SURFACE-ACIDITY OF CARBONS CHARACTERIZED BY THEIR CONTINUOUS PK DISTRIBUTION AND BOEHM TITRATION

The surface acidity of several activated carbons was evaluated using t he Boehm and potentiometric titration methods. Experimental conditions (particle size, rate of titration) were varied and several procedures to collect raw data for proton binding isotherms (slow continuous add ition of titrant, incremental addition conditioned by a pH stability c riterion and batch experiments) were compared. Proton binding isotherm s were analyzed at two levels. First, continuous pK distributions were derived and the inventory of surface functionalities was characterize d in terms of amount and pK values. Then these data afforded calculati ons of the base neutralizing capacity of the carbons studied at any pH level. The results were compared with those from Boehm titration of t he same samples. Best results were found for titration of finely powde red carbons. Continuous titration denatures the binding isotherms and damps significant features in the pK distribution. On the other hand, titration by incremental addition with a pH stability criterion provid es reliable results which can be compared to those retrieved from Boeh m titration provided the proper common metric is used. The agreement w as quantitative when the equilibrium pH of the supernatant of the Boeh m bases was taken as the endpoint for counting neutralized sites. Adva ntages of analyzing potentiometric titration data in terms of its acid ity distribution function with respect to providing a comprehensive ch aracterization of the inventory of surface functionalities as well as its predictive power to assess a carbon's base neutralizing capacity u nder different experimental conditions are discussed. Copyright (C) 19 97 Elsevier Science Ltd.