Derivation and application of a Jovanovic-Freundlich isotherm model for single-component adsorption on heterogeneous surfaces

A new Jovanovic-Freundlich isotherm model is derived for describing single-component adsorption equilibria on heterogeneous surfaces, The equation is obtained by assuming that the rate of decrease of the fraction of the surface unoccupied by the adsorbate molecules is proportional to a certain power of the partial pressure of the adsorbate, The equation reduces to the Jovanovic equation when the surface becomes homogeneous, At low pressures, the equation reduces to the Freundlich isotherm but at high pressures, a monolayer coverage is achieved, This model has been applied successfully to the description of the adsorption behavior of a series of chlorinated hydrocarbons on a microporous silicagel, at different temperatures, The monolayer capacity and the heterogeneity parameter exhibit a weak temperature dependence, The third parameter of the model decreases exponentially with increasing temperature, The fit of the experimental data to the new model described is shown to be better than the comparable fits to classical isotherms used for heterogeneous surfaces, The energy distribution function corresponding to the model for Langmuir local adsorption behavior was derived using the Sips procedure and evaluated numerically in a few selected cases. This distribution is an exponential decay. (C) 1996 Academic Press, Inc.