Study On The Surface Modification And Photocatalytic CO₂ Reduction Property Of CsPbBr₃ Nanocrystals

Energy is one of the three pillars for the development of human society,which is the driving force of the continuous development of society.The widespread use of fossil energy such as coal,oil and natural gas has greatly improved the living standard for the humanity.However,the massive use of fossil energy has also led to a series of problems,such as environmental pollution and climate change.In addition,the non-renewable nature of fossil energy has also led to human concerns about energy exhaustion in the future.In order to solve the above-mentioned energy and environmental problems faced by the development of human society,the development of new clean and renewable energy has become a global research hotspot.As a kind of abundant and clean energy,solar energy is expected to replace fossil energy to meet the energy requirement of human beings.Through the means of photocatalysis,employing low-cost and efficient catalyst to reduce CO₂ to high value-added chemicals or fuels,namely solar energy to chemical energy conversion,is considered to be one of the ideal choices to solve the problems of energy depletion and greenhouse gas effect.Halide perovskite nanocrystal（NC）materials,which have emerged in recent years,have great application potential in the field of photocatalytic CO₂ reduction due to their unique advantages in preparation cost,generation and transport of photogenerated carriers,and defect tolerance that are incomparable to other traditional catalysts.However,the lack of sufficient active sites for halide perovskite photocatalysts and insufficient separation of photogenerated carriers have been the bottleneck restricting their development in the field of photocatalysis.This thesis has carried out the following exploration works around the above issues:（1）Doping cocatalysts by cation-exchange is hard to achieve for halide perovskite NCs owing to the stable octahedron of[Pb X₆]^4-consisted of halogen and lead.Herein,we have successfully developed a simple and efficient method for cation doping of Cs Pb Br₃ nanocrystals by replacing partial Br^-with acetate（Ac^-）.The results show that a small amount of Ac^-instead of Br^-does not change the crystal structure of halide perovskite.Owing to the weaker interaction between acetate and lead in comparison with bromide,the corresponding octahedron structure containing acetate can be easily opened to realize efficient cation-exchange.Compared with traditional Cs Pb Br₃ nanocrystals,the doping amount of Ni²⁺in Cs Pb Br₃ nanocrystals prepared based on this method is significantly increased,resulting in higher charge separation efficiency.The CO generation rate of this nanocrystal reaches up to 44.09μmol g^-1 h^-1,which is over 8 and 3 times higher than those of traditional pristine Cs Pb Br₃ and nickel doped Cs Pb Br₃ NC,respectively.（2）Considering that the presence of ligands on the surface of the halide perovskite NCs is not conducive to the charge transfer at the heterojunction interface,we have utilized holey graphitic carbon nitride（g-C₃N₄）nanotube as the substrate and employed the spatial confinement effect of its pore structure to successfully prepare ligand-free Cs Pb Br₃ NCs through simple slow recrystallization approach.The absence of surface ligands enables close contact and strong electronic coupling between Cs Pb Br₃ and g-C₃N₄,which significantly accelerates the interfacial electron transfer between Cs Pb Br₃ and g-C₃N₄.The resultant enhanced efficiency of photogenerated carrires endows Cs Pb Br₃/g-C₃N₄ heterojunction with remarkably increased photocatalytic activity for CO₂ photoredution.In the absence of sacrificial reagents,the yeild of CO₂-to-CO converstion of Cs Pb Br₃/g-C₃N₄ reaches up to 103.60μmol g^-1h^-1,which is almost 20 and 6 times over those of tranditional Cs Pb Br₃ NCs with ligand capping（L-Cs Pb Br₃）and corresponding L-Cs Pb Br₃/g-C₃N₄ heterojunction.