Controlled Construction Of Double-Perovskite Cs₂AgBiBr₆ Heterojunction And Its Photocatalytic Performance

With the acceleration of human development and industrialization,global environmental pollution and energy shortage restrict the sustainable development of human economy and society.Clean and efficient photocatalytic technology uses solar energy to break down harmful substances into non-toxic substances or convert CO₂ into chemical energy for storage and use.However,limited visible light absorption range,low carrier separation efficiency,high cost,and short life span lead to few photocatalysts that meet the requirements of practical applications.Therefore,measures should be taken to improve the photocatalytic performance of photocatalysts.At present,doping metal or non-metal ions,supporting cocatalyst and constructing heterojunction are the main methods for the modification of semiconductor materials.In recent years,lead-free halide double perovskite Cs₂AgBiBr₆ with excellent photochemical properties has made important progress in photocatalysis.However,due to the easy recombination of photogenerated carrier Cs₂AgBiBr₆,the available charge is not much and the slow redox kinetics hinders the photocatalytic reactivity,which limits its further application in the field of photocatalysis.Therefore,this paper improved it by constructing heterojunction method,and studied its performance as photocatalytic degradation of pollutants and carbon dioxide reduction.Through the construction of heterojunction,the absorption capacity of light is improved and the separation of photogenerated carrier is promoted,so as to realize the efficient utilization of solar energy.The research of this paper is mainly divided into the following two aspects:（1）The method of constructing heterojunctions was used to improve the efficiency of photogenerated charge separation while broadening the absorption range of semiconductor materials for light.2D nanosheet WO₃ was first synthesized by hydrothermal method,and then 2D nanosheet WO₃ was added to the synthesis of Cs₂AgBiBr₆ by in situ self-assembly method,and 2D nanosheet WO₃ was loaded on the surface of Cs₂AgBiBr₆ crystal during the growth of Cs₂AgBiBr₆ crystal to form a heterojunction with strong interfacial connection.The efficient and tight interface between the Cs₂AgBiBr₆/WO₃ composites was characterized by XPS tests through the formation of chemical bonds,which promoted the charge transfer and the formation of Z-scheme heterojunctions.UV-vis absorption spectroscopy revealed that the formation of heterojunctions extended the light absorption range and promoted the photogenerated charge generation.The superoxide radical and hydroxyl radical were proved to be the main active species by radical trapping experiments and ESR techniques,and the electron transfer mode of Cs₂AgBiBr₆/WO₃ composites was demonstrated to be due to the formation of Z-scheme heterojunctions.In addition,by liquid chromatography-mass spectrometry,we investigated the possible intermediate processes of degradation of methyl orange and rhodamine B.Through a series of studies,we proposed the photocatalytic degradation mechanism of Z-scheme heterojunction Cs₂AgBiBr6/WO₃.（2）The method of electrostatic self-assembly was used to construct heterojunctions to improve the tightness of the interface and the separation efficiency of the photogenerated charges of the two semiconductor materials.Firstly,Cs₂AgBiBr₆ crystals and Bi₂WO₆ultrathin nanosheets were prepared by crystallization method and simple hydrothermal method,respectively,and the surface charges of both were detected by zeta potential test to provide a theoretical basis for the synthesis process of electrostatic self-assembly.For the thermally assisted photocatalytic CO₂ reduction,we analyzed the suitable conditions for the introduction of thermal energy using thermogravimetric analysis.In addition,to further verify the superiority of Cs₂AgBiBr₆/Bi₂WO₆ composites as photocatalytic materials,we also performed photocatalytic degradation of methyl orange and found that the Cs₂AgBiBr₆/Bi₂WO₆ composites exhibited excellent degradation activity and maintained good cycling stability.The active species affecting the pollutant degradation was demonstrated by radical trapping experiments,and through a series of studies,we proposed the corresponding photocatalytic mechanism of Cs₂AgBiBr₆/Bi₂WO₆ heterojunction.