The Construction And Electronmagnetic Wave Absorption Properties Of Magnetic Alloy/Carbon-Based Composites Derived From MOFs

It is of great significance to develop high performance electromagnetic wave absorbing materials in modern defense industry and electronic information technology.As a new porous crystalline material,metal organic frameworks（MOFs）have attracted wide interest from researchers in the field of new functional materials research due to their characteristics of designable structure,adjustable properties,large specific surface area,uniform pore distribution,diverse morphology and so on.Based on their characteristics of structure,performance and morphology mentioned above,MOFs as precursors show unique advantages in constructing high performance electromagnetic wave absorbing materials with specific composition,structure and morphology.In this thesis,bimetallic MOFs as precursors based on their structural design,a series of magnetic alloy/carbon-based composites with specific composition and morphology were obtained by in-situ pyrolysis of precursors under specific conditions.The main research contents of this thesis are as follows:Firstly,three core-shell bimetallic Co-MOF-74@M-MOF-74（M=Fe,Ni,Mn）precursors were prepared by solvent thermal method using monometallic Co-MOF-74as templates and subjected to high-temperature pyrolysis under argon protection to obtain three composites,Co-Co₃Fe₇@C,Co-Ni@C and Co-Mn O₂@C.The effects of compositions and morphologies of composites were investigated for the electromagnetic wave absorption performance.The characterization analysis and performance tests of the three composites revealed that Co-Co₃Fe₇@C had the most excellent electromagnetic wave absorption performance.The minimum reflection loss value（RL）was-29.2 d B at the thickness of 2.5 mm,and the maximum effective absorption bandwidth was 5.28 GHz.Secondly,bimetallic Co Fe-MOF-74 precursors was prepared by one pot method and Co Fe@C-600,Co Fe@C-700 and Co Fe@C-800 composites were obtained by high-temperature pyrolysis of precursor at different temperatures.The effect of different calcination temperatures was investigated for the electromagnetic wave absorption performance of composites.The characterization analysis and performance tests of three composites revealed that Co Fe@C-700 obtained at 700°C exhibited the best electromagnetic wave absorption performance.The minimum reflection loss value reached-48.5 d B at the thickness of 4 mm and the maximum effective absorption bandwidth reached 5.56 GHz with the thickness of 3.5 mm.Finally,melamine（MA）were introduced to bimetallic Ni Fe-MOF nanosheets by solvent evaporation method to obtain Ni Fe-MOF/MA precursor,which were pyrolyzed at different temperatures to obtain CN/Fe Ni₃@C-x composites.The effects of the introduction of melamine and different calcination temperatures were investigated for the electromagnetic wave absorption performance of composites.The performance tests revealed that the pure Ni Fe-MOF derived Fe Ni₃@C-700 had poor electromagnetic wave absorption performance,while the introduction of melamine could improve the electromagnetic wave absorption performance.The CN/Fe Ni₃@C-700 obtained at 700°C showed the best absorption performance,the minimum reflection loss value reached-43.50 d B at the thickness of 2.7 mm and the maximum effective absorption bandwidth reached 4.27 GHz with the thickness of 2mm.