Vanadium oxide gels derived from aqueous solutions of V2O5 and H2O2 have been investigated using in situ 51V NMR and laser Raman spectroscopic techniques. On the basis of this characterization, a pathway for peroxovanadate decomposition has been proposed, including the presence of two peroxovanadate dimers. New Raman bands and assignments for these species are reported. Gelation was observed to begin both during and after the peroxovanadate decomposition, depending on the initial molar ratios of H2O2/V and the total concentration of vanadium. Experimental 51V NMR evidence suggested that the VO2 + species was directly involved in the formation of the gel.

Vanadium oxide gels derived from the reaction of H2O2 and V2O5 have been investigated using 51V MAS NMR, TGA, XRD, SEM, and laser Raman spectroscopy. Based primarily on the 51V MAS NMR and TGA results, the coordinations of five distinct vanadia sites have been detailed, which possibly include a previously unreported dimer. The relative concentration of these sites changed as dehydration progressed, and a model of this process has been proposed based on the numerical analysis of the NMR MAS spectra. In addition, the coordination of the most tightly bound water has been postulated. Depending on sample treatment, it was possible to synthesize both layered and nonlayered materials. The laser Raman spectra revealed differences between layered and nonlayered materials. These differences have been attributed to the interaction of coordinated water molecules, which were trapped between layers and held firmly in place, thus restricting or altering certain Raman-active vibrations.

The environments for oxygen sites in crystalline V(2)O(5) and in layered vanadia gels produced via sol-gel synthesis have been investigated using (17)O MAS and 3QMAS NMR. For crystalline V(2)O(5), three structural oxygen sites were observed: V=O (vanadyl), V(2)O (doubly coordinated), and V(3)O (triply coordinated). Line-shape parameters for these sites were determined from numerical simulations of the MAS spectra. For the vanadia gels at various stages of dehydration, assignments have been proposed for numerous vanadyl, doubly coordinated, and triply coordinated oxygen sites. In addition, by correlating the (17)O MAS and 3QMAS NMR, (51)V MAS NMR, and thermogravimetric analysis data, the coordination of water sites has been established. On the basis of these results, the gel structure and its evolution at various stages of hydration have been detailed. Upon rehydration of the layered gel, we observed a preferred site for initial water readsorption. The oxygen atoms of these readsorbed water molecules readily exchanged into all types of oxygen sites even at room temperature.