Multilayer adsorption and capillary condensation processes by mesoporous silica

Detailed examination of the sigmoidal adsorption isotherm for physisorption of inert nitrogen vapor on mesoporous silica has been analyzed in terms of the Polanyi sorption potential (excess surface work) decrease with respect to the amount adsorbed. The multilayer sorption isotherm is analyzed in terms of two parameters: (1) An initial sorption potential, E(0), and (2) an intensity term, n(m), related to the statistical monolayer capacity). The linear trend is noted up to ca. 6 monolayer equivalents. At pressures corresponding to menisci radii, capillary condensation commences and increases in accord with the fractal roughness of the surfaces and/or interparticulate voids. The merits of the autoshielding potential model for physisorption is discussed.