CORRELATION OF CONCENTRATION-DEPENDENT SURFACE DIFFUSIVITY IN LIQUID-PHASE ADSORPTION

Concentration dependency of surface diffusivity of nitrobenzene and benzonitrile was measured at different temperatures for adsorption from aqueous solution onto an activated carbon, by batch kinetic experiments within limited ranges of amount adsorbed. The isotherms obeyed the potential theory of adsorption, and were only partially expressed by Freundlich equations. Eyring's rate theory was applied to the elemental steps of surface diffusion with the assumption that the rate-controlling step was the hole-making step for the systems under the potential theory. The activation energy was found to be a certain fraction of the sum of the evaporative energy of adsorbate and the adsorption potential. Thus the derived correlation equation had two parameters, and was tested with the measured concentration/temperature dependence of surface diffusivity. Good correlation was obtained, with reasonable values of the parameters from the viewpoint of their definition and/or accord with other research results. The success in the correlation manifested the importance of the hole-making step in surface diffusion.