| Hydrogen as an ideal new energy has the advantages of clean pollution-free and high combustion value.At present,the production of hydrogen?H2? by photocatalytic splitting of water to hydrogen is a feasible scheme among many methods for hydrogen production.In the process of photocatalytic decomposition of water to produce hydrogen,the key factor that determins the efficiency and cost of hydrogen production is the catalyst.Polyoxometalates?POM?are inorganic metal oxygen clusters formed by pre-transition metals.POMs have similar electronic and optical response properties to inorganic metal oxide semiconductors and can perform rapid and reversible multi-electron transfer without changing their structures.Therefore,POMs are potentially ideal photocatalysts.However,the traditional POM materials have a narrow light absorption range?generally they only absorb ultraviolet light?.In order to increase the visible light absorption capacity of POM catalysts,it is often necessary to introduce a co-catalyzed precious metal cocatalyst into the catalytic system,which leads to the final catalytic system.The high cost of hydrogen limits the widespread use of POM catalyst materials for photocatalytic decomposition of water to produce hydrogen.In order to break through the technical bottleneck of narrow absorption range of traditional POM photocatalysts and avoid the problem of higher cost of hydrogen production due to the introduction of precious metal catalysts,this article provides a strategy for the preparation of high-performance POM-based non-precious metal catalysts:under hydrothermal conditions,POMs were modified with complexes consisting of transition metals and organic ligands,and six new POM-based non-precious metal catalysts were prepared.1.Two novel POM-based metal organic compounds were synthesized by introducing two Mo-based POMs into two metal-organic ligand systems?Cu+pzta+bpy and Cu+pzta+bibe?by hydrothermal synthesis.Their molecular formula is as follow:[HMo10O34][Cu ?Cu 2??bpy??pzta?2](Cu?Cu 2?-Mo10)?1?[H2Mo8O26][Cu2??bibe??pzta?2]?Cu2?-Mo8??2?pzta=3-?pyrid-4-yl?pyrazolebpy=4,4'-bipyridinebibe=4,4'-bis?imidazolyl?biphenylCu?Cu 2?-Mo10 is a POMOF?POM-based Metal-Organic Frameworks,POMOFs?structure with a three-dimensional metal-organic framework encapsulating POM.Cu 2?-Mo8 is a two-dimensional network structure.The crystal morphology,optical properties and band gap width of the two compounds were studied.The electrochemical impedance spectra,photocurrent-time profiles and photoluminescence spectrum show that the separation ability of photogenerated charges was also followed the order of Cu 2?-Mo8>Cu?Cu 2?-Mo10>Mo O7?parent POM?,and photolysis of hydrogen from water It is proved that Cu 2?-Mo8has a better photolysis rate of hydrogen production from water than Cu ?Cu 2?-Mo10.The higher photocatalytic activity of Cu 2?-Mo8is mainly attributed to more active sites for Cu? hydrogen production,which can transfer more The photo-generated electrons undergo a proton reduction reaction.2.The POM-based transition metal-pzta ligand hybrid material with high photocatalytic decomposition and hydrogen activity is prepared under the control of different transition metals,and the molecular formula is as follows:(HSi W12O40)[Co ??pzta?3][Co??pzta?3]·4H2O(Co 2?/?-Si W12)?3?(HSi W12O40)[Fe III?pzta?3][Fe??pzta?3]·4H2O(Fe 2?/?-Si W12)?4?(H2SiW12O40)[Zn??pzta?3]2·4H2O(Zn2?-SiW12)?5?(H2SiW12O40)[Cd??pzta?3]2·4H2O(Cd2?-SiW12)?6?pzta=3-?pyrid-4-yl?pyrazoleThe analysis of single crystal X-ray diffraction indicate that four compounds have the same three-dimensional supramolecular frame structure.The electrochemical impedance spectra,photocurrent-time profiles and photoluminescence spectrum showed that the introduction of d metal-organic complexes could effectively promote the separation and transport of photogenerated electrons and holes.The property tests of photocatalytic decomposition of hydrogen production in water show that the hydrogen production rates of Co 2?/?-SiW12,Fe 2?/?-SiW12,Zn 2?-SiW12,Cd 2?-SiW12are 8222.36,3117.19,121.45 and 112.91?mol·g-1h-1,in which the hydrogen productivity of Co 2?/?-Si W12and Fe 2?/?-SiW12is 95.27 and 36.12 times of the hydrogen production of parent POM,respectively.The cycle stability of Co 2?/?-SiW12in the experiment of photocatalytic decomposition of hydrogen by water was proved.In addition,based on the above results,the mechanism of photocatalytic decomposition of hydrogen in aquatic products was investigated. |
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