Preparation And Absorption Properties Of Biomass-carbon Composites With Magnetic Functionalization

Nowadays,advanced electromagnetic wave(EMW)absorbing material has been widely used in various emerging fields to address the challenges brought by electromagnetic interference and communication security.Although significant progress has been achieved in novel EMW absorption materials,the complexity of the synthesis process,impedance mismatches and low attenuation capability still make the development of new absorbing materials face many challenges.Biomass-derived carbon(BDC)has the advantages of low cost,environmental protection,sustainability and easy preparation,which could be directly converted into carbon material by pyrolysis method.Although BDC has excellent potential in microwave absorption,the high complex permittivity and low permeability will lead to impedance mismatch,which hinders the development of biomass carbon materials in advanced EMW absorbing materials.In view of the excellent dielectric-magnetic complementarity among the magnetic carbon components,incorporating the magnetic constituents into dielectric material has proved to be an effective method to optimize the attenuation capability and impedance matching of absorber.Therefore,we propose a reasonable combination of magnetic components and BDC to prepare a novel high efficiency EMW absorbing material.(1)Biomass porous carbon with 3D structure was prepared from wheat flour by KOH activation and high temperature carbonization.After that,magnetic particle ZnFe₂O₄ was introduced to obtain a composite composed of porous carbon and ZnFe₂O₄ nanospheres(PC@ZnFe₂O₄).The results showed that PC have abundant nanopores.After solvent-thermal reaction,a large number of ZnFe₂O₄ nanospheres were uniformly dispersed on the surface of PC and the carbon material still retained its 3D porous structure.Due to the ideal synergistic effect of PC and ZnFe₂O₄ nanoparticles,the impedance matching and attenuation constant of the absorbent with the 20 wt%filling content reached the ideal values.When the ultra-thin thickness was 1.8 mm,the minimum reflection loss(RL_min)value reached-54.1 d B at 14.1 GHz and the effective absorption bandwidth(EAB)was 3.9 GHz(12.3-16.2 GHz).(2)BDC was prepared by mixing pine nut shell powder with Na OH and heating at 600?for 90 min under N₂.A novel 3D porous carbon@nickel carbon spheres(PC@Ni/C)nanocomposite was synthesized by a facile solvothermal and subsequent annealing treatment method.Morphological analysis showed that the 2D nanosheets were stacked with each other to form a unique 3D structure.Ni/C nanospheres with a size of about 300 nm were distributed evenly between the ultrathin carbon nanosheets.A large number of ultra-small Ninanoparticles(about 5 nm in size)were widely distributed on the surface of the translucent carbon nanosheets.The optimized PC@Ni/C nanocomposites exhibited remarkable microwave absorption properties.When the filler ratio was 20 wt%,the RL_min value of PC@Ni/C reached-73.8 d B,and the corresponding EAB achieved 5.8 GHz with a thickness of only 2.2 mm.(3)A multi-dimensional porous carbon@NiCo-layered double hydroxides@Nichains(PC@NiCo-LDHs@Ni)was prepared by the solvothermal and subsequent freeze-drying process.The produced BDC aerogel was kept with metal salt solution in a reactor at 170?for14 h.Subsequently,the PC@NiCo-LDHs@Niaerogels were freeze-dried by mixing with Nichains.The layered NiCo-LDHs were uniformly attached to the pine nut shell-derived carbon surface and wrapped around the carbon skeleton.The Nichains were widely distributed and interspersed to form bridges between the 3D structures.Owing to its special multidimensional structure,the aerogel exhibited excellent thermal insulation,compressive and corrosion resistance properties.The RL_min value of PC@NiCo-LDHs@Nireached-57.4 d B at 13.3 GHz and the EAB was 6.4 GHz.