Polymer Self-assembly Mediated Preparation Of Transition Metal Doped Carbon-based Materials For Electromagnetic Wave Absorption

With the increasing demand for wireless communication,the use of the fifth-generation mobile communication technology（5G）at the gigahertz frequency has brought great convenience to our daily life.However,it also brings serious electromagnetic pollution problems,which will pose a threat to human health and the normal operation of electronic equipment.Absorbing material is an important technical core to solve the above problems,and has received extensive attention.Single magnetic absorbing materials often exhibit a series of problems such as high density,large coating thickness,narrow effective absorbing band,etc.The composite of carbon materials and magnetic materials can optimize the impedance matching,and overcome the above problems through the magneto-dielectric loss synergism mechanism,which is an important research direction of absorbing materials at present.In this paper,the main research idea is to control the preparation of magneto-dielectric absorbing materials by polymer self-assembly technology.Through polymer coordination induced self-assembly and crystallization induced self-assembly,the hierarchical metal-doped carbon materials are precisely constructed.The influence of polymer soft template and precursor on carbon and transition metal components during high-temperature pyrolysis are analyzed,and the magneto-dielectric loss synergism mechanism is explored.Generally,the research will promote the application of polymer self-assembly in the field of microwave absorption,and is expected to provide scientific basis for the preparation of new magneto-dielectric absorbing materials.The main research contents are as follows:（1）Preparation and application of iron doped carbon-based absorbing materials by applying double-hydrophilic hyperbranched copolymer（HPG-g-HPEI）as soft-template.HPG-g-HPEI was synthesized through the synthesis of alkynyl polyol（HPG）and its copolymerization with hyperbranched polyethyleneimine（HPEI）.The polymer micelles containing transition metals were prepared by the coordination-induced self-assembly process of HPFG-g-HPEI and Fe³⁺,which were then in situ combined with phenolic resin to form composite assemblies.The composite assemblies were transformed into porous Fe/C composites through high temperature pyrolysis.The results showed that Fe/C-800composite exhibited the maximum absorption at the frequency of 11.2 GHz when the matched thickness is 3.4 mm and the filling loading is 10 wt%.The minimum reflection loss is-57.8 d B,and the corresponding effective absorption bandwidth（EAB）is 5.3 GHz,which can cover the whole X-band.（2）Preparation and application of Fe Co/Co doped carbon-based absorbing materials from polyimide（PI）crystallization-induced self-assembly.By using Fe-MOF as template,Fe-MOF@PI assemblies were first prepared via PI crystallization-induced self-assembly,and then Fe-MOF@PI@Co（OH）₂composites were constructed by in site formation of cobalt-containing hydroxide on Fe-MOF@PI surface.After high temperature pyrolysis,a hierarchical nitrogen-doped absorbing materials containing Fe Co/Co metal（Fe Co/Co@NC）were finally prepared.The results showed that Fe Co/Co@NC-800composite can achieve the maximum low frequency absorption at a frequency of 5.4 GHz with a thickness of 4.8 mm and a filling capacity of 20 wt%.The minimum reflection loss is-59.61 d B and the effective absorption bandwidth is 2.16 GHz（4.50 GHz～6.66 GHz）.