Influence of properties of adsorbent, and of the surface and bulk solutions on adsorption from solution

Abstract

To elucidate the effect of the molecular field of surface solution on adsorption equilibrium the experimental adsorption isotherms of toluene from solutions in n-heptane on the hydroxylated surface of silica gel and on weakly oxidized and non-oxidized channel carbon blacks were analyzed using expressions following from the model of monolayer adsorption and the thermodynamics of adsorption from solutions. Assuming an ideal surface solution, the thermodynamic equation approximately describes the experimental isotherm only for strong specific adsorption of toluene on the hydroxylated silica gel. It completely fails to describe the isotherm (having an azeotropic point) for weak non-specific adsorption on the non-oxidized carbon black. The calculated activity coefficients in the surface solutions and equilibrium constants reflect the decrease in the specific interaction of toluene with the adsorbents in passing from the hydroxylated silica gel surface through weakly oxidized carbon black to non-oxidized carbon black.