Preparation And Microwave Absorption Properties Of Metal-Organic Frameworks Derived Magnetic Metal/Carbon Composites

Carbon materials have a low density,good chemical stability and excellent electrical conductivity,so it is a potential absorbing material.In recent years,Metal-Organic Frameworks?MOFs?have been characterized by their structural diversity,porosity,tailorability,and ultra-high specific surface area,and have found that MOFs are precursors and inert.High temperature pyrolysis in the atmosphere?Ar or N₂?can generate magnetic metal/carbon composites in situ.In this paper,three kinds of MOFs-derived magnetic metal/carbon-based composite materials were obtained by simple synthesis methods?room temperature aging-high temperature pyrolysis,solvothermal-high temperature pyrolysis?,and explored their microwave absorption performance and microwave absorption mechanism.This paper provide a certain reference value for further research on the preparation of microwave absorbing materials by metal-organic framework as precursor.?1?In the first chapter,the precursors of bimetal?Co,Zn?-MOFs were obtained by aging at room temperature,and then the N-doped cobalt tetroxide/cobalt/carbon?Co₃O₄/Co/C?magnetic composites were prepared by high-temperature pyrolysis of the precursors.The structure,composition,microscopic morphology,magnetic properties and electromagnetic parameters of the composites were systematically studied by using a variety of analytical techniques.The results show that the N-doped Co₃O₄/Co/C magnetic composite has typical diamond dodecahedron structure,high magnetic properties and excellent microwave absorption performance.Carbon matrix of composite material is doped with a large number of nitrogen atoms,and cobalt catalysis can form carbon nanotubes in situ,which is conducive to the absorption of electromagnetic waves.Its minimum reflection loss(RL_min)reaches-66.7 dB,and the effective absorption bandwidth?RL?-10 dB,EAB?reaches 4.2 GHz,and the thickness?d?is 2 mm.Finally,the microwave absorption mechanism of nitrogen-doped Co₃O₄/Co/C magnetic composites and the dipole polarization and interfacial polarization effects of materials,synergistic effects of conductance loss,dielectric loss and magnetic loss,excellent impedance matching and moderate electromagnetic attenuation characteristics,etc.?2?In the second chapter,the N-doped cobalt-carbon/multi-wall carbon nanotubes?Co-C/MWCNTs?magnetic composites were prepared for the samples prepared in the first chapter with weak conductivity.Firstly,different masses of acid MWCNTs were added to the precursor of the bimetallic MOFs.The precursors of bimetallic?Co,Zn?-MOFs/MWCNTs were obtained by room temperature aging,the precursor was subjected to high temperature pyrolysis to obtain N-doped Co-C/MWCNTs magnetic composites,subsequently.The structure,composition,microstructure,magnetic properties and electromagnetic parameters of nanocomposites with different acid treatment of MWCNTs were systematically studied by various analytical techniques.The results show that the composite material exhibits a similar and more uniform dodecahedral shape,and as the amount of MWCNTs added increases,the MWCNTs are wound around the carbon skeleton,connecting the frames together to form a conductive network,so that the microwave absorption performance of the composite material is excellent.When the addition amount of MWCNTs is 12.5 mg,the sample has the best microwave absorption performance.When the filling ratio is 25 wt%and d is 2.5 mm,the RL_min of Co-C/MWCNTs?12.5 mg?sample reaches-50.0 dB,EAB is3.6 GHz?8.2-11.8 GHz?,covering 86%of the X-band?8.2-12.4 GHz?,the dipole polarization and interfacial polarization effects of the material,the synergistic effect of conductance loss,dielectric loss and magnetic loss,excellent impedance matching and moderate electromagnetic attenuation characteristics improve its microwave absorption performance.?3?In the third chapter,the Fe-MOFs-derived Fe₃O₄-carbon/reduced graphene oxide?Fe₃O₄-C/RGO?magnetic composites with special morphology were prepared by solvothermal-high temperature pyrolysis two-step method.Firstly,different masses of graphene oxide?GO?were added to the precursor of Fe-MOFs.The Fe-MOFs/RGO precursor was obtained by solvothermal method,and then the precursor was subjected to high temperature pyrolysis to obtain Fe₃O₄-C/RGO magnetic composites.A variety of analytical techniques were used to systematically study the structure,composition,microstructure,magnetic properties and electromagnetic parameters of nanocomposites with different GO additions.The results show that the Fe₃O₄-C/RGO magnetic nanocomposites have a special fusiform octahedron morphology,high magnetic properties and excellent microwave absorption properties.The best microwave absorption properties are obtained when the GO addition amount is 80 mg.The sample achieved a RL_min of-49 dB at a fill ratio of 25 wt%and a d of 1.61 mm,and the EMB of 5.4 GHz at a thickness of 1.5 mm;In addition,by changing the thicknesses of the coating,the RL_min corresponding to the maximum microwave absorption of different thickness gradually appears at different frequencies,and the absorption band??-10 dB?covers almost 2-16 GHz?S,C,X,Ku bands?bands,and the absorption intensity can be adjusted by changing the coated thicknesses.The microwave absorption mechanism of Fe₃O₄-C/RGO magnetic composites can be attributed to its synergy dipole polarization and interfacial polarization effects,synergistic effects of conductance loss,dielectric loss and magnetic loss,excellent impedance matching and moderate electromagnetic attenuation characteristics.Figure[52]Table[9]Reference[134]...