Effect of HNO3 treatment on the surface acidity of activated carbons

Abstract

A homologous series of activated carbon samples was prepared from a low ash source carbon by controlled oxidation using nitric acid. The physicochemical properties (specifically, BET surface area, ash content, acid/base neutralization, and ammonia adsorption) were determined. Each property value changed systematically with increasing oxidation treatment; the more oxidized sample showed higher surface acidities without significant changes in BET area or ash content. The point of zero charge (PZC) of each sample was determined by mass and acid/base potentiometric titration. The PZC values also changed systematically with the extent of oxidation; the more oxidized the carbon, the lower its PZC. It is concluded that the PZC can be used as a convenient index for correlating changes in surface acidity of carbons.