CHARACTERIZATION OF THE SURFACES OF ACTIVATED CARBONS IN TERMS OF THEIR ACIDITY CONSTANT DISTRIBUTIONS

A method for characterization of carbon surfaces' acidity using a continuous distribution of acidity constants is proposed. The method is based on potentiometric titration measurements. Titration curves are transformed into proton adsorption isotherms, and are analyzed to yield the distribution of acidity constants. Calculation of the distribution function is sensitive to experimental errors, and therefore a careful smoothing treatment must be applied to the experimental data. The method is tested by application to organic compounds, and the calculated pK values are in excellent agreement with literature data. The method is then applied to study the evolution of acidic groups, in terms of their pK values, subsequent to modification processes such as oxidation and reduction of activated carbons. It is demonstrated that the method is sensitive to the changes in the number and character of surface acidic groups.