Microcalorimetric study of acid sites on ammonia- and acid-pretreated activated carbon Original Research Article

This study was designed to determine the value of microcalorimetry as a probe of acid/base sites on carbon surfaces. Calorimetric studies of ammonia adsorption on acid and ammonia pretreated activated carbon (BDH) samples demonstrated that the technique does titrate acid sites (at equilibrium) according to their relative strengths. However, only in conjunction with other techniques, including Boehm titration, point of zero charge (PZC) and temperature programmed desorption (TPD) is it possible to determine the probable identity of the acid sites present on a given carbon. Collective consideration of the data from all techniques suggests that ammonia pretreatments create a surface whose chemistry is completely different from that of the original carbon. Not only are new acidic sites created, but a high concentration of basic sites are introduced as well. Thus, the final surface is clearly amphoteric, to an extent which is largely dictated by the pretreatment temperature.