Preparation And Study On Electromagnetic Wave Absorption Properties Of Carbon-based Composites

In recent years,as technology and electronic industry are developed rapidly,electromagnetic pollution has gradually become an increasingly serious environmental pollution problem.The study of electromagnetic(EM)wave absorbers provides an effective way to solve electromagnetic pollution.Among the numerous absorbing materials,graphene is favored by more and more researchers due to its light-weight,good chemical stability,excellent electrical and thermal conductivity.However,the preparation of graphene is cumbersome and high-cost,this paper is devoted to the fabrication of composite based on graphitized carbon spheres.Furthermore,as an important wide band-gap semiconductor,ZnO has been widely used in catalysts,sensors,solar cells and so on.Therefore,the composites synthesized with carbon and ZnO may possess enhanced EM wave absorption properties.In the meantime,the introduction of nitrogen atom into carbonaceous materials to form polarization centers also has significant contribution to improving EM wave absorption properties due to the close atomic radius of nitrogen and carbon atoms.This paper is devoted to the synthesis of novel absorbing materials,which meet the requirements of "light-weight,thin-coating,wide and strong",by composites of carbonaceous materials,ZnO and nitrogenous materials,and the structure,morphology and EM wave absorption properties are studied minutely by XRD,XPS,SEM and VNA,respectively.The main research contents and results are as follows:(1)C/ZnO composites with increased EM wave absorbing features have been synthesized through a simple one-pot hydrothermal process and subsequent high temperature carbonization under the protection of argon.The results depicted that the maximum absorption of C/ZnO composites synthesized with the optimal molar ratio of zinc acetate to glucose is-50.43 dB at 15.77 GHz.The 1.16-mm-thick coating showed a wide effective absorption bandwidth(3.52 GHz)of EM wave(RL?-10 dB).The thin coating thickness of the C/ZnO composites is desirable for decreasing the absorber weight in EM wave absorption.And there were no other reagents used throughout the synthesis process except for the green glucose and zinc acetate.(2)Nitrogen-doped carbon spheres were fabricated through a hydrothermal method and annealing process,and the effects of annealing temperature on EM wave absorption properties were studied.Nitrogen-doped carbon spheres with certain adhesivity were relatively uniform in size,and a part of carbon spheres exhibited graphitized structure.As annealing temperature increases,the EM wave absorption properties of nitrogen-doped carbon spheres increased first and then decreased.The maximum absorption of nitrogen-doped carbon spheres with the optimum annealing temperature was-51.20 dB at 12.39 GHz,and the effective absorption bandwidth was obviously promoted to 6.09 GHz when the coating thickness was 2.32 mm.(3)Nitrogen-doped carbon spheres annealed with different temperatures were encapsulated in ZnO by constant temperature water bath method and then annealed at 400?to obtain ZnO wrapped nitrogen-doped carbon spheres composites,whose morphology was spherical with uniform size.In ZnO wrapped nitrogen-doped carbon spheres composites,the crystallinity of ZnO was good,while carbon spheres mainly showed amorphous and graphitized structure.The maximum absorption of ZnO wrapped nitrogen-doped carbon spheres annealed at 730? was promoted to-68.55 dB at 12.22 GHz,the 2.22-mm-thick coating showed a wide effective absorption bandwidth(5.94 GHz)of EM wave.Accordingly,ZnO wrapped nitrogen-doped carbon spheres composites were promising novel EM wave absorbing materials.Furthermore,the loss mechanism was analyzed by phase analysis,interfacial polarization,conductive loss and Cole-Cole semicircles.