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.