Construction Of Z-Scheme BiOBr/Bi/Bi₂SiO₅ Composite And Its Application In Photocatalystic Reduction Of CO₂

With the continuous development of the industrialization process,energy and environmental issues(such as global warming,floods,etc.)caused by excessive carbon dioxide emissions have attracted widespread human attention.Photocatalytic reduction CO₂ is a green and sustainable technology that uses a semiconductor catalyst to convert carbon dioxide into hydrocarbon fuel under light,thus achieving the carbon cycle.One of the scientific challenges of the new era is how to use solar energy for the resourceful conversion of carbon dioxide,the core of which is the construction of highly efficient photoresponsive catalysts.Therefore,the development and design of new and efficient photocatalytic materials and the construction of efficient and reasonable photocatalytic reaction systems have become the research focus.Bi₂SiO₅ is considered one of the most desirable photocatalysts because of its unique layered structure,excellent stability,good photocatalytic properties and cheap and easy availability.However,Bi₂SiO₅ have shortcomings such as high recombination rate of photogenerated carriers and insufficient photoresponse ability restrict its wide use.In this paper,based on the structural characteristics of the material and the principle of photocatalytic reduction of CO₂,the new catalysts of Bi/Bi₂SiO₅ was prepared by in situ deposition to solve the problems of wide band gap and high photogenerated electron-hole separation rate of Bi₂SiO₅;Secondly,based on the issues of carrier utilisation and photoresponsiveness,the Z-type BiOBr/Bi/Bi₂SiO₅composite catalyst was designed and prepared from the theoretical construction principle.The main research contents and results can be summarized as follows:(1)Preparation and performance of photocatalytic reduction of CO₂ of Bi/Bi₂SiO₅Firstly,using ethylene glycol as the solvent and Na OH(2M)as the p H regulator,a series of Bi/Bi₂SiO₅ composites with different contents of metal Bi were prepared by a simple one-step hydrothermal method.Secondly,as-prepared Bi/Bi₂SiO₅ samples are characterized by XRD,XPS,SEM,HRTEM,BET and UV-vis DRS.The results show that changing the addition amount of Na OH(2M)in the reaction system,the specific surface area of the BSO-13 sample(p H=13)is 57.92 m² g^-1,which is about 1.54 times that of BSO-10(p H=10);at the same time,the content of elemental bismuth in the composite can also be controlled by the Na OH(2M)(for example,the elemental content of bismuth in BSO-13 is about 9.76%).Finally,a series of BSO-X(X=10,11,12,13 and 14)samples were tested for the performance of photocatalytic reduction of CO₂.The experimental results show that BSO-13 has good photocatalytic reduction activity and stability of CO₂(under simulation light,the yield of CO is 438.93?mol·g^-1 after 7 h,which is about 3.3 times that of pure Bi₂SiO₅).According to the experimental phenomenon,an interesting linear relationship between the dissolution amount of metallic Bi and the volume of 2M Na OH is found,which should provide significant theoretical and experimental guidance for the development and research of Bi/Bi-based composite materials.(2)Preparation and performance of photocatalytic reduction of CO₂ of BiOBr/Bi/Bi₂SiO₅The BiOBr/Bi/Bi₂SiO₅ composites was prepared with Bi/Bi₂SiO₅(Na OH dosage 3.8 m L,p H value about 13)as the precursor and nitric acid(6M)as the acid regulator.Under the assistance of ultrasound,the BiOBr/Bi/Bi₂SiO₅ composite was prepared.Firstly,the results show that controlling the ultrasonic time of the reaction process allows the conversion of Bi₂SiO₅ to BiOBr with ultra-thin and highly exposed(110)crystal surfaces.Secondly,a series of samples with different ultrasonic times were subjected to photocatalytic CO₂ reduction activity studies.The results showed that the SBO-20(sample under ultrasound for 20 min)has excellent photocatalytic reduction activity of CO₂(the yield of CO is 1520.04?mol·g^-1 after 7h,which is about 2.85 times that of the precursor).Thirdly,based on the characterization results,the Z-type photocatalytic CO₂ reduction mechanism of BiOBr/Bi/Bi₂SiO₅was proposed.In summary,the new catalyst of BiOBr/Bi/Bi₂SiO₅ has excellent photocatalytic reduction of CO₂ performance,high selectivity and good stability.This work provides certain guidance for the design and preparation of high-efficiency photocatalytic reduction of CO₂ catalysts.