THERMODYNAMICS OF ADSORPTION FROM SOLUTIONS - NONELECTROLYTE SYSTEMS

The concept of global activity coefficients is developed in terms of a dsorption at the liquid/solid interface. These coefficients evaluated from the excess adsorption data characterize non-ideality of the surfa ce phase resulting from differences in molecular interactions which ar e additionally perturbed by heterogeneity of the solid. A method for s eparating a non-ideality of the adsorbed phase caused by intermolecula r forces from that generated by surface heterogeneity is presented. It is shown theoretically that the global activity coefficients plotted as functions of the bulk or surface phase composition are characterist ic for a given adsorption system and are useful for assessing adsorben t heterogeneity effects. The results presented are also helpful for ev aluating the surface phase capacity which is a very important quantity in the study of adsorption from solutions on solids.