On the characterization of acidic and basic surface sites on carbons by various techniques

Active carbons of different origins have been oxidized with H2O2 and (NH4)( 2)S2O8 and their oxygen surface complexes have been characterized by TPD, c lassical titration following Boehm's method and by neutralization calorimet ry. The net enthalpies of neutralization, determined by immersion calorimet ry into NaOH and HCl 2 N lead to -41.1+/-1.8 and -52.3+/-2.0 kJ eq(-1) for the acidic and basic sites on the surface. Experiments with NaHCO3 lead to -39.7+/-1.7 kJ eq(-1) for the carboxylic groups alone. These results sugges t that the surface groups of active carbons can also be characterized by im mersion calorimetry. Results are also given for the variation of the pH of the point of zero charge with the total oxygen content of the surface. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.