Evaluating Pore Sizes in Mesoporous Materials: A Simplified Standard Adsorption Method and a Simplified Broekhoff−de Boer Method

Abstract

The diameters of primary mesopores in materials with well-defined cylindrical pores can be accurately determined by the 4V/A method when the volume and surface area are determined by a standard adsorption method and 13.5 Å2 is used as the molecular area of adsorbed nitrogen. A simple method for determining standard adsorption using the statistical thickness of the adsorbed gas layer defined by Frenkel−Halsey−Hill (FHH) theory is described. For materials in which the pores are not cylindrical or well-defined, a simplified Broekhoff−de Boer method can be used to determine pore dimensions. The use of Hill's approximation for the thickness of the adsorbed gas layer in the Broekhoff−de Boer method simplifies its use. The results of these methods on small pore MCM-41 materials, large pore SBA-15 materials, and spherical pore mesocellular foams are reported.