Fabrication Of Carbon Based Nanofibrous Membranes For High-efficiency Electromagnetic Wave Absorption

With the rapid advancement of up-to-date technology,electromagnetic wave?EMW?absorption materials become more and more indispensable to daily life,widely required for various applications and even national strategic areas.Nevertheless,it has remained a great challenge and highly desired to produce and develop lightweight,flexible and high-efficiency EMW absorbing materials that are able to alleviate the unfavorable interferences in wide-ranging frequency.In this dissertation,we have fabricated different carbon based composite nanofibrous membranes via electrospinning method,then examined and compared their performance to EMW absorption application in a broad frequency range with proper thicknesses.The high-performance EMW absorption materials have been fabricated from diverse materials such as conductive polymers,carbon-based nanostructures and magnetic metal oxides.Additionally,to achieve proper EMW absorption performance,we have fabricated composite materials with special features such as porous structures in addition to use the materials with an excellent permittivity()and permeability()parameters to improve the properties of the final composite.The main contents of the dissertation are below:Firstly,we reported a scalable strategy to create Co₃O₄/carbon composite nanofibrous membrane by electrospinning technique followed by stabilization and carbonization processes.An optimal reflection loss?R_L?value of-36.27 dB is reached at 13.76 GHz for a layer of 2 mm thickness.R_L exceeding-20 dB can be realized in any interval within the 4.5-14.4 GHz range by selecting a proper thickness of the absorbing layer between 1 and 5 mm.The Co₃O₄/carbon composite nanofibrous membrane could serve promising and attractive candidates for lightweight and enhanced EMW absorbing materials.This fabricated composite provides an innovative and effective approach to design the novel EMW absorbing material in a broad frequency range for practical applications.Secondly,we fabricated a porous and lightweight carbon nanofibers?CNFs?membrane combined with reduced graphene oxide?rGO?and magnetic nanoparticles by the electrospinning process followed by calcination.The composite membrane exhibited high-efficiency absorption abilities due to its particular porous structure and introduced components in the final sample.Specifically,both cobalt and iron nanoparticles captured into CNFs are advantageous to the electrical conductivity of the membrane by lessening the contact loss via creating the metal-metal crossing points within the membrane.The introduced components are capable of enhancing the absorption performance due to the improvedandin the composite structure.The R_L value was demonstrated to be-43.60 dB at 5.84 GHz with a matching thickness of 5 mm.The R_L can be obtained up to-10 dB in a wide range of 4.3-18 GHz by selecting an optimal thickness,indicating that most of the EMW can be successfully absorbed.The synthesis of nanofibrous composite in this work identifies a new direction to fabricate advanced EMW absorption materials towards broad practical applications.Thirdly,we proposed a new route to produce high performance EMW membranes by combining techniques of electrospinning,stabilization and carbonization processes.NiFe₂O₄ nanoparticles and multiwall carbon nanotubes?MWCNTs?were respectively selected as the effective magnetic material and dielectric material to construct the highly flexible NiFe₂O₄/MWCNTs doped CNFs.The fabricated composite membrane exhibits superior EMW absorption behavior in a wide frequency range.For the EMW absorption performance in C-band?4-8 GHz?,X-band?8-12 GHz?and Ku-band?12-18 GHz?,the R_L exceeding-20 dB are obtained in the frequency range of 5.36-18 GHz at a sample thickness of 2-5 mm.Similarly,the R_L value of-45.60 dB can be realized for NiFe₂O₄/MWCNTs CNFs with a bandwidth of 12.96 GHz at a thickness of 2.5 mm.The as-synthesized NiFe₂O₄/MWCNTs CNFs nanofibrous membrane can be a promising candidate for light-weight and excellent EMW absorbers.This fabricated material will afford an alternative solution for the fabrication of EMW absorbing materials for wide practical applications.Finally,we designed to fabricate the magnetic and dielectric nanofibrous membranes,which can be effectively used as EMW absorption materials by a facile electrospinning process.The as-fabricated composite CNFs,which combined the components of nickel,cobalt antioxidant nanoparticles and carbon nanotubes,exhibited outstanding magnetic,dielectric properties and strong absorption ability in a wide frequency range.These nanoparticles encapsulated in CNFs are extremely beneficial to the electrical conductivity of the composites through decreasing the contact loss within the CNFs by the formation of the metal-metal interfaces.Correspondingly,the R_L value of-46.60 dB was reached at the 4.88 GHz frequency range with a layer thickness of 5.5 mm for these mechanically light and flexible membranes.The enhanced absorption performance?<-10 dB?in the wide frequency band?4.16-18 GHz?can be achieved by selecting a suitable thickness of the material.Results demonstrate that theandof developing samples have been largely improved due to the integrated interaction of all introduced components in the structure.The composite membranes are promising candidates for scalable,lightweight and high performance EMW absorption materials in the frequency range from C band to Ku band?4-18 GHz?.This dissertation clarifies the design strategies for fabricating composite nanofibrous membrane constructed with highly magnetic and dielectric materials,which enables high-efficiency EMW absorption in broader frequency range.These fabricated flexible,lightweight and cost-effective EMW absorption materials can be broadly applied in many fields.