Recyclable UV and visible light photocatalytically active amorphous TiO2 doped with M (III) ions (M = Cr and Fe)

Samples of amorphous TiO2 doped with Cr(III) and Fe(III), designated as Cr-TiO2 and Fe-TiO2, were prepared via modified impregnation method. The resulting products were characterized by X-ray diffraction, scanning electron microscopy, specific surface area by the Brunauer, Emmett and Teller method, UV-vis absorption and diffuse reflectance spectroscopy, and electron spin resonance spectroscopy. Experimental results revealed that the concentrations of dopants under studied, from 0.05 to 0.2 mol%, had no effect on the phase of products. The band gap energies shifted from 3.28 eV in the undoped amorphous TiO2 to 2.50 eV and 2.86 eV for Fe-TiO2 and Cr-TiO2, respectively. The doped amorphous TiO2 showed photocatalytic activities under both UV and visible light with optimal results at 0.1 mol% dopants. Under UV irradiation, the 0.1 mol% doped samples decolorized methylene blue solutions to the same extent as the commercial TiO2 samples (P25 and anatase) in 5 h. Under visible light, the doped samples decolorized dye solutions in 12 h while the commercial ones were much less active. The used catalysts can be recycled many times without any special treatment. (C) 2010 Elsevier B.V. All rights reserved.