On comparing BJH and NLDFT pore-size distributions determined from N2 sorption on SBA-15 substrata

Abstract

SBA-15 silica materials consisting of a collection of non-intersecting cylindrical pores of varying diameters have been utilized to try to reconcile the pore-size distribution results proceeding from the classical Barrett–Joyner–Halenda (BJH) and modern non-local density functional theory (NLDFT) approaches. To assess such pretended concordance, it is necessary to perform BJH pore-size estimates on the basis of a modified Kelvin equation that makes allowance for the adsorption potential field emanating from the solid walls of the adsorbent towards the adsorbate molecules. Under this context, critical conditions for capillary condensation and evaporation to happen in cylindrical pores have been specifically calculated via a treatment previously developed by Broekhoff and de Boer (BdB). In this way, BJH-BdB pore-size distribution results, obtained from the analyses of both ascending and descending boundary curves of N2 sorption isotherms at 76 K on a series of model SBA-15 substrata that have been synthesized in this work, are compared with homologous curves proceeding from a NLDFT treatment performed on the descending boundary curve and very reasonable agreement has been found.