The Optical Properties Regulation And Photocatalytic Application Of Lead-free Perovskite Materials

Since the industrialization of human society,CO₂ emissions have continued to increase,and the trend of global warming has become increasingly severe.Using photocatalytic technology to reduce CO₂ storage and emissions is increasingly important for the development of human society.Photocatalytic technology uses solar energy as the energy source to drive the semiconductor materials to produce hydrogen,degrade pollutants and synthesize organic compounds.Metal halide perovskite material is a kind of photocatalyst with great potential,which has the advantages of wide absorption range,adjustable band gap,high absorbance coefficient,long carrier transport distance,low cost and easy preparation.However,the humidity sensitivity of the material and the toxicity of heavy metal Pb greatly limit the scope and conditions of application of photocatalysts.In response to the above problems,this paper uses low-toxic or non-toxic Sb³⁺,Pd⁴⁺ions to replace Pb²⁺and halogen regulation,which greatly improves the stability of the material,adjusts the position of the material conduction band and the light absorption range,and reduces the harm of catalyst to the environment.Thereby,those results improve the photocatalytic performance of perovskite.The main conclusions are as follows:1.First,we investigated a perovskite structure Cs₃Sb₂X₉(X=Br,I).The hexagonal system of mixed halogenated perovskite crystal Cs₃Sb₂(Br_xI_1-x)₉(x=1,0.8,0.7,0.6,0)was prepared at room temperature,and its energy band position met the thermodynamic requirements of photocatalytic reduction of CO₂.By optimizing the ratio of Br and I in perovskite material,the position of valence band can be changed,which has a significant effect on the photocatalytic performance.A series of materials have good visible light absorption performance and stability.Under visible light,the mixed halide perovskite shows excellent photocatalytic efficiency of CO₂.The optimized catalyst Cs₃Sb₂(Br_0.7I_0.3)₉ possesses average electron consumption rate of 18.47?mol/g/h.2.On the basis of the Cs₃Sb₂Br₉ excellent photoreduction performance,further research on its oxidizing ability.The effect of the synthesis temperature on the activity of the Cs₃Sb₂Br₉ catalyst for selective oxidation of benzyl alcohol to benzaldehyde was investigated.The optimal reaction temperature was obtained,and the conversion of benzyl alcohol under 8 h visible light irradiation could reach 80%.A series of physical and chemical methods were used to detect the structure and optical properties of the prepared photocatalyst.3.The ligandless Cs₂Pd Br₆ perovskite microcrystas and nanocrystals were prepared by means of confining palladium in the perovskite structure at room temperature,the effect of long chain ligand oleic acid and oleamine on CO₂photocatalysis was eliminated.The particle size of perovskite does not affect the crystal structure of Cs₂Pd Br₆ perovskite,but greatly changes its physical properties,which has a significant effect on the catalytic performance.The experimental results show that the average photocatalytic electron consumption rate of Cs₂Pd Br₆ perovskite nanocrystals is49?mol/g/h,which is higher than that of the traditional single perovskite structure.