ADSORPTION OF POLAR GASES ON MODEL SILICA-GEL

Two models are developed to study the influence of polar surface group s present in silica gel on adsorption of polar gases. Both are based o n the composite sphere model of Kaminsky and Monson (J. Chem. Phys. 19 91, 95, 2936-2948). The surface groups are incorporated either as disc rete dipoles or as a continuum (smeared) dipolar bilayer. The behavior of each of these descriptions is explored through the calculation of Henry's constants in various microstructures, water adsorption isother ms, isosteric heats of adsorption, and adsorbate structural correlatio n functions. Comparison to experimental data shows that while both mod els produce good qualitative agreement, only the discrete approximatio n results in a model adsorbent that is sufficiently heterogeneous to p redict the correct trends in the isosteric heats of adsorption.