Zirconium and iodine co-doped titanium dioxide (Zr-I-TiO2) was prepared by the hydrolysis of tetrabutyl titanate, premixed with zirconium nitrate in an iodic acid aqueous solution, followed by calcination in air. The structure and properties of the resultant catalyst powders were characterized by X-ray diffraction, the Brunauer-Emmett-Teller method, X-ray photoelectron spectroscopy, transmission electron microscopy, and UV-vis absorption spectroscopy. The catalytic activity of the catalyst was evaluated by monitoring the photocatalytic decolorization of methyl orange under visible light irradiation. The results showed that the activities of Zr-I-TiO2 catalysts were higher than that of TiO2 doped with iodine alone (I-TiO2), and the optimal doping concentration in the Zr-I-TiO2 calcined at 400 degrees C was determined to be about 0.05 (molar ratio of Zr:Ti). In addition, the photocatalytic activity of Zr-I-TiO2 calcined at 400 degrees C was found to be significantly higher than that calcined at 500 or 600 degrees C. Based on the physico-chemical characterization, we concluded that the role of zirconium on the I-TiO2 surface is to increase the number of reactive sites by generating a small crystal size and large surface area. The inhibition of electron-hole pair recombination, by trapping photo-generated electrons with Zr4+, did not contribute markedly to the improved photocatalytic activity of Zr-I-TiO2. (C) 2011 Elsevier B. V. All rights reserved.