Vanadia–silica aerogels from vanadylacetylacetonate

For the preparation of vanadium pentoxide doped silica gels, vanadium(V) oxide trialkoxides are the precursors of choice [A.E. Stiegman, H. Eckert, G. Plett, S.S. Kim, M. Anderson, A. Yavrouia, Chem. Mater. 5 (11) (1993) 1591; D.C.M. Dutoit, M. Schneider, P. Fabrizioli, A. Baiker, Chem. Mater. 8 (1996) 734] as they possess already the desired oxidation number. In vanadylacetylacetonate, the oxidation number of vanadium is only +4 instead of +5. However, vanadylacetylacetonate is less reactive with water and thus easier to handle, less toxic and cheaper than vanadium(V) oxide triisopropoxide. Gels were prepared using vanadylacetylacetonate, tetramethoxysilane, methanol and water containing HCl or NH3 as catalyst. After supercritical drying with respect to CO2 and heat treatment in air, vanadia doped silica aerogels show the same colour change upon adsorption of water molecules as vanadium(V) oxide triisopropoxide doped silica xerogels. Structural properties were investigated by N2-absorption and SAXS measurements