Influence of acidic surface oxides of activated carbon on gas adsorption characteristics

Abstract

An activated carbon was oxidized by HNO 3 at boiling temperature. The influence of acidic surface oxides of the activated carbon was experimentally studied on the adsorption characteristics of eleven different gases or vapors. In the adsorption of cyclohexane, benzene, 2-propanol and 2-butanol, the adsorption capacity decreased greatly with oxidizing the carbon by 13.2 N HNO 3. This was because the surface area and micropore volume had decreased by the strong oxidation as suggested by the t-plot analysis of oxidized carbons. When methanol, ethanol, acetone, acetonitrile and sulfur dioxide were adsorbed on the carbons, it was found that the isotherms on the carbon oxidized by 13.2 N HNO 3 were much lower than those on the original carbon except in the low partial pressure range. On the other hand, the adsorption capacity of ammonia or water increased greatly with increasing surface oxides on the carbon. Especially, ammonia was strongly adsorbed on the surface oxides, and irreversible adsorption appeared. The experimental results suggest that the adsorption sites increase greatly with the surface oxides for the polar molecules whose polarizability is very small.