Study On The Synthesis And Catalytic Properties Of Functional Fe-based And Zr-based MOFs

Metal-organic frameworks?MOFs?are a new type of organic/inorganic hybrid porous materials,which has gain significant attention due to their designable structure,tailoring pore size and functionality.MOFs have been widely used in the fields of gas storage and separation,molecular recognition,sensing and catalysis.Particularly,MOFs is one of the most promising heterogeneous catalysts owing to their unique properties,such as high specific surface area,high density of catalytic active sites and the design able catalytic groups.However,many challenges remain with regard to the applications of MOFs in catalysis:?1?The conventional solvothermal or hydrothermal synthesis of MOFs often requires a high temperature and high pressure reactor,which not only has disadvanteges in high energy consumption,low yield,but also limits large scale preparation;?2?Most of MOFs show poor stability in aqueous solu-tion,which can be problems in long-term stability and water-sensitivity catalysis;?3?The catalytic sites decorated in MOFs channels could be blocked due to the small pore size and the steric hindrance of the functional group.In this thesis,we have investigated the sysnthesis and catalysitic applications of Fe-based MOFs and Zr-MOFs owitng to their unique properties.?1?We Developed a rapid,green and mild synthetic route for the preparation of highly crystalline MIL-100?Fe?in aqueous phase and used as photocatalysts for organic dye degradations.?2?Hollow carbon polyhedra?HCPs?derived from MIL-100?Fe?was used as electrode materials for supercapacitors.?3?Design and synthesis of a TEMPO?2,2,6,6-tetramethylpiperidinyloxy?radical decorated Zr-MOF,UiO-68-TEMPO,and the investigate the catalytic performance of UiO-68-TEMPO toward the selective oxidation of alcohols.The main research resultsare following:1.By using either ferrous salts?such as ferrous sulfate,ferrous chloride,ferrous acetate?or ferric salts?such as FeCl₃,Fe?NO₃?₃?and trimesate salt as raw materials,we have synthesized MIL-100?Fe?at room temperature in aqueous phase.A plausible mechanism for the growth of highly crystalline MIL-100?Fe?or poorly crystalline Fe-BTC coordination polymers was proposed:the formation of[Fe?III?₃??-O??CO₂?₆]secondary building unit?SBU?is essential for growing highly crystalline MIL-100?Fe?.The rapid reaction between Fe³⁺and trimesate leads to formation of defective[Fe?III?₃??-O??CO₂?₆]SBU.In the case of Fe²⁺as metal source,Fe²⁺was slowly oxide?e,g.by air?into Fe³⁺,thus,dramatically slow down the coordination reaction with btc^3-,facilitating the formation of perfect[Fe?III?₃??-O??CO₂?₆]SBUs.Despite similar chemical compositions and optical absorption properties(the band gap are estimated to be 2.3 eV and 2.5 eV for MIL-100?Fe?and Fe-BTC,respectively,between MIL-100?Fe?and Fe-BTC,great differences in crystal structure,pore structure and surface morphology were observed.The small particle size of Fe-BTC nanoparticles offers higher specific surface area,compared to MIL-100?Fe?,resulting a higher catalytic efficiency toward the photodegratdation of organic dyes.2.High-temperature pyrolysis of MIL-100?Fe?under argon atmosphere at 800oC for 30 minutes results in hollow carbon polyhedra?HCPs?featuring high degree of graphitization and hierarchical pore structures.The obtained HCPs are excellent electrode materials for electric double-layer capacitors?EDLCs?,and show a specific capacitance of 214F g^-11 at current density 50 mA g^-1.Moreover,the HCP-based supercapa-citors can endure more than 5000 cycles without significant degradation of capacitance.The unique structure of HCPs,including hollow polyhe-dral shape,hierarchical micro/mesopore structures,and ultrathin layer of highly graphitized carbon shells,endows the superior performance of HCPs based EDLCs with specific capacitance and high rate capability.3.Incorparation of TEMPO radicals?2,2,6,6-tetramethylpiperidinyl-oxy?into 4,4-triphenyl dicarboxylic acid,and employing Zr?IV?as metal nodes,we have synthesized a TEMPO radical decorated Zr-MOF,named UiO-68-TEMPO.The crystal structure and chemical composition of obtained UiO-68-TEMPO were studied by single crystal diffraction,paramagnetic electron resonance spectroscopy,powder XRD diffraction and BET specific surface area measurement.Based on the above measurements,we concluded that the successful synthesis of TEMPO functionalized Zr-MOF featuring both radical and highly porous nature.UiO-68-TEMPO displays excellent catalytic activity toward the selective oxidation of primary aromatic alcohols,secondary aromatic alcohols,heteratomic alcohols and aliphatic alcohols into their corresponding aldehydes or ketones,demonstrating the potential applications as heterocatalsysts.4.The effects of modulators,e.g.,benzoic acid,acetic acid,L-proline,hydrochloric acid and trifluoroacetic acid with regard to the morphology,size and defects of UiO-68-TEMPO crystals were investigated.Detailed catalytic studies and DFT theoretical calculations reveal that the synergistic effect between the TEMPO radicals and hydrophilic and defective Zr-nodes endows UiO-68-TEMPO with superior catalytic activity toward aerobic oxidation of alcohols.Our work not only offers a new route to design and synthesize highly effective MOF catalysts but also provides insights into the synergism between multiple catalytic sites.