Study On The Construction Of CdS-based Photocatalysts And Its Photocatalytic Decemposition Of Water For Hydrogen Evolution

With the excessive collection and utilization of fossil energy,human beings are faced with more and more serious energy crisis and environmental pollution problems.It is urgent to find a new energy that can effectively replace fossil energy.Hydrogen energy,as a new energy with high calorific value,clean combustion products and easy transportation,can effectively replace fossil energy.Hydrogen production by using solar energy to decompose water is an effective way to convert solar energy into chemical energy,and this process ensures the source and product of hydrogen production process clean.As one of the photocatalysts,CdS has been widely studied in the field of photocatalysis because of its ideal energy band structure.However,sole CdS still has many defects,such as sluggish photogenerated electron transfer rate,low photogenerated electron hole separation efficiency and serious photocorrosion,which seriously affects its practical application in photocatalyst decomposition of water for hydrogen production.In order to solve the problems of sole CdS,it was modified to synthesizeα-Nis-β-Nis/CdS binary composite photocatalyst.By introducing cocatalyst,the light absorption performance and the photogenerated electron transfer rate of the photocatalytic system were improved.On this basis,the ternary composite photocatalyst NH₂-UIO-66/α-Nis-β-Nis/CdS was synthesized by introducing MOF to further improve the separation efficiency of the photo electron-hole pair.The transfer mode of the photo electron-hole pair in the composite photocatalyst and the effect of the organic ligand in MOF on the photocatalytic activity of the composite photocatalyst were studied.The following research contents are specifically completed:（1）Theα-Nis-β-Nis/CdS binary composite photocatalyst was successfully synthesized by simple combination of hydrothermal and solvothermal method.The existence of bothαphase andβphase of the prepared NiS was confirmed by XRD and HRTEM.The results showed that the photoabsorption performance of the composite photocatalyst was significantly improved after introducedα-NiS-β-NiS,and the photochemical characterization of EIS,PL and I-T proved that the binary composite photocatalyst could effectively improve the photoelectron transfer and the separation rate of the photo electron-hole pair.The hydrogen production rate of binary composite photocatalyst with the best ratio was 7.05 mmol·h^-1·g^-1,while the hydrogen production rate of single CdS was 1.87 mmol·h^-1·g^-1.The hydrogen production rate of binary composite photocatalyst was 3.77 times that of single CdS.（2）The ternary composite photocatalyst NH₂-Ui O-66/α-NiS-β-NiS/CdS was synthesized by solvothermal method on the basis ofα-NiS-β-NiS/CdS.The effects of organic ligands on the energy band structure of metal-organic-frameworks materials and the photocatalytic mechanism of the composite photocatalyst were studied by changing the organic ligands in the synthesis process of metal-organic-frameworks materials.Research have shown that the UV-Vis absorption ability of metal-organic-frameworks with different organic ligands is different,and the change of organic ligands will greatly affect its light absorption cutoff edge,resulting in the change of the band gap of metal-organic-frameworks material.At the same time,the change of organic ligands will affect the valence band of metal-organic-frameworks material,which has a great influence on the photocatalytic mechanism of the composite photocatalyst.Through XPS,M-S,EPR and UV-vis DRS characterization,it is proved that NH₂-Ui O-66 can form an effective Z-type structure withα-NiS-β-NiS/CdS.The establishment of Z-scheme structure can effectively improve the separation rate of photogenerated electron and hole pair and the transfer rate of photogenerated carrier,so as to improve the photocatalytic performance.Thephotocatalyticdecompositionrateof NH₂-UIO-66/α-NiS-β-NiS/CdS was 17.88 mmol·h^-1·g^-1,which was 2.5 times and 7.9 times higher than that of binary composite photocatalyst and CdS alone,respectively.