On the mechanism of interaction between TiCl4 vapour and surface OH groups of amorphous SiO2

Abstract Chemical analysis data concerning Cl and Ti contents in various samples of amorphous SiO 2 treated with TiCl 4 vapour have shown that the Cl/Ti ratio cannot be a reliable criterion in the interpretation of the mechanism of surface reactions. An attempt is made to explain the mechanism of surface processes on the basis of infrared spectroscopy studies. It is shown that the hydrogen chloride evolved during the reaction takes part in a competitive reaction which leads to partial halogenation of the surface and formation of water molecules. Depending on the nature of the substrate, the water molecules are coordinated on the surface silicon or titanium ions and can interact with TiCl 4 . For this reason, the reaction of the SiO 2 surface with the TiCl 4 vapour cannot be used for determining the concentration of silanol groups. The differences observed in the reactions of TiCl 4 with the silanol groups of silica gel and aerosil are due to differences in their coordination ability which is less pronounced with aerosil but changes upon deposition of molecular titanium oxide layers.