Effect of Surface Oxidation of Active Carbon on Ammonia Adsorption

The behavior of ammonia adsorption was studied on various types of surface-treated active carbon (HNO3-AC, H2SO4-AC, HCl-AC, NaOH-AC, CuO-AC, and H2-AC) under 0-75 kPa and 323-473 K. Amount of ammonia adsorption on active carbon was increased by the surface oxidation through acid treatment or metal nitrate decomposition. It was decreased by the hydrogen treatment at 1173 K. The equilibrium amount of ammonia adsorption was found to relate with the amount of surface organic oxygen. Ammonia adsorption was analyzed through the isotherm and classified into three types: (1) strong adsorption relating to surface organic oxygen content and being independent of pressure, (2) weak adsorption relating to surface organic oxygen content and depending upon the pressure, (3) van der Waals adsorption. The model well represented the data, and the average relative error was 10%. When the samples are assumed to be used for ammonia separation with temperature swing adsorption method (323-473 K, 40 kPa), H2SO4-treated active carbon was found to have the highest ammonia separation capacity (2.58 mmol g^-1).