Vanadia gel synthesis via peroxovanadate precursors. 2. Characterization of the gels

Vanadium oxide gels derived from the reaction of H2O2 and V2O5 have been investigated using V-51 MAS NMR, TGA, XRD, SEM, and laser Raman spectroscopy. Based primarily on the V-51 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.