Changes in surface chemistry of activated carbons by wet oxidation

A series of activated carbons with different degrees of activation were oxi dized with H2O2, (NH4)(2)S2O8 and HNO3 in order to introduce different oxyg en surface complexes. Changes in the surface chemistry of the activated car bons after their oxidizing treatments were studied by different techniques including temperature-programmed desorption (TPD), X-ray photoelectron spec troscopy (XPS), Fourier transformed infrared spectroscopy (FTIR), titration s with HCl and NaOH, measurements of the pH of the point of zero charge and catalytic dehydration of methanol. Results showed that treatment with (NH4 )(2)S2O8 fixed the lowest amount of both total oxygen and surface acid grou ps. However, this treatment yielded the acid groups with the highest acid s trength. This could be because it favors fixation of carboxyl groups close to other groups, such as carbonyl and hydroxyl, which enhances their acidit y. (C) 2000 Elsevier Science Ltd. All rights reserved.