Directed Syntheses And Photoelectric Catalytic Performance Of Metal-organic Framework Functional Materials

Metal-organic frameworks(MOFs)are a class of porous crystalline framework materials formed by strong chemical bonds between inorganic and organic components.Over the past 20 years,MOFs have developed rapidly as a star material due to their excellent performance in storage,separation and catalysis.The excellent application performance of MOFs is due to their inherent porous structure and highly adjustable pore environment.The size,function,and diversity of pore space can be precisely optimized at the molecular level through the proper design of building blocks and synthetic procedures.Especially in terms of catalysis,functionalized MOFs can provide a large number of catalytic sites and appropriate reaction space,which can provide an ideal reaction platform for a variety of heterogeneous catalytic reactions.In order to further enhance the MOFs performance in practical applications,researchers try to integrate MOFs with metal nanoparticles,quantum dots,polyoxometalates,molecular species,biological enzymes,silica and organic polymers and other kinds of functional species/materials forming composite materials.A large number of studies have demonstrated that MOFs and functionalized species/materials can play significant synergistic roles in various catalytic processes.Compared with single materials,the catalytic activity,selectivity and stability of composite catalysts have been significantly improved.Besides,reasonable design,modification of inorganic components(metal ions/metal clusters)and organic components(connectors)of MOFs can also introduce optical,electrical and magnetic properties into frame materials,greatly enhancing the development space of MOFs materials in catalytic applications.However,for traditional MOFs,the few active sites,poor electrical conductivity,weak light conversion ability and other shortcomings,to a large extent,restrict the further application of MOFs in heterogeneous catalysis field.Therefore,how to accurately synthesize functional MOFs and MOF composites has become the goal pursued by researchers.In view of the above research background,functionalized MOFs were precisely synthesized by the insertion method of functionalized organic connectors in this thesis.MOFs with adjustable pore environment can carry out efficient photocatalytic oxidation of organic compounds;The quantum dots are encapsulated into the MOFs channels to construct the strong interaction between the two materials,which can be used for electrocatalytic oxygen reduction and oxygen precipitation reactions in highly efficient aprotic systems;Redox bifunctional catalysts are constructed by using photofunctional semiconductor materials loaded with MOFs nanoparticles to photocatalyze the reduction of carbon dioxide to syngas.The main results of this thesis include the following three parts:1.A simple one-pot synthesis strategy has been developed to introduce multifunctional organic ligands into a stable zirconium-based organic layer(Zr-MOL)by means of secondary ligand column supports.31 multifunctional MOFs were systematically prepared by combining Zr₆-BTB(BTB=benzene-1,3,5-tribenzoic acid)metal-organic layer with a variety of secondary ligands,including ditopic and tetratopic linkers.In particular,the method successfully integrated metal phthalocyanine fragments into Zr-MOL system,which provided an ideal platform for selective catalytic oxidation of anthracene compounds.Using PCN-135(Co TCPc)as photocatalyst,the yield reached 95%under green reaction conditions with air as oxidant.In this work,we developed a universal method for the preparation of multi-component functional pore MOFs,demonstrating that the design and adjustment of the pore environment of porous materials can improve the catalytic performance of the materials significantly.2.CsPbBr₃ nanocrystals(4-5 nm)were encapsulated into stable Fe-based MOF channels(?5.5 and 4.2 nm)by sequential deposition method to obtain the perovskite-MOF composite Cs Pb Br₃@PCN-333(Fe).The Cs Pb Br₃ quantum dots were successfully encapsulated in the mesoporous cages of PCN-333(Fe).The Cs Pb Br₃ quantum dots were characterized by transmission electron microscopy(TEM),i DPC-STEM techniques and corresponding element mapping analysis(EDS).The existence form of Cs Pb Br₃ quantum dots were further confirmed by powder X-ray diffraction(PXRD),infrared spectroscopy(IR)and N₂ adsorption isotherm.Density functional theory(DFT)calculations showed that when Pb halide perovskite quantum dots were close to the ligand and metal clusters,the efficient electron channels formed significantly increased the electron transfer rate at the interface.Cs Pb Br₃@PCN-333(Fe)composite as a catalyst for oxygen reduction reaction(ORR)and oxygen precipitation reaction(OER)exhibited good and stable catalytic activity in aprotic system,which may be attributed to the full diffusion of ions and gas molecules facilitated by the void microporous cage of PCN-333(Fe)without encapsulated gust materials.In addition,Cs Pb Br₃@PCN-333(Fe)composite material can also be used as the photoelectric positive electrode of light-assisted Li-O₂batteries.The polarization of the cell can be maintained at about 0.25 V in the absence of any additional carbon material,the discharge platform can be up to 3.19 V,and the round-trip efficiency was 92.7%.3.The Zn-based stabilized metal-organic framework IFMC-3 was loaded on semiconductor Zn In₂S₄ by in-situ growth method.The uniform distribution of IFCM-3 particles accelerated the separation and transfer of photogenerated carriers,which enhanced the CO₂ photoreduction ability of the composites.In addition,due to the presence of pores and tetrazole ligands in IFMC-3,the composite photocatalyst also had the ability to capture CO₂,which helped to enrich CO₂ in the catalytic center,thereby reducing the distance from the reaction substrate to the reaction center.Using blue LED(?=420 nm)as light source and triethanolamine(TEOA)as sacrificial reagent,the production rates of CO and H₂ were 44 and 838?mol g^-1 h^-1,respectively.To further exploit the oxidative capacity of photogenerated holes in the composite catalyst,benzylamine(BA)was used instead of the traditional sacrifice reagent TEOA to convert it into the high chemical value-added compound N-benzylidenebenzylamine(BDA).The improvement of oxidation half reaction promoted the reduction half reaction and showed obvious synergistic effect.The production rates of CO and H₂ reached 497 and 8024?mol g^-1 h^-1,respectively,which was about 10 times that of TEOA.After 8 hours of LED light source irradiation,the conversion rate of BA can reach 94.5%,and the selectivity of BDA was 92%.