Modified activated carbon with an enhanced nitrobenzene adsorption capacity

Abstract

To enhance nitrobenzene removal from aqueous solution, commercial activated carbon (AC) was modified by oxidation with HNO3 followed by heat treatment in a nitrogen atmosphere. The modification process introduced oxygen-containing functional groups and changed the charge properties of the AC surface. The effects of surface chemical properties and pore structure on the adsorption of nitrobenzene by the AC were investigated through kinetics and equilibrium isotherms. HNO3 oxidation modified the surface chemical properties and increased the number of acidic oxygen-containing surface groups, but had an almost negligible effect on the pore structure. Subsequent heat treatment caused decomposition of oxygen-containing functional groups on the AC surface, increased the pH point of zero charge (pHPZC) and increased the number of mesopores. The maximum adsorption capacity achieved by the modified AC was 1,443.53 mg g−1, 3.33 times of that unmodified AC. HNO3 oxidation combined with heat treatment was an effective method for the preparation of AC with high nitrobenzene adsorption capacity and fast adsorption kinetics. An appropriate pHPZC, amount of surface oxygen groups and the presence of well-developed mesopores together with micropores were the main reasons for the high nitrobenzene adsorption capacity of the modified AC.