Microcalorimetric study of acid sites on acid-pretreated activated carbon

This study was designed to determine the value of microcalorimetry as a pro be of acid/base sites on carbon surfaces. Calorimetric studies of ammonia a dsorption on acid and ammonia pretreated activated carbon (BDH) samples dem onstrated that the technique does titrate acid sites (at equilibrium) accor ding to their relative strengths. However, only in conjunction with other t echniques, including Boehm titration, point of zero charge (PZC) and temper ature programmed desorption (TPD) is it possible to determine the probable identity of the acid sites present on a given carbon. Collective considerat ion of the data from all techniques suggests that ammonia pretreatments cre ate a surface whose chemistry is completely different from that of the orig inal carbon. Not only are new acidic sites created, but a high concentratio n of basic sites are introduced as well. Thus, the final surface is clearly amphoteric, to an extent which is largely dictated by the pretreatment tem perature. (C) 2000 Elsevier Science Ltd. All rights reserved.