Controllable Preparation Of Surface Modified Sulfur-zinc-cadmium Catalyst And Mechanism Of Hydrogen Production From Photocatalytic Water Splitting

Environmental crisis and energy crisis are the major problems at present.In this context,the development of environmentally friendly,carbon-free renewable clean energy to replace fossil fuels is a very forward-looking topic.In the context of China’s"dual carbon"policy,the development of green technology is appropriate.As we all know,Photocatalytic water splitting technology can achieve the conversion of solar energy to chemical energy.The core of achieving efficient conversion solar energy-chemical energy is the development and applications of the high activity,high stability and high selectivity catalysts.Therefore,it is very important to understand the structure-performance relationship between catalysts and their catalytic activity.In recent years,the solid solution Sulfur-Zinc-Cadmium(Cd_0.5Zn_0.5S)has been widely used in the field of photocatalysis driven by solar energy,due to its suitable band gap and adjustable position of conduction band and valence band.In this thesis,Cd_0.5Zn_0.5S（CZS）is act as the research model.Aiming at the problems of high photogenerated electron and hole recombination rate and insufficient catalytic reaction kinetics,the modification strategies are developed in the functionalization of acidic/basic functional groups,activation of catalytic active sites and physical/space separation of reaction sites.The relationship between acidic/basic functional groups and photocarrier transfer path is explored,and the interaction law and reaction mechanism between the structure of catalytic system and the activity of photocatalytic water splitting are revealed.The main research and achievements of this paper are as follows:（1）A facile heat treatment strategy is developed to obtain Sulfur-Zinc-Cadmium nanoparticles with amino（-NH₂）and sulfur-group(S^2-)modification(N-CZS-S^2-).By transient surface photovoltage（TPV）characterization analysis,it is found that the intrinsic electronic structure of N-CZS-S^2-change from negative to positive and negative due to surface-NH₂ group and S^2-group modification,compared with the Sulfur-Zinc-Cadmium before modification.（2）On the basis of previous research,a novel composite photocatalyst(Ni_x/N-CZS-S^2-)with physical separation of catalytic reduction site and oxidation site is synthesized by photodeposition technique with the assistance of specific functional groups.Through the physical characterization analysis,it is found that the injection of Ni clusters does not affect the intrinsic characteristics of the main catalyst,but play a role of activating the reaction point.Then,we discuss how the Ni clusters affect the photochemical properties of the materials.Compared with N-CZS-S^2-sample,Ni_x/N-CZS-S^2-system exhibits lower electron and hole recombination rate,longer fluorescence lifetime and stronger photocurrent density.Hydrogen production performance tests show that Ni₂/N-CZS-S^2-(32.02mmolg^-1h^-1)has better hydrogen production activity than N-CZS-S^2-(16.20mmolg^-1h^-1)under visible light irradiation.The mechanism of catalytic reaction shows that CZS photogenerated electrons are transferred to metal clusters Ni for hydrogen evolution through bridge groups-NH₂,and the holes are consumed by sacrificial agent through bridge group S^2-.Physical separation of reduction site and oxidation site is realized.（3）We further optimize the structure distribution of catalytic reaction sites.Using the photochemical instability of CO-MOF,the flower-like cocatalyst formed by 2D nanosheet assembly is designed and supported on 1D CZS main catalyst to construct 2D@1D composite photocatalyst（Co S_x-C/N_y@CZS）with unique spatial separation of catalytic reduction site and oxidation site.In order to better study the physical/spatial separation mechanism of the reaction site,the comparison material 0D/1D Co S_x/CZS composite is prepared.Through electron microscope characterization analysis,2D@1D Co S_x-C/N_y@CZS photocatalytic system can achieve the spatial separation of catalytic reduction site and oxidation site through the spatial separation of the light absorption center and the catalytic active center in the morphological structure.Further analysis of the chemical composition and electronic structure of the material show that the Co-S-C/N charge channel is innovatively developed using ZIF-67 as a template,which can improve the rate of charge transfer.Then,we also discuss how high/low dimensional cocatalysts affect the photochemical properties of materials.Compared with Co S_x/CZS sample,Co S_x-C/N_y@CZS system exhibits lower electron and hole recombination rate,lower interfacial resistivity and stronger photocurrent density.Hydrogen production performance tests show that Co S_x-C/N₂@CZS(18.57 mmolg^-1h^-1)has better activity than Co S_x/CZS(13.16 mmolg^-1h^-1)under visible light irradiation.The mechanism of catalytic reaction shows that photogenerated electrons are transferred to 2D catalytic active center Co S_xvia Co-S-C/N charge channel for hydrogen evolution,while photogenerated holes remain in 1D photo-absorption center CZS are eliminated by sacrificial agent.The spatial separation of reduction site and oxidation site is realized,and the problem on accumulation of catalytic active site in physical separation structure is solved.