| Energy depletion and environmental pollution have impelled people to find efficient,affordable and environmentally friendly renewable energy sources,and solar energy as a well-stocked and accessible energy can be used to produce sustainable new energy sources represented by hydrogen.g-C3N4 has unique semiconductor band structure and excellent thermochemical stability,attracts much attention in the field of photocatalytic water splitting.However,as a photocatalyst,it still remains some problems,such as the high recombination rate of photo-generated electron-hole pairs,the relatively low quantum efficiency,and the low sunlight utilization efficiency.Meanwhile,the photocatalytic activity of g-C3N4 is low due to its small specific surface area and limited transfer and separation efficiency of the photo-generated charge carriers.In this thesis,in order to improve the performance of g-C3N4,enhance the sunlight absorption range of g-C3N4 and suppress the recombination rate of photo-generated charge carriers,it is an effective way to form semiconductor heterojunction with other semiconductor materials.Metal Organic Frameworks（MOFs）material is composed of organic ligand and metal ions or metal clusters,it is a novel crystal materials with porous structure.It can be used as catalysts form heterogeneous catalyst with g-C3N4.Using the advantage of MOF to combine g-C3N4 with MOF to form a semiconductor heterojunction,it is expected to increase the specific surface area and photochemical properties of g-C3N4,and improving the photocatalytic hydrogen production performance of g-C3N4.On the other hand,using g-C3N4 as a precursor to combine g-C3N4/ZnCdS heterojunction can promote the light absorption of g-C3N4/MOF and enhanced g-C3N4photochemical properties,meanwhile improving the efficiency of photocatalytic hydrogen production of g-C3N4.Polyoxometalate is a kind of polymetallic oxygen cluster compound formed by the connection of the former transition metal ions through oxygen.Polyoxometalate has a strong redox property,which can promote charge transfer,and polyoxometalate can change the composition of the elements and improve the catalytic performance.ZIFs is a kind of MOFs series,which is a porous crystal material with zeolite structure connected by transition metal atoms and imidazole derivatives.ZIFs series materials not only posesses high stability of traditional zeolites,but also exhibits the advantages of MOFs series materials.Using g-C3N4/polyoxometalate as precursor to compound ZIF-8 to compose g-C3N4/polyoxometalate/ZIF-8 photocatalyst.It improves the separation efficiency of g-C3N4 cavitation and carrier and enhances the photochemical properties of,and further increases the photocatalytic hydrogen production rate of g-C3N4.Meanwhile,The microstructure,morphology and optical properties of the synthesized g-C3N4 based hybrid catalysts were characterized using X-ray diffraction（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,photoluminescence（PL）emission spectroscopy and UV-visible diffuse reflectance analysis.The main research contents and results are as follows:（1）The g-C3N4/MOF composite catalysts were fabricated by in-situ deposition.At the same time,we proved that the bimetallic MOF has hydrogen production performance,and g-C3N4/ZnCo-ZIF,g-C3N4/ZnCu-ZIF and g-C3N4/ZnNi-ZIF composite bimetal MOF promoter is constructed.The hydrogen production performance of g-C3N4/ZnNi-ZIF catalyst is the best.The metal Pt was loaded on the basis of the g-C3N4/MOF composite catalyst,and the hydrogen production rate was further improved.（2）We use g-C3N4/ZIF-8 as precursor for one-step synthesis g-C3N4/ZnCdS semiconductor heterostructures by hydrothermal method.Then doped P by hydrothermal method,which further improved the hydrogen production performance of g-C3N4.The results show that the transmission efficiency of g-C3N4 carrier is improved by forming the heterojunction and the photocatalytic performance of g-C3N4 is improved.（3）In this paper the polyoxometalate which we choose is[Ni4（H2O）2(PW9O34)2]10-.The g-C3N4/[Ni4（H2O）2(PW9O34)2]10-,g-C3N4/ZIF-8photocatalystandg-C3N4/[Ni4（H2O）2(PW9O34)2]10-/ZIF-8 photocatalyst were fabricated by hydrothermal method.The characterization showed that the photocatalytic activity and visible light absorption of g-C3N4could be improved by single component recombination,but the synergistic effect of[Ni4（H2O）2(PW9O34)2]10-and ZIF-8 could further improve the photocatalytic efficiency advisible light absorption capacity.The order of the photocatalytic performance is g-C3N4<g-C3N4/[Ni4（H2O）2(PW9O34)2]10-<g-C3N4/ZIF-8<g-C3N4/[Ni4（H2O）2(PW9O34)2]10-/ZIF-8. |
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