Modification Of Fe-MOF And Its Application In Photocatalytic Oxidation Of Benzyl Alcohols

MOFs(Metal-Organic Framework)is a kind of crystalline porous material,which is well known to scholars in some fields due to its high porosity,diverse structure and controllable chemical composition.The porous framework of metal nodes and organic ligands not only facilitates functional modification and provides abundant metal active sites,but also responds to external light exposure.These characteristics create favorable conditions for the application of MOFs materials to photocatalytic reactions.Among many MOFs-based photocatalysts,Fe-MOF has attracted much attention due to its advantages such as low raw materials,good stability,appropriate valence band location,unsaturated Fe metal coordination center for Lewis acid,and good visible light absorption.Selective oxidation of primary and secondary alcohols to corresponding aldehydes and ketones is an important reaction.In this thesis,the synthesis and modification of Fe-MOF(MIL-53(Fe))were described,and the photocatalytic activity of Fe-MOF was enhanced by coupling with other traditional semiconductor materials.XRD,FT-IR,XPS,SEM,TEM and other characterization techniques were used to analyze the structure,composition and morphology of the material,and the photocatalytic oxidation mechanism of benzyl alcohol was reasonably predicted by ESR,free radical capture experiment,Mott-Schottky experiment and transient photocurrent experiment.The following is the main research work of this paper and its summary and innovation:1.Bismuth ferrate/MIL-53(Fe)nanocomposites with tight heterojunction were synthesized by in situ etching-regeneration method.By partially destroying the peripheral structure of the hexagonal bipyramidal MIL-53(Fe)and exposing Fe-O bonds,bismuth ferrite nanosheets were anchored to grow on the surface of MIL-53(Fe).The shared Fe-O bond connected the heterojunction between bismuth ferrate/MIL-53(Fe),accelerating electron transfer at the interface.A rougher outer surface facilitated visible light absorption and exposed more active site.The composite material showed good photocatalytic performance in the photocatalytic selective oxidation of benzyl alcohol.Acetonitrile as solvent,molecular oxygen as oxidant and visible light irradiation as energy drive can achieve the optimal benzyl alcohol conversion(58.5%).The mechanism of photocatalytic oxidation of benzyl alcohol was also speculated.2.In order to further promote the transfer of photogenerated electrons,a layer of Au nanoparticles was loaded on the surface of MIL-53(Fe)by photochemical reduction method,and then a layer of WO₃ nanosheets was pasted on the surface of MIL-53(Fe)/Au by ultrasonic method to form the structure of MIL-53(Fe)/Au/WO₃ sandwich and further constructed as a Z-scheme heterojunction.Under visible light irradiation,photoelectrons generated by MIL-53(Fe)and holes generated by WO₃ quickly meet on Au nanoparticles,which effectively separates holes from MIL-53(Fe)and electrons from WO₃,thus contributing to the photocatalytic activation of benzyl alcohol.The local surface plasmonic effect and Schottky junction formed by Au between the two phases promoted visible light absorption and charge transfer.The prepared MIL-53(Fe)/Au/WO₃ composite showed good activity and stability in selective oxidation of benzyl alcohol.At the same time,two possible charge transfer mechanisms in composite materials are speculated.