Synthesis And Microwave Absorption Properties Of Polyaniline And Polyaniline-Derived Carbon-Based Magnetic Composites

Electromagnetic wave（Electromagnetic wave,EMW）is an electromagnetic field that cannot be seen or touched and does not need any medium to propagate.It satisfies the duality of wave and particle,and is widely used in military,medical and civil applications.While creating convenience for human beings,there are also excessive EMWs that harm human health.In view of the application requirements of"stronger","wider","thinner"and"lighter"EMW absorbing materials,the design of materials should meet the premise of impedance matching,and improve the attenuation capacity of materials as far as possible.This work takes polyaniline（PANI）and its derived carbon as the research object,and adopts composite magnetic materials(BaFe₁₂O₁₉,Ni,Fe,Ni₃Fe)to achieve the synergistic effect of dielectric loss and magnetic loss.The doping of heterogeneous elements can effectively improve the performance of effective absorption bandwidth of materials,and even trigger magnetic response conducive to absorbing waves.The one-step carbonization of materials can not only achieve nitrogen doping into carbon material,but also reduce metal oxides at the same time,so as to obtain the composite of magnetic metals and alloys.In addition,introducing rich attenuation modes is a channel to expand the absorption performance.Therefore,the application of carbonized polyaniline products in the field of EMW absorption will open a new idea.The main research conclusions of this work are as follows:（1）To explore the best scheme of sol-gel self propagating synthesis of BaFe₁₂O₁₉,and take it as the core of the composite,wrap PANI prepared by in-situ synthesis on the outside,and adjust the composite ratio to obtain BaFe₁₂O₁₉/PANI composites.The cooperation between the dielectric type PANI and the magnetic conductive type BaFe₁₂O₁₉ realizes the adjustment of electromagnetic parameters of each other,which affects the absorption performance of the BaFe₁₂O₁₉/PANI composites.Under a certain thickness,the absorption bandwidth of three samples can be as high as 8.24 GHz,7.60GHz,and 9.26 GHz,with an optimal absorption intensity of-67.36 d B.（2）Considering that PANI has unstable microwave absorption performance and contains nitrogen elements,it is subjected to carbonization treatment.Ni O/PANI with different stoichiometric ratios were prepared as the precursor,and N-doped PDC/Ni composites were obtained by self-reduction reaction at high temperature in a tubular furnace under nitrogen protection.The carbonization process caused the collapse of the flocculent morphology of PANI and coated Ni metal.XPS analysis showed that the N element from PANI was successfully doped in carbon,and widening the effective absorption bandwidth at a relatively thin thickness.The optimal effective absorption bandwidth was 5.68 GHz and reached-61.93 d B,with thickness was 1.72 mm.（3）Fe₂O₃/PANI with different stoichiometric ratios were prepared by in-situ synthesis method as the precursor.Considering the valence variability of Fe element,the composites ratio was expanded and the ratio gap between different samples was narrowed.N-doped PDC/Fe composites were prepared by high temperature self-reduction method.The BET analysis of the samples before and after carbonization showed that carbonization introduced more micropores and mesoporous pores conducive to EMW attenuation into the microstructure of the material.The sample exhibits multiple strong absorption peaks at high frequencies when determining its thickness.The optimal absorption performance reaches-66.92 d B at 2.46 mm,and effective absorption bandwidth reached 6.40 GHz（11.60 GHz to 18.00 GHz）at 2.36 mm.（4）Ni₃Fe precursor was prepared by hydrothermal method,and N-doped PDC/Ni₃Fe composites were prepared by in-situ synthesis and high temperature self-reduction.The carbonized porous structure provides convenience for uniform dispersion and embedding of spherical Ni₃Fe,and the abundant interface also attenuates the incident EMW for many times to increase the absorption intensity.Compared with the absorption performance of single-phase materials Ni₃Fe and derived-carbon,the absorption strength of composites greatly increased,with a maximum of-80.91d B,when the thickness is2.62mm,the effective absorption bandwidth was 4.24 GHz（8.80 GHz-13.04 GHz）,and the strength reached-49.97 d B.Figure[56]Table[9]Reference[139]...