Surface Ti3+-Containing (blue) Titania: A Unique Photocatalyst with High Activity and Selectivity in Visible Light-Stimulated Selective Oxidation

A one-step synthesis procedure at elevated temperature was used to prepare Ti3+-tcontaining blue titania. The prepared material was characterized by X-ray powder diffraction (XRD), UV-vis, Raman, and X-ray photoelectron spectroscopy (XPS), and N-2 adsorption and desorption measurements. The blue titania sample was found to be crystalline, with a surface area of 22 m(2)/g. Its phase composition consists of 85% rutile and 15% anatase with a multitude of defect surface VO-Ti3+ sites. The blue titania showed an absorption red-shifted as compared to that of rutile, with a calculated bandgap of 2.93 eV. The photocatalytic performance of the blue titania was evaluated in the liquid phase selective photo-oxidation of methylcyclohexane (MCH) by illumination at 375 +/- 10 nm (UV) and 425 +/- 10 nm (visible light). The activity was monitored by attenuated total reflectance-Fourier transform infrared analysis. A high activity was observed for blue TiO2, remarkably equal in magnitude at both investigated wavelengths. The activity of the blue titania surpassed the activity of other (commercial) titania catalysts (rutile and P25), in particular at 425 nm, and the obtained selectivity for ketones was also greater. The activity data are discussed in relation to the properties of the three catalysts investigated, i.e., the texture, phase composition, and presence or absence of surface defects, of which the latter appears to be dominant in explaining the performance of the blue titania.