Study On The Preparation And Photocatalytic Performances Of Bismuth Based Heterojunction Visible-light-responsive Photocatalysts

As a kind of visible-light-response photocatalyst,Bismuth-based photocatalyst has emerged as a tempting photocatalytic system.However,the fast recombination of photogenerated electron-hole pairs restrict its practical application seriously.Therefore,this work focuses on improving separation efficiency of photo-generated electron-hole pairs of bismuth-based photocatalyst.Specifically,the construction of heterojunction architectures has been proven a promising strategy to design tunable band structures,endowing as-fabricated hybrids with advanced properties superior to their individual components.In this thesis,BiVO₄/RGO,Bi₂S₃/SnS₂/Bi₂O₃,?-Bi₂O₃/Bi₂S₃ and SnO₂/BiOCl Bi-based heterojunction photocatalysts with high capability of visible-light response were prepared by simple hydrothermal method or solvothermal method.A variety of characterization techniques have been adopted to investigate the crystallinity,chemical construction,morphology,adsorption property,band structure,optical and electrical properties.The photocatalytic activities were evaluated by the degradation of dye,metal or antibiotic simulated wastewater The formation process of specific shaped photocatalyst?SnO₂/BiOCl yolk-shell microspheres?,and the degradation mechanism of the antibiotic contaminants?CIP?have been systematic probed,which reveals the relationship between the morphology,band structures and the advanced photocatalytic performance,explore the mechanism of the enhancement in the visible-light-driven photocatalytic performances of Bi-based heterojunction photocatalysts,and provide fundamental understanding towards the preparation and application of Bi-based visible-light-responsive heterojunction photocatalysts.The main conclusions are as follows:?1?Sphere-shaped BiVO₄/RGO was synthesized by a simple and cost-effective low temperature hydrothermal method.It was found that,in a certain range,the photocatalytic activity of BiVO₄/RGO for the degradation of Rhodamine B first increased then decreased with the increase compound quantity of RGO.When the mass fraction of RGO was in the range of 0.25%⁵%,the photocatalytic activities of BiVO₄/RGO samples were all higher than that of pure BiVO₄.Among them,the 3% BiVO₄/RGO possessed the highest photocatalytic activity,which was 68.85% higher than that of pure BiVO₄.The improved photocatalytic activity of BiVO₄/RGO composite is attributed to the formation of well-defined BiVO₄-RGO interfaces,which greatly enhances the charge separation efficiency.Overcoating would decrease the photocatalytic activity due to the decreased absorbing light rate.?2?In this study,we reported for the first time the controlled preparation of Bi₂S₃/SnS₂/Bi₂O₃ double Z-scheme heterojunction photocatalyst by a simple one-pot solvothermal route.When the mole ratio of Sn: Bi was in the range of 0.03-0.25,the as-fabricated Bi₂S₃/SnS₂/Bi₂O₃ heterojunctions can significantly enhance photocatalytic activity in comparison with pure Bi₂S₃ with regard to rhodamine B?RhB?degradation.In addition,the optimized Sn:Bi=0.15?BiS-4?sample possessed good simulated-sunlight photocatalytic efficiency towards the degradation of other types of dyes,including methyl orange,methylene blue,orange ? and crystal violet.By further probing the charge separation and migration behaviors,studying the band structure,as well as conducting the active species trapping experiments,a possible Bi₂S₃/SnS₂/Bi₂O₃ photocatalytic mechanism was proposed,which not only benefited the efficient photogenerated electron-hole pair separation but also demonstrated advanced capacity for the removal of organic dyes.?3?We demonstrate the design and fabrication of ?-Bi₂O₃/Bi₂S₃ hollow microspheres with sheet-like hierarchical nanostructures targeting an advanced visible-light-responsive photocatalytic system.The as-obtained ?-Bi₂O₃/Bi₂S₃ heterojunction photocatalyst exhibited a markedly enhanced sunlight photocatalytic activity towards the photo-degradation of rhodamine B.and the degradation rate constant of?-Bi₂O₃/Bi₂S₃ was 0.048,0.054 and 0.050 min^-1 higher than pure ?-Bi₂O₃,Bi₂S₃ and physical mixture of?-Bi₂O₃ and Bi₂S₃.Following,the property of the ?-Bi₂O₃/Bi₂S₃ on the Cr???photocatalytic reduction was then evaluated.Operating conditions such as ?-Bi₂O₃/Bi₂S₃ mass,tartaric acid concentration,and initial Cr???concentration were analyzed.The results showed that a suitable reduction condition was selected as,?-Bi₂O₃/Bi₂S₃ dosage 25 mg,initial concentration 20 mg·L^-1 and molar ratio of Cr???/tartaric acid 1:20.The outstanding photocatalytic performances of the hybrid photocatalyst are mainly attributed to that the intimate interfacial contact of ?-Bi₂O₃ and Bi₂S₃,which could provide efficient charge separation to suppress the electron-hole recombination,and the hollow microspheres structure could enhance light harvesting.?4?Novel hierarchical SnO₂/BiOCl yolk-shell microspheres were prepared using a facile one-pot solvothermal route,and the growth mechanism was systematically studied.The SnO₂/BiOCl composite photocatalyst exhibited excellent photocatalytic efficiency in the degradation of rhodamine B,ciprofloxacin,metronidazole and sulfamonomethoxine under natural sunlight irradiation.The first-order kinetic rate constant of SnO₂/BiOCl was demonstrated to be 51,3 and 6 times higher than that of bare SnO₂,BiOCl and commercial TiO₂ for Rh B degradation,owing to its enhanced visible light harvesting and improved separation efficiency of photo-induced carriers.The degradation mechanism was accordingly explored.Furthermore,the main degradation by-products were recognized by UPLC-MS/MS technique to propose the degradation pathways especially for CIP.