Vanadia Gel Synthesis via Peroxovanadate Precursors. 1. In Situ Laser Raman and ⁵¹V NMR Characterization of the Gelation Process

Abstract

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.

Practical aspects of 51V and 93Nb solid-state NMR spectroscopy and applications to oxide materials

“…VO 3 (OH), (VO 3 ) n , VO 2 (OH) 2 , V 10 O 26 (OH) 2 , VO(OH) 3 , V 10 O 27 (OH), (V 2 O 7 ) 4À , or V 10 O 28 6À , depending on the net surface pH, as was demonstrated using Raman spectroscopy by Deo and Wachs [253]. This agrees with recent 51 V NMR data, which have also shown that surface complexes remain attached to the surface, though not as strongly as in the dehydrated state [148,254,255]. Surface vanadia species in hydrated VO x /SiO 2 are similar to those found in V 2 O 5 AEnH 2 O gels.…”

“…Based on 51 V and 17 O NMR data, a total of five different vanadium species were identified and quantified in vanadia gels at various stages of hydration [148,254,255]. Comparative analysis of 17 O MAS and 3QMAS NMR, 51 V MAS NMR, and thermogravimetric data has provided an additional insight into the coordination states of water molecules during hydration, and led Fontenot et al to propose a model for the gel structure.…”

V2O5 Aerogel as a Versatile Cathode Material for Lithium and Sodium Batteries

“…The evolution of the reaction was confirmed by extensive oxygen evolution. A red flocculate was obtained after 24 h as a consequence of the higher H 2 O 2 /V 2 O 5 ratio, which delays the condensation step, as reported by Fontenot et al [22] SEM micrographs of the powders obtained after supercritical drying are shown in Figure Thermogravimetric analysis (TGA) of the dried powders is shown in Figure 2 a. The total weight loss for V 2 O 5 -1 and V 2 O 5 -2 was 15 and 25 %, respectively.…”

Li+-intercalation electrochemical/electrochromic properties of vanadium pentoxide films by sol electrophoretic deposition

“…A diluted V 2 O 5 sol was prepared using a method reported by Fontenot et al [27] was decomposed by heated at 70-80 • C, and a red-brown gel was obtained. The resultant gel was then re-dispersed in DI-water, resulting in the formation of brownish sol, which contained 0.01 mol/l vanadium with a pH of 2.7.…”