Relationship between chemical and physical surface properties of activated carbon

The relationships between structural (chemical or physical) and more general properties such as the surface electrokinetic potential (zeta potential or isoelectric point) or spreading pressure of water were investigated for three powder activated carbon (PAC) samples (manufactured from woods, coconut shell and coal). The PAC samples were characterized by physical parameter measurements (such as zeta potential, specific surface area, spreading pressure) and chemical parameters; surface functional groups and structural mineral elements. Chemical studies show that all PAC samples contain large quantities of mineral ions, mostly calcium, sulfate and phosphate ions. These groups influence surface properties in the same way as do acidic or basic organic surface functional groups. The thermal treatment of activated carbon decreases acidic surface functional groups and this reaction accompanies an increase in the electrokinetic potential. The “grafting” of a cationic polymer adds positive charge to activated carbon surfaces, but the quantity of surface functional groups is also modified by this process. Adsorption isotherms of water in activated carbon enable us to estimate initial polar adsorption sites. The localised adsorption of water on activated carbon is a function of the number of mineral ions and surface functional groups. Quantitative adsorption of water is related to the microporous volume.