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

Abstract

Diffuse reflectance FTlR (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.

A Study of Acidity and Structure of Hydroxy-Cr Intercalated Bentonites

“…SAIEUS was successfully applied to the analyses of potentiometric titration data used for characterization of 21). The advantage of these methods is their local character which allows for their direct application to the data measured acidic properties of different solids (22)(23)(24)32). Figure 6 shows the proton binding isotherms obtained in the limited experimental window.…”

Changes in Acidity of Fe-Pillared/Delaminated Smectites on Heat Treatment

“…sorption isotherms are collected in Table 1. For all samples a Both samples have similar isotherm shapes, indicating the presence of a heterogeneous surface with a significant contri- (17,18,(20)(21)(22)(23)(24)(25). The titration curves span the pH window from 3 to 10.…”

“…This suggests that they represent a couple of the same ferric hydroxide species havevaluate the affinity distributions from titration data (17, 18, ing different pK a . It is assumed that chemical reactions do [20][21][22]28). In this procedure the distribution function, f, is not occur to a great extent in our system (no sharp inflection represented by a linear combination of the B-spline functions points on the isotherms) due to the very low solubility of (29).…”

“…This occurs at the end of our experimental window where an uncertainty in the number of groups exists due to the possible dissolution of mineral (26) and/or water autoprotolysis (30). As in the previous study we assume that the introduced metal complexes are the main source of acidity in our clay samples (17,18,20,21). The obtained pK a are characteristic for iron complexes and are in agreement with results described in the literature (13,14); the pK a s reported for different mono-and polynuclear species of Fe(III) are between 5 and 6 and between 10 and 11.…”

Síntese e estudo de propriedades coloidais de esmectita pilarizada com polihidroxicátion de alumínio

“…Além da acidez existente na argila natural, há também aquela proveniente do pilar localizado na entrecamada do mineral, em que natureza, quantidade e força dependem do método de síntese. Bandosz et al (1994) Após a retirada de matéria orgânica e dos óxidos de ferro secundários, o material foi disperso com solução de Na 2 CO 3 0,1 g L -1 e peneirado (< 270 mesh) para remoção da fração areia. A fração que passou na peneira foi transferida para proveta de 1 litro, na qual houve sedimentação das partículas e separação da fração com diâmetro inferior a 2µm (JACKSON, 1979).…”