Study On The Stability Of Halide Perovskite Nanocrystals For Photocatalytic CO₂ Reduction

As humans’demand for energy grows rapidly,so do the emissions of CO₂ and other greenhouse gases.This not only causes the energy crisis,but also brings a battery of environmental problems.By simulating photosynthesis of plants,developing efficient artificial photosynthesis system can contribute to effectively alleviate energy crisis and reduce greenhouse gas content in the atmosphere.To date,there are two main problems in artificial photosynthesis technology:catalysts with high active depend on using precious metals,and slow kinetics of water oxidation necessitates the use of expensive electron sacrifice agents.Therefore,the development of high efficiency and low-cost artificial photosynthesis catalyst is the core problem to be solved urgently.Metal halide perovskite（MHP）nanocrystals（NCs）materials provide an important choice for the development of efficient and low-cost photocatalytic CO₂ reduction catalysts due to their low material preparation cost,easy tailoring of energy levels,high defect tolerance and excellent photoelectric properties.However,MHP materials also have some disadvantages.On the one hand,the ionic crystal structure determines that it is very sensitive to polar solvents such as water,which affects the stability of the photocatalytic CO₂ reduction.On the other hand,the lack of highly catalytic active sites on the surface and the inadequate separation of photogenerated carriers lead to lower catalytic activity.Focusing on the above problems,this thesis has carried out the following two exploratory works based on in-situ coating strategy:（1）:In order to improve the stability of MHP materials in water-contained reaction system,we first take inorganic CsPbBr₃ NCs as the object,and form an ultrathin Pb SO₄protective layer on their surfaces by introducing inorganic sulfate ions.The results show that the stability of the CsPbBr₃/Pb SO₄ composite material in the artificial photosynthesis system with CO₂ and H₂O as raw materials is significantly improved compared with the pristine CsPbBr₃ NCs,which is mainly due to the good water resistance of Pb SO₄.In addition,ultrathin Pb SO₄ shell has no obvious effect on charge transport,and the photocatalytic activity of CsPbBr₃/Pb SO₄ composite is well maintained.（2）:It is known that PbSO₄ and other insulating layers cannot improve charge separation of MHP NCs effectively.To further improve the photocatalytic activity of MHP NCs for CO₂ reduction,FAPb Br₃ NCs,which has wider visible light response than CsPbBr₃,were taken as the research object,and Pb I₂ thin layers were formed on the surfaces of FAPb Br₃ NCs by a simple Zn I₂ isopropyl alcohol treatment.Experimental results show that the as prepared FAPb Br₃/Pb I₂ composite exhibits superior stability in the artificial photosynthesis system with CO₂ and H₂O as raw materials under the protection of Pb I₂ layer.More importantly,a heterojunction was formed between Pb I₂ and FAPb Br₃,which significantly improves the photocarrier separation efficiency,bringing forth a remarkable improvement of CO₂ photoreduction efficiency.In the absence of organic sacrificial agents,the electron consumption yield of FAPb Br₃/Pb I₂ for photocatalytic CO₂ reduction can reach to 2053μmol g^-1 after 70h of illumination,which is 7-fold over that of sole FAPbBr₃ NCs.