A series of titania-silicas containing from 5 to 30% by mass of TiO 2 has been synthesized by repeating a cycle of chemi-sorption on the SiO2 surface followed by hydrolysis.
In the IR spectra of the synthesized samples there is no absorption at 950 cm -1, which shows that the Si-O-(Ti) bond as well as the bond assigned to v(Ti-OH) is absent. In addition, the intensity of the adsorption band assigned to isolated silanol groups v(Si-OH) at 3750 cm -1 is practically unchanged up to a TiO2 content of 20 wt.%, and only then begins to decrease.
An X-ray phase investigation of the synthesized titania-silicas has shown that even in the sample containing 5.1% TiO2 (the amount necessary for monolayer formation) the anatase phase is present. At the same time, at a uniform TiO2 distribution on the surface, at least four monolayers are necessary for obtaining a diffraction pattern. Therefore, it is obvious that in the given case, TiO 2 cannot be in the form of a surface monolayer and is organized in a separate polycrystalline phase.
The titanium dioxide produced in this process is not deposited uniformly as layers on the SiO2 surface but is isolated as a separate phase consisting of islet-like crystalline structures.