In adsorption, an “adsorbate” such as an atom, ion, or molecule is held onto a material’s surface. Adsorption can occur via physical processes, where adsorbates are held by attractive van der Waals forces between the adsorbate and the material surface, or chemical processes, where adsorbates are held to a solid surface by chemical bonds as a result of a chemical reaction between the adsorbate and the surface.
Activated carbon is effective at adsorbing chemical contaminants for several reasons. Its high surface area means it can adsorb a higher quantity of adsorbates at higher rates. Furthermore, activated carbon has a chemical affinity for many organic molecules. Both types of materials are nonpolar – electrical charges are evenly distributed throughout the materials – so they readily attract one another. Activated carbon can also remove residual disinfectants such as chlorine through chemical adsorption, or “chemisorption.”