CHEMISORPTION AND HYDROLYSIS OF TICL4 ON THE SURFACE OF PYROGENIC SILICA

A series of titania-silicas containing from 5 to 30% by mass of TiO2 h as 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 nu(Ti-OH) is absent. In ad dition, the intensity of the adsorption band assigned to isolated sila nol groups nu(Si-OH) at 3750 cm(-1) is practically unchanged up to a T iO2 content of 20 wt.%, and only then begins to decrease. An X-ray pha se investigation of the synthesized titania-silicas has shown that eve n in the sample containing 5.1% TiO2 (the amount necessary for monolay er formation) the anatase phase is present. At the same time, at a uni form TiO2 distribution on the surface, at least four monolayers are ne cessary for obtaining a diffraction pattern. Therefore, it is obvious that in the given case, TiO2 cannot be in the form of a surface monola yer 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.