In chemisorption, or chemical adsorption, the pollutants attach themselves to
the grain surfaces as a result of the formation of a chemical (usually covalent)
bond. In this case, the energy of attachment is very much greater than in
physical adsorption. Thus, a molecule undergoing chemisorption arising from
bond formation with the surface atoms. Although it is very difficult to
differentiate between physical and chemical adsorption, one can generally say
that the amount of physically adsorbed material decreases with increasing
temperature, while this relation for chemically adsorbed material is reversed.