Multilayer Adsorption of Polyatomic Species on Homogeneous and   Heterogeneous Surfaces
  In this work we study the multilayer adsorption of polyatomic species on homogeneous and heterogeneous bivariate surfaces. A new approximate analytic isotherm is obtained and validated by comparing with Monte Carlo simulation. Then, we use the well-known Brunauer-Emmet-Teller's (BET) approach to analyze these isotherms and to estimate the monolayer volume, $v_\mathrm{m}$. The results show that the value of the $v_\mathrm{m}$ obtained in this way depends strongly on adsorbate size and surface topography. In all cases, we find that the use of the BET equation leads to an underestimate of the true monolayer capacity. 
F. O. Sanchez-Varretti, G. D. Garcia, A. J. Ramirez-Pastor, F. Roma