| In recent decades,energy shortages and environmental pollution have become major issues that need to be resolved for the sustainable development of modern society and economy.Hydrogen is a fuel with clean combustion products and high combustion enthalpy ratio,and is recognized as one of the renewable resources that can effectively solve energy problems.Semiconductor photocatalytic water splitting to produce hydrogen is one of the important technologies to deal with future energy and environmental challenges.The key to achieving large-scale application of photocatalytic water splitting to hydrogen is to develop and synthesize highly efficient photocatalysts.Metal-organic frameworks(MOFs),as a type of crystalline porous materials,are organic-inorganic hybrid materials formed by self-assembly of metal nodes(metal clusters or ions)and organic connectors.They have high specific surface area,porous structure and functional capabilities.The adjustment characteristics have caused widespread concern in the field of photocatalysis.However,in the field of photocatalysis,MOFs materials still have two problems that restrict their catalytic efficiency:(1)The spectral response range of MOFs materials is narrow,which makes the utilization rate of solar energy low;(2)MOFs’ own ordered periodic structure makes photogenic After electrons are excited by light,the recombination rate of photo-generated electrons and holes is fast,resulting in low catalytic efficiency.A significant advantage of metal sulfide semiconductors is that they have suitable band gaps and band positions,which ensures that many metal sulfides can be used as photocatalysts responsive to visible light.Indium zinc sulfide(ZnIn2S4)is a representative ternary chalcogenide compound.Due to its strong visible light absorption and suitable energy band position,it has catalytic activity for visible light catalyzed hydrogen production and exhibits considerable chemical stability.However,ZnIn2S4 has a low separation efficiency and poor mobility,which hinders the effective separation of electrons and holes,resulting in poor photocatalytic hydrogen production activity of pure ZnIn2S4.In view of the narrow spectral response range of MOFs and the high recombination rate of photogenerated electrons and holes,this paper uses two strategies to solve these problems.One strategy is to build a three-phase heterojunction between MOFs and semiconductors to improve the absorption and utilization of light,promote the separation of light-induced charge carriers,and thereby improve the catalytic performance of the catalyst.Another strategy is to control the morphology of MOFs to obtain the composite of MOF with hollow structure and metal sulfide.Because the hollow structure has a large specific surface area,abundant reactive sites,and the hollow thin shell structure shortens the charge transfer distance,assists the separation of electrons and holes,and the refraction effect in the cavity enhances the use of light,thereby improving photocatalysis effectiveness.The specific work content of this paper is as follows:(1)UiO-66 was grown in situ by solvothermal reaction using g-C3N4 as the substrate,and UiO-66@g-C3N4(U@G)samples were generated as the substrate of the three-phase composite material.U@G and metal sulfide ZnIn2S4 are synthesized by hydrothermal synthesis of UiO-66@g-C3N4@ZnIn2S4(U@G@Z)nanocomposite to form a ternary heterojunction,increase the visible light absorption of the catalyst,and shorten the charge Transmission distance,thereby inhibit electron-hole recombination to increase the photocatalytic hydrogen production rate.And by changing the ratio of each component in the compounding process,to study the changes in the performance of photocatalytic hydrogen production,and through a series of characterizations,analyze the reasons for the performance of hydrogen production.Comprehensive characterization shows that ZnIn2S4 nanosheets are evenly decorated on UiO-66@g-C3N4(U@G-30%).System research shows that UiO-66@g-C3N4@ZnIn2S4(U@G@Z-54.4)due to the contact interface between U@G-30%and ZnIn2S4 and the well-matched band structure,it is conducive to the effective photochemical charge Separation and transfer.The optimal nanocomposite U@G@Z-54.4 exhibits high photocatalytic hydrogen production activity under visible light irradiation,and the hydrogen production rate can reach 435.42μmol·g-1·h-1,which is about 2.3 times that of pure ZnIn2S4.Compared with U@G-30%,loading ZnIn2S4 can increase the photocatalytic hydrogen production rate of the catalyst.(2)The research of nanocomposite materials formed by combining Ni-MOF with a hollow structure and metal sulfide ZnIn2S4 in the direction of photocatalytic hydrogen production.Using Ni-MOF as a template,metal sulfide ZnIn2S4 is compounded on its surface to generate Ni-MOF@ZnIn2S4(N@Z-X)nanocomposite materials.The hollow structure of the N@Z-X composite material makes the Ni2+catalytically active sites highly dispersed,and provides a large specific surface area for water splitting,shortens the charge transport distance,accelerates the charge separation and mobility,and promotes the hydrogen evolution reaction.Through the characterization of the material structure and performance,ZnIn2S4 nanosheets are well coated on the surface of Ni-MOF,Ni-MOF@ZnIn2S4 nanocomposite has a good energy band structure,and the close contact between Ni-MOF and ZnIn2S4 The effective separation of photo-generated charges and the directional transfer of electrons are realized,and the recombination of electrons and holes in ZnIn2S4 is reduced.The N@Z-27.2 composite exhibits high catalytic activity under visible light irradiation,with a hydrogen production rate of 2384.1 μmol·g-1·h-1.Compared with pure ZnIn2S4,the hydrogen production rate of the N@Z-27.2 composite is increased by 11.45 times,and shows good stability in multiple cycles. |
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