COMPARISON OF METHODS TO ASSESS SURFACE ACIDIC GROUPS ON ACTIVATED CARBONS

The effect of oxidation with nitric acid on activated carbons from different origins has been studied by inverse gas chromatography at infinite dilution, Boehm titration, and mass titration to determine the point of zero charge (PZC) of carbons. The effect of oxidation is to generate acidic groups, and this becomes more pronounced as the temperature of oxidation is increased. We find that the Boehm titration results and the carbons' PZCs correlate with the severity of the oxidation treatment. These methods "study" the surface of carbons by its response to an aqueous environment. Inverse gas chromatography results show that increasing acidity is reflected by an increase in the specific interaction of pi-electrons in n-alkenes with acidic centers on the surface of carbons. This method probes the donor/acceptor nature of the carbon's surface and provides information complimentary to that supplied by the other methods.