Vanadia gel synthesis via peroxovanadate precursors. 1. In situ laser Raman and V-51 NMR characterization of the gelation process

Vanadium oxide gels derived from aqueous solutions of V2O5 and H2O2 have be en investigated using in situ V-51 NMR and laser Raman spectroscopic techni ques. On the basis of this characterization, a pathway for peroxovanadate d ecomposition has been proposed, including the presence of two peroxovanadat e dimers. New Raman bands and assignments for these species are reported. G elation was observed to begin both during and after the peroxovanadate deco mposition, depending on the initial molar ratios of H2O2/V and the total co ncentration of vanadium. Experimental V-51 NMR evidence suggested that the VO2+ species was directly involved in the formation of the gel.