Activated carbon pre-filters are most common in water purifiers. The large internal surface area of activated carbon makes it a very good adsorbent for many contaminants in drinking water. The sources of activated carbon are mainly coal (anthracite, bituminous coal, lignite), coconut shell, peat and petroleum-based residues.
Most carbonaceous materials do have a certain degree of porosity and have an internal surface area in the range of 10-15 m 2 /g (m 2 /g). The activation of carbon consists of a process in which controlled oxidation of carbon atoms is carried out by high temperature steam, the inner surface of which is enhanced to 1000-1200 m 2 /g.
The activation process creates a network of tiny openings (holes or cavities) of different diameters on the carbon surface, which becomes the path of water into the extended inner surface resulting from activation. The apertures are usually grouped as follows: Micropores <4nm，Middle hole 4-500nm，Large holes > 500 nm (usually 500-2000 nm).
The adsorption of contaminants in water on the surface of activated carbon may be caused by the hydrophobicity of the molecules. It may also be due to the affinity of the contaminant molecule for carbon, or it may be due to both.
The hydrophobic material will bind better than the carbon surface to the hydrophilic material. Most organic contaminants in drinking water are inherently hydrophobic. They bind well to the non-polar carbon surface in the pores. Activated carbon removes organic pollutants, including many volatile organic compounds, pesticides and herbicides, and disinfection by-products such as trihalomethanes.