Photophysical and photocatalytic properties of TiO2-Cr sol–gel prepared semiconductors

Chromium–titania photocatalysts were prepared at different contents in chromium oxide (0.1–5.0 wt.%) by gelling titanium alkoxide and chromium nitrate. Nanostructured titania with crystallite sizes between 22 and 40 nm and high specific surface areas (68–113 m2/g) were obtained in solids annealed at 500 °C. The determination of the band gap energy showed a shift to the visible region in samples containing high amounts of chromium oxide (3.8–1.8 eV). XPS spectroscopy evidenced the presence of Cr(III) and Cr(VI) in the annealed semiconductors. The photocatalyst with low doping content (0.1 wt.% Cr) was observed to provide effective Cr–Ti interaction and allow the maximum photoactivity.