Benzene Adsorption Isotherms on MCM-41 and their Use for Pore Size Analysis

This work is focused on the elaboration of methodology for adsorption characterization of porous silicas by using benzene adsorption isotherms measured on good quality MCM-41 materials. Three MCM-41 samples were synthesized by using tetraethyl orthosilicate (TEOS) as silica source and surfactants, octyltrimethylammonium (C8), decyltrimethylammonium (C10) and cetyltrimethylammonium (C16) bromides as templates. A characteristic feature of this synthesis was relatively long hydrothermal treatment (5 days) at 373 K, which gave well ordered samples as evidenced by powder XRD analysis. Benzene adsorption isotherms measured on these MCM-41 samples were used to evaluate such standard quantities as the BET specific surface area, total pore volume, external surface area and the volume of ordered mesopores, and to obtain the statistical film thickness (t-curve) as well as the Kelvin-type relation, which describes the dependence between pore width and condensation pressure for benzene on silica at 298 K. The latter relations were incorporated into the Barrett-Joyner-Halenda algorithm to extend its applicability to calculate the pore size distributions from benzene adsorption data.