Adsorption hysteresis on disordered kaolinite

Abstract

Adsorption-desorption isotherms for nitrogen, argon, ethyl chloride and water on a disordered kaolinite are reported. Hysteresis in the amount adsorbed was observed with each system, but hysteresis at pressures below monolayer saturation was found only with the two polar species. Depletion of surface hydroxyl groups by high-temperature vacuum outgassing and by treatment with trimethylchlorosilane caused a disproportionate decrease in the monolayer capacity for ethyl chloride, and the destruction of low pressure hysteresis with that adsorbate. Low pressure hysteresis in the amount adsorbed is attributed to structural hysteresis of the monolayer resulting from the rearrangement of the adsorbate film under the influence of polar surface groups.