Study On The Synthesis, Characterization And Water Oxidation Properties Of Metal-Organic Frameworks(MOFs)

MOFs is a kind of high porosity structure of the crystalline material.And it has become a potential catalyst with the development of catalytic materials due to its high porosity structure and high thermal stability.Therefore,the development of the MOFs materials which are based on non-noble metals and it's application for the artificial photosynthesis system will provide a theoretical significance and application value.This research have summarized the research progress of water oxidation catalyst and MOFs materials in the field of catalytic applications.We have prepared three kinds of MOF-Fe,one kind of MOF-Eu and two kinds of MOFs composites.Then we have measured the photocatalytic performance and mechanism of those MOFs materials for the oxidation of water and benzyl alcohol.The main research content and innovation are shown as follows:?1?The MOF/GO composites based on rare earth metal europium was synthesized through electrostatic self-assembly method with different amount of GO.Then they were measured by SEM,XRD,FT-IR and Raman spectrum,then applied to photocatalytic the oxidation of water and benzyl alcohol under different conditions.The existence of GO effectively enhanced the photocatalytic activity due to the improvement of the electron transport rate and the reduction of the recombination for photo-generated electron-hole pairs according to the results.The excellent absorption performance of the precursor MIL-LIC-1?Eu?for visible light made this kind of MOFs to developed a multi-functional catalyst which can act as photosensitizer in the water oxidation system.The capture experiments found that photogenerated holes and·OH were the active intermediates in the catalytic process.Then we detected performance of MIL-LIC-1?Eu?and it's composite for the oxidation of benzyl alcohol.The results show that water is an important source of oxygen during the catalytic process.In the alcohol oxidation system,the best conversion rate of benzyl alcohol can reach at 85.4%.Therefore,this part of research will provide a new idea for the other light-driven oxidation reaction with water as oxygen source.?2?Three kinds of iron based metal-organic materials?MIL-53?Fe?,NH₂-MIL-53?Fe?and MIL-100?Fe??which have different organic ligands were prepared by solvent thermal method.And the corresponding organic ligands were terephthalic acid,2-amino-terephthalic acid and trimesic acid).Then the effect of the ligands for catalytic activity was analyzed by BET,cyclic voltammetry,photoelectric properties and active intermediates.MIL-100?Fe?show the best catalytic activity,and the TON value reached 119.4,TOF is 0.75 min-1.The results show that the length and size of organic ligands and the amount of coordination carboxylic acid are directly related to the catalytic activity.A MOFs material with larger molecular volume and longer length of organic ligand has a larger pore size and will expose more effectively active sites.Furthermore,more active sites will be formed with the addition of carboxylic acid functional group.Therefore,the design and selection of a ideal organic which have more coordination sites,suitable molecular length and moderate size would be helpful for a high efficient water oxidation catalyst of MOFs.?3?A novel iron/cobalt bimetallic MOFs complex?FBNC?was prepared by post-modification method on the basis of NH₂-MIL-53?Fe?,and detected by SEM,XRD,FT-IR and Raman spectrum.The water oxidation activity of FBNC was detected under different catalytic conditions.The changes of valence states and photoelectric conversion properties of the composites were studied via electrochemical methods.The results show that the introduction of cobalt effectively enhances the water oxidation and photoelectric conversion properties of precursor NH₂-MIL-53?Fe?,and prove FBNC is a kind of multi-functional photocatalyst which also can act as photosensitizer and electron acceptor.The highest TON value of water oxidation was 110.5,and the oxidation conversion rate of benzyl alcohol was 91.1%.Hence,the synthesis of this multi-functional iron-cobalt bimetallic MOFs composite will provides a new idea for the design and functionalization of photoactive materials.