Design And Preparation Of Zinc Cadmium Sulfide-based Semiconductor Catalyst And Its Photocatalytic Water Splitting Performance For Hydrogen Production

Photocatalytic hydrogen production using solar energy has great potential to solve energy shortages,and semiconductor materials stand out among photocatalytic materials due to their wide photoresponse range and suitable energy band positions.However,most semiconductor materials have problems such as photocorrosion and low efficiency,so it is of great practical significance to design and prepare efficient and stable semiconductor photocatalysts.Cd S and Zn S have been widely studied in photocatalysis as typical sulfide semiconductors,but Cd S suffers from severe photocorrosion and low charge separation efficiency under strong light irradiation,Zn S has a low response to visible light due to its large band gap（3.66 e V）,and these disadvantages seriously affect its photocatalytic activity and potential applications.As a solid solution material of Zn S and Cd S,Cd_1-xZn_xS can effectively avoid these disadvantages.For example,the light response range is wide,and the size of the band gap can be adjusted by the molar ratio of Zn and Cd.In this paper,the photocatalytic hydrogen evolution activity was improved by modifying Cd_0.5Zn_0.5S solid solution and constructing a heterojunction,and the reaction mechanism of photocatalytic hydrogen evolution was discussed.The main research contents and conclusions are as follows:1.Research the p H of precursor reaction solution on the crystal phase,morphology and catalytic activity of the Cd_0.5Zn_0.5S solid solution.The results show that the pure hexagonal Cd_0.5Zn_0.5S solid solution is easier to form under alkaline conditions.Under the condition that the p H of the precursor solution is 10,the obtained CZS10（p H=10）nanoparticles have smaller size,more uniform particles,larger specific surface,wider light absorption range,and more suitable band gap.The photocatalytic activity test found that the hydrogen production rate of CZS10 was as high as 28.47 mmol g^-1h^-1 under the irradiation of simulated sunlight,which was 5.9times that of CZS7(Cd_0.5Zn_0.5S without p H adjustment,4.83 mmol g^-1h^-1).A series of photo-electrochemical tests prove that CZS10 has higher charge separation efficiency and higher reducing ability.2.Based on the research in the first part,a series of CZS10/Zn O heterojunction catalysts with different molar ratios were successfully prepared by hydrothermal method.It was found that the hydrogen production rate of of the best catalyst 20%CZS10/Zn O was 40.14 mmol g^-1h^-1,which was 31.9 times and 1.4 times that of pure Zn O and CZS10,respectively,and the apparent quantum yield is 22.8%at 420 nm wavelength.The results show that the CZS10/Zn O heterojunction has a wide photoresponse range and high electron-hole separation efficiency.ESR and M-S test results show that the charge transfer path of CZS10/Zn O heterojunction catalyst belongs to the direct Z-Scheme heterojunction photocatalytic system.3.Three-dimensional ordered macroporous Zr O₂ was synthesized by colloidal template method and 3DOM-Zr O₂/Cd_0.5Zn_0.5S（Zr3D/CZS10）heterojunction material was prepared by hydrothermal method for the first time.It is found that the three-dimensional macroporous structure effectively improves the charge transport of the heterojunction catalyst.The photocatalytic test results show that 2Zr3D/CZS10has the highest hydrogen evolution performance,up to 83.12 mmol g^-1h^-1,which is214 times and 2 times that of pure Zr O₂ and CZS10 under the same light intensity,respectively.The apparent quantum yield at 450 nm wavelength is 44%.According to the band positions and ESR results,a possible photocatalytic mechanism is proposed.When simulated sunlight irradiates Zr3D/CZS10,the photogenerated electrons in the conduction band of Zr O₂ migrate to the valence band of Cd_0.5Zn_0.5S and recombine with their photogenerated holes,while the electrons left in the conduction band of Cd_0.5Zn_0.5S undergo a reduction reaction,and the holes left in the valence band of Zr O₂ undergo an oxidation reaction and are continuously consumed by the sacrificial agent.This charge transfer method effectively inhibits the recombination of electron-hole pairs in Zr O₂ and Cd_0.5Zn_0.5S,greatly improves the catalytic activity of Cd_0.5Zn_0.5S,and provides a reference for the application of three-dimensional ordered macroporous zirconia materials in the field of photocatalytic hydrogen production..