| As the coal, crude oil and other fossil fuels are running out, human beings are facing a huge energy crisis. Besides, the consumption of these fossil fuels has caused a serious environmental pollution problem. Semiconductor photocatalysis, which could utilize the abundant solar energy for water splitting, organic pollutants photodecomposition and carbon dioxide photoreduction, is of great significance to the world's new energy exploitation and environmental decontamination. However, the large band gap of conventional TiO2heterogeneous photocatalyst render it only responsive to ultraviolet light, which accounts for small portion of the sunlight energy. Moreover, the rapid recombination of the photoinduced carriers in TiO2leads to its low quantum efficiency. Given the practical application, it is crucial and promising to exploit novel efficient visible-light-driven photocatalysts. Recently, bismuth-based semiconductors have been reported to show excellent photocatalytic activity under visible light irradiation, which paves a new path for the development of highly efficient photocatalysts with visible light response.The properties of materials are determined by their structures, including the crystal, electronic, surface and interface structures. Meanwhile, it can also provide a way to improve its performance by modifying the structure. Since the photocatalytic performance of a semiconductor photocatalyst is influenced by the light absorption range and carrier separation rate, the structures can be tuned to facilitate the harvest light and the transport of photogenerated carriers so that the high photocatalytic efficiency of the photocatalytic materials can be realized.In this thesis, our research is focused on the bismuth-based layered semiconductor materials. The unique layered structures could favor the effective separation and transport of the photoinduced carriers. Furthermore, their structures could be tailored by intercalation, exfoliation, pillaring and ion exchange reactions due to the high reactivity of the interlamination ions. According to the structure-property correlation, we adopted an access of efficient visible light photocatalysts by structure design, controlled synthesis and functional assembly.In chapter one, we briefly introduced the principal mechanism and main applications of semiconductor photocatalysis, and reviewed the latest progress in visible light photocatalysts. Then the relationship between structures and photocatalytic performances of semiconductors was discussed. The structural features and intercalation chemistry of inorganic layered materials were introduced. The bismuth-based layered compounds were also introduced. Finally, the significance, research ideas and the outline of this thesis were summarized.In chapter two, we studied the effect of microstructure modulation, especially the three-dimensional (3D) hierarchical architectures, on the photocatalytic performance of bismuth-based layered semiconductors.(1) Hierarchical BiOBr hollow microspheres (HMSs) were synthesized by a miniemulsion-assisted solvothermal route. By choosing different solvents, BiOBr products with various shapes were obtained. The structures, morphologies and optical properties of BiOBr samples were systematically investigated, and the formation mechanism of BiOBr HMSs was discussed. The photocatalytic activity was evaluated by the photodegradation of Rhodamine B (RhB) dye and photoreduction of Cr(VI) ions under visible irradiation. Among the various shapes of BiOBr samples, the hollow microspheres showed the highest photocatalytic activity.(2) Hierarchical Bi2WO6HMSs were prepared by an anion exchange reaction accompanied by Kirkendall effect. The effect of reaction temperature on the phase structure of the products was studied. The morphologies, photoabsorption and nitrigen sorption of Bi2WO6samples were systematically investigated. Photocatalytic CO2reduction on the Bi2W06samples was investigated, and the results showed that Bi2WO6HMSs could convert CO2into methanol in high efficiency. The plausible mechanism was also studied on the basis of CO2adsorption and FT-IR spectra.(3) Hierarchical Bi2O2CO3microflowers were fabricated by a low-temperature wet chemical method. By altering the molar ratio of Bi3+/CO32-in precursor solution, various microstructures of Bi2O2CO3were obtained. We studied the structural and morphological features of Bi2O2CO3microflowers. According to the observation of the intermediate product and the crystal structure, the growth process mechanism of the Bi2O2CO3microflowers was proposed. The photocatalytic activity was evaluated by photodegradation of methyl orange (MO) dye.In chapter three, we studied the composite photocatalysts of bismuth-based layered semiconductors.(1) The AgI/BiOI nanostructured composite photocatalyst was designed and fabricated by chemical bath method. We studied the structure, morphology and optical property of the composite. The photocatalytic performance was evaluated by decomposition of MO and phenol solution, and the AgI amount plays an important role in determining the photocatalytic property of the AgI/BiOI nanostructured composites. The mechanism for the high photocatalytic activity and stability of the Agl/BiOI nanostructured composite was also discussed.(2) The novel Ag/AgBr/BiOBr hybrid was designed according to the surface plasmon resonance of noble metal nanoparticles and synthesized by in situ ion exchange between BiOBr microspheres and Ag(NO3)3followed by partial photoreduction. The role of BiOBr hierarchical microspheres in preparing AgBr nanoparticles was discussed. The photocatalytic activity was evaluated by decomposing MO dye and sterilization of E. coli under visible light irradiation. The superior photocatalytic activity of the hybrid was discussed.(3) By combining the quantum size confinement of narrow band gap semiconductors, we designed and prepared the novel efficient Bi2S3nanocrystals (NCs)/BiOCl hybrid photocatalyst by an anion exchange reaction. The structure and morphology of the hybrid were studied, and the photocatalytic performance was carried out by decomposing2,4-dichlorophenol (2,4-DCP) solution. We systematically investigated the effect of Bi2S3NCs size on the photocatalytic of the Bi2S3NCs/BiOCl hybrids, and discussed the plausible photocatalytic process mechanism of the hybrids.In chapter four, we studied the effect of the crystal and electronic structures on the photocatalytic performance of the bismuth-based compounds. (1) Three polymorphs of Bi2O3samples, including monoclinic a-Bi2O3, tetragonal β-Bi2O3and cubic δ-Bi2O3, were prepared under different conditions. The photocatalytic performances were examined by photodecomposition of MO dye and4-chlorophenol solution, and their activities followed the order: β-Bi2O3>a-Bi2O3>δ-Bi2O3. A systematical investigation of the synergistic effect of crystal and electronic structures on the photocatalytic performances of Bi2O3polymorphs was discussed, and the results manifested that β-Bi2O3can be used as a highly efficient visible-light-driven photocatalyst.(2) The metastable Bi2oTi032material was prepared by a high temperature quenching method. The effect of experimental procedure on the final phase production was discussed. The structure, morphology and optical property of Bi2oTi032material were studied. The photocatalytic activity was evaluated by decomposition of MO dye solution. The mechanism for the photocatalytic process was discussed on the basis of band calculations.In chapter five, we summarized our work, and discussed the problems remained to be solved. Finally, we made a plan and looked forward to the future work.In summary, bismuth-based compound materials have shown efficient photocatalytic activities under visible light irradiation, which could resolve the light harvesting and the separation of the photoinduced carriers. On the basis of structure-property correlation, the visible light photocatalytic performances of the bismuth-based compounds can be optimized through structural design and functional assembly, which is of great significance to environmental decontamination and carbon dioxide treatments.
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