Synthesis And Visible-light Photoactivity Of BiOX Hierarchical Structures

Energy crisis and environmental pollution are currently two puzzles facing the world. Semiconductor photocatalysis driven by clean and renewable solar energy is capable not only of photosplitting water to produce hydrogen and reducing carbon dioxide to generate hydrocarbon fuels, relieving the energy crisis, but also of degrading harmful pollutants, remedying environmental pollution, and is thus considered to be one of the most promising technologies to solve these two problems. Traditional semiconductor photocatalysts such as TiO2 exhibit low utilization rate of visible light, which limits its application. Developing visible light responsive semiconductor photocatalysts is one of the research points at present. BiOX (X=Cl, Br, I) is a kind of bismuth-based materials which exhibits high photocatalytic efficiency. Proper morphological modification of BiOX can prominently enhance its photoactivity. Bismuth-containing resources are abundant in our country. Thus, developing bismuth-based visible light photocatalysts is practically meaningful. The preparation and visible light photocatalytic activity of BiOX hierarchical structures were studied in this paper, in order to provide the basis for the development of Bi-based visible light photocatalysts.Based on the above research, the main contents and conclusions of this dissertation are listed as follows:(1) BiOI hierarchical flower-like microspheres were hydrothermally prepared, using tetrabutylammonium iodide as a template and iodine source. We investigated the effects of hydrothermal temperature and time on the crystallinity and morphology of BiOI microspheres. BiOI hierarchical flower-like microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption measurements, and ultraviolet-visible diffuse reflectance spectroscopy. We investigated the photoactivity of the samples under visible light irradiation for degrading Rhodamine B (RhB). The BiOI microspheres prepared by heating at 160℃ for 30 h exhibited the highest photoactivity, and the photodegradation efficiency of RhB on the BiOI microspheres was more than five times higher than that of BiOI nanosheets. It indicated that the morphology played an important role in photoactivity. The photocatalytic efficiency of the BiOI microspheres was positively correlated to the morphologic factor (the ratio of specific surface area to nanosheet thickness) that we defined. The BiOI microspheres exhibited excellent stability and reusability.(2) BiOX nanobelts were synthesized using bismuth subsalicylate as a hard template and bismuth source via a facile hydrothermal route, and characterized by XRD, XPS, SEM, TEM, nitrogen sorption measurements, ultraviolet-visible diffuse reflectance spectroscopy and PL spectroscopy. We investigated the photoactivity of the samples under visible light irradiation. Results showed that BiOX nanobelts were composed of irregular single-crystals with highly exposed (010) facet, and exhibited much higher photoactivity than BiOX nanosheets with highly exposed (001) facet. The excellent photocatalytic performance of BiOBr nanobelts arises from their large BET surface area and strong visible light-adsorption capability.