Study On Photocatalytic Hydrogen Evolution Of Cobalt-based Materials Supported Transition Metal Semiconductor

The over-exploitation of conventional energy causes great damage to the earth’s ecological environment,and the non-renewable of conventional energy makes the global energy reserve decline day by day.Especially in the current situation of the new century,fossil fuels,natural gas and other resources are vulnerable to force majeure factors,resulting in imbalance between supply and demand.The development of clean energy is of vital strategic importance in human development.Hydrogen energy,with its zero carbon emissions,high energy density advantages among the forefront of energy research and development.Since the discovery of Honda-Fujishima Effect in the last century,people began to study the photocatalytic hydrogen evolution with inorganic semiconductor powder materials.Photocatalysis technology has realized the conversion,storage and utilization of solar energy to hydrogen energy,and has gradually become the leading force in the field of environmental and energy catalysis.The key to realizing industrial hydrogen evolution by artificial photosynthesis is to design and prepare photocatalysts with excellent and stable performance.Semiconductor materials can absorb visible light and become excellent hydrogen producing materials.When different semiconductors are supported by each other,the hydrogen production rate can be greatly improved.In this project,cobalt-based molybdate and metal-organic framework loaded transition metal semiconductor were constructed as composite photocatalytic materials,aiming at improving the hydrogen evolution performance of the catalyst under visible light and producing hydrogen efficiently and quickly.The specific work content is as follows:（1）A new type of S-scheme heterojunction was constructed by using Zn S and Co Mo O₄,and the reason of hydrogen evolution advantage and high performance of the system was explained by related characterization.The photocatalytic hydrogen evolution experiment shows that the composite has good catalytic performance.The results show that the hydrogen production rate can reach 1233μmol·g^-1·h^-1 when the amount of Zn S supported on Co Mo O₄ is 5%.The ball-and-stick structure of the composite catalyst was proved by different characterization,which complemented the S-scheme heterojunction mechanism.Various studies have shown that Zn S and Co Mo O₄ have broad application prospects.The special electron transfer path of S-scheme heterojunction provides theoretical model support for high performance hydrogen evolution.（2）The S-scheme heterojunction contact interface was constructed by electrostatic adsorption.The S-scheme can improve the separation rate of photogenerated carriers through the built-in electric field,and the hydrogen evolution rate of the system can reach871.9μmol·g^-1·h^-1.The system shows good photoelectric response in UV-Vis DRS and electrochemistry,and has excellent hydrogen evolution performance.DFT simulation was also carried out for the heterojunction interface formed by the system.The relative value of the surface work function indicates the direction and path of electron transfer.（3）ZIF-67 and ZIF-67-L（Leaf）were intercalated into Ni₅Al₄O₁₁·18H₂O by in situ growth method,and the nanoflose-hexagonal prism hydrogen evolution system and nanoflose-leaf hydrogen evolution system were constructed,respectively.The results show that both systems have good hydrogen evolution ability,and the nano-flower-hexagonal prism structure has the best hydrogen evolution ability,up to 1629.3μmol·g^-1·h^-1.In such a coupled semiconductor system,the light energy induction of the photosensitizer,the electronic transition of the active semiconductor,the organic ligands and metal clusters of the ZIF-67 semiconductor constitute the whole-domain directional electron flow of the system.（4）ZIF-8 was grown on Cu₂O surface in situ to prepare a new type of composite.The visible light excitation of semiconductor andπ-π*conjugation effect of metal-organic skeleton are used to improve the mobility of photogenerated carriers and accumulate electrons to participate in hydrogen ion reduction.XRD,SEM and XPS have proved the synthesis and excellent morphology of the composite.The mechanism of electron transfer in photocatalytic reaction of composite materials was studied by electrochemical and spectroscopic methods.The excellent hydrogen evolution performance(981.8μmol·g^-1·h^-1)and the stability test showed that the coupling of ZIF-8 and semiconductor Cu₂O successfully improved the catalytic performance of the material.The whole domain of directional electron flow is formed in the composite system,which complements the study of photocatalytic reaction mechanism to a certain extent,and will provide some ideas for the development of new hydrogen evolution materials.（5）The potential of photocatalysis will be greatly stimulated by the construction of heterogeneous interfaces of new composites constructed by coupling Co-MOF with conventional semiconductors.The growth of Co-MOF with different morphology was accurately controlled by adjusting the ratio of raw materials.With the increase of dimethylimidazole content,the thin-layer six-prism morphology（Co-MOF-H）,leaf morphology（Co-MOF-B）and Daisy morphology（Co-MOF-D）were synthesized in turn.The experimental results show that H-g-C₃N₄ has the best catalytic activity when adsorbing six-prism Co-MOF.When the ratio of H-g-C₃N₄ reached 125 mg,the optimal hydrogen evolution activity reached 1033μmol·g^-1·h^-1.Abundant characterization methods were used to explain the effect of morphology regulation on the hydrogen evolution ability of Co-MOF,and the hydrogen evolution mechanism of Co-MOF/H-g-C₃N₄ composite catalyst was explored.