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 Å, 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 polyvanadate-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 ≈ Nax(Al2-xMgx)(OH)2Si4O10. The dramatic changes in the solubility and aggregation properties corroborate the spectroscopic evidence of strong interactions between polyvanadic acid and the bentonite particles.