MSE 05 Water Filtration Using Activated Carbon

This lab shows how activated carbon’s ultra-porous surface adsorbs dye molecules from water, turning a simple colored-water setup into a clear, visual model of real-world filtration.

Introduction

Clean drinking water is essential for life, yet access to safe water remains a global challenge. As of 2025, approximately 2.1 billion people (about one in four worldwide) still lack access to safely managed drinking water. This has driven the development of various water purification methods, from boiling and chemical disinfection to advanced filtration systems. One widely used method is filtration with activated carbon, a form of carbon processed to be extremely porous. Activated carbon (also called activated charcoal) is commonly used to filter contaminants from water and air. It is “activated” by creating a network of tiny pores that greatly increase its surface area available for adsorption – the process by which molecules adhere to a surface. (Adsorption is not to be confused with absorption, where substances are taken up into the volume of a material.) The experiment described in this report demonstrates how activated carbon can remove impurities from water through adsorption. By using a simple setup with colored (contaminated) water and activated carbon, we can visualize the purification process and relate it to real-world water treatment applications.

[Figure 1 Placeholder: Two clear jars side by side containing colored water; the jar on the left has activated carbon added. Over time, the water in the carbon-treated jar becomes clear while the control jar remains colored. This illustrates activated carbon removing the dye (impurities) from water.]

Aim

The aim of this experiment is to demonstrate the effectiveness of activated carbon in removing impurities from water through the process of adsorption. In particular, the experiment will show how activated carbon can adsorb a colored contaminant from water, resulting in visibly cleaner water.

Context

Access to water purification is crucial both in laboratory settings and everyday life. In households, many people use activated carbon filters (for example, in pitcher filters or faucet attachments) to improve the taste and safety of tap water. These filters use activated carbon granules that act like a sponge to reduce impurities such as chlorine (which causes bad taste/odor) and even certain heavy metals. Activated carbon filtration is also employed on a larger scale: most municipal wastewater treatment plants use activated carbon to help purify water (and even air emissions) before release. The reason activated carbon is so broadly used is its remarkable adsorption capacity. Thanks to its microscopic pore structure, activated carbon has an enormous internal surface area – it has more surface area per gram than almost any other material used in filtration. In fact, just a teaspoon of activated carbon can have more surface area than a football field. This tremendous surface area provides abundant sites for trapping contaminants. In the context of global water needs, low-cost filters made with activated carbon (often derived from charcoal or coconut shells) offer a promising solution for removing pollutants from drinking water in both developed and developing regions. By conducting this experiment, we connect a simple classroom demonstration to these real-world water purification challenges and technologies.

Materials

1. Activated carbon (available at pet stores, aquarium shops, or online).

2. Contaminated water:

   • Create your own by mixing tap water with impurities like food coloring, dirt, or oil.

3. Filter materials:

   • Cotton balls or coffee filters.

   • Sand and small pebbles (optional, for multi-layer filtration).

4. Plastic bottle or funnel:

   • A 1- or 2-liter plastic bottle cut in half works well.

5. Rubber bands or tape (to secure filters).

6. Measuring cups (for consistency in water volumes).

7. Clear containers (to collect filtered water for comparison).

8. Optional testing tools:

   • TDS (Total Dissolved Solids) meter, pH strips, or turbidity meter.

Procedure

Step 1: Prepare the Filter

1. Cut the Bottle:

   • Cut the plastic bottle in half. The top half will act as a funnel for the filter, and the bottom half can collect the filtered water.

2. Layer the Filter Base:

   • Place a cotton ball or coffee filter at the narrow end of the bottle’s neck to act as the first filtration layer and prevent carbon or sand from passing through.

Step 2: Add Filtration Layers

1. Activated Carbon Layer:

   • Add a layer of activated carbon (about 5 cm thick) on top of the cotton ball or coffee filter. This is the primary filtering material.

2. Optional Layers:

   • Add a layer of fine sand (3 cm) above the activated carbon to trap larger particles.

   • Add a layer of small pebbles or coarse sand (3 cm) above the fine sand for pre-filtration.

Step 3: Prepare the Contaminated Water

1. Create Impurities:

   • Mix tap water with visible contaminants like soil, food coloring, or vegetable oil to simulate dirty water.

2. Measure:

   • Use a measuring cup to pour a consistent amount of contaminated water into the filter.

