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).

Graphical abstractUniform and crystalline anatase nanocrystals with optimum chromium(III) produces highest visible light photocatalytic activity where as presence of rutile as well as less crystalline anatase phase screening effect by chromium titanate layer formed, lowers the activity of Cr3+ doped titanium dioxide compositions, calcined at 800 °C.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► An aqueous sol–gel method for the preparation of mesoporous Cr3+ doped TiO2 is being reported for the first time. ► High photocatalytic activity, simplicity and effectiveness of the processing are the novelty of this work. ► A significantly higher photoactivity has been achieved for Cr3+ doped titania compared to the same of pure and commercially available materials. The maximum activity has been achieved for the 0.25 mol% Cr3+ doped titania at an optimum calcination temperature of 800 °C.