碳纳米纤维因具有大比表面积，高纵横比，良好的磁学和力学性质已经成为研究热点。静电纺丝法具有操作简单，低成本，环保，可大批量制备的优势，现已成为生产一维纳米纤维材料的一种必不可少的技术。磁性金属（Fe, Co, Ni）及其化合物纳米结构由于具有独特的物理性质，特别是优异的磁学性质而被广泛用做电磁波吸收材料。近年来，将磁性纳米晶与电纺丝纤维结合已成为静电纺丝领域中最引人注目的研究课题之一，制备出的复合材料在电磁波吸收方面有着潜在的应用。本论文主要内容包括：通过静电纺丝方法合成电磁性能增强的Co与N掺杂碳纳米纤维复合材料；通过静电纺丝技术结合高温煅烧的途径可控合成不同Fe含量的Fe3C与N掺杂碳纳米纤维复合材料；利用同样的方法分别合成了NiFe2O4和CoFe2O4纳米晶与碳纳米纤维复合材料。通过X射线粉末衍射仪（XRD）、拉曼光谱仪（Raman）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、氮气吸脱附比表面积分析仪（BET）、X射线光电子能谱（XPS）和微波矢量网络分析仪等测试手段对产物的结构、形貌、组成、磁性能与吸波性能进行测定与分析。具体内容如下： 1. 以乙酰丙酮钴（Ⅱ）和聚丙烯腈为原料，通过静电纺丝技术首先制备出前驱体纤维，再通过在氩气氛围中碳化得到两种形貌的Co纳米晶与N掺杂碳纳米纤维复合材料（Co/N-C NFs）, 分别是实心和大孔Co/N-C NFs材料。纤维长度可达数十微米，并且在纤维表面和内部均匀分布着大量Co纳米晶，Co纳米晶尺寸约为20 nm。大孔Co/N-C NFs材料具有分级孔结构。实心Co/N-C NFs材料具有优异的电磁波吸收能力，当样品在石蜡中百分含量仅为5 wt%，吸波体厚度为2 mm时，最小反射损耗（RL）值为 -25.7 dB，有效频带宽度（RL≤ -10 dB）为4.3 GHz。此外，通过调节样品层的厚度和掺杂样品的含量，这些材料可以应用在不同的电磁波吸收领域。 2. 使用静电纺丝技术结合高温碳化过程，以乙酰丙酮铁（Ⅲ）和聚丙烯腈为原料，制备了磁性Fe3C纳米晶与N掺杂碳纳米纤维复合材料。通过改变反应物中乙酰丙酮铁和聚丙烯腈的比例，得到不同金属Fe含量的产物。研究结论显示，所有产物都具有类似的形貌：在N掺杂碳纳米纤维上分布着大量磁性Fe3C纳米晶。另外与已报道的其他磁性碳基复合吸波材料进行比较，我们合成的复合材料在掺杂量较低（10 wt%）和金属Fe含量较少情况下，表现出卓越的吸波性能。实心Fe3C/N-C NFs 材料（Fe：14.5 wt%），在7.6 GHz下具有 -33.4 dB的最佳反射损耗值。对于实心Fe3C/N-C NFs-2材料（Fe：15.0 wt%），RL值均低于-10 dB的有效吸收带宽在样品厚度仅为2 mm时可高达6.2 GHz。大孔Fe3C/N-C NFs材料（Fe：6.9 wt%），在3 mm处具有4.8 GHz的宽带吸收区域，当调节吸波体厚度在2-6 mm范围内时，有效频带宽度可以在3.6-18.0 GHz频率下获得。因此得出结论：我们合成的实心和大孔Fe3C/N-C NFs 材料有望成为轻便，高性能和低金属负载量的吸波材料。 3. 以硝酸铁，硝酸钴和硝酸镍为金属源，聚丙烯腈和聚乙烯吡咯烷酮为原料，采用静电纺丝技术，通过调节煅烧气氛和温度，得到CoFe2O4纳米晶与碳纳米纤维复合材料（CoFe2O4/C NFs）和NiFe2O4纳米晶与碳纳米纤维复合材料（NiFe2O4/C NFs）。CoFe2O4/C NFs纤维长度约100 μm左右，直径约250 nm左右，纤维表面有直径约为10 nm左右的碳纳米管。与CoFe2O4/C NFs材料相比，NiFe2O4/C NFs材料的长度更长，有几百微米，直径也更小，仅有100 nm左右，纤维表面有很多纳米管生成。电磁波吸收性能测试表明，与相同条件制备的纯碳纤维相比，两种复合材料的微波吸收性能大大改善。

Carbon nanofibers have become a research hotspot due to their large specific surface area, high aspect ratio, and outstanding magnetic and mechanical performance. Electrospinning has the superiority of simple operation, low cost, environmentally friendly, and high-volume preparation. An indispensable technology for one-dimensional nanofiber materials, magnetic metal (Fe, Co, Ni) and its nanostructures are widely used as electromagnetic (EM) wave absorbing materials due to their excellent physical properties and excellent magnetic properties. The combination of magnetic nanocrystals and electrospun fibers has become one of the most exciting research topics in the field of electrospinning. The composite materials have potential applications in microwave absorption materials. The thesis is mainly about synthesizing cobalt and N-doped carbon composite nanofiber materials with enhanced EM properties by simple electrospinning method, synthesizing of Fe3C and N-doped carbon composite nanofibers with different iron contents by electrospinning combined with high-temperature calcination methods, preparing the CoFe2O4 nanocrystals composite carbon nanofibers and NiFe2O4 nanocrystals composite carbon nanofibers using the same electrospinning and annealing methods. The crystal structures, morphologies composition and properties of the as-prepared samples are analyzed and studied by XRD, Raman, SEM, TEM, XPS, BET, superconducting quantum interference device and microwave vector network analyzer. The main research content are as follows: 1. Using cobalt acetylacetonate (II) salt and polyacrylonitrile as raw materials, the precursor fibers are prepared by electrospinning method, and then the nanocomposites are synthesized by