Study On The Modifications Of Inorganic Perovskites And Photocatalytic CO₂ Reduction

The overexploitation of fossil fuels and the release of carbon dioxide（greenhouse gas）,are the most austere problems in human society.Converting carbon dioxide into usable energy through solar energy can not only reduces carbon dioxide emissions,but also reduces the use of fossil fuels,which is considered as a promising strategy.As a new type of semiconductor materials,metal halide perovskite is a promising candidate for photocatalyst,because of their many attractive properties,suah as wide absorption range,high extinction coefficient,and long electron hole diffusion length.In addition,most perovskites have appropriate conduction band and valence band edge,which can meet the thermodynamic requirements of catalytic reduction of CO₂.The application of optoelectronics has aroused great research interests.In addition,the photoelectric conversion efficiency of perovskite solar cells has reached 22.1 percent.Stimulated by the achievements of solar cells,halide perovskite materials have made great stride in photocatalysis.However,the catalytic performance of perovskite is still low,which is mainly due to the serious carrier recombination in the perovskite and the low chemical stability of perovskite in the catalytic process,which limit its practical application.In view of the above problems,this work focus on reducing the photogenerated charge carrier recombination,improving the charge carrier transport dynamics of perovskite by combining perovskite with other semiconductors and surface ligand treatment,thereby improving the photocatalytic CO₂reduction performance of perovskite.The specific research contents are as follows:（1）Firstly,high quality CsPbBr₃ QDs was synthesized by heat injection method,and then combined with Bi₂WO₆ nanosheets to form Z-Scheme heterojunction for photocatalytic CO₂ reduction.Here,the 0-dimensional CsPbBr₃ quantum dots/2-dimensional Bi₂WO₆（CPB/BWO）nanosheets heterojunction was first constructed by a simple ultrasonic composite method for photocatalytic CO₂ reduction.The CsPbBr₃/Bi₂WO₆photocatalyst has excellent photocatalytic performance,and the total yield of CO₂reduction to CH₄/CO is 503μmol·g^-1,which is about 9.5 times of the photocatalytic efficiency of the original CsPbBr₃.In addition,CPB/BWO heterojunction also showed good stability in the photocatalytic reaction process.The mechanism of charge transfer in CPB/BWO direct Z-Scheme heterojunction was investigated and verified by various technical means.Since the photoexcited carriers in the CPB/BWO heterojunction can not only carry out effective space charge separation,but also have strong oxidation and reduction ability,so the photocatalytic performance is improved.A direct Z-Scheme heterojunction photocatalytic system based on metal halide perovskite was reported in this paper.The proposed new strategy significantly enhances the catalytic activity of photocatalysts,which may bring new opportunities for the development of metal halide perovskites.（2）A facile approach to modify the surface defects of CsPbBr₃ QDs was demonstrated using tetrafluoroborate salts（BF₄^-）as defects treatment agent and loading Co²⁺as a co-catalyst.Most of the reported metal halide perovskites based photocatalysts showed relativly low photocatalytic CO₂ reduction activity due to the severe surface defects.The inevitable surface defects may induce serious charge recombination and play a deleterious role in photocatalysis applications.Herein,we demonstrated a facile approach to modify the surface defects of CsPbBr₃QDs using tetrafluoroborate salt as a surface treatment agent for photocatalytic CO₂reduction.The surface defects and capping ligands are effective eliminated by BF₄^-treatment.As a result,high efficient photocatalytic CO₂reduction reaction was achived under visible light irradiation.Further,loading optimum amount of Co²⁺as co-catalyst on the modified surface of CsPbBr₃resulted in dramatically improved the photocatalytic CO₂reduction,indicating the advantages of synergistic effect of the surface engineering.This work provides a facile approach to modify the surface defects of the CsPbBr₃QDs for high efficient photocatalytic CO₂reduction and broadens the photocatalytic applications of halide perovskites.An in-depth understanding of the surface modification on the perovskite QDs would bring us new opportunities in photocatalysis.Finally,summary and outlook.The problems and opportunities faced by the further development of perovskite materials as photocatalysis are analyzed.