Study of Water Adsorption on Activated Carbon with Different Surface Oxygen Complexes

An investigation was made to correlate between amount of oxygen complex present on activated carbon and its water adsorption behavior. Activated carbon was oxidized with HNO3 at 340 K for 30 hours, followed by a subsequent pre-heat treatment under argon atmosphere for 8 hours at various temperatures in order to remove oxygen complexes progressively on the oxidized activated carbon. The types and amounts of oxygen complexes were estimated by temperature programmed desorption (TPD). Characteristics of pore structure, represented as BET specific surface area, on the carbons were determined by nitrogen adsorption at 77 K. The water adsorption isotherms on the carbons with different amount of oxygen complexes were also obtained at 298 K. The water isotherms were affected by both of surface oxygen complexes and carbon pore characteristics; therefore, the data acquisition was made, in this study, solely to study the effect of surface oxygen complexes. The amounts of adsorbed water were related to those of oxygen complexes present on the carbon surfaces, especially to the CO2 and H2O producing complexes that attracted water molecules at a low vapor pressure range, rather than CO producing complexes did.