Fruit Peel Biochar for Dye Removal

ISEF Category: Chemistry

Subcategory: Environmental Chemistry  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

Textile dye pollution is not just a factory problem. A tiny color change in water can mean a lot of dissolved dye is still there. You can turn food waste into a filter material and measure how well it pulls dye out of water. That gives you a real chemistry project with a real environmental angle.

What Is It?

This project tests whether burned and processed fruit peels can act like a sponge for dye molecules. The final material is called biochar. Biochar is a carbon-rich solid made by heating plant material with little oxygen. Think of it like turning kitchen scraps into a porous black powder with lots of tiny spots where dye can stick.

You then mix that biochar with dyed water and measure how much color disappears. Methylene blue and Congo red are common lab dyes, so they work well as stand-ins for textile wastewater. The key idea is adsorption, which means molecules cling to a surface instead of dissolving into the water. Your job is to see how fast that happens, how much the biochar can hold, and which math model fits the data best.

Why This Is a Good Topic

This is a strong science fair topic because you can change one variable at a time and measure a clear result, like dye removal or adsorption capacity. It connects to water cleanup, waste reuse, and textile pollution, so the real-world value is easy to explain. You can also learn real research skills, including calibration curves, controlled trials, and model fitting. Those are the same ideas used in published environmental chemistry papers.

Research Questions

• How does the type of fruit peel, banana or orange, affect dye adsorption capacity?
• What is the effect of biochar dose on the percent removal of methylene blue?
• What is the effect of biochar dose on the percent removal of Congo red?
• To what extent does contact time change the adsorption rate of dye onto peel biochar?
• Which isotherm model, Langmuir or Freundlich, fits the adsorption data better?
• Does particle size of the biochar change the final dye removal efficiency?
• To what extent does solution pH change dye uptake by peel biochar?

Basic Materials

• Banana peels or orange peels.
• Kitchen oven or school lab furnace access for pyrolysis.
• Heat-safe ceramic or metal tray.
• Aluminum foil or covered heat-safe container for controlled heating.
• Mortar and pestle or clean grinder for crushing dried biochar.
• Digital kitchen scale with 0.1 g accuracy.
• Beakers or clear cups with known volume markings.
• Measuring spoons or graduated cylinder.
• Coffee filters or filter paper.
• Funnel.
• Distilled water.
• Methylene blue or Congo red dye from a school lab source.
• Stirring rod or magnetic stirrer.
• Dropper or pipettes for small transfers.
• Clear glass jars or test tubes for repeated trials.
• Smartphone camera for color comparison.
• White background for consistent photos.
• Disposable gloves and safety glasses.

Advanced Materials

• UV-Vis spectrophotometer.
• Quartz or plastic cuvettes matched for the chosen wavelength.
• Analytical balance with 0.001 g accuracy.
• Muffle furnace or controlled pyrolysis setup.
• pH meter with calibration buffers.
• Orbital shaker or magnetic stirrer with speed control.
• Vacuum filtration setup.
• Sieve set for particle size separation.
• BET surface area data if available from a shared lab facility.
• Zeta potential instrument for surface charge analysis.
• Deionized water system.
• Lab-grade methylene blue and Congo red standards.
• AAS or TOC instrument if you expand to broader water-quality measurements.

Software & Tools

• Google Sheets: Organizes trial data, builds calibration curves, and compares adsorption models.
• ImageJ: Measures color intensity from standardized photos when you do not have a spectrophotometer.
• Python: Fits isotherm and kinetic models, then graphs residuals and goodness of fit.
• R: Runs statistical tests and helps compare multiple biochar treatments.
• PubMed: Finds review articles and primary papers on biochar adsorption and dye removal.

Experiment Steps

1. Define the exact question you want to answer, then choose one dye, one peel type, and one main variable to change.
2. Plan how you will make the biochar so each batch starts from the same kind of fruit peel and heating setup.
3. Build a color measurement method that turns water color into numbers, either with a spectrophotometer or a controlled smartphone photo setup.
4. Decide your controls, including dye-only samples, blank water samples, and any unheated peel comparison you want to include.
5. Map out how you will collect enough data points to test adsorption models, not just one before-and-after result.
6. Plan your analysis before you start, including how you will compare Langmuir, Freundlich, and pseudo-second-order fits.

Common Pitfalls

• Using unevenly heated biochar batches, which makes one trial adsorb far more dye than another.
• Measuring color from photos taken under changing room light, which causes fake differences in dye concentration.
• Skipping a calibration curve, which leaves you with color changes but no reliable concentration values.
• Letting fine biochar particles stay in the liquid, which makes the sample look darker and hides the true adsorption result.
• Comparing peel types without matching surface area or particle size, which mixes material effects with size effects.

What Makes This Competitive

A stronger project goes beyond a simple before-and-after cleanup test. You can compare two peel sources, test more than one dye, and use real model fitting to show which adsorption theory matches your data. You can also look at error bars, replicate runs, and model residuals instead of reporting only percent removal. That turns your project into a real materials and environmental chemistry study.

Project Variations

• Test pineapple peel biochar as a comparison material for dye adsorption.
• Compare adsorption of an anionic dye and a cationic dye to see how dye charge changes performance.
• Add a pH analysis to see how surface charge shifts dye uptake across acidic and basic water samples.

Learn More

• PubMed: Search review articles on biochar adsorption, textile dye removal, and Langmuir or Freundlich modeling.
• NIH PubChem: Look up methylene blue and Congo red properties, including structure, charge, and solubility.
• USGS Water Science School: Read background on water contamination, adsorption, and basic water-quality concepts.
• MIT OpenCourseWare: Search chemistry and environmental engineering courses for adsorption, surface chemistry, and data analysis examples.
• Journal of Environmental Chemical Engineering: Search for peer-reviewed studies on agricultural-waste biochar and dye adsorption.
• Bioresource Technology: Search for papers on converting plant waste into adsorption materials and comparing kinetics.