Controlled Preparation Of Halide Perovskite Based Catalysts And Their Photocatalytic Performances For CO₂ Reduction

Under the background of striving to achieve carbon peak and carbon neutralization as soon as possible and completely solve the energy problem,building an efficient and robust artificial photosynthesis system,mimicking the process of natural photosynthesis,is undoubted one of the most promising strategies to solve the above problems.Recently,metal halide perovskite(MHPs)nanocrystals(NCs)have attracted wide attentions due to their adjustable energy band structures,excellent photoelectric properties and facile preparation processes.However,with its preliminary application in the field of artificial photosynthesis,the lack of catalytic active sites on the surface,the relative deficiency of photogenerated carrier separation and the poor catalytic stability leading to low catalytic activity have also emerged.In order to solve these problems,we proposed some strategies to improve the photocatalytic activity,including surface modification with hydrophobic ligands,transition metal functional doping,Z-scheme heterojunction design,morphology regulation and rich surface defects.It mainly includes the following four parts:(1)In order to solve the problem of the poor stability for MHPs in water-contained system,we have prepared the CsPbBr₃/Cs₄PbBr₆ composite NCs using the short chain hydrophobic molecule heptafluorobutyl acrylate as the ligand,which exhibit good stability in aqueous system.The problem of limited electron transfer between photogenerated electrons and catalytic sites is overcomed by directly doping metal ions on the surface of the NCs.Based on these strategies,we have realized efficient photocatalytic CO₂ reduction with MHPs NCs as photocatalysts in pure water system for the first time in the word.The results show that the strategy based on direct surface metal ion doping not only effectively increases the active sites of photocatalytic reaction,but also greatly shortens the electron transfer distance between the photogenerated carriers in MHPs NCs and the catalytic active sites,leading to a significant improvement of the charge separation efficiency.Further studies show that the strategy of surface doping has good universality to enhance the activity of MHPs based photocatalysts.(2)Considering the poor water oxidation ability of MHPs NCs,we have employed ultra-thin and small-size graphene oxide(USGO)nanosheets as substrate and electronic conductors to construct an efficient CsPbBr₃ based all solid-state Z-scheme heterojunction catalyst(CsPbBr₃/USGO/?-Fe₂O₃),by combing CsPbBr₃ NCs and traditional water oxidation semiconductor(?-Fe₂O₃)based on a simple electrostatic self-assembly method.High resolution TEM and XPS measurements show that CsPbBr₃ and ?-Fe₂O₃ are tightly anchored on USGO nanosheets by forming chemical bond,respectively.The excellent electron transport property of USGO nanosheets endows CsPbBr₃/USGO/a-Fe2O3 with an efficient interfacial charge separation ability.Furthermore,in-situ irradiated XPS measurements show that the interface charge transfer path conforms to the Z-scheme heterojunction mode.Using water as the electron source,CsPbBr₃/USGO/?-Fe₂O₃ heterojunction exhibits significantly enhanced photocatalytic activity for photocatalytic CO₂ reduction,and the corresponding electron consumption rate reaches to 147.6mmol g^-1 h^-1,which is 19times higher than that of single CsPbBr₃ NCs.(3)Considering the light shielding effect caused by the introduction of electronic conductor,we have further constructed a direct Z-scheme heterojunction(LF-FAPbBr₃/?-Fe₂O₃)by the growth of ligand-free MHPs NCs(LF-FAPbBr₃)on the surface of?-Fe₂O₃ nanorods based on the strategy of"solvent assistance,in-situ growth".The direct contact between LF-FAPbBr₃ NCs and ?-Fe₂O₃ without ligand hindrance enhances the interface electron coupling between them,which can promote the efficient interfacial charge transfer between LF-FAPbBr₃ and ?-Fe₂O₃,and the internal charge separation in LF-FAPbBr₃ and ?-Fe₂O₃.The charge separation efficiency(?separation)of LF-FAPbBr₃/?-Fe₂O₃ reaches up to 93%,which is much higher than that of ligand-capped-FAPbBr₃/a-Fe2O3(11%).The electron consumption rate of LF-FAPbBr₃/?-Fe₂O₃ for photocatalytic CO₂ reduction is 175mmol g^-1 h^-1,which is16 times higher than that of L-FAPbBr₃with organic ligand.(4)A novel 3D-calliandra-like CsPbBr₃ nanoflowers(LF-CPB NFs)have been synthesized via a ligand-free seed assisted growth strategy.The resultant nanoscale LF-CPB NFs not only have large specific surface area,but also bring forth many surface Br vacancy defects due to the absence of organic ligand passivation.These defects can capture photogenerated carriers and act as catalytic active centers,which make up for the deficiency of the lack of catalytic sites in traditional MHPs NCs.The anisotropy of the LF-CPB NFs morphology can also improve the dissociation of photogenerated carriers.The electron consumption rate of LF-CPB NFs for photocatalytic CO₂reduction is 7 and 20 times higher than those of traditional organic ligand capped CsPbBr₃ NCs(L-CPB NCs)and CsPbBr₃bulks,respectively.In addition,due to the absence of organic insulating ligands,LF-CPB NFs can be in close contact with TCPP(Fe)cocatalyst,which can significantly accelerate the interfacial charge transfer and further improve the photocatalytic activity.The electron consumption rate of LF-CPB NFs/TCPP(Fe)is 14 times higher than that of L-CPB NCs/TCPP(Fe).