Characterization of acidity of pillared clays by proton affinity distribution and DRIFT spectroscopy

Abstract

Diffuse reflectance FTIR (DRIFT) spectra and potentiometric titration data have been obtained for montmorillonite samples pillared with different polycations. The IR spectra are interpreted after deconvolution into Voigt band profiles. The titration data are analysed using a stable numerical method for the solution of the adsorption integral equation (SAIEUS). The pK distributions obtained are used to characterize the acidic properties of the modified minerals to demonstrate the relationship between these properties and the coordination of cations in the pillaring species. Heat treatment enhances the acidity of the materials which may be the result of the rearrangement of pillars (dehydroxylation). The approach presented enables one to assess both qualitatively and quantitatively the number and strength of acidic sites present on the surface of pillared clays.