Characterisation of the microporosity of chromia- and titania-pillared montmorillonites differing in pillar density - II. Adsorption of benzene and water

The microporosity of chromia- and titania-pillared montmorillonites (Cr-PMs and Ti-PMs) differing in pillar density was explored using benzene and water adsorption data. The results were analysed by means of the alpha (s) method and the BET, Dubinin-Radushkevich (DR), and D'Arcy-Watt approaches. The shape analysis of the C6H6 isotherms indicates that the porous structure of Cr-PMs and Ti-PMs contains a significant amount of ultramicropores accessible to the adsorbate. The total sorption capacity for C6H5 and the BET surface area increase continuously with decreasing pillar density. The a, method realistically describes the micropore volume of the pillared interlayered clays (PILCs) derived from benzene adsorption. The water adsorption on Cr-PM with maximum pillar density results in an unusually shaped isotherm. The lowering of the surface polarity and/or the content of ultramicropores with decreasing pillar density results in a decrease of the H2O sorption capacity and of the BET surface area of the PILCs. The shape analysis of the alpha (s)-plots for water provides qualitative information about the surface homogeneity of the PILCs. The DR approach provides a satisfactory fit of the micropore volume of the PILCs derived from water adsorption. The D'Arcy-Watt approach can be used to analyse water adsorption isotherms, and it can also distinguish between different types of adsorption sites of PILCs. (C) 2001 Published by Elsevier Science B.V.