Preparation Of Bismuth Multiplex Oxide And Its Application For Photocatalytic Reduction CO₂

Fossil fuels were consumed overly with the rapid development of economy. It not only bringed to energy crisis but also released a large amount of CO₂ which leaded to global warming. Photocatalytic reduction of CO₂ into hydrocarbon fuels is a the most promising technology which can solve the energy crisis and greenhouse effect. The most prominent disadvantage of photocatalytic reduction of CO₂ for the moment is that the low intensity of photo-absorption, low quantum efficiency and poor ability of product selectivity or separation. In order to solve the above problems,it is crucial and promising to exploit novel efficient visible-light-driven photocatalysts.Recently, bismuth multiplex oxides 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. In our study, we mainly perpared a series of modified Bi₂WO₆ materials and flower Bi₂ Mo O₆ microspheres materials, and researched their photocatalytic activities of reduction CO₂. The main conclusion are as follows:（1） Novel Mo S₂/Bi₂WO₆ composite materials has been successfully prepared by a simple impregnation-calcining method, and photocatalytic reduction of carbon dioxide was investigated under visible light irradiation for the first time. The result showed that the promoting effect caused by Mo S₂ can be attribute to improve the efficiency of electronic transmission, the suppression of recombination between electron-hole and the visible light catalytic activity. The Mo S₂/Bi₂WO₆ composite materials showed good photocatalytic activity than pure Bi₂WO₆ obviously, When the loading amount of Mo S₂ was increased to 0.4%, the higest photocatalytic activity was obtained, methanol and ethanol yield was 36.7 and 36.6 μmol gcat-1, respectively,which is 2 times higher than that of pure Bi₂WO₆.（2） SnS₂, Bi₂WO₆ and different mole ratio of SnS₂/Bi₂WO₆ composite semiconductors photocatalysts were successfully prepared by a facile solvothermal process in this paper. The SnS₂/Bi₂WO₆ composite materials show higest visible-light photocatalytic reduction of CO₂ performance than pure SnS₂ and Bi₂WO₆ obviously.the SnS₂/Bi₂WO₆ composite material with an optimal mole ratio of 0.1 exhibits the highest photocatalytic activity, its methanol and ethanol yield were 50.2 and 19.7μmol gcat-1, respectively, which is 3 and 4 times higher than that of pure SnS₂ and Bi₂WO₆. This study not only demonstrated suppression of recombination betweenelectrons and holes, but also improved the intensity of visible light absorption,showed the excellent photocatalytic performance.（3） The hierarchical flower-like Bi₂ Mo O₆ microspheres were successfully synthesized via a facile hydrothermal approach, employing PVP as the crystal growth modifier. The building units of the hierarchical flower-like Bi₂ Mo O₆ were constructed by two-dimension thin flakes, which intercrossed with each other and aggregated together to form the three-dimension flower-like structure. The effects of PVP amount and hydrothermal time were studied, and found to play crucial roles in the formation of the Bi₂ Mo O₆ architectures. A possible mechanism in the formation of the flower-like microstructures was proposed. The Bi₂ Mo O₆ samples were first evaluated for the photocatalytic reduction of CO₂ into methanol and ethanol as solar fuels under visible-light irradiation. It is found that the hierarchical flower-like Bi₂ Mo O₆ exhibits highly efficient photocatalytic activity. After 4 h, the yield of methanol and ethanol can be achieved 24.8 and 18.8 μmol gcat-1, respectively, higher than that obtained over the previously reported the ordinary structure of Bi₂ Mo O₆ materials. as a result,changing the structure of the materials is also an effective way to improve the photocatalytic efficiency.