Elsevier

Carbon

Volume 151, October 2019, Pages 36-45
Carbon

Alginate-templated synthesis of CoFe/carbon fiber composite and the effect of hierarchically porous structure on electromagnetic wave absorption performance

https://doi.org/10.1016/j.carbon.2019.05.025Get rights and content

Abstract

Natural alginate fibers are used as templates to fabricate CoFe alloy-decorated hierarchically porous carbon fibers (HPCFs). Due to the coordination with negatively charged α−L−guluronate blocks, transition metal (TM) ions could be confined in the “egg box” structure of alginate, which convert to CoFe alloy particles that homogenously embedded in HPCFs during carbonization. The composition and weight ratio of magnetic particles could be well controlled by adjusting the absorbed TM ions and carbonization temperature. Unlike previous analogues with uniform mesopores, this composite fiber simultaneously possesses a number of mesopores and a high proportion of submicron macropores which not only facilitates the accommodation of large-sized CoFe particles, but also induces abundant interfacial polarization and EMW multi-scattering. Remarkably, the CoFe/HPCF with a filler loading as low as 15 wt% in matrix achieves an extremely strong reflection loss of −69.1 dB at a thin thickness of 1.6 mm, and its effective absorption bandwidth reaches 5.2 GHz, showing better comprehensive properties than other similar absorbers. This work highlights the importance of hierarchically porous structure (especially macroporous structure) on improving EMW absorption. The synthetic strategy is green, low cost, scalable, and can be used to synthesize other highly efficient composite absorbers.

Introduction

Due to the aggravation of electromagnetic (EM) pollution and interference issues, electromagnetic wave (EMW) absorbing materials capable of converting EM energy to thermal energy through dielectric loss or/and magnetic loss have attracted considerable attention for military, civilian and commercial applications [1,2]. Advanced EMW absorbers are required to possess the advantages of strong absorption, broad bandwidth, thin thickness and lightweight [3,4]. Composite absorber consisting of both dielectric and magnetic components attracts considerable attention, because the EMW absorption properties can theoretically benefit from the complementarities between the permittivity and permeability of materials. Among various magnetic materials, magnetic metals such as Fe, Co, Ni and related alloys are more suitable for high-frequency EMW absorption due to their higher saturation magnetization and Snoek's limit, compatible dielectric loss, as well as distinguishable permeability in gigahertz frequency [5]. In particular, bimetallic alloys recently stimulate considerable interest because the alloying process could induce electron transfer and enhance spin polarizability which contribute to better EMW absorption properties [6,7].

To achieve lightweight feature, carbon fibers (CFs) with the advantages of low density, excellent electrical conductivity, good thermal and chemical stabilities, and low cost, have been considered as one of the most potential candidates for dielectric components [8]. The one-dimensional (1D) structure with large aspect ratio enables CFs readily construct a continuous conductive network in matrix which is favorable to dissipate EMW via induced current. Compared with typical 1D carbon material, i.e. carbon nanotubes, CFs can be designed with applicable electrical conductivity, which facilitates the optimization of impedance matching [9]. So far, many magnetic particle/CF composite absorbers have been successfully fabricated using electrospinning and electrodeposition methods, such as FeNi/CF, Fe/CF and FeCo/CF [[9], [10], [11]]. The electrospinning usually needs organic solvents to dissolve polymer (carbon resource) during the synthetic process, which causes environmental burden and increases the manufacturing cost. Meanwhile, the slow production rate and low yield of electrospinning limit the large-scale fabrication. As to electrodeposition method, the deposited magnetic metal/alloy particles exclusively distribute on the CF surface. Thus, the generated heterointerfaces between magnetic particles and CFs are quite limited which restricts the interfacial polarization effect. So far, the magnetic particle/CF composites derived from electrospinning and electrodeposition methods seem to reach a ceiling of EMW absorption performance. Therefore, there is an urgent need to develop new synthetic methods that are green, fast, low cost, and scalable. Meanwhile, a deeper understanding on the structure-performance relationship is highly desirable for better guiding the design of CF-based absorbers.

