Preparation Of Polyacrylonitrile-based Carbon Nanofibers By Electrospinning And Their Microwave Absorbing Properties

With the rapid development of science and technology,wireless communication and radar technology have brought great convenience to human society,but also produced a lot of electromagnetic pollution and other problems.Therefore,it is of great significance to study efficient electromagnetic wave absorption materials.Carbon materials have become the research hotspot in recent years in the field of microwave absorption materials because of their advantages such as good conductivity,low density,and the chemical stability.In this paper,a series of carbon nanofibers with a one-dimensional structure were prepared by using polyacrylonitrile(PAN)as the carbon source,combined with electrospinning and high temperature pyrolysis technology.To improve the microwave absorption efficiency of carbon nanofibers,different modifications have been carried out.X-ray diffractometer(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),Raman spectrometer(Raman)and other means were used to characterize the composition and microstructure of materials.The vector network analyzer(VNA)was used to test the electromagnetic parameters.The effect of magnetic particles and element doping on electromagnetic wave-absorbing properties was systematically studied.The main research contents of this paper are as follows:(1)Firstly,iron((?))acetylacetonate was added to the electrospinning precursor solution,and carbon nanofibers embedded with magnetic Fe3C(FeCFs)were prepared by carbonization.The introduction of Fe3C can improve the magnetic loss and impedance matching characteristics of carbon fiber,thereby improving the microwave absorption performance of the sample.The sample can achieve a maximum reflection loss of-54.94 dB when the thickness is 1.36 mm When the matching thickness is 1.55 mm,the effective absorption bandwidth can reach 4.5 GHz(13.3-17.8 GHz).(2)Secondly,Co-based zeolitic imidazolate framework ZIF-67 was prepared.Then,ZIF-67 and PAN were mixed in a certain ratio for electrospinning.After carbonization,porous carbon nanofibers containing Co were obtained.The samples were named as Co-CNF-1,Co-CNF-2,Co-CNF-3(different ratios ofZIF-67 and PAN).The study found that the introduction of ZIF-67 can improve the electromagnetic wave absorption performance of carbon fibers and Co-CNF-2 showed the best performance.When the matching thickness is 1.65 mm,the effective absorption bandwidth can reach 5.5 GHz(12.1-17.6 GHz),almost covering the entire Ku band.In addition,the one-dimensional morphology of the fibers also has important influence on the microwave absorption performance.When ZIF-67 was added too much,the one-dimensional conductive network in Co-CNF-3 was destroyed and the electromagnetic performance is reduced compared to Co-CNF-2.(3)Finally,using PAN as the carbon source and nitrogen source,and sublimation sulfur as the sulfur dopant,sulfur-nitrogen co-doped carbon nanofiber materials(S-NCFs)were prepared by electrospinning.The effect of sulfur element doping on the microwave absorbing properties of carbon fibers was studied.The experimental results and theoretical calculations showed that nitrogen-containing carbon nanofibers doped with sulfur can not only generate a large number of electric dipoles,but also help to improve the electrical conductivity,thereby improving the dielectric loss of the material.When the matching thickness is 1.39 mm,the maximum reflection loss can reach-48.67 dB at 16.4 GHz,and the effective absorption bandwidth can reach 4.90 GHz at 1.53 mm.In summary,we prepared a series of carbon nanofiber composite materials by electrospinning technology,and the influence of the microstructure and composition of the material on electromagnetic parameters and microwave absorption performance was studied.Lightweight,high-strength and broad band absorption microwave absorption was obtained.This work provides a simple and efficient method for the preparation of lightweight and efficient carbon-based microwave absorbing materials.