Photodeposition Construction Of Composite Catalysts And Study On Hydrogen Production Performance Of Photocatalytic Glycerol

The development of clean and renewable energy is an important strategy to meet the growing global energy demand and to address the environmental problems caused by excessive consumption of fossil fuels.Using solar energy to split water hydrogen has been widely regarded as a promising sustainable development approach.Up to now,in the field of photocatalysis,splitting water still has some difficulties,and there are not many fruitful studies,so at present,the photocatalytic water splitting for hydrogen is mainly based on the presence of sacrificial agents.Photocatalytic hydrogen production process is only a"half reaction"of water decomposition,and the presence of oxidizing end-sacrificial agent is essential in the whole system.Sacrificial agents may be biomass,organic fertilizers or their derivatives.Glycerol is less common than traditional sacrificial agents,such as triethanolamine,Na₂S/Na₂SO₃,lactic acid,methanol,ethanol,glycol,etc.However,glycerol is a promising sacrificial agent.It is a major by-product of the biodiesel industry,and China alone produced 260,000 tons of glycerol in 2019.In addition,glycerol itself is a low-value chemical and production far exceeds current demand.In order to use it effectively,photocatalytic hydrogen production systems were constructed by using it as a hole trapping agent.In this process,a safe,simple and low energy consumption photodeposition method is applied to prepare the transition metal-based catalyst,which is more suitable for the concept of green chemistry.The main research contents of this article are as follows:1.Cd S is one of the most significant photocatalytic water splitting materials for hydrogen production.Cd S has a narrow visible light response band gap（Eg=2.4 e V）and an appropriate absorption edge,and meets the thermodynamic demand for photocatalytic hydrogen production,which can produce hydrogen under visible light.However,the rapid recombination of photogenerated carriers results in severe photocorrosion performance of Cd S（poor photogenic stability）,S^2-is also oxidized to S⁰ by photogenic holes,resulting in the destruction of its own structure and significantly reduced photocatalytic performance.In this study,in order to improve the photoinduced stability of Cd S photocatalyst,Na₂S/Na₂SO₃ was selected as the sacrificial agent,and the p-type Cu₂O layer was placed between Cd S and cocatalyst Ni O_x through two-step photodeposition.A composite catalyst was formed.Compared with no Cu₂O,the hydrogen-producing activity of the catalyst was increased by 5times.Electrochemical test shows that the action of Cu₂O intermediate layer accelerates the holes transfer of Cd S,promotes the charge separation,and improves the hydrogen production activity and stability.The introduction of Cu₂O intermediate layer and the study of its role have some guiding significance for the design and development of efficient water decomposition photocatalyst.In addition,the photocatalytic hydrogen production of the composite catalyst in glycerol aqueous solution was initially investigated.It provided reference for the following system research from the aspects of experimental method and modification.2.g-C₃N₄ has been widely studied by researchers at home and abroad in photoresponse semiconductors.The band gap is 2.7 e V,thus providing good sun trapping capability.However,the charge and hole recombination of single g-C₃N₄ induced by light excitation results in very low photocatalytic activity.g-C₃N₄ was chosen composite withα-Fe₂O₃.Using the method of photodeposition,on this basis,highly dispersed Ni was loaded to formα-Fe₂O₃/Ni@2D g-C₃N₄ composite photocatalyst.The structural characteristics of the composite catalyst were demonstrated by multiple characterization.Then it was placed in glycerol aqueous solution system for photocatalytic hydrogen production.The hydrogen production rate was 210.45μmol/g/h,in the hydrogen production reaction with glycerol as sacrificial agent,the performance is relatively ideal.3.Cd_xZn_1-xS solid solution has been proved to be an excellent visible reaction catalyst in the presence of sacrifying reagent.By controlling the phase structure,morphology and surface modification of Cd_xZn_1-xS,various researches have been carried out on solid solution in order to seek for better visible light response and photocatalytic efficiency.In the past decade,great efforts have been made in the construction of Cd_xZn_1-xS solid solution nanostructures through energy band regulation and high crystal equality.In order to improve the hydrogen-producing activity of glycerol photocatalytic system,in this paper,the transition metal Ni-based phosphates were loaded on solid solution by the method of photodeposition,and modified by this method to form Ni_xP/Cd_xZn_1-xS composite photocatalyst.Glycerol was used as sacrificial agent to achieve more efficient hydrogen production performance under visible light irradiation.When the molar ratio Cd:Zn=1:1,the hydrogen production rate of catalyst Ni_xP/Cd_0.5Zn_0.5S reached 21.65 mmol/g/h,and the activity of Ni_xP without load was only 0.09mmol/g/h.It also indirectly indicates that the cocatalyst can effectively inhibit the photoelectron and holes recombination and thus improve its photocatalytic hydrogen production activity.The rate of hydrogen production is excellent in reports of glycerol as sacrificial agent.In addition,the elemental composition,structural characteristics and catalytic mechanism of the composite photocatalyst were also investigated.