XANES and XPS Study of Silica-Modified Titanias Prepared by the Glycothermal Method

Silica-modified titania with the anatase structure having high thermal stabilities was prepared by the glycothermal method, and XANES and XPS techniques were applied for investigating the local structure of Si atoms in these samples. For comparison, two silica-modified titania samples were prepared by impregnation of TEOS or silica sol on titania. The surface concentration of Si atoms in the glycothermal product, as determined by XPS, was smaller than those of the reference samples prepared by the impregnation method, suggesting that in the glycothermal product silicon atoms are highly dispersed in the anatase matrix. The Si K-edge XANES spectra of the glycothermal products exhibited a main peak at 1847.1 eV due to the tetrahedrally coordinated Si atoms. However, a shoulder peak at 1849 eV was detected, which was attributed to the octahedrally coordinated Si atoms. The proportion of the latter component in the glycothermal product was larger than those in the reference samples and became large as the Si content decreased. These results clearly indicate the formation of the silica−titania solid solution. The thermal stabilization effects of Si atoms are discussed in detail.