Study On The Preparation And Photoreduction CO₂ Performance Of Halide Perovskite Based Composite Catalysts

Energy crisis and environmental pollution are two major challenges for the sustainable development of human.Simulating artificial photosynthesis,converting abundant solar energy into chemical energy is one of the effective means to solve energy and environment problems.Recently,lead halide perovskite（LHPs）nanomaterials have attracted extensive attentions in the field of artificial photosynthesis due to their advantages of low cost,high absorption coefficient,long carrier lifetime and easily regulated energy band structures.However,their stability is poor in water or other polar solvents,due to the ionic properties of LHPs nanomaterials themselves.Moreover,they also have the disadvantages of less intrinsic catalytic sites and insufficient photogenerated carrier separation efficiency,resulting in low photocatalytic CO₂reduction performance.In order to improve the activity and stability of photocatalytic CO₂ reduction of LHPs nanomaterials,this thesis focuses on the structural modulation and construction of heterojunctions and their charge transfer dynamics as follows:（1）Considering the problem of poor stability of lead-based halide perovskite in water-containing system and fast crystallization kinetics,we adopted the strategy of"sequential deposition,in-situ growth"to encapsulate methylamine lead iodine（MAPbI₃）quantum dots（QDs）in the pores of iron porphyrin-based metal-organic framework material（PCN-221（Fe））.A series of MAPbI₃@PCN-221（Fe_x）（x=0～1）composite catalysts were successfully constructed.It is shown that the stability of MAPbI₃ QDs is significantly improved by the protection of PCN-221（Fe）.In addition,the close contact between the QDs and the active site Fe facilitates the rapid transfer of photogenerated electrons from QDs to the catalytic site.Using water as the electron source,MAPbI₃@PCN-221（Fe_x）（x=0～1）composite catalysts exhibit significantly enhanced activity for photocatalytic CO₂ reduction.The total yield of CO and CH₄ with MAPbI₃@PCN-221(Fe_0.2)as photocatalyst reaches up to 1559μmol g^-1 after 80 h of illumination.The corresponding electron consumption rate is 112μmol g^-1 h^-1,which is the 38 times higher than that of pristine PCN-221(Fe_0.2).（2）It is known that 2D halide perovskite nanosheets usually feature better stability with respect to LHP nanocrystals in the water-contained system,thus we prepared ultra-thin CsPbBr₃ nanosheets by room temperature method.Compared with traditional CsPbBr₃ nanocrystals,it is found that ultra-thin CsPbBr₃ nanosheets exhibit superior photocatalytic activity,owing to a large proportion of low coordination metal atoms and a short carrier diffusion distance.In addition,CsPbBr₃ nanosheets possess improved stability compared to CsPbBr₃ nanocrystals in the reaction system containing water.In order to enhance the absorption of CsPbBr₃ nanosheets in visible light region,we constructed a series of CsPs Br_3-xI_x（x=0.3,0.6,0.9）catalysts via surface halogen exchange.Using water as the electron source,the photocatalytic CO₂-to-CO yield of CsPbBr_2.4I_0.6 nanosheets is 43.9μmol g^-1 h^-1 in the gas-solid reaction system.The corresponding electron consumption rate is 87.8μmol g^-1 h^-1,which is 7 times higher than that of traditional CsPbBr₃ nanocrystals.（3）In order to improve the photogenerated carrier separation efficiency and water oxidation ability of CsPbBr₃ nanosheets,we combined water oxidation catalyst Sn S₂nanosheets with ultra-thin CsPbBr₃ nanosheets to prepare a series of Z-scheme heterojunction catalysts CsPbBr₃/Sn S₂-X（X=1,2,3,4）through electrostatic self-assembly.Microstructural characterization confirmed that CsPbBr₃ and Sn S₂ were closely bonded in S-Pbmode.Further photophysical measurements shown that the photogenerated carriers of CsPbBr₃ and Sn S₂ are efficiently separated by Z-scheme charge transfer pathway.With water as the electron source,compared with CsPbBr₃nanosheets,CsPbBr₃/Sn S₂-X（X=1,2,3,4）heterojunctions exhibit significantly enhanced photocatalytic CO₂ reduction activity in gas-solid reaction system.The electron consumption rate of CsPbBr₃/Sn S₂-2 heterojunction reaches up to 151.2μmol g^-1 h^-1,which is 3.5 times and 31.9 times higher than those of CsPbBr₃ nanosheets and Sn S₂ nanosheets,respectively.（4）Considering that the interface charge transfer of heterojunctions constructed by electrostatic self-assembly method is often limited by the hindrance of surface ligands,we proposed a strategy for the in-situ construction of ligand-free halide perovskite heterojunctions.We prepared PbI₂ nanosheets and employed it as substrate to construct a series of II-type heterojunction catalysts of PbI₂/CsPbBr₃-X（X=1,2,3,4）,by depositing ultra-thin 2D CsPbBr₃ nanosheets on the surface of PbI₂ via in-situ partial conversion.Benefitting from the close contact interface of PbI₂/CsPbBr₃,the photogenerated carriers in theⅡ-type heterojunction can be transferred and separated rapidly through double charge transfer pathway.Without using any sacrificial reagents,PbI₂/CsPbBr₃-X（X=1,2,3,4）heterojunction catalysts exhibit superior photocatalytic performance.The electron consumption rate of Co_0.05-PbI₂/CsPbBr₃ for photocatalytic CO₂ reduction to CO reaches up to 1204μmol g^-1 h^-1,which is 27.9 times higher than that of pure thin 2D CsPbBr₃ nanosheets.