Excess adsorption isotherms for solid-liquid systems and their analysis to determine the surface phase capacity

Abstract

This review surveys methods for determining the surface phase capacity from the excess isotherms, which are generally measured to characterize physical adsorption at the solid-liquid interface. The surface phase capacity, i.e., the total amount of substances in the surface phase, is an important quantity in the study of adsorption from solutions; it characterizes sorption properties of the solid adsorbent and is necessary for the calculation of the surface phase composition. This quantity is also useful in the calculation of those thermodynamic functions which characterize competitive adsorption at the solid-liquid interface. Since the excess adsorption data are used to calculate the surface phase capacity, Section 2 presents a short description of methods for measuring the excess adsorption isotherms and contains a survey of the experimental excess isotherms of adsorption from binary non-electrolytic liquid mixtures on solid adsorbents. The next section presents the main surface phase models and their significance for determining the surface phase capacity from the excess adsorption isotherms. This discussion, connected with a general thermodynamic analysis of the excess adsorption isotherm, demonstrates various physical aspects important in evaluation of the surface phase capacity, and it provides some suggestions concerning its determination. Section 4 presents an attempt to classify methods used for determining the surface phase capacity together with a short description of each. The most popular and useful methods are applied to calculate the surface phase capacity for many adsorption systems in order to compare them. These comparative studies give rise to some suggestions for determining the surface phase capacity from the excess adsorption data (Section 5).