Characteristics of the Hydration Layer Structure in Porous Titania−Silica Obtained by the Chemical Vapor Deposition Method

Abstract

The titania−silica samples prepared by means of the chemical vapor deposition technique on the basis of mesoporous silica with different contents of grafted TiO2 were investigated. For these samples, the chemical shifts of adsorbed water, the thickness of the hydrate shell, and the free surface energy of aqueous medium were measured using the 1H NMR method. It was estimated that the chemical shift (δ) of the adsorbed water is between 2.6 and 3.8 ppm. For the sample with 7.7 wt % TiO2, the signal of strongly bonded water with δ = 1.3 ppm is present in the spectra of adsorbed water. Probably this signal is caused by the water molecules, which form the electron−donor complexes with Ti atoms. With increasing TiO2 concentration, the free surface energy (ΔGΣ) at first decreases from 160 mJ/m2, for the initial silica gel, to 90 mJ/m2 for the sample containing 4.5 wt % TiO2 and then increases up to 130 mJ/m2 for the sample with 7.7 wt % TiO2 concentration. The values of ΔGΣ for porous and nonporous materials were compared.