy in build direction was kept at a comparably low level; for an IN718 alloy, Serrano-Munoz et al. demonstrated that the texture index can approx. be reduced by half when a 67° rotation is applied instead of a 90° alternating xy -scanning scheme as a columnar grain growth with preferred < 001 > orientation over several layers is inhibited [ 77 ]. Accordingly, as stated by Safaei et al. for NiTi alloys, suppressing the grain orientation leads to a decline in anisotropy [ 71 ].

Further mechanical testing revealed differences in between bulk and LPBF material. An in situ heat treatment was assumed for the LPBF parts above. Still, the resulting microstructure did not reveal coarse and equiaxed grains as in hot-extruded parts but a finer, ten times smaller, and elongated shaping. The fact that LPBF produces a finer and non-equiaxed grain structure as present in conventional manufacturing processes has already been shown frequently in the literature for many alloy systems, including several Ni-based ones [ 2 , 87 , 88 , 89 ]. This grain refinement in AM parts leads inevitably to a hardening of the structure, resulting in the superior mechanical properties found for yield strength and ultimate tensile strength up to 530 °C. Still, slight residual keyhole porosity was found for the additively manufactured parts by Chlupová et al., facilitating crack initiation and resulting in a more brittle material failure type than in the reference parts [ 90 ]. This gives reason for the overall lower ductility.

4.4 Reconsideration of the volume energy density as key performance indicator

As identified throughout the DoE studies, hatching of 80 µm was generally found to be unsuitable in order to reach high densities (Fig.  5 ). With a laser focus of approximately 50 µm, the resulting porosity can be correlated to residual lack of fusion in between scanning lines. This evidence exemplifies precisely the problem of utilizing the volume energy density as the main target figure of parameter optimizations in laser powder bed fusion processes; no matter how the residual parameters (among others, laser power, scanning speed, layer height, etc.) are adapted for a constant hatch distance, the resulting part density may not be raised to a satisfactory high value. Complete melting of the entire powder bed is not achievable for hatch distances being too broad, independently from an energy increase through, e.g., a higher laser power or a slower scanning velocity. Anyway, in modern LPBF parameter development, it is considered a general agreement to search for the optimum e V range. Although similar volume energy densities may consist of completely different parameter combinations, this approach is widely used as applied and discussed in [ 48 , 91 , 92 ]. In other words, as stated in the results section, equal volume energy densities are likely to result in very different optical relative densities, which is why the e V can only be consulted as an approximate orientation (Fig 7 a). This issue has been addressed by Scipioni Bertoli et al. in stating that e V does not adequately describe the melt pool dynamics and must therefore be used very cautiously in LPBF parameter optimization [ 49 ]. Estrada-Díaz et al. further supported this finding by stating that the LPBF process can only be described partially with the help of VED as it lacks information on powder ejection and sublimation [ 93 ]. Single process parameters must be interpreted against the background of their interaction with other process parameters. DoE instead consists of smooth continuous parameter functions which map single parameters adequately. As the regression equation consists of the three target values of laser power, scanning speed, and hatch distance, the found parameter set fits accurately into this system. Moreover, as identified above for uncoordinated parameter sets, several kinds of defects can be found for a single layer (Fig.  8 ). High energy input would result in keyhole porosity, while lack of fusion and unmolten particles can be correlated with low energy introduced into the layer [ 51 , 94 ]. Hence, the energy density is not distributed equally over one layer, further proof that optimum fabrication is attributable to process parameters instead of e V . The approach of focusing on the process parameters revealed a high potential for the present Alloy 400 as high densities were achievable. While this work focused on the correlation of p L , s S , and d H (input variables) with the resulting density (output variable) reduced by keyhole porosity, unmolten particles, and lack of fusion, further potential outputs such as distortion, balling, or cracking as a function of several input parameters could be investigated as well to overcome the uncoordinated nature of single process parameters. Here, applying Buckingham’s π-theorem, setting the focus on the most significant physical interactions occurring, and dimensional analysis, describing a process as the sum of dimensionless products, counteract poorly adjusted parameter sets as well [ 95 ].

5 Conclusion

In this study, a holistic AM process route for Alloy 400 was established, reaching from application and alloy design according to standard specifications over in-house powder generation and characterization to a DoE-assisted laser powder bed fusion process, resulting in part microstructure analysis and comparison to conventionally fabricated material. The concrete results were then discussed and put into perspective, resulting in the following notable findings and overall conclusions of this work:

The usable powder can be generated via the application of a close-coupled gas atomization setup using a high-temperature ceramic crucible. The final particle size distribution of 15 to 63 µm was adjusted by sieving and air-separation post-processing, resulting in spherical and flowable particles which provided the basis for successful LPBF fabrication.

The standard target chemical composition was in line with powders, LPBF parts, and hot-extruded reference Alloy 400, allowing us to conclude the chemical purity and consistency of the applied processes. Hence, a comparison in between the various states was enabled and carried out.

