Structural Model of Low Pressure ``Physical'' Adsorption

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Abstract
This article describes a proposed new type of adsorption potential associated with surface strain induced in the elimination of unbonded electron orbitals (``first‐order strain''), and strain due to surface (chemical) heterogeneities, or surface impurities (``second‐order strain''). These surface strains are assumed to give rise to a ``semi‐chemical'' adsorbate‐adsorbent attachment in the first layer of multimolecular films. This is termed ``structural adsorption'' and is considered to be largely responsible, along with ordinary van der Waal's potentials, for the low pressure region of the type II isotherm. The theory is applied in the calculation of the adsorption isotherms for pure nitrogen, pure oxygen, and mixtures of nitrogen and oxygen on anatase. It is further applied in determining the composition of the adsorbate in mixed gas adsorption and in the computation of the surface pressure of these films over the entire range of relative pressures from zero to p/p0=1.0. Excellent agreement with experimental observations is achieved.

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