Relationship between Pore Connectivity and Mean Pore Size in Modulated Mesoporous Vanado-Phosphoro-Aluminates and Some Similarities with the Branching of Trees

Abstract

Sixteen mesoporous vanado-phosphoro-aluminate solids, of the general formula Al100PXVY (X, Y = 0, 5, 10, 20), have been prepared and characterized by their N2 adsorption/desorption isotherms. The materials were truly mesoporous, and the addition of P and/or V affects in a very precise and profound way the corresponding specific surface areas Sp (m2 g-1), specific pore volumes (cm3 g-1), the mean hydraulic pore diameter dp (4Vp/Sp) (nm), the maximum of the pore size distribution (psd) dmax (nm), and the full width at half-maximum (fwhm) (nm) of the psd. The pore connectivity c was also determined and the dimensionality Dcc of adsorption was estimated in the pressure range where capillary condensation of N2 in the pores takes place. The dimensionality Dcc was found to be related to the dmax, reduced over the fwhm, via the relation Dcc ≈ 3.7(dmax/fwhm). The two parameters, dimensionality Dcc and connectivity c, are also related to each other via the simple relation log c ∝ −1.83 log Dcc, which in turn result...