XPS studies of SiO 2-TiO 2 powders prepared by sol-gel process

Abstract

SiO 2, TiO 2 and SiO 2-TiO 2 powders have been prepared via a sol-gel process using silicon tetraethoxysilane (TEOS) and titanium tetraisopropoxide Ti(OPr i) 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°C). The lineshape of the Si 2p and Ti 2p peaks indicate that silicon and titanium are present as SiO 2 and TiO 2 oxide both for the starting and thermal-treated powders. These results are confirmed by consideration of O 1s and O KVV bands, which makes possible to distinguish between the single O-Ti and O-Si bonds and also to disclose the presence of cross-linking Si-O-Ti bonds that act as bridges between SiO 2 and TiO 2 moieties. Starting from 600°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 O 1s components and on the Ti2p 3 2 and Si 2p peaks, show changes of the surface chemical composition of thermal-treated powders.