Synthesis, Modification And Performance Study Of Bismuth-Based Photocatalysts

Bismuth-containing complex oxides, as excellent visible light photocatalysts, that were layer structure composed of [Bi2O2]2+slabs interleaved by double slabs of different atoms which could diversify the photocatalytic activity of bismuth-containing complex oxides, have attracted extensive attention these days. The layered structure endowed the complex oxides with high carrier mobility and small probability of the recombination of photogenerated electrons and holes. On the one hand, dyes were demanded and produced in a large scale in industry. On the other hand, traditional chemical methods were difficult in decomposing dyes due to the steady molecule structure of dyes. Hence, the application of photocatalytic method in dye wastewater cleaning could be important development in future. Unluckily, in the photodecomposition process of dye wastewater treatment, the yielded intermediates could be more toxic than the dye molecule itself. Furthermore, the light shielding effect of dyes wastewater could affect the absorption and utilization of light. The photocatalytic efficiency could not only depend on the catalyst composition, but also closely relate to the structure and morphology. This thesis focused on the synthesis of bismuth-containing complex oxides (BiOBr and Bi2MoO6) with various morphologies and the hierarchical flower-like RE/Bi2MoO6and BiOBr/Bi2MoO6spheres by solvothermal technology, and then the cleaning wastewater by photocatalysis for various organic compounds. The photocatalysts were further optimized by the cutting and adjusting of the structure. Based on the above results and the systematic characterization, the formation and crystal growth mechanism of the photocatalysts with various morphologies were studied. Meanwhile, the reaction kinetics and reaction mechanism of photocatalytic process was disclosed. Then, the correlation of the photocatalytic performances or the mineralization ability to the morphology has been discussed based on the photocatalytic activity with various morphologies. The research work could be described in the following four parts:(1) Microwave-assisted ionic liquid self-assembly of BiOBr nanosheets in microcube with enhanced photocatalytic activityBiOBr with various morphologies has been successfully synthesized via microwave-assisted ionic liquid self-assembly method. Ionic liquid, which could play the oriented role, could help to achieve BiOBr with the high crystallinity and regular morphology structure, combined with microwave. The visible light reflection among the nanosheets of microcube could enhance light absorption, and then increase the photocatalytic activity of BiOBr nanosheets in microcube. Simultaneously, it was observed that the photocatalytic performance of the uncalcined hierarchical BiOBr microcube was superior to that of the calcined hierarchical BiOBr due to the sensitization effect of the organics on the surface.(2) Aerosol-spraying preparation of Bi2MoO6, A visible photocatalyst in hollow microspheres with a porous outer shell and enhanced activityBi2MoO6hollow microspheres with cage-like pores on the outer shell were synthesized by aerosolspraying with glucose as a template. The aerosol-spraying temperature and the amount of glucose played key roles in determining the crystal phase and the Bi2MoO6morphology including outer shell thickness and number of cage-like pores on the outer shell. The photocatalytic degradation of rhodamine B under visible-light irradiation was examined which revealed that the reaction followed first order kinetics with respect of rhodamine B concentration and rhodamine B was completely degraded into CO2via de-ethylation process with the formation of5intermediates. The as-prepared Bi2MoO6exhibited high activity owing to the high surface area and additionally because of multiple light reflections in the hollow chamber.(3) In situ rare-earth doped Bi2MoO6visible light photocatalyst with enhanced activityA series of Bi2MoO6visible light photocatalysts were doped with various rare-earth via in-situ synthesis and used for photocatalytic degradation of RhB. The Gd3+-modification was superior over other rare-earth due to Gd3+with particular4f electron structure, and the in-situ synthesis was better than traditional impregnation method since the Gd3+was incorporated into the Bi2MoO6crystal lattice to form donor level, which facilitated photocatalystic activation with visible lights illuminating, retarded the photo-induced electron-hole recombination, and inhibited the leaching of dopants, leading to the enhanced activity and stability.(4) Solvothermal preparation of BiOBr/Bi2MoO6heterostructures with enhanced photocatalytic propertyThe flower-like BiOBr/Bi2MoO6microsphere was synthesized by a simple solvothermal method. The0.20-BiOBr/Bi2MoO6sample exhibited excellent adsorption, photocatalytic abilities, and mineralization ability for the degradation of RhB under visible light irradiation (>420nm), due to the heterojunction structure, higher SBET and the BiOBr strong adsorption abilities for RhB. In this system, h+was the dominant reactive specie. The photocatalyst degradation processes of RhB for before and after modified were uniform.