At grain boundaries in powders, Cu segregations were clearly detectable and verified via SEM on the microscale as expected for this alloy type. Still, within printed parts, only slight micro-segregations were detected via TEM. Heat-induced diffusion processes, resulting from the iterative sequence of the LPBF process, give reason for this phenomenon as chemical imbalances may almost dissolve completely into the solid solution.

As typical for LPBF-produced parts, a wide range of dislocations was found to be present, primarily along cell walls and occasionally inside cells. These cells were classified as micro-dendritic structures within the superordinate grains.

The design of experiments approach for LPBF parameter development led to a final parameter set that enabled the fabrication of highly dense parts, consisting of p L  = 85 W, s S  = 1050 mm/s, d H  = 50 µm, and t L  = 20 µm, resulting in an e V  = 80.95 J/mm 3 . A rotating scanning strategy of 67° in between layers, a green laser with a wavelength of 532 nm, and a pre-heating of the build plate of 80 °C completed the parameter setup. In any case and beforehand, the basic requirement for AM material development is the identification of key parameters and resulting defect formation that prevent the production of high-density parts.

The DoE-based approach revealed the high importance of the interdependency of single process parameters. Based on the finding that similar or even the same volume energy densities may result in very different part densities, the search for a single parameter set was found to be most expedient. Hence, for process parameter development of LPBF processes, this work greatly encourages to shift in the focus from a broad energy density range to a more integrated course of action of identifying a single optimum parameter combination. DoE does not only increase the efficiency of AM process parameter development, but the smaller number of parameter sets that need to be tested also results in overall fewer resources such as the number of build jobs, energy consumption, powder demand, and man hours.

Mechanical properties of LPBF parts being manufactured in an upright orientation within the build space showed lower strength but higher ductility than parts being manufactured perpendicularly to the build direction. This finding was correlated with changing melt pool formation, preferred texture, and varying anisotropy along building direction for different specimen orientations.

At room temperature and at 530 °C, the fine-grained LPBF variant of Alloy 400 performed equally or better in terms of strength when compared to the hot-extruded, bulk reference material, revealing comparably coarse grains. At higher temperatures instead, the conventional material performed better as slight residual keyhole porosity in AM parts amplified crack initiation, compensating its beneficial microstructure.

For elongation, the AM parts did not reach the performance of the conventional ones, which is also due to porosity acting as a fracture trigger and causing a more brittle failure mode. Moreover, this is connected to the inverted relationship between strength (which is higher in AM parts) and elongation.

The hardness of LPBF-built parts was significantly higher compared to conventionally fabricated material being correlated to the coarser grain size of the hot-extruded material.

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Acknowledgements

The authors would like to acknowledge Sepehr Hatami, Ph.D.; Erik Adolfsson, Ph.D.; and Anton Dahl-Jendelin for the chance to perform joint investigations on powder particle rheology at the RISE Research Institutes of Sweden laboratories in Mölndal, Sweden. The authors would further like to acknowledge Zdeněk Chlup, Ph.D. of the Institute of Physics of Materials at the Czech Academy of Sciences for his investigations on tensile testing in Brno, Czech Republic. Moreover, the authors would like to acknowledge Dr. Jörg Fischer-Bühner of Indutherm Erwärmungsanlagen GmbH, Walzbachtal, Germany, for the information exchange on gas atomizations. Also, the authors would like to acknowledge Thomas Volkery of KME Germany GmbH, Osnabrück, Germany, for his great support in specimen preparation and light optical microscopy. This work has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 958192 which is gratefully acknowledged.

Open Access funding enabled and organized by Projekt DEAL. This work has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 958192 which is gratefully acknowledged.

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Jan-Philipp Roth & Katrin Jahns

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Jan-Philipp Roth: conceptualization, data curation, formal analysis, investigation, methodology, software, supervision, validation, visualization, and writing—original draft and review and editing. Ivo Šulák: investigation and writing—review and editing. Tomáš Kruml: supervision and writing—review and editing. Wojciech Polkowski: supervision and writing—review and editing. Tomasz Dudziak: supervision and writing—review and editing. Peter Böhlke: resources, supervision, and writing—review and editing. Ulrich Krupp: conceptualization, funding acquisition, project administration, resources, supervision, and writing—review and editing. Katrin Jahns: conceptualization, funding acquisition, project administration, resources, supervision, validation, and writing—review and editing.

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Roth, JP., Šulák, I., Kruml, T. et al. Establishing a process route for additive manufacturing of NiCu-based Alloy 400: an alignment of gas atomization, laser powder bed fusion, and design of experiments. Int J Adv Manuf Technol (2024). https://doi.org/10.1007/s00170-024-14328-7

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DOI : https://doi.org/10.1007/s00170-024-14328-7

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