Preparation Of Bismuth-based Perovskite Photocatalysts And Organic Pollutant Degradation

Water pollution（containing pollutants from agriculture,sanitation and industry）and declining air quality is hazardous to agricultural production and health.Toxic residues from agricultural pesticides directly contaminate soil and water,and agricultural irrigation affects agricultural production.In this sense,the solution to problems agricultural environmental pollution is crucial for sustainable and more environmental-friendly agriculture.Photocatalytic technology for environmental remediation has attracted extensive attention due to its brilliant photocatalytic performance that can decompose organic pollutants and water without secondary pollution under sunlight.Among various photocatalysts,bismuth-based perovskite bismuth tungstate（Bi₂WO₆）is used for water purification by virtue of its ideal band gap,unique layered structure and strong stability.However,the photocatalytic activity of Bi₂WO₆ is still restricted by the low photoconversion efficiency and rapid complexation of photoinduced carriers.In order to overcome the above drawbacks,this thesis couples Bi₂WO₆ with another semiconductor to construct a heterojunction based on appropriate band positions so as to achieve close contact between inorganic semiconductors,promote effective spatial separation of photoexcited charge carriers,and retain photogenerated electrons and holes with higher redox potentials to boost photocatalytic performance.The effects of different ratios on the crystal structure,surface morphology,optical properties,elemental compositions and photocatalytic performance of the materials are investigated as follows:（1）Bi₂WO₆/Bi OCl_xBr_1-x composites are prepared through an ultrasound-assisted two-step solvothermal method.This thesis explores the effects of the ratio of two sodium halides on the energy band,crystal structure,surface morphology and photocatalytic performance.Meanwhile,the crystal structure and microstructure of the samples are analyzed by mesns of XRD and TEM.PL and EIS are used to study the separation of photogenerated carriers.Under visible light（λ>420 nm）degradation of rhodamine B（Rh B）（10 mg/L）,ciprofloxacin（CIP）（10 mg/L）and rifampicin（RFP）（10 mg/L）to analyze the photocatalytic activity of the system.Experiments have shown that the visible light absorption of the prepared Bi₂WO₆/Bi OCl_xBr_1-xheterojunctions photocatalysts is enhanced.Among the photocatalytic degradation experiments of Rh B,CIP and RFP,the degradation rate with Bi₂WO₆/Bi OCl_0.5Br_0.5was 2.14 times higner than that of the original Bi₂WO₆（Rh B）under optimized conditions,with degradation efficiencies of 97.89%,88.86%and 83.45%,respectively.In the photocatalytic reaction h⁺and·O₂^-are the main radicals,which are produced under visible light irradiation and boost the fast degradation of organic pollutants.After five cycles of experiments,the photocatalytic performance and crystal structure of the materials had no significant changes,and the Bi₂WO₆/Bi OCl_0.5Br_0.5 composite has stable photocatalytic degradation activity.（2）Bi₂WO₆/Cs₂Ag Bi Br₆ composites are prepared by simple hydrothermal,ball milling and thermal evaporation methods to boost the absorption range of visible light absorption range and charge separation.The effects of different Bi₂WO₆ contents on the energy band,crystal structure,surface morphology and photocatalytic performance of Bi₂WO₆/Cs₂Ag Bi Br₆ are investigated.The results have shown that the Bi₂WO₆/Cs₂Ag Bi Br₆ exhibit optimal photocatalytic performance when the mass ratio of Bi₂WO₆ to Cs₂Ag Bi Br₆ is 3:1.3D floral sphere Bi₂WO₆/Cs₂Ag Bi Br₆Photocatalyst provide abundant adsorption and catalytic active sites,and enhance the adsorption of Rh B,norfloxacin（NOR）and RFP.The visible light（λ>420 nm）photocatalytic evaluation for ethanol phase removal of Rh B,NOR and RFP showed that degradation efficiencies of Rh B is 97.4%in 6 min,and degradation efficiencies of NOR and RFP are 63.1%and 93.21%respectively in 60 min.·OH and·O₂^-are the important reactive species produced by 3Bi₂WO₆/Cs₂Ag Bi Br₆ Z-type heterojunction in photocatalytic degradation.The degradation efficiency of 3Bi₂WO₆/Cs₂Ag Bi Br₆for Rh B can still reach more than 95%after five cycles of experiments,which indicats that 3Bi₂WO₆/Cs₂Ag Bi Br₆ is an efficient and stable photocatalyst.The heterogeneous structure of double-perovskite Bi₂WO₆/Cs₂Ag Bi Br₆ can achieve close interfacial contact between the components to effectively separate photogenerated carriers and achieve strong visible light absorption.