Titania–silica mixed oxides investigated with density functional theory and molecular dynamics simulations

Abstract

AbstractMixed phases of titania and silica have raised interest for their high activity as photocatalysts and for their optical properties, such as a high refractive index. To rationalize their properties, it is necessary to understand their atomic structure in crystalline and amorphous phases. We have investigated Ti–Si mixed oxide phases by density functional theory and molecular dynamics. A polarizable potential has been developed for and has been employed to sample the configuration space. Mixed phases are metastable with respect to separate and , but they are only slightly higher in energy, and therefore might form under technologically relevant conditions. All Ti–Si mixed oxides considered, regardless of cation coordination, display peaks in IR and Raman spectra in the region of frequencies 880–950, while Ti‐only phases do not, even if titanium is in a tetrahedral coordination. Our calculations thus confirm that these peaks are a signature of Ti–O–Si links, but they do not deliver information on the actual atomic structure of the material. Phases with titanium in a tetrahedral coordination display a higher electronic band gap than phases with titanium in octahedral coordination. This should have important consequences for the photocatalytic activity of mixed oxides of titania and silica.