XPS STUDIES OF SIO2-TIO2 POWDERS PREPARED BY SOL-GEL PROCESS

SiO2, TiO2 and SiO2-TiO2 powders have been prepared via a sol-gel process using silicon tetraethoxysilane (TEOS) and titanium tetraisopropoxide Ti(OPri)4. X-ray photoelectron spectroscopy (XPS) is used for studying the chemical bondings of silicon, titanium and oxygen as a function of the air thermal treatment temperature (up to 1000-degrees-C). The lineshape of the Si 2p and Ti 2p peaks indicate that silicon and titanium are present as SiO2 and TiO2 oxide both for the starting and thermal-treated powders. These results are confirmed by consideration of 0 ls and O KVV bands, which makes possible to distinguish between the single 0-Ti and O-Si bonds and also to disclose the presence of cross-linking Si-O-Ti bonds that act as bridges between SiO2 and TiO2 moieties. Starting from 600-degrees-C, these bonds are broken and the formation of new Ti-O and Si-O bonds takes place. Furthermore, Si/Ti atomic ratios based both on curve-fitting measurements of the single 0 Is components and on the Ti 2P3/2 and Si 2p peaks, show changes of the surface chemical composition of thermal-treated powders.