Abstract
Activated carbons (ACs) prepared by CO2 activation of five different precursors and commercial coconut shell AC were used for benzene adsorption (5 ppmv) from air at relative humidities (RHs) of 0, 50 and 70%. Benzene adsorption capacities of the ACs prepared in the laboratory were similar at RH 0%, but differed significantly in the presence of moisture. The negative influence of moisture on benzene uptake was greater in case of the ACs with large amounts of surface polar sites. Average micropore sizes of the ACs up to 0.8 nm were beneficial for benzene adsorption at RH 70%, while the average micropore sizes above 0.8 nm for benzene adsorption at RH 50%. The desorption of benzene from the ACs after adsorption was examined by temperature programmed desorption (TPD) method. It was found that the desorption profiles of the ACs were similar at the same RH, suggesting that the adsorption of benzene occurred on the similar adsorption sites in all ACs, despite the differences in their origin and in porous and chemical properties. At RH 70%, benzene was adsorbed only on the high-energy sites, which resulted in the shift of desorption profiles to higher temperatures.
