Layered Double Hydroxide Based Nanofibers As Highly Efficient Electromagnetic Wave Absorber

In recent years,with the increasing demand for reducing electromagnetic radiation and resistance to electromagnetic interference,electromagnetic wave absorbing materials have been widely used in industrial,commercial,and military fields.Electromagnetic wave absorbing materials can absorb incident electromagnetic waves by converting electromagnetic energy into thermal energy and other form of energy.However,traditional absorbing materials have the disadvantages of narrow frequency band and high density.It is still a challenge to develop new kinds of absorbing materials with thin thickness,low density,wide frequency bandwidth and strong absorption.The loss mechanisms of traditional electromagnetic wave absorbing materials are single.Dielectric materials such as carbon,ceramics,and conductive polymers can only attenuate electromagnetic wave energy through dielectric loss,while magnetic materials such as oxides and alloys possess only magnetic loss mechanism,which is unfavorable to achieve impedance matching and result in poor absorption performance.Therefore,it is necessary to construct various composite materials to improve the electromagnetic wave absorption efficiency through the synergistic effect between different components.This paper proposes a method for preparing LDH-based nanofiber materials and the electromagnetic wave absorption properties.The main contents and results of our research are as follows:1.The structure of carbon nanofibers doped iron-nickel alloy and nickel ferrite was designed.The nanofiber materials with a core-shell structure were synthesized by coaxial electrospinning technology.The shell layer was polyacrylonitrile doped with FeOOH(FeOOH/PAN),and the core layer was polyacrylonitrile doped with carbon nanotubes(CNTs/PAN).CNTs/PAN@NiFe-LDH were obtained by in-situ growth of NiFe-LDH on Carbon Nanotubes/Polyacrylonitrile(CNTs/PAN)fibers,and transformed to short carbon nanofibers containing FeNi alloy and NiFe2O4 particles(NiFe@CNF-x composite)at different calculation temperature.The topological transformation of NiFe-LDH into magnetic nanoparticles was studied in detail.The NiFe@CNF-900 sample exhibited the best reflection loss of-49.5 dB at a thin thickness of 1.4 mm,and possessed a wide effective absorption bandwidth of 4.72 GHz at 1.5 mm.2.The structure of hollow carbon nanofibers doped with cobalt-iron alloy and metal oxide was designed.Coaxial electrospinning technology was used to synthesize nanofiber materials with a core-shell structure.The shell layer is polyacrylonitrile(PAN/CoFe-LDH)doped with CoFe-LDH and the core layer was polystyrene(PS).The core layer was removed by high-temperature calcination to prepare the carbon nanofiber composite material with hollow structure.Further,the pumping speed rate of the shell layer and the core layer was changed to adjust the ratio of the core layer and the shell layer of the material and the electromagnetic parameters of the material.The electromagnetic wave absorption properties of carbon nanofiber composites with different shell thicknesses were studied.As for the sample S3,the minimum reflection loss value reaches-35.1 dB at 15.36 GHz with the matching thickness of 1.5 mm and the effective absorption bandwidth of 4.64 GHz.