MOFs-derived N-doped Porous Carbon And Its Composites And Study On Their Wave Absorption Properties

With the change of society and technological leap,human beings enjoy high technology,but also accompanied by serious electromagnetic pollution,reduce the harm of electromagnetic wave,has become one of the most difficult problems today.Metal-Organic Frameworks（MOFs）have a unique 3D structure and strong stability.The treated MOFs can maintain the special morphology of the precursors and have good electromagnetic wave absorption performance,whether it is to form porous carbon materials by calcination at high temperature or to form metal oxides,or to vulcanize them into sulfides by in-situ topological transformation.The morphology of molybdenum disulfide is varied and has a special nanopore structure.Ferrite materials,with excellent performance at high frequency,have a long history of development,simple preparation method and low price,is one of mature microwave absorption materials（MAMs）.Graphene,as one kind of new material,has a large number of defects in its special two-dimensional structure,and its low density,light weight and good electrical conductivity contribute to the attenuation of electromagnetic waves.Through the above analysis,on the basis of studying the porous carbon derived from MOFs,the above materials were composite in different ways and proportions,and their structure and morphology were characterized by various methods.The performance and electromagnetic parameters of the samples were tested by VSM and VNA respectively,and the performance and mechanism were discussed.The main contents are as follows:（1）The precursor material ZIF-8 was prepared by stirring at room temperature and carbonized into nitrogen-doped porous carbon by calcination at high temperature.The sample obtained was relatively pure,without other impurities,with complete morphology,presenting special rhomboid dodecahedron with a size of about 300 nm and uniformly dispersed.The single NPC has a poor performance,with a minimum reflection loss of-17.27 dB at15.2 GHz.（2）Molybdenum disulfide（MoS₂）material with high dielectric loss was prepared by hydrothermal method,the morphology was intact,which was like flower balls,and the size of the samples was about 3μm.The porous carbon doped with nitrogen was loaded on its surface to form NPC/MoS₂ binary composites.The synergistic effect between nitrogen doped porous carbon and molybdenum disulfide improves the impedance matching of the absorber.With the increase of MoS₂ content,the complex dielectric constant of the material increases continuously.When the amount of MoS₂ is 50wt%,the material has the best absorbing performance.When the thickness is 3.0 mm,the lowest reflection loss is-34.94 dB at 12 GHz,and the bandwidth is 6.08 GHz（8.56-14.64 GHz）.（3）Nitrogen-doped porous carbon/cobalt ferrite（NPC/Co Fe₂O₄）binary composites were prepared by hydrothermal method.The crystal shape of the samples was intact.The size of the cobalt ferrite was about 50-80 nm,and the agglomeration phenomenon appeared slightly due to its magnetic properties.There are many different interfaces between the composite materials,resulting in the interface polarization effect.In addition,due to the magnetic properties of cobalt ferrite itself,the magnetic loss of the composite material to the electromagnetic wave is increased.When the doping amount of cobalt ferrite is15 wt%,the material has the best absorbing performance,the best matching thickness is 3.5 mm,the lowest reflection loss can reach-19.09 dB at 10.24GHz,and the effective absorption band is 4 GHz（8.48-12.48 GHz）.（4）Nitrogen doped porous carbon/cobalt ferrite ternary composites coated with reduced graphene oxide（RGO）were obtained by Hummers method after chemical reduction.The porous carbon of rhomboid dodecahedron and spherical cobalt ferrite are loaded on the surface of lamellar graphene.Different interfaces between materials enhance the interfacial polarization,and the addition of graphene causes more defects on the surface of the material,which induces dipole polarization.When the amount of graphene is 9 wt%,the minimum loss of the sample at 15.28 GHz is-40.74 dB,the thickness is 2.5mm,and the effective absorption bandwidth is 4.96 GHz（13.04-18 GHz）.