USE OF SIMULATED ADSORPTION-ISOTHERMS TO STUDY SURFACE AND STRUCTURAL HETEROGENEITIES OF MICROPOROUS SOLIDS

Surface and structural heterogeneities of various solids are often characterized in terms of the adsorption energy distribution, which can be evaluated from the experimental adsorption isotherm by inverting the well-known integral equation. For microporous solids both heterogeneities are significant, and their estimation on the basis of the adsorption energy distribution is complex. In the current work the simulated adsorption isotherms of argon in slitlike micropores of different widths, obtained by the grand canonical Monte Carlo (GCMC) method, were used to explore possibilities of extracting information about surface and structural heterogeneity of microporous solids from experimental adsorption data. Simulations were carried out under the assumption that the micropore walls are: (i) energetically homogeneous or (ii) composed of two equal patches characterized by different adsorption energies. The adsorption energy distribution functions, F(U), were evaluated from simulated isotherms by using a regularization method. A comparative study of F(U) for uniform slitlike micropores and biporous systems with either energetically homogeneous or heterogeneous walls allowed to make some recommendations concerning estimation of surface and structural heterogeneities of microporous carbons to be made on the basis of experimental adsorption data.