| With the ever-increasing energy crisis and environmental problems,the development of sustainable energy to substitute the fossil fuels has become the focus of global attention over the past decades.Recently,hydrogen is considered as the sustainable and renewable clean energy source,and its development has become an important research hotspot today.Metal-organic frameworks(MOFs)can be used as the substrate to prepare porous composite photocatalysts with different structures and components.Because of their porous structure,large specific surface area,high porosity,good material transport ability,flexible design of pore structure,easy functionalization and other outstanding advantages,MOFs-based composites are widely used in the fields of batteries,supercapacitors,adsorption,sensing,environmental science,and catalysis.Although there have been many research reports on MOFs in recent years,there are still many aspects worthy of study,such as the simple preparation of MOFs-based composite materials combined with the widely used industrial radiation method,the simple preparation of yolk-shell,hollow and 2D MOFs derived materials for photocatalytic hydrogen production,which may expand the new preparation of MOFs-based composite materials and applications in the field of photocatalysis.In this thesis,MOFs was used as a platform to prepare composite photocatalysts.By means of composition control and structure design,porous materials with different compositions and different morphologies(such as yolk shell struture,hollow structure and two-dimensional nanosheets)are prepared.The application of composite materials in the field of photocatalysis is also studied.These reserches provides new methods and new ideas for the flexible design of porous composite photocatalysts with improved photocatalytic hydrogen production performance.The main research content of this thesis is briefly summarized as follows:(1)Preparation of the ternary composite photocatalyst CdS/Pt/MIL-125 by y-radiation method and research on its hydrogen production performance.In this work,CdS/Pt/MIL-125 nanocomposite has been fabricated by using y-ray irradiation,where Pt and CdS nanoparticles with clean surfaces are well dispersed inside and on the surface of the MIL-125,respectively,which greatly promotes effective space separation of photogenerated carriers and thus improves the visible-light catalytic activity.The hydrogen generation rate of CdS/Pt/MIL-125 nanocomposite is found up to 6783.5?mol·g-1·h-1 under visible-light illumination,which is 7.3 times that of CdS/MIL-125 without Pt as electron trap reservoirs,and 4.4 times that of Pt/CdS/MIL-125 without effective spatial separation between CdS and Pt.The reason is attributed to the synergy of ternary CdS/Pt/MIL-125 with a unique ordered mesoporous structure that may widen the absorption range of the light,improve the efficiency of light harvesting,facilitate mass transfer,prevent the aggregation of CdS and Pt nanoparticles,suppress the e-h pair recombination and provide more active sites.Moreover,the loading amount of Pt or CdS nanoparticles also affects the activity of CdS/Pt/MIL-125 nanocomposite for visible-light catalytic H2 evolution.In view of the extensive use of y-ray irradiation in industry,this research presents a rational route to the fabrication of novel hybrid photocatalysts for improved visible-light catalytic hydrogen evolution.(2)Preparation of MIL-125-derived yolk-shell and hollow structure composite photocatalysts by y-radiation method and study on its photocatalytic performance.The yolk-shell MIL-125/TiO2/Pt/CdS and hollow TiO2/Pt/CdS visible-light catalysts were successfully synthesized from MIL-125 by y-ray irradiation.What is interesting that during the reduction process by y-ray irradiation,MOFs are partially or completely hydrolyzed to TiO2 nanosheets,forming the unique yolk-shell or hollow structure.And the hydrogen production rate of yolk-shell structure photocatalyst is 2983.5?mol·g.-·h-1 and that of hollow structure photocatalyst is 1934.2 ?mol·g-1·h-1 under visible light,respectively,which is 7.9 to 5.1 times higher than that of CdS.These excellent properties of the photocatalysts may be due to the effective absorption and utilization of the light,the porous yolk-shell or hollow structure derived from MIL-125 to facilitate mass transfer and close contact among TiO2 nanosheets,CdS and Pt nanoparticles to accelerate the transfer of carriers.This research can provide a simple and new method for the construction of efficent photocatalysts derived from MOFs using the y-ray irradiation.(3)Preparation and application of two-dimensional photocatalysts derived from MOFs.In recent years,2D nanomaterials have attracted more and more attention due to their unique size-related chemical properties.Among them,the 2D MOF nanosheets have attracted great attention due to their high surface area,regular pores and a large number of open unsaturated sites.Generally,2D MOF nanosheets can be peeled off 3D MOF layered crystals by the "top-down" method,or directly obtained by the "bottom-up" method.In this work,a surfactant-free 2D MOF nanosheet was successfully synthesized at room temperature.Then,the simple ion exchange method was used to synthesize two-dimensional CdS/ZnS/PdS nanosheet materials,which skillfully combines the three strategies of controlling morphology,constructing heterostructures,and compositing promoters.Its photocatalytic hydrogen production rate is as high as 19634.9 ?mol·g-1·h-1,which is attributed to the confinement function of the two-dimensional structure to make the components completely combining together on the nanometer scale and forming a large number of intimate contact interfaces,so that promotes the separation and transfer of photo-generated charges,and thus effectively improves the rate of photocatalytic hydrogen production. |
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