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Preparation, Modification and Visible-Light-Driven Photocatalytic Performance of Bismuth Molybdate Complex Oxides

Author: ZhuLi
Tutor: ZhangWeiDe
School: South China University of Technology
Course: Physical and chemical
Keywords: Hollow microspheres Composite photocatalyst Coupling of semiconductors Visible-light-driven photocatalytic performance Purification of wasted water
CLC: O643.36
Type: Master's thesis
Year: 2011
Downloads: 428
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Abstract


Degradation of organic pollutants by solar energy is of vital significance for solving energy crisis and environmental problems. Developing highly effective visible-light-active photocatalysts is the key to utilize solar energy more efficiently. There are two main approaches for the current research of novel photocatalysts responsive to visible light. One is to modify TiO2 in order to make its absorbance wavelength to shift to visible light range. The other is to design novel photocatalysts responsive to visible light, which involves the knowledge of chemistry, physics, material, photoelectronics and so on. The second approach has become an interesting challenge and has drawn increasing attention in current photocatalysis research. The semiconductor Bi2MoO6, as the simplest Aurivillius oxides possessing a layered structure, has great potential photocatalytic activity responsive to visible light. It can absorb visible light with an absorbance wavelength near 491 nm. The layered Bi2MoO6 as an excellent photocatalytic material has shown excellent photocatalytic activity in solar energy diversion and environmental purification under visible light irradiation. The size, morphology and structure of the semiconductive materials are closely related to their physical and chemical performance. Therefore, the research on morphology-controlled synthesis and visible-light photocatalytic performance for the Bi2MoO6 semiconductive materials has important academic significance and practical value. Based on the above consideration, in this thesis, Bi2MoO6 with different morphologies were successfully synthesized by simple solvothermal and hydrothermal process. Meanwhile, in order to further improve their visible-light-driven photocatalytic activity for the degradation of organic dye pollutants, studies on modified Bi2MoO6 by other semiconductor such as TiO2 and their application for degradation of organic dyes have been carried out. Some valuable results were successfully obtained. The main points of this thesis are summarized as follows:Firstly, Bi2MoO6 hollow microspheres prepared in ethylene glycol/absolute ethanol mixture solvents were successfully synthesized by a simple solvothermal process for the first time. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller （BET） surface areas analyzer and UV-vis absorption spectra. The tunable preparation conditions such as the volume ratio of ethylene glycol to absolute ethanol and urea content allow for the control of morphology of Bi2MoO6 hollow microspheres. The formation mechanism of the Bi2MoO6 hollow microspheres was also discussed. Furthermore, in order to investigate the relationship between the morphology of the Bi2MoO6 and its visible-light-driven photocatalytic performance, Bi2MoO6 particles were synthesized by a simple hydrothermal process. The photocatalytic properties of the Bi2MoO6 with different morphologies were evaluated by the photodegradation of Rhodamine B （RhB） under visible-light irradiation. The experimental results revealed that the Bi2MoO6 hollow microspheres exhibited higher catalytic activity than the Bi2MoO6 particles for degradation of Rhodamine B under the same conditions.Secondly, modification of Bi2MoO6 hollow microspheres by TiO2 facilitates the separation of the photoinduced carriers, which further enhances the photocatalytic activity. TiO2/Bi2MoO6 heterostructures with different Bi2MoO6 content were synthesized through a simple hydrothermal method at a low temperature by coupling Bi2MoO6 hollow microspheres with TiO2 nanoparticles. Meantime, by changing the composite order of two different semiconductors, Bi2MoO6/TiO2 heterostructures with different Bi2MoO6 content were synthesized by depositing Bi2MoO6 nanoparticles onto TiO2 nanorods. The photocatalytic performance of the composite photocatalysts were evaluated by photodegradation of methylene blue （MB） under visible-light irradiation （λ> 420 nm）. The experimental results revealed that the composite photocatalysts based on heterostructures of Bi2MoO6 and TiO2 exhibited much higher photocatalytic activity than the single-phase Bi2MoO6 or TiO2 and the mechanical mixture of Bi2MoO6 and TiO2 for degradation of methylene blue under the same conditions. The photocatalytic activity of the Bi2MoO6 composite photocatalysts with different Bi2MoO6 content was also evaluated by photodegradation of methylene blue under visible-light irradiation. The experimental results demonstrated that the composite photocatalysts based on Bi2MoO6 and TiO2 have the optimal composite ratio for degradation of methyl blue. Moreover, with increasing the Bi2MoO6 content continuously, the photocatalytic activity of the Bi2MoO6 composite photocatalyst will decrease reversely. The investigation indicates that the morphology of the complex oxide greatly influences the visible-light-driven photocatalytic performance of the catalysts. The coupling of two different semiconductors can further enhance the photocatalytic activity due to the separation of the photoinduced carriers efficiently. The results reported in this study provide insight to construct other complex metal oxides with hollow structure and composite photocatalysts. The as-prepared photocatalysts exhibit excellent visible-light-driven photocatalytic activity for the degradation of the organic dyes. Therefore, it is promising to degrade organic organic pollutants in the field of waste purification.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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