Step 4: Filtration Process

1. Pour Water:

   • Slowly pour the contaminated water into the top of the filter. Let gravity pull the water through each layer.

2. Collect Filtered Water:

   • Allow the water to drip into the container below. The filtered water will be clearer and free of most visible impurities.

Step 5: Evaluate the Results

1. Visual Comparison:

   • Compare the clarity of the filtered water to the original contaminated water. Look for changes in color, turbidity, or presence of particles.

2. Optional Testing:

   • Use a TDS meter or pH strips to measure improvements in water quality.

   • Check for odors to determine if the activated carbon removed any smells.

Analysis

1. Effectiveness of Activated Carbon:

   • Activated carbon adsorbs organic compounds, chlorine, and odors, improving water quality.

   • Compare different amounts of activated carbon to test its efficiency.

2. Impact of Additional Layers:

   • Test the difference between using activated carbon alone and a multi-layer filter with sand and pebbles.

Optimization

• Flow Rate:

  • Experiment with the water flow rate. Slower filtration typically results in better adsorption and cleaner water.

• Layer Thickness:

  • Vary the thickness of the activated carbon layer and observe the changes in filtration performance.

Applications

• Demonstrates the principles of adsorption and filtration in materials science.

• Highlights the importance of activated carbon in water purification systems (e.g., household filters, industrial use).

Observations and Results

During the experiment, the following pattern was observed: initially, both the control and the activated carbon jars contained water with the same deep red color from the added food dye. Within a few hours, a difference became noticeable. The water in the activated carbon jar began to lighten in color, whereas the control jar remained vividly red. After about 4 hours, the treated water’s red hue was visibly paler than the control. By the next day (24 hours later), the water in the activated carbon jar was almost completely clear, while the control jar was still as red as it was at the start. On the second day of observation, the treated water became totally clear and colorless, indicating that the red dye had been almost entirely removed. In contrast, the control jar remained colored, with no significant change over the same period. There were no obvious changes in the volume of water in either jar (aside from minor evaporation) and no new odors noted; however, a small amount of fine carbon sediment was visible at the bottom of the treatment jar. Table 1 (below) summarizes the visual results:

• Time 0 (Start): Both jars red; no difference.

• After 4 hours: Treated jar = light red/pink; Control jar = red (unchanged).

• After 24 hours: Treated jar = very pale pink/almost clear; Control jar = red.

• After 48 hours: Treated jar = completely clear; Control jar = red.

These results clearly show that the activated carbon removed the red coloring from the water over time, whereas without treatment the color remained. The disappearance of the red dye in the treated sample is evidence that the impurity (representing a contaminant) was effectively removed from the water and captured by the activated carbon. The changes were qualitative (visual) in this experiment, but they are dramatic enough to confirm the key outcome: activated carbon adsorption leads to visibly cleaner water.

(No numerical measurements were taken in this simple demonstration, but the visual evidence was sufficient to draw conclusions. If available, one could use tools like a colorimeter or turbidity meter to quantify the reduction in color or suspended matter.)

Analysis

The experiment demonstrates the principle of adsorption as the mechanism by which activated carbon purifies water. In the treated jar, the red dye molecules were gradually pulled out of the water and adhered to the surface of the carbon particles. Activated carbon is extremely effective at this because of its porous structure and huge surface area. During the manufacturing process, carbon (such as wood or coconut shell charcoal) is “activated” by heating it to high temperatures in the absence of oxygen, sometimes followed by steam or chemical treatment. This process creates myriad tiny cracks, holes, and channels in the carbon, greatly increasing its surface area. The result is a network of micropores – essentially a microscopic sponge. These pores provide countless binding sites where impurity molecules can attach. In fact, due to this structure, one gram of activated carbon can have well over 3,000 m² of internal surface area. This enormous area is what allows a small amount of carbon to purify a relatively large volume of water.

When the colored water was mixed with activated carbon, the dye molecules (which are larger organic molecules) encountered the carbon’s surfaces in the pores. Adsorption occurred: the dye molecules broke their bonds with the water and attached to the solid carbon surface. This is different from absorption – here the dye wasn’t “soaking into” the carbon like a liquid into a sponge’s bulk; instead, the dye molecules stuck onto the outer and inner surfaces of the carbon particles. Several forces and factors drive this process. One important factor is the attraction between the contaminant molecules and the carbon. Activated carbon’s surface is mostly non-polar (carbon-based), so it tends to attract other non-polar or relatively large molecules (many dyes, organic chemicals, etc.) that don’t like to remain dissolved in water. The interaction is often due to van der Waals forces – weak intermolecular forces – and sometimes chemical interactions that cause molecules to prefer the carbon surface over staying in solution. In simpler terms, the dye molecules find the carbon surface “stickier” than water, so they detach from the water and cling to the carbon. As more and more dye molecules adsorb onto the carbon, the water loses its red color and becomes clear. The dye molecules are essentially being trapped on the carbon, which is why the carbon in the jar became tinted by the dye. If we were to remove the carbon and examine it, we would find the dye concentrated on its surface.

