Spectroscopy of Amorphous and Crystalline Titania−Silica Materials

Abstract

Both amorphous and crystalline silica doped with Ti(IV) ions have properties ranging from selective chemical catalysis to useful thermal and optical characteristics. These properties are related to the distribution of titanium sites in the silica lattice. It has been proposed that the Ti(IV) isomorphically substitutes for Si in the lattice in an essentially tetrahedral geometry. In this study we compare the electronic and vibrational spectroscopic characteristics of a series of both dense and porous amorphous titania−silica materials with crystalline titania−silicalite (TS-1). All of the spectroscopic properties are referenced to titania−cristobalite, which contains titanium in a rigorous crystallographic environment that deviates only slightly from tetrahedral. It is found that the amorphous materials have spectroscopic properties that are extremely close to Ti-cristobalite while TS-1 deviates significantly.