Effects of I and F codoped TiO2 on the photocatalytic degradation of methylene blue

Nanocrystalline I-F-codoped TiO2 was prepared by a sol-gel-impregnation method, using tetrabutylorthotitanate in a mixed NH4I-NH4F aqueous solution. The as-prepared TiO2 was characterized with UV-vis diffuse reflectance spectra, X-ray diffraction and nitrogen adsorption. The degradation of methylene blue (MB) over as-prepared TiO2 in aqueous solution under simulated sunlight irradiation was remarkably enhanced by codoping with I and F. The effects of codoping and calcination temperature on the photocatalytic activity and microstructures were investigated. The photocatalytic activity of as-prepared I-F-codoped TiO2 was remarkably higher than that of pure, I-doped, and F-doped TiO2 when the molar ratios of I and F to Ti were kept in the value of 10. The influence of I-F-modification on the photocatalytic activity was discussed by considering the higher surface area, entire anatase phase, effective dopant content, and stronger absorbance of sunlight, corresponding to the higher quantum efficiency. In addition to a complete removal of color, the as-prepared TiO2 was simultaneously able to oxidize MB and small amounts of intermediates such as formic acid and phenol were detected. After prolonged sunlight irradiation some intermediates almost vanished, and MB appeared to be eventually mineralized to NH4+, NO3- and SO42-. (C) 2009 Elsevier B.V. All rights reserved.