Bismuth-doped TiO2 submicrospheres were synthesized by ultrasonic spray pyrolysis. The prepared bismuth-doped titania was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS). Aqueous photocatalytic activity was evaluated by the decomposition of methyl orange under visible-light irradiation. The results indicate that doping of bismuth remarkably affects the phase composition, crystal structure, and the photocatalytic activity. The sample with 2% Bi exhibits the optimum photocatalytic activity. 1. Introduction Photocatalytic oxidation of pollutants has increasing interests in recent years because of its advantages such as high redox capability, nonselectivity, and efficient solar utilization. Different kinds of photocatalytic materials have been studied such as metal oxides, nitrides, and sulfides [1–7]. Among them, TiO2 is the most commonly used photocatalyst owing to its high redox power, photostability, chemical inertness and low cost. However, the relatively low quantum efficiency of TiO2 photocatalysts limits its real application. To overcome this problem, a lot of efforts have been paid to improve the photocatalytic efficiency of TiO2 from the viewpoint of practical use. It has been reported that the crystal size, specific surface area, morphology, and texture have great effects on the photocatalytic properties of semiconductors. Nano/microspheres structure has attracted great interests due to their thermodynamically favorable state in terms of surface energy. Recent researches have demonstrated their potential application in many fields such as photonic crystals [8], biomedicine [9, 10], sensing [11, 12], and solar cells [13, 14]. In particular, some studies found that the nano/microspheres structure of semiconductor have promising properties in the region of photocatalysis [15–17]. Various approaches have been used for the preparation of spherical semiconductor materials. The most common approach is based on the use of various removable templates. The removal of template materials is complex and usually requires high temperature processes or wet chemical etching, which is expensive and not easy for mass application. Therefore, it is promising to develop a simple and inexpensive way without using template for the preparation of semiconductor nano/microspheres. Many reports have shown that the photocatalytic properties of TiO2 can be modified strongly by doping with different elements.
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