Vanadyl ion stability in silica gels

Silica gels doped with vanadium were prepared from tetra ethyl orthosilicate and an aqueous solution of NH₄VO₃, at a final sol pH of 1.5–2.5. Absorption and electron paramagnetic resonance (EPR) spectral studies establish that under ambient conditions the incorporated pentavalent vanadium is stabilized as tetravalent vanadyl ion in the gel monoliths. Dried gels were very stable under ambient conditions, however, transformation of V⁴⁺ to V⁵⁺ was noted during gel densification.