Mountjoy, G. and Pickup, D.M. and Wallidge, G.W. and Anderson, R. and Cole, J.M. and Newport, R.J. and Smith, M.E. (1999) XANES study of Ti coordination in heat-treated (TiO2)(x)(SiO2)(1-x) xerogels. Chemistry of Materials, 11 (5). pp. 1253-1258. ISSN 0897-4756.
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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 (Ti-, Ti-, and 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 Ti-, which is converted to anatase after heating at 500 degrees C. Samples with x = 0.18 contain a majority of isolated, distorted Ti- before heating, which is converted to Ti- substituted for Si after heating at 750 degrees 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 degrees C showed concentration limits of 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 Ti- before heat treatment. There is no evidence of significant amounts of Ti-.
|Subjects:||Q Science > Q Science (General)|
|Divisions:||Faculties > Science Technology and Medical Studies > School of Physical Sciences > Functional Materials Group|
|Depositing User:||I.T. Ekpo|
|Date Deposited:||05 Apr 2009 20:05|
|Last Modified:||06 Sep 2011 02:12|
|Resource URI:||http://kar.kent.ac.uk/id/eprint/16947 (The current URI for this page, for reference purposes)|
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