Design And Synthesis Of Bismuth Vanadate Heterojunction Materials And Regulation Of Their Photocatalytic Performance

Bismuth vanadates are promising photocatalysts due to their stable photochemical properties,nontoxicity,and the ability of oxidizing water to produce oxygen and eliminating environmental pollutants.However,the severe recombination of charge carriers in bulk bismuth vanadates significantly restricts their photocatalytic applications.Construction of heterojunction has been reported to be one of most effective methods to improve the carrier separation and photocatalytic activity of materials.In this paper,aimed at enhancing the carrier separation efficiency and visible light absorption of bismuth vanadates,two bismuth vanadate heterojunctions have been constructed and employed in photocatalytic tetracycline（TC）degradation.Moreover,the mechanism of photocatalytic activity enhancement of bismuth vanadate heterojunctions was investigated.The main findings of this thesis are as follows:（1）Construction of Bi VO₄/Bi₂₅VO₄₀ heterojunction via alkali treatment strategy.Bi VO₄ was first synthesized by hydrothermal method,which was then gradually converted to stable Bi₂₅VO₄₀ by alkali treatment.In addition,the Bi VO₄/Bi₂₅VO₄₀heterojunctions with various relative contents are prepared by the regulation of alkali treatment conditions.The XRD Rietveld refinement was employed to analyze the crystal structure and phase composition of heterojunctions.Combined with the characterization of morphology and microstructure,the in situ growth of Bi VO₄/Bi₂₅VO₄₀ heterojunction follows the mechanism of dissolution-recrystallization.The photocatalytic performance of Bi VO₄/Bi₂₅VO₄₀ heterojunctions was evaluated by photocatalytic removal of tetracycline under visible light irradiation.The results indicated that Bi VO₄/Bi₂₅VO₄₀ heterojunctions showed much higher activity than the single components and the removal efficiency can be tuned by the relative contents of Bi VO₄ and Bi₂₅VO₄₀.Among them,the sample obtained by alkali treatment of 1 h exhibited the optimal performance and good stability,which is stemmed from improved visible light absorption and charge carrier separation by heterojunction construction.The radical trapping experiments were carried out and demonstrated that the superoxide radical plays a dominant role in the degradation of tetracycline.Furthermore,the mechanism of photocatalytic activity enhancement of Bi VO₄/Bi₂₅VO₄₀ heterojunction was proposed based on the results of HPLC-MS and photoelectrochemical characterization.（2）Construction of Bi₂S₃/Bi₂₅VO₄₀ heterojunction via deposition-precipitation method.Bi₂S₃was in situ deposited on the surface of Bi₂₅VO₄₀ by a deposition-precipitation method and the content of Bi₂S₃was tuned to prepare a series of Bi₂S₃/Bi₂₅VO₄₀ heterojunctions by utilization of the visible light sensitization of Bi₂S₃.The structure and morphology characterizations showed that the intimate heterojunctions were formed between Bi₂S₃and Bi₂₅VO₄₀.The Bi₂S₃/Bi₂₅VO₄₀composites show excellent performance in photocatalytic removal of tetracycline under visible light irradiation with the optimum activity achieved at the sample of 0.25 of Bi₂S₃/Bi₂₅VO₄₀relative content.The photocatalytic mechanism was investigated by UV-vis DRS,time-resolved PL,and some photoelectrochemical characterization,which indicated that the improved visible light absorption and charge carrier separation contribute to the enhanced photocatalytic activity of Bi₂S₃/Bi₂₅VO₄₀.