Study On The Construction And Photocatalytic CO₂ Reduction Performance Of Co₃O₄/Cs₂AgBiBr₆ P-n Heterojunction

Photocatalysis technology can realize the conversion of solar energy to other forms of energy under mild conditions,which is an important mean to deal with the increasing shortage of energy.Among them,using solar energy to convert CO2 into high value-added chemicals over catalysts can effectively alleviate energy crisis and reduce the concentration of atmospheric greenhouse gas,which has a good application prospect in the field of solar energy utilization and ecological protection.The current international competition in this field is focused on the development of high efficiency and low-cost catalysts.Metal halide perovskite materials have attracted extensive attention in the field of photocatalytic CO2 reduction in recent years,due to their good light-harvesting ability and low cost.However,the photocatalytic CO2 reduction efficiency of metal halide perovskite materials is still low due to the disadvantages of weak water oxidation capacity and insufficient photogenerated carrier separation.In order to improve the CO2 reduction activity of n-type lead-free halide perovskite photocatalyst,this thesis focuses on the construction of p-n type heterojunction and the modulation of interfacial charge transfer kinetics as follows by introducing p-type water oxidation semiconductor:(1)Firstly,traditional n-type Cs2AgBiBr6 nanosheets with surface ligands were synthesized by hot injection method,and combined with p-type water oxidation semiconductor Co3O4 nanosheets by electrostatic attraction to construct a series of p-n heterojunctions of Co3O4/Cs2AgBiBr6.Thermodynamic and photophysical studies shown that the interface between p-type Co3O4 and n-type Cs2AgBiBr6 forms a built-in electric field from Cs2AgBiBr6 towards Co3O4,which is conducive to the transfer of photogenerated electrons from the conduction band of Co3O4 to the valence band of Cs2AgBiBr6.Therefore,the photomenerated carriers of Co3O4/Cs2AgBiBr6 are separated by Z-scheme charge transfer pathway.Compared with Cs2AgBiBr6,Co3O4/Cs2AgBiBr6 not only exhibits effectively improved photogenerated carrier separation efficiency,but also possesses stronger oxidation capacity of photogenerated holes.Using CO2 and water as raw materials,the photocatalytic CO2 reduction performance of Co3O4/Cs2AgBiBr6 heterojunction is significantly improved,and the electron consumption rate reaches 232.4 μmol g-1 h-1,which is 7.4 and 48.4 times higher than those of the individual Cs2AgBiBr6 and Co3O4 nanosheets,respectively.(2)Considering that the obstruction of ligands on the surface of traditional Cs2AgBiBr6 nanomaterials is not conducive to the interfacial charge transfer of heterojunction,porous Co3O4(p-Co3O4)were further prepared by sacrificial template method and employed as substrate to grow ligand-free Cs2AgBiBr6 in situ.A series of p-Co3O4/Cs2AgBiBr6 heterojunctions were successfully constructed.The results of studies shown that the photogenerated carriers of p-Co3O4/Cs2AgBiBr6 heterojunction are also effectively separated by Z-scheme charge transfer pathway,and the photogenerated electrons and holes are accumulated on the conduction band of Cs2AgBiBr6 and the valence band of p-Co3O4,respectively.Compared with Co3O4/Cs2AgBiBr6 heterojunction,p-Co3O4/Cs2AgBiBr6 features a stronger interfacial electron coupling,thus the photocatalytic CO2 reduction performance of pCo3O4/Cs2AgBiBr6 is further improved with an electron consumption rate of 501.0μmol g-1 h-1.