A simple model for studying multilayer adsorption of noninteracting polyatomic species on homogeneous and heterogeneous surfaces

In this work we study a simple model of multilayer adsorption of noninteracting polyatomic species on homogeneous and heterogeneous surfaces. A new approximate analytic isotherm is obtained and validated by comparing with Monte Carlo simulation in one- and two-dimensional lattices. Then, we use the well-known Brunauer-Emmet-Teller (BET) approach to analyze these isotherms and to estimate the monolayer volume, v(m). In this way, we confirm previous observations that the value of the v(m) obtained by the BET equation depends strongly on adsorbate size and surface heterogeneity. In all cases, we find that the use of the BET equation leads to an underestimate of the true monolayer capacity. Nevertheless, a compensation effect is found for the adsorption on a patchwise bivariate surface, but this is not enough to eliminate the decrease of v(m) caused by the molecular size. In addition, we consider also the possibility to use the model to study the adsorption on nanotube bundles.