Calculations of Pore Size Distributions in Nanoporous Materials from Adsorption and Desorption Isotherms

The recently developed density functional theory method for pore size distribution analysis from nitrogen adsorption and desorption isotherms is extended to materials with pores ranging from 2 to 100 nm. The method is based on the nonlocal density functional theory (NLDFT) of capillary condensation hysteresis in cylindrical pores. It is shown that NLDFT correctly predicts both the adsorption and desorption branches of the hysteretic isotherms in materials with cylindrical pores wider than ca. 5 nm. For pores larger than ca. 6 nm, the NLDFT results agree well with the thermodynamic theory of Derjaguin-Broekhoff-de Boer. When pore-blocking (networking) effects are insignificant, both branches of the experimental isotherm produce identical pore size distributions. The NLDFT method is validated against literature data on capillary condensation in MCM-41 type materials with pores from 5 to10 nm.