carbonization of as-electrospun precursor fibers in an argon atmosphere. As a result, the solid and macroporous N-doped carbon nanofibers composed of Co nanocrystals are obtained. The solid Co/N-C NFs has lengths up to several tens of micrometers and a large amount of cobalt nanocrystals are uniformly distributed on the surface and inside of the fibers. The cobalt nanocrystals are about 20 nm. The macroporous Co/N-C NFs has a special hierarchical porous structure. The solid Co/N-C NFs has superior microwave absorption. When the sample is only 5 wt% in paraffin and the matching thickness is 2 mm, the sample reached the lowset reflection loss (RL) value of -25.7 dB. The material also has a broadband effective absorption area (RL≤-10 dB) of 4.3 GHz. Furthermore, by changing the thickness of the absorber layer and the filler loading, these materials can be used in different fields of electromagnetic absorption. 2. Using simple electrospinning and annealing methods, the magnetic Fe3C nanocrystals decorated in N-doped carbon nanofibers were prepared through carbonization of as-electrospun polyacrylonitrile/iron acetylacetonate nanofibers precursors. By adjusting the content of iron acetylacetonate in the reactants, a series of solid and macroporous N-doped carbon nanofibers composed of Fe3C nanocrystals (solid Fe3C/N-C NFs and macroporous Fe3C/N-C NFs) with different metal iron contents are obtained. The results show that all the as-prepared six materials have similar morphology, and the magnetic Fe3C nanocrystals are uniformly dispersed on the N-doped carbon fibers. In addition, compared with other magnetic carbon-based nanocomposite absorbing materials in related literatures, the six materials exhibit excellent microwave absorption performance with extremely low doping amount (10 wt%) and low iron content. The solid Fe3C/N-C NFs (Fe: 14.5 wt%) have an optimum RL value of -33.4 dB at 7.6 GHz. For solid Fe3C/N-C NFs-2 (Fe: 15.0 wt%), the effective absorption bandwidth for RL values below -10 dB can be as high as 6.2 GHz at 2 mm. The macroporous Fe3C/N-C NFs (Fe: 6.9 wt%) has a broadband absorption region of 4.8 GHz at 3 mm. When the sample thickness is adjusted to 2-6 mm, the effective bandwidth can be obtained at a frequency of 3.6-18.0 GHz. It can be seen that these Fe3C nanocrystals and carbon nanofiber composites can be used as lightweight, high efficiency and low-metal content microwave absorbing materials in 1-18 GHz. 3. Using ferric nitrate, cobalt nitrate, nickel nitrate, polyacrylonitrile and polyvinylpyrrolidone as raw materials, through simple electrospinning and annealing methods to obtain the CoFe2O4 nanocrystals composite carbon nanofibers (CoFe2O4/C NFs) and NiFe2O4 nanocrystals composite carbon nanofibers (NiFe2O4/C NFs). CoFe2O4/C NFs has lengths up to 100 microns and a large amount of CoFe2O4 nanocrystals are distributed on the fibers. The average diameter of composite nanofibers is about 250 nm, and the carbon nanotubes on fiber surface has diameter of about 10 nm. Compared with CoFe2O4/C NFs, NiFe2O4/C NFs have longer lengths up to hundreds of micrometers, and the fiber diameters only about 100 nm. There are many nanotubes on the fiber surface. The EM wave absorbing ability tests show that the absorbing performance of the two composites are greatly improved, compared with the pure carbon nanofibers (CNFs) prepared under the same conditions.