It’s important to note that adsorption has a finite capacity – eventually, an activated carbon filter can become “saturated” when most of its pores and surface sites are occupied by contaminants. In our small-scale experiment, the amount of dye was low enough and the amount of carbon high enough that the carbon could adsorb all the dye present, achieving complete (visible) purification. In practical water treatment, once activated carbon is saturated with contaminants, it must be replaced or regenerated. Fortunately, activated carbon used in large filters can often be reactivated (for example, by heating it to drive off the adsorbed contaminants).

Overall, the analysis confirms that the hypothesis was correct: activated carbon can remove molecules from water by adsorption. This process is what makes activated carbon a powerful water purification medium. The experiment vividly illustrates how a contaminant (modeled by food coloring) can be effectively removed from water, which is analogous to how real pollutants (like organic chemicals, tastes, and odors) are removed in water purification systems.

Applications

Activated carbon is used in a wide range of real-world applications for water purification. Here are a few notable examples:

• Household Water Filters: Many home water filtration systems (such as pitcher filters like Brita® and faucet-mounted filters) rely on activated carbon. The carbon in these filters adsorbs chlorine (improving taste and odor of chlorinated tap water) and can remove other contaminants like certain heavy metals and organic chemicals. For instance, Brita’s activated carbon filters (made from coconut shells) reduce chlorine, mercury, benzene, and even lead (when combined with an ion-exchange resin) from drinking water, resulting in cleaner, better-tasting water straight from the tap.

• Municipal Water Treatment: City and town water treatment facilities often use activated carbon (typically in granular form) as one stage of treatment. Granular activated carbon filters help remove natural organic compounds, pesticides, and industrial chemicals that could cause health risks or unpleasant color, taste, or odors in drinking water. Activated carbon is particularly useful for removing chlorine and chloramine (used as disinfectants) and the disinfection by-products they produce. Many wastewater treatment plants also employ activated carbon to adsorb toxic organic compounds or pharmaceuticals from water before it’s discharged or reused. Essentially, activated carbon acts as a polishing step to ensure water is free of trace contaminants.

• Emergency and Portable Filtration: Activated carbon is found in portable water filters and emergency purification systems. Hikers and campers use lightweight filter straws or pump-filters that contain activated carbon to remove foul tastes (from algae or decaying matter) and chemical pollutants from river or lake water. In humanitarian emergencies or remote areas without clean water, simple gravity drip filters with activated carbon can provide safe drinking water by removing harmful organic chemicals and improving taste. Because activated carbon is derived from natural materials like coconut shells or wood, these filters are relatively affordable and can be lifesaving in areas with contaminated water supplies.

• Aquarium and Pool Filtration: In aquariums, activated carbon filters help maintain water quality by removing dissolved organic substances that can discolor the water or produce odors. Similarly, some swimming pool filtration systems use activated carbon cartridges to adsorb oils, lotions, or organic residues that are not captured by mechanical filters. This keeps water clear and reduces the load on disinfection chemicals.

(These applications highlight the versatility of activated carbon in water purification – from personal use to municipal systems. In all cases, the principle is the same: contaminants are trapped on the surface of the carbon, thereby removing them from the water.)

Chemical Composition and Structure of Activated Carbon

To understand why activated carbon is so effective at filtration, we look at its composition and structure. Activated carbon is essentially pure carbon in a processed form. On a chemical level, it is largely made up of carbon atoms arranged in a network of sheets or microcrystals similar to graphite, but with significant disorder and defects. What truly sets activated carbon apart is its porous structure. When carbon-rich materials (like wood, coal, or coconut shells) are converted to charcoal and then activated, the high-temperature treatment (often 800–1100°C in the absence of oxygen) causes the carbon structure to develop a myriad of tiny pores and tunnels. In activated carbon, these pores range from visible cracks to nanopores on the scale of molecules. This structure gives activated carbon an extremely high surface area. As mentioned earlier, a single gram of activated carbon may have on the order of 3,000 m² of surface area available for adsorption. For comparison, that is roughly the area of half a soccer field packed into a pinch of carbon powder!

