Accurate measurements of the height and position of the preedge peak in Ti K-edge XANES (X-ray absorption near-edge structure) can distinguish 4-, 5-, and 6-fold coordination of Ti by O ([4]Ti, [5]Ti, and [6]Ti, respectively), and mixtures thereof. This approach has been applied to titania−silica xerogels, (TiO2) x (SiO2)1 - x , prepared from Si and Ti alkoxides using a prehydrolysis step and acid catalyst, with 0.18 < x < 0.75. As expected, samples with x = 0.75 contain phase-segregated, amorphous, pre-anatase [6]Ti, which is converted to anatase after heating at 500 °C. Samples with x = 0.18 contain a majority of isolated, distorted [6]Ti before heating, which is converted to [4]Ti substituted for Si after heating at 750 °C. This is the first time that the changes in the coordination of isolated Ti have been unambiguously described. Xerogels with 0.25 < x < 0.35 and heat treatment at 750 °C showed concentration limits of [4]Ti substitution for Si of 10−15mol %. Slightly higher values were obtained for xerogels prepared using acetylacetone, but the main difference was that the latter had a significantly larger content of distorted [6]Ti before heat treatment. There is no evidence of significant amounts of [5]Ti.

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The version in the Kent Academic Repository may differ from the final published version. Users are advised to check http://kar.kent.ac.uk for the status of the paper. Users should always cite the published version of record.

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