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The arc-discharged Ni-cored carbon onions with enhanced microwave absorption performances
Materials Letters 265 (2020) 127408
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
The arc-discharged Ni-cored carbon onions with enhanced microwave absorption performances Lei Zhang a, Qin Zhou a, Hongtao Zhao b, Chao Ruan c, Yujin Wang d, Zhigang Li b, Yongfu Lian a,⇑ a
Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, China Institute of Technical Physics, Heilongjiang Academy of Sciences, Harbin 150009, China c Jiangxi Copper Technology Research Institute Co., LTD., Nanchang, China d Institute for Advanced Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150080, China b
a r t i c l e
i n f o
Article history: Received 4 September 2019 Received in revised form 3 January 2020 Accepted 21 January 2020 Available online 28 January 2020 Keywords: Ni-cored carbon onions Microwave absorption Carbon materials Defects Polarization relaxation sites
a b s t r a c t Carbon-based microwave absorbers are important for the rapid development of electronic devices. Herein Ni-cored carbon onions with wide particle size distribution were prepared via arc discharge method, and their structures were characterized by electron microscope, X-ray diffraction, Raman spectroscopy. The three-dimension porous structure, thick carbon shell and large number of defects endows Ni-cored carbon onions with various polarization centers that can stimulate multiple dielectric resonances, leading to wide response frequency bandwidth and multiple strong microwave absorption features. It was evidenced that the bandwidths over 10 dB were from 3.4 to 18.0 GHz when the thickness of samples ranged from 1.5 to 5.0 mm. Ó 2020 Elsevier B.V. All rights reserved.
1. Introduction With the need for solving the issues caused by expanded electromagnetic interface, electromagnetic wave (EMW) absorbing materials have attracted considerable attention [1]. Ideal EM wave absorbers should be thin in thickness, light in weight, wide in absorption band and strong in absorption capacity. Among the applicable candidates [1,2], carbon materials are the most attractive because of their relatively low density, multiple and controllable structures, easy preparation and low cost. In the past decade, carbon nanotubes, carbon nanofibers, mesoporous carbon and graphene have been investigated in the field of microwave absorption [3]. Recently, researchers paid much attention to carbon onions (CNOs), since their onion-like shells might contribute greatly to EMW absorption. Jiang et al. [4] ascribed the good EMW absorption properties of the defective CNOs to their various polarizations in carbon shells, and the encapsulation of metal particles in CNOs leaded to the improvement of impedance matching. Wang et al. [5] proposed that the core–shell interfacial architecture at nanoscale could not only broaden the response frequency bandwidth
⇑ Corresponding author. E-mail address: [email protected] (Y. Lian). https://doi.org/10.1016/j.matlet.2020.127408 0167-577X/Ó 2020 Elsevier B.V. All rights reserved.
but also enhance the absorption intensity of CNOs. Recently, it was reported that some metal encapsulated CNOs (M@CNOs) demonstrated excellent EMW absorption properties [2,6]. Herein we applied DC arc discharge to the preparation of Ni-cored CNOs, in which nickel particles might play a role of nucleation centres for the growth of Ni@CNOs. The as-prepared sample showed a wide absorption band at high frequency, indicative of the potential application of such obtained Ni@CNOs in EM absorption.
2. Experimental 2.1. The preparation of Ni@CNOs The Ni@CNOs with wide particle size distribution were prepared in an arc discharge chamber [7]. In brief, graphite and nickel powder were mixed and filled into a graphite rod with a hole drilled in the centre, and the content of nickel powder was approximately 10% (wt/wt) in the composite graphite rod. The composite graphite rod was employed as anode while another graphite block as cathode, and an arc was generated with a current of 110A in a helium atmosphere of 450 Torr. The as-prepared Ni@CNOs were collected after the chamber was cooled down to room temperature.
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2.2. The characterization of Ni@CNOs The morphology of Ni@CNOs was observed by a field-emission scanning electron microscope (SEM, QUANTA 200S, FEI, Holland) and a transmission electron microscope (TEM, JEM2100, JEOL, Japan), and the structure of Ni@CNOs was investigated by X-ray diffraction (XRD, D8 Advance, Bruker, German) and Raman scattering recorded on a confocal Raman spectroscopic system (Renishaw, In Via) excited with a laser of 633 nm. The relative permeability and permittivity of Ni@CNOs were determined on an Agilent N5230A vector network analyzer (Agilent, USA) within the frequency range of 2–18 GHz, and the reflection loss was calculated in line with the achieved data of the relative permeability and permittivity. The sample for microwave absorption measurement was a composite of Ni@CNOs and paraffin in a weight ratio of 1:1, which was pressed into a ring with outer diameter, inner diameter and thickness of 7, 3 and 2 mm, respectively.
3. Results and discussion Shown in Fig. 1 are the SEM and TEM images of the as-prepared Ni@CNOs. It can be seen from Fig. 1a and b that the as-prepared Ni@CNOs are aggregated nanoparticles and the measured size ranges from 10 to 80 nm, which are spherically stacked into a three-dimension (3D) porous structure. It is believed that such
kind of 3D porous structures are important for the transmission and dissipation of microwaves. From the TEM image shown in Fig. 1c, it is observable that Ni@CNOs are of a shell/core structure composed of a crystalline core and a coating onion-like shell. The diameter distribution of nickel core is 3–50 nm and the thickness of carbon shell is 3–15 nm. Demonstrated in Fig. 1d is a typical TEM image of a Ni@CNO with a diameter about 18 nm. The diameter of the nickel nanoparticle core is about 10 nm, and the onionlike shell is made up of a dozen of carbon layers with an interval spacing of about 0.34 nm, corresponding to the [0 0 2] lattice plane of graphite layers. Shown in Fig. 2 are the powder X ray diffraction (XRD) pattern, Raman spectrum of the as-prepared Ni@CNOs. The XRD peaks observable in Fig. 2a are assigned to crystalline graphite or the single-phase fcc-Ni lattice planes. In comparison with that of [1 1 1] Ni, the intensity of [0 0 2] graphite plane is not extremely high, indicates a relative medium degree of graphitization for the carbon shells. According to Mering-Maire equation [8], the degree of graphitization was calculated to be 58.1%. On the other hand, four Raman dominated bands are observed in Fig. 2b, which can be assigned to the D peak, G peak, G0 peak and D + G combined peak, respectively. The ID/IG ratio was calculated to be 1.15, also reflecting a medium degree graphitization for carbon shells. Moreover, the relative high intensity of D peak along with the presence of D + G combined peak indicates that the in-plane hexagonal carbon layers was destroyed to some extent by the introduction of
Fig. 1. The SEM (a, b) and TEM (c, d) images of the as-prepared Ni@CNOs.
L. Zhang et al. / Materials Letters 265 (2020) 127408
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Fig. 2. The XRD pattern (a) and Raman spectrum (b) of the as-prepared Ni@CNOs.
sp3 hybrid carbon atoms and the curvature of onion-like shell [9]. Shown in Fig. 3a is the real and imaginary part of complex permittivity of Ni@CNOs/paraffin composite are in the frequency range of 2–18 GHz. The value of the