The equation of vapor-phase sorption on heterogeneous surfaces with local Guggenheim-Anderson-De Boer model

Abstract

Recently, we proposed a new four-parametric MGAB equation (modified Guggenheim-Anderson-De Boer equation, GAB) for fitting of experimental isotherms of vapor-phase sorption on geosorbents. In the present study, the theoretical meaning of MGAB equation was elucidated. For this purpose, the properties of the equation of multilayer adsorption on a heterogeneous surface with local characteristics described by GAB model and Zeldovitsh-Roginskiy energy distribution function ρ(ε) were derived and the satisfaction of MGAB equation with these properties was shown. MGAB model has two parameters connected with GAB model: vm is the monolayer sorption capacity and k is the constant of the multilayer sorption, as well as two parameters of sorption energy distribution function ρ(ε): α, characterizing heterogeneity of ρ(ε) and C0, reflecting energy baseline. The influence of parameters α and C0 on the shape of both ρ(ε) and model sorption isotherm was established. The applicability of MGAB model for the description of surface heterogeneity of a natural sorbent by example of 13 different sorbate-sorbent systems dried and moistened has been discussed. For these systems equilibrium sorption isotherms were measured, corresponding energy distribution functions ρ(ε) were calculated, and obtained α values were compared. On the whole, the differences in α values responded to the real tendencies of heterogeneity changes in these systems. © 2006 Elsevier B.V. All rights reserved.