A structural study of (TiO2)x(SiO2)1-x (x=0.18, 0.30 and 0.41) xerogels prepared using acetylacetone

• Published in: Journal of materials chemistry 1999, Vol.9 (6), p.1299-1305
• Main Authors: PICKUP, D. M, MOUNTJOY, G, WALLIDGE, G. W, ANDERSON, R, COLE, J. M, NEWPORT, R. J, SMITH, M. E
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal gels. Colloidal sols; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/a809810g

When titania-silica mixed oxides are prepared by the sol-gel route, the different rates of hydrolysis of the Si and Ti alkoxides can cause phase separation. The effect of modifying the Ti alkoxide used to synthesise the oxides was studied. A combination of 29Si and 17O MAS NMR, EXAFS and FTIR spectroscopy were used to study the atomic structure of (TiO2)x(SiO2)1-x (x = 0.18, 0.30 and 0.41) xerogels prepared using an acetylacetone stabilised Ti(OPri)4 precursor. In the as-prepared materials, Ti is present in a distorted octahedral coordination with a significant proportion still complexed by acetylacetone. For the first time in such an amorphous solid, a 17O NMR resonance was observed at 110 ppm which is attributed to (O5)Ti-O-Si groups. Heat treatment of these xerogels tends to convert TiO6 into TiO4 where the Ti is substituted into the silica network. The results are in accord with previous work which suggests that the upper limit for solubility of TiO2 in SiO2 is about 15 mol%. Clear evidence of some phase separation in the (TiO2)0.41(SiO2)0.59 sample after heat treatment to 750 C is presented, although the 17O MAS NMR results show that the use of acetylacetone significantly increases the amount of Ti-O-Si bonding at this composition compared to samples prepared without it. 29 refs.