Synthesis Of Cadmium Sulfide-based Composite Materials And Study Of Their Photocatalytic Hydrogen Production Performanc

In order to reduce fossil energy consumption and improve the ecological environment of the earth,scientists have tried to solve the problem of energy shortage and environmental pollution by studying semiconductor photocatalysis technology in recent decades.Among them,developing efficient photocatalyst is the key to solve these problems.Semiconductor CdS not only has a suitable band structure,but also has the good visible light response range.The element content of CdS is rich and the synthesis cost is low,so its application in the field of photocatalytic hydrogen production shows great prospects.However,the active sites of CdS are insufficient in the photocatalytic hydrogen production reaction,and the photogenerated electrons and holes are easy to recombine.At the same time,CdS becomes unstable in the long reaction process due to the effect of photocorrosion.In order to solve the above problems,the method of constructing Schottky junction and wrapping anti-corrosion layer is adopted,Ni₃S₄/CdS and NiCo₂S₄/CdS@Al₂O₃ composites were designed respectively,and their photocatalytic hydrogen production in water decomposition was studied.The contents of the study and the main conclusions are as follows:（1）The composite Ni₃S₄/CdS with Schottky junction was synthesized by a simple hydrothermal method.The composite was characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Scanning electron microscopy（SEM）and High-resolution transmission electron microscopy（HRTEM）.It was found that the visible light absorption capacity of Ni₃S₄/CdS was enhanced compared to that of CdS.At the same time,the photocatalytic hydrogen production performance of Ni₃S₄/CdS was tested.The molar ratio of Nito Cdwas 1:5,and the hydrogen production rate reached 40.8mmol·g^-1·h^-1,which was 11 times higher than that of pure CdS.By analyzing the results of UV-visible diffuse reflection spectroscopy（DRS）,Photoluminescence spectroscopy（PL）,photochemical tests,and theoretical calculations based on first principles,the improved hydrogen production performance can be attributed to the formation of Schottky junction,which facilitates the separation and transfer of photogenerated carriers.（2）Photocatalyst NiCo₂S₄/CdS@Al₂O₃with a metal-insulator-semiconductor（MIS）structure was synthesized by multi-step hydrothermal reaction.And thin Al₂O₃shells with different thicknesses were prepared on the surface of CdS by adjusting the mass ratio of Al₂O₃to CdS.The characterization by XRD,XPS,SEM,HRTEM and Fourier transform infrared spectrometer（FTIR）showed that NiCo₂S₄/CdS@Al₂O₃composite photocatalyst was successfully prepared.The results showed that 1%-NiCo₂S₄/CdS@Al₂O₃photocatalyst showed best photocatalytic hydrogen production performance under the synergistic effect of CdS,Al₂O₃and NiCo₂S₄,and the hydrogen production rate reached 46.3 mmol·g^-1·h^-1,which was 14 times that of pure CdS.By analyzing the test results of DRS,PL and photoelectrochemistry and theoretical calculation based on first principles,the possible role of ultra-thin Al₂O₃in the overall structure of photocatalyst was put forward,and the mechanism of photocatalytic hydrogen production of NiCo₂S₄/CdS@Al₂O₃ composite was expounded.