What chemical compounds might be present in drinking water?
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# 4.2 Home water filters

Many people use home water filters. These effectively remove both hardness and impurities that may alter the taste of tap water, such as residual chlorine. Have you ever wondered what is inside a refill cartridge (Figure 23)?

Figure 23 Photo of a home water-filter cartridge.
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- The filter contains an adsorbent material that adsorbs a wide range of compounds, including organic molecules such as pesticides.
- Activated carbon is commonly used as it has a high surface area.
- The structure of activated carbon is similar to graphite. It differs in having a smaller particle size and lower crystallinity.
- Also the edge of the graphite-like sheets (Figure 24) have been oxidised which helps improve its absorbent properties.

Figure 24 An illustration of the edge of a graphite type sheet in activated carbon.
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Why might the additional functional groups from oxidation make activated carbon a better adsorbent than graphite with a similar surface area?

## Answer

The additional functional groups enable additional intermolecular interactions between the adsorbent and the pollutant. For example, the hydroxyl groups can hydrogen bond with anions such as chloride or nitrate. Similarly the carboxylic acid and carbonyl groups can coordinate cations such as calcium or magnesium.

Activated carbon is also widely used as an adsorbent to treat industrial wastewater.

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