Photoinduced hydroxyl radical and photocatalytic activity of samarium-doped TiO2 nanocrystalline

SM3+-doped TiO2 nanocrystalline has been prepared by sol-gel auto-combustion technique and characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, and also UV-vis diffuse reflectance spectroscopy (DRS). These Sm3+-doped TiO2 samples were tested for methylene blue (MB) decomposition and (OH)-O-center dot radical formation. The analysis of (OH)-O-center dot radical formation on the sample surface under UV irradiation was performed by fluorescence technique with using terephthalic acid, which readily reacted with (OH)-O-center dot radical to produce highly fluorescent product, 2-hydroxyterephthalic acid. It was observed that the presence of Sm3+ ion as a dopant significantly enhanced the photocatalytic activity for MB degradation under UV light irradiation because both the larger specific surface area and the greater the formation rate of (OH)-O-center dot radical were simultaneously obtained for Sm3+-doped TiO2 nanocrystal line. The adsorption experimental demonstrated that Sm3+-TiO2 had a higher MB adsorption capacity than undoped TiO2 and the adsorption capacity of MB increased with the increase of samarium ion content. The results also indicated that the greater the formation rate of (OH)-O-center dot radical was, the higher photocatalytic activity was achieved. In this study, the optimum amount of Sm3+ doping was 0.5 mol%, at which the recombination of photo-induced electrons and holes could be effectively inhibited, the highest formation rate of (OH)-O-center dot radicals was, and thereby the highest photocatalytic activity was achieved. (c) 2007 Elsevier B.V. All rights reserved.