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

A combination of Si-29 and O-17 MAS NMR, EXAFS and FTIR spectroscopy have been 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 O-17 NMR resonance has been observed at 110 ppm which is attributed to (O-5)Ti-O Si groups. Heat treatment of these xerogels tends to convert TiO6 into TiO4 where the Ti is substituted into the silica network. Our results are in accord with previous work which suggests that the upper limit for solubility of TiO2 in SiO2 is cn. 15 mol%. Clear evidence of some phase separation in the (TiO2)(0.41)(SiO2)(0.59) sample after heat treatment to 750 degrees C is presented, although the O-17 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.