GELATION OF VANADIUM(V)OXIDE-TRIISOPROPOXIDE DOPED SILICA-GELS

Gelation of mixtures of vanadium(v)oxide-triisopropoxide, tetramethoxy silane, methanol and water has been studied. Catalyst type and concent ration as well as vanadium content were varied over a wide range. Gels were also prepared with tetraethoxysilane, ethanol or isopropanol. Fo r higher vanadium contents the use of ethanol or isopropanol as solven t caused precipitation while the use of methanol led to transparent so ls. Due to the acidity of the vanadium oxide containing silica sol, ge l times as long as four weeks were observed. Gel times are reduced if a basic catalyst is employed, although the content must exceed the van adium content. Neutralization of the starting solution is closely corr elated with a decolorization of the sol or gel. Aerogels were prepared using supercritical drying with respect to CO2. UV/VIS/NIR-spectrosco py was employed to measure the optical transmission of vanadia-doped s ilica aerogels. (C) 1998 Elsevier Science B.V. All rights reserved.