Chemically, carbon is a versatile element that forms stable bonds with many substances. The internal surfaces of activated carbon (the walls of all those tiny pores) provide countless sites where atoms or molecules can bind. The binding can occur through physical forces (van der Waals forces, electrostatic attractions) or through chemical interactions. Because the carbon surface is largely non-polar (hydrophobic), it has a particular affinity for organic molecules (which tend to be non-polar or hydrophobic) and for compounds like chlorine and disinfection by-products. Many impurities in water, such as organic dyes, benzene or other solvents, and even tastes and odors, are effectively captured by activated carbon due to this affinity. Additionally, activated carbon can be treated or “impregnated” with other substances to enhance its performance. For example, some activated carbons are coated with silver to add antimicrobial properties, or combined with ion-exchange resins to also remove heavy metals or fluoride. But even in its basic form, activated carbon’s composition (pure carbon) and structure (highly porous) make it an ideal filter medium.

It’s also worth noting that activated carbon comes in different forms – mainly granular activated carbon (GAC), which consists of millimeter-sized granules, and powdered activated carbon (PAC), which is a fine powder. The choice of form depends on application. GAC is common in water filter cartridges and large treatment systems, while PAC can be added to water like a powdered treatment (for instance, dosed into water that needs temporary treatment for a contaminant spike). In all forms, the carbon’s functionality is rooted in the same structural features described above.

[Figure 2 Placeholder: A schematic illustration of an activated carbon particle’s internal structure. The figure might show a cut-away view of a carbon granule, highlighting the numerous microscopic pores and channels. It could also depict molecules of a contaminant adhering to the surfaces within these pores, demonstrating how adsorption occurs on the carbon’s internal surfaces.]

Conclusion

In this lab experiment, we successfully demonstrated water purification using activated carbon and gained insight into the underlying mechanism of adsorption. The activated carbon effectively removed a colored impurity (food dye) from water, turning the water from red to clear over the course of 1–2 days, while an untreated sample remained colored. This clear contrast showed that the activated carbon adsorbed the dye molecules, trapping them on its surface and thereby cleaning the water. Through our observations and analysis, we concluded that activated carbon’s high porosity and surface area are key to its ability to filter out contaminants. The dye molecules adhered to the carbon’s extensive surfaces inside its pores, exemplifying how many water pollutants can be similarly removed.

This simple experiment models real-world water treatment scenarios. From improving the taste of tap water in a kitchen filter to removing dangerous pollutants in a city’s water supply, the principles observed here apply on multiple scales. We discussed how activated carbon filters are used in household devices, municipal treatment plants, and other applications to provide safer, cleaner water. The chemical structure of activated carbon – essentially pure carbon with a sponge-like internal geometry – enables these applications by offering a vast area for impurities to stick to.

In summary, the aim of the experiment was achieved: we demonstrated that activated carbon can purify water by adsorbing impurities. The experiment underscores the effectiveness of adsorption-based filtration and helps build a foundational understanding of water purification techniques. For students and aspiring engineers or scientists, this lab serves as a valuable illustration of how a material’s micro-structure can have a profound impact on its macroscopic function. Clean water is a pressing need worldwide, and activated carbon provides a powerful yet accessible tool to meet this need. Future investigations could explore factors such as the quantity of carbon, different contaminants (like actual pollutants or odors), or how to regenerate and reuse activated carbon, thereby extending this foundational experiment into more advanced inquiries.

References

Brita. (2025). How Do Brita Filters Work? Brita® Better Water Education.

Nowicki, H. (2016). The basics of activated carbon adsorption. Water Technology, 39(2), 14-17.

The Homeschool Scientist. (n.d.). Charcoal Water Purifying Experiment.

United Nations Children’s Fund (UNICEF) & World Health Organization (WHO). (2025, August 25). Fast facts: 1 in 4 people globally still lack access to safe drinking water. [Press release].

University of Nebraska–Lincoln Extension. (n.d.). Drinking Water Treatment: Activated Carbon Filtration (NebGuide G1489 by B. Dvorak & S. Skipton).

Wikipedia. (2025). Activated carbon. In Wikipedia, The Free Encyclopedia.