Preparation Of Lignin-based Magnetic Composite Carbon Nanofibers And Their Application In Microwave Absorption

Lignin is the second abundant renewable biopolymer in nature.The preparation of carbon nanofibers by electrospinning method provides a new way for high value-added utilization of lignin.By electrospinning,dielectric loss materials can be combined with magnetic loss materials,and their electromagnetic matching characteristics can be effectively controlled during preparation of composite carbon nanofibers absorbing materials.This procedure not only broadens the source of carbon fiber materials,but also shows the potential of these biomass-based composite carbon nanofibers in the utilization of microwave absorption.porous carbon nanofibers?HPCNFs?were respectively fabricated by electrospinning and co-axial electrospinning followed by stabilization and carbonization processes,with the bagasse acetate lignin as carbon source,iron???acetylacetonate as magnetic precursor,polyvinylpyrrolidone as pore inducer and styrene acrylonitrile copolymer as core electrospinning solution.Meanwhile,lignin-based solid and hollow pure carbon nanofibers were prepared from bagasse acetic acid lignin.The resultant carbon nanofibers were oxidized by nitric acid,and then blended with iron???acetylacetonate to synthesize Fe₃O₄/lignin-based solid pure carbon nanofibers?Fe₃O₄/CNFs?and Fe₃O₄/lignin-based hollow pure carbon nanofibers?Fe₃O₄/HCNFs?via a solvothermal method.The structure changes of pure carbon nanofibers before and after nitric acid oxidation treatment were characterized by Fourier transform infrared?FT-IR?and Raman spectroscopy?Raman?.The morphology,particle composition,porous properties and magnetic property of composite carbon nanofibers were studied by Scanning electron microscopy?SEM?,X-ray diffractometer?XRD?,specific surface and porosity analyzer?BET?and vibrating sample magnetometer?VSM?,respectively.The as-prepared composite carbon nanofibers were used as absorbing materials,and their electromagnetic parameters and microwave absorption performance in the frequency range of1?18 GHz were analyzed and studied by a vector network analyzer?VNA?.The results were shown as below:1.Lignin-based solid carbon nanofibers?SCNFs?were fabricated by electrospinning of bagasse acetate lignin.The fiber diameters were 100?300nm;particle diameters of SCNFs-15were 30?50 nm,and the main components of particle were Fe₃C and Fe.All SCNFs exhibited weak ferromagnetism.The SCNFs were used as absorbing materials.SCNFs-15 had the best microwave absorption performance,with the minimum reflection loss of-12.8 d B at 13.23GHz and the bandwidth of reflection loss below-10 d B was 3.13 GHz?11.97?15.1 GHz?.As the thickness of the absorber changed within 1.5?3 mm,the bandwidth below-10 d B could cover 9.34 GHz?5.76?15.1 GHz?.2.Lignin-based hollow porous carbon nanofibers?HPCNFs?were fabricated by co-axial electrospinning with PVP as pore inducer in shell electrospinning solution and SAN as core electrospinning solution.HPCNFs-5 appeared as a hollow structure with a diameter of about900nm,the other samples were flat and curved.All fibers had a small number of mesoporous mainly with the size of 4?10 nm.The main components of particulate matter were Fe₃O₄,Fe₃C and Fe.All HPCNFs exhibited typical ferromagnetism.The HPCNFs were used as absorbing materials.HPCNFs-10 had the best microwave absorption performance,with the minimum reflection loss of-11.1d B at 7.04GHz,and the bandwidth below-10d B was 0.72GHz?6.63?7.35GHz?.3.Fe₃O₄/lignin-based solid pure carbon nanofibers?Fe₃O₄/CNFs?and Fe₃O₄/lignin-based hollow pure carbon nanofibers?Fe₃O₄/HCNFs?were respectively synthesized by blending nitric acid treated lignin-based solid and hollow pure carbon nanofibers,respectively,with iron???acetylacetonate via a solvothermal method.The diameters of CNFs were 200?500 nm,and that of HCNFs were about 1.7?m.The diameter of Fe₃O₄ nanoparticles,which was uniformly loaded on the carbon fibers surface,was about 100nm.The average pore size of the two composites was 14.8 nm and 10.2 nm,respectively,and both samples exhibited super paramagnetism.The Fe₃O₄/CNFs and Fe₃O₄/HCNFs were used as absorbing materials.The microwave absorption performance of Fe₃O₄/HCNFs was better than Fe₃O₄/CNFs,with the minimum reflection loss of-11.8 d B at 9.28 GHz,and the bandwidth below-10 d B was 1.12GHz?8.74?9.86 GHz?.As the thickness of the absorber changed within 1?2.5mm,the bandwidth below-10d B could cover 9.47 GHz?5.28?14.75GHz?.