Modified BET theory for actual surfaces: implementation of surface curvature

Abstract

The Brauner–Emmett–Teller (BET) theory was originally based on adsorbing surfaces of zero curvature. The theory is elaborated to include a curvature parameter. The theory has been developed for mono-size dense particles (spherical or rod-like) and porous materials with a sharp pore size distribution (spherical or cylindrical pores). Validation was performed considering 62 relevant published results. It is shown that for porous materials with cylindrical pores (15 cases), while the average error in the calculation of the specific surface area using the original BET theory is ca. 46%, that from the modified theory is ca. 11%. For porous materials with spherical pores (20 cases), an average error of 58% (BET theory) is reduced to 15%. To apply the new theory to dense materials, in addition to the probe-gas adsorption isotherm, skeletal density is needed. For meso-porous materials, the curvature parameter is calculated using the BJH theory.