An aqueous sol–gel synthesis of chromium(III) doped mesoporous titanium dioxide for visible light photocatalysis

Nanoparticles of titanium dioxide doped with Cr3+ ions have been prepared through an aqueous sol–gel method. The mesoporous nature of both pure and Cr3+ doped TiO2 powders, with specific surface area of 7.4 and 6.6 m2 g−1, respectively, is maintained even at calcination temperature of 800 °C. The transformation of TiO2 from the anatase to rutile phase is suppressed up to 800 °C by Cr3+ ion doping. Even though surface area values are decreased, the doped materials show improved photocatalytic activity, which may be due to increased crystallinity of the anatase phase without the formation of rutile. Doped materials have a red-shift in the band gap energy and hence, photoactivity under visible light. The rate of photodegradation of methylene blue dye for both pure and doped TiO2 under visible light has been monitored in this study. The 0.25 mol% Cr(III) doped photocatalyst, calcined at 800 °C, shows the highest photocatalytic activity under visible light with a rate constant of ∼15.8 × 10−3 min−1, which is nearly three times higher than that of commercially available Degussa P25 titania (5.8 × 10−3 min−1).