Recent advances in carbon-based absorbers have revealed that the void structure in carbon not only benefits the reduction of weight density but also significantly changes the EMW absorption performance. Theoretically, the void could induce interfacial polarization, act as an “effective medium” to modulate dielectric property, and provide scattering centers for EMW multi-scattering that leads to more EM energy loss by increasing the propagation path of EMW [[12], [13], [14], [15]]. Compared with carbon materials containing monoscale void, the latest findings report that the well-designed multiscale voids may be more conductive to the improvement of EMW absorption performance. For instance, Xu et al. reported that the carbon microspheres containing mesoporous carbon shell and submicron cavity exhibited much better EMW absorption properties than hollow carbon microspheres and solid carbon microspheres [16]. Qiu et al. found that the EMW absorption properties of activated carbon with hierarchical pore structure outperformed other carbon materials with uniform mesopores [17]. Although the “multiscale-pore effect” has only been attempted in very limited carbon structures, it motivates us to fabricate hierarchically porous CFs composed of submicron/micron-sized and nanoscale pores. Relevant exploration may find the chance to greatly improve the EMW absorption performance of CF absorbers, and further deepen the understanding of multiscale void in modulating EMW absorption properties.

In this work, we report a green and scalable strategy for fabricating CoFe/hierarchically porous CF (HPCF) composite using alginate fiber as a template. The naturally rich and non-toxic alginate contains a large number of “egg-box” which could accommodate metal ions via coordination with negatively charged α−L−guluronate (G) blocks [18]. The type and amount of metal ions immobilized in the “egg-box” can be easily adjusted by changing the metal salt solution, thus enabling the modulation of composition and loading of the magnetic particles on HPCFs. Compared with the previously reported mesopores CF composite absorbers, the high proportion of submicron macropores in CoFe/HPCF leads to a considerable improvement of EMW absorption. Remarkably, the CoFe/HPCF achieves a significant reflection loss (RL) of −69.1 dB and a broad absorption bandwidth of 5.2 GHz with a filler loading as low as 15 wt% and a quite thin matching thickness of 1.6 mm. The comprehensive absorption properties of CoFe/HPCF are superior to other analogues. In addition, a series of highly efficient composite absorbers were prepared using this method, including CoNi/HPCF, Fe/HPCF and Co/HPCF. We believe that the disclosed multiscale pore effect and the proposed synthetic method can provide more ideas and guidance for high-performance absorber design.

Section snippets

Materials

Sodium alginate was purchased from the Xilong Scientific Co., Ltd. Calcium chloride anhydrous (CaCl2), cobalt chloride hexahydrate (CoCl2·6H2O), iron chloride hexahydrate (FeCl3·6H2O), nickel acetate tetrahydrate (C4H6O4Ni·4H2O) and ethanol were purchased from J&K Scientific Ltd and used without further purification. Hydrochloric acid (HCl) was purchased from Beijing Chemical Works.

Synthesis of Ca−alginate fiber

Calcium−alginate fiber (Ca−AF) was produced by wet spinning according to a previous report [19]. Briefly, sodium

Results and discussion

Fig. 1(a)−(c) illustrate the synthesis of CoFe alloy/carbon fiber composite using alginate fiber as a template. As shown in Fig. 1(a) and Fig. S3(a), the white-colored Ca−AF prepared by a wet-spinning method, is straight and smooth with a uniform diameter of ∼10 μm. After being protonated via ion exchange reaction between Ca2+ and H+, the obtained H−AF was immersed in a mixed solution containing Co (II) and Fe (III) salts. Thus, the CoFe−AF was produced through immobilizing the Co2+ and Fe3+

Conclusion

CoFe/HPCF composite absorber with hierarchically porous structure is designed and prepared for highly efficient EMW absorption. Natural alginate fibers were used as templates to immobilize Co2+ and Fe3+ ions in abundant “egg box” structure via coordination with negatively charged α−L−guluronate blocks. During carbonization process, the alginate fibers were converted to porous CFs; simultaneously metal ions aggregated and formed CoFe2O4 octahedral particles at low temperature, followed by

Acknowledgments

This work was financially supported by National Natural Science Foundation of China (U1832138, 51731002 and 51671010), Beijing Municipal Natural Science Foundation (No. 2172031), Beijing Municipal Science and Technology Project (No. Z161100002116029), Aeronautical Science Foundation of China (No. 2016ZF51049), and Fundamental Research Funds for the Central Universities.

References (61)

  • J.J. Pan et al.

    Porous coin-like Fe@MoS2 composite with optimized impedance matching for efficient microwave absorption

    Appl. Surf. Sci.

    (2018)
  • S.S. Xiao et al.

    Ultralight lamellar amorphous carbon foam nanostructured by SiC nanowires for tunable electromagnetic wave absorption

    Carbon

    (2017)
  • T. Zhang et al.

    Ultra-light h−BCN architectures derived from new organic monomers with tunable electromagnetic wave absorption

    Carbon

    (2018)
  • D. Ding et al.

    Rational design of core-shell Co@C microspheres for high-performance microwave absorption

    Carbon

    (2017)
  • H. Zhao et al.

    A novel hierarchically porous magnetic carbon derived from biomass for strong lightweight microwave absorption

    Carbon

    (2019)
  • J. Yan et al.

    Covalently bonded polyaniline/graphene composites as high-performance electromagnetic (EM) wave absorption materials

    Compos. Part A-Appl. Sci. Manuf.

    (2017)
  • L. Quan et al.

    Magnetic graphene for microwave absorbing application: towards the lightest graphene-based absorber

    Carbon

    (2017)
  • H.L. Xu et al.

    Mesoporous carbon hollow microspheres with red blood cell like morphology for efficient microwave absorption at elevated temperature

    Carbon

    (2018)
  • Y.C. Wang et al.

    Microwave-based preparation and characterization of Fe-cored carbon nanocapsules with novel stability and super electromagnetic wave absorption performance

    Carbon

    (2018)
  • X. Liu et al.

    Modulation of electromagnetic wave absorption by carbon shell thickness in carbon encapsulated magnetite nanospindles–poly(vinylidene fluoride) composites

    Carbon

    (2015)
  • Y.H. Cheng et al.

    Achieving tunability of effective electromagnetic wave absorption between the whole X-band and Ku-band via adjusting PPy loading in SiC nanowires/graphene hybrid foam

    Carbon

    (2018)
  • D. Estevez et al.

    Complementary design of nano-carbon/magnetic microwire hybrid fibers for tunable microwave absorption

    Carbon

    (2018)
  • L. Wang et al.

    Facile synthesis and electromagnetic wave absorption properties of magnetic carbon fiber coated with Fe–Co alloy by electroplating

    J. Alloy. Comp.

    (2011)
  • Y.Z. Wan et al.

    Engineering carbon fibers with dual coatings of FeCo and CuO towards enhanced microwave absorption properties

    J. Alloy. Comp.

    (2016)
  • F.Y. Wang et al.

    Microwave absorption properties of 3D cross-linked Fe/C porous nanofibers prepared by electrospinning

    Carbon

    (2018)
  • F. Ye et al.

    Direct growth of edge-rich graphene with tunable dielectric properties in porous Si3N4 ceramic for broadband high-performance microwave absorption

    Adv. Funct. Mater.

    (2018)
  • F. Shahzad et al.

    Electromagnetic interference shielding with 2D transition metal carbides (MXenes)

    Science

    (2016)
  • H. Lv et al.

    A voltage-boosting strategy enabling a low-frequency, flexible electromagnetic wave absorption device

    Adv. Mater.

    (2018)
  • Q. Liu et al.

    CoNi@SiO2 @TiO2 and CoNi@air@TiO2 microspheres with strong wideband microwave absorption

    Adv. Mater.

    (2016)
  • H. Li et al.

    Optimizing the electromagnetic wave absorption performances of designed Co3Fe7@C yolk-shell structures

    ACS Appl. Mater. Interfaces

    (2018)
  • Cited by (174)

    View all citing articles on Scopus
    View full text