Interaction of aqueous solutions of phenol with commercial activated carbons:: an adsorption and kinetic study

Three microporous commercial carbons were treated with HCl, H2F2 and HNO3. The effects of these treatments on the specific surface area and porosity, on the surface functional groups and on the adsorption behavior of phenol are studied by means of N-2 adsorption at 77 K, temperature-programmed desorption (TPD) and phenol adsorption isotherms, respectively. The results show that there are carbonates and silica impurities that are occluded in all pore ranges of the activated carbons. These inorganic impurities do not have an effect on the phenol adsorption. When the carbons are oxidized (by treatment with HNO3 solution), the surface oxygen functional groups are principally placed on the micropores entrance. From TPD experiments some minor amounts of carboxylic groups on the surface of the original carbon have been found. On the oxidized carbons TPD experiments show a strong increase in the amount of carboxyl groups and the appearance of anhydride, peroxidic and phenolic groups. The adsorption of phenol on oxidized carbons remarkably diminished, in comparison with untreated carbons, as a consequence of the presence of oxygen surface groups. Also, a change from L-shaped to stepped isotherms has been detected and a shorter time is required to reach the adsorption equilibrium in comparison with the original carbons. (C) 1999 Elsevier Science Ltd. All rights reserved.