Fabrication Of Bismuth Subcarbonate-based Complex Catalysis Systems And The Light-induced Catalytic Activity Enhancement Mechanism

In recent years,photo-induced degradation of environmental pollutants and highly efficient energy conversion over semiconductor materials has becomeahot and confusing issue in the field of inorganic materials research.Although,bismuth subcarbonate?Bi₂O₂CO₃?materials featured with unique layed structure shows preferablephotocatalytic performance,it still sufferes from the drawbacks of the UV-light response property due to its wide band gap and the relatively fast recombination rate of photo-generated carriers,which limits its practical applications in environmental photocatalysis and energy photocatalysis.Therefore,it is of significant importance to developBi₂O₂CO₃-based complex systemsto realize the enhanced photocatalytic activity by regulating the bulk or surface structure.In this thesis,based on the first principle theory calculation,a series of bismuth subcarbonate-based complex systems weredesigned and synthesized.By analyzing the effects of the complex systems on the photocatalytic efficiency,the structure-activity relationship was discussed.Meanwhile,the mechanism of the photo-induced catalytic efficiency enhancement for bismuth subcarbonate-based complex systems wereproposed,which could direct the design and synthesis of highly efficient bismuth-related photocatalysts,as well as the practical application of photo-induced heterogeneous catalysis.The main work are summarized as follows.1.Based on first principle calculation and experimental studies,the photocatalytic activity enhancement of halide ions doped Bi₂O₂CO₃ was investigated.It was found that the halide ions doping could efficiently extend the light absorption region of Bi₂O₂CO₃ to visible light,and simultaneously facilitate the carriers generation under visible light.It also benefits the surface charge transfer and suppresses the recombination of the photo-excited electrons and holes.Due to the variation in intrinsic character of Bi₂O₂CO₃through halide ions doping,the photocatalytic activity of halide ions doped Bi₂O₂CO₃for organic pollutants degradation,includingorganic dyes and antibiotics was improved.Moreover,the photocatalytic activity of Br-doped Bi₂O₂CO₃ for oxytetracycline degradation was investigated in detail.It was found that the Br-doped Bi₂O₂CO₃ samples exhibited excellent activity for oxytetracycline degradation in a wide pH range.The presented humic acid and different cations and anions in the waste water have an influence on the oxytetracycline photodegradation efficiency of Br-doped Bi₂O₂CO₃.The Br-doped Bi₂O₂CO₃ sample also shows high stability after five recyclying experiment and remains the highest oxytetracycline mineration ratio of 67.9%,indicating that the halide ions doped Bi₂O₂CO₃ materials have excellent potential application prospect for the photodegradation of antibiotics in waste water.This work paved a new way to enhance the visible light photocatalytic activity for semiconductor photocatalysts with wide band gap.2.The charge transfer process at the interface between g-C₃N₄ and Bi₂O₂CO₃ in g-C₃N₄ surface-decorated Bi₂O₂CO₃ wasinitiallysimulated through the first principle calculation,and the possibility of photocatalytic activity enhancement of Bi₂O₂CO₃through g-C₃N₄ surface decoration was discussed.Based on this,g-C₃N₄ surface decorated Bi₂O₂CO₃materials were successfully fabricated via a facile hydrothermal method,which showed higher photocatalytic efficiency than that of bare Bi₂O₂CO₃sample.Among them,10 wt%g-C₃N₄/Bi₂O₂CO₃ exhibits the highest efficiency for tetracycline and hydrochlorine tetracycline degradation under the simulated solar light irradiation.Moreover,the sample also showed high photodegradation efficiency for other organic pollutants,such as oxytetracycline,congo red,methylene orange,malachite green,andmethyl blue.The photoelectrochemical and fluorescence result illustrates that g-C₃N₄ surface decoration could facilitate the charge transfer and suppress the carriers recombination rate.This work not only develops a new method for the synthesis ofg-C₃N₄ modified Bi₂O₂CO₃photocatalyst,but also provides a strategy for enhancing photocatalytic activity of UV-light response semiconductor through surface decoration.3.Based on the first principle calculation,the effect of introduced oxygen vacancy of Bi₂O₂CO₃ on the structure and physichemical properties of Bi₂O₂CO₃was investigated,and the possibility of photocatalytic activity enhancement of Bi₂O₂CO₃ with oxygen vacancy was also evaluated.Subsequently,bismuth subcarbonate with oxygen vacancy was successfully fabricated via a facilesolvothermal method in a mixedsolvent of deionized water and ethylene glycol.The photocatalytic activities of oxygen vacancy-involvedBi₂O₂CO₃ for the degradation of quinolone antibiotics?e.g.enoxacin?was improved under simulated solar light irradiation.The result shows that the sample with proper oxygen vacancy amount?BOC-2?exhibited the highest photocatalytic activity,which could degrade 95.3%enoxacinwithin 3 h upon simulated solar light irradiation and remain high photocatalytic activity after 5 recycling use.The photoelectrochemical,fluorescence andelectron paramagnanetic resonance?EPR?measurement illustrates that the existence of oxygen vacancy could promote the charge generation,facilitate the charge transfer and inhibit the recombination of photo-generated electrons and holes,which benefits the enhancement of active species generation including both superoxide anion radicals?·O₂^-?and hydroxyl radicals?·OH?,thus resulting in the enhancement of the photocatalytic activity of the materials.The influence of environmental factors on the photocatalytic activity of Bi₂O₂CO₃ with oxygen vacancy was also investigated.The Bi₂O₂CO₃ sample with modest oxygen vacancy content?BOC-2?exhibits high photocatalytic efficiency for enoxacin degradation within a wide pH range?pH?7?.And the coexisting organic compounds,various cations and anions have a slight effect on the enoxacin degradation.Moreover,the Bi-supported Bi₂O₂CO₃sample with oxygen vacancy inhibits the enoxacin degradation,indicatingthat oxygen vacancy might be reactive site of enoxacin degradation overoxygen defected Bi₂O₂CO₃sample.This work establishesthe theoretical foundation for enhancing the photocatalytic activity of wide bandgap semiconductor through involving oxygen vacancy.