Modeling of type II high-resolution sorption isotherms: Evaluation of different approaches

Abstract

Several classical sorption isotherm equations were fitted to experimental high-resolution data for type II multilayer isotherms. Both the models and the experimental data (sorption of Ar (87 K), N2 (77 K), H2O (303 K), n-pentane (298 K), neopentane (273 K) on macroporous silica are taken from the literature. Further data include N2 sorption on nonporous functionalized silica and α-alumina. The following equations are tested: Brunauer-Emmett-Teller (BET), its modification by Anderson, Aranovich, the ζ-isotherm, Harkins-Jura, Frenkel-Halsey-Hill (FHH), that of de Boer and Zwikker manifesting itself in later work of Fuller, Condon, and Adolphs, the dual-site Langmuir equation with monolayer clustering recently presented by Calzaferri et al., and at last the general cluster sorption isotherm (GCSI, Micropor. Mesopor. Mater. 316 (2021) 110909). The GCSI describes all experimental data with high accuracy, not only for homogeneous but also for heterogeneous surfaces with a Gaussian energy distribution. All other models fail more or less, depending on the initial slope of the experimental isotherm. Besides theoretical considerations, the quality of each isotherm modeling is evaluated by the pure statistical Akaike criterion.