Chemisorption and hydrolysis of TiCl 4 on the surface of pyrogenic silica

Abstract

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 SiO 2 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 ν(SiOH) is absent. In addition, the intensity of the adsorption band assigned to isolated silanol groups ν(SiOH) at 3750 cm −1 is practically unchanged up to a TiO 2 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% TiO 2 (the amount necessary for monolayer formation) the anatase phase is present. At the same time, at a uniform TiO 2 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 SiO 2 surface but is isolated as a separate phase consisting of islet-like crystalline structures.