Characterization and properties of mixed bentonite-vanadium(V) oxide xerogels

Polyvanadic acid interacts with bentonite clay in aqueous colloidal suspension, yielding a green, flocculent material. The slow evaporation of the xerogel suspensions leads to insoluble lamellar solids, exhibiting basal distances of 13.0 Angstrom, and a strong intervalence transfer band around 1150 nm. Scanning electron microscopy images show the existence of interconnected nodules containing a uniform distribution of vanadium ions and aluminum-silicates. Evidence of poly vanadate-bentonite interaction is provided by the FTIR spectra, from the appearance of a strong peak at 835 cm(-1), tentatively ascribed to a V-O-Si vibration. The constitution of the green composite depends on the relative amounts of bentonite and polyvanadic acid employed in the synthesis, following the approximate composition bentonite.y(V2O5).z(H2O), where y = 1.5-4.0, and z = 5-12, and bentonite approximate to Na-x(Al2-xMgx)(OH)(2)Si4O10. The dramatic changes in the solubility and aggregation properties corroborate the spectroscopic evidence of strong interactions between polyvanadic acid and the bentonite particles. (C) 2001 Elsevier Science Ltd. All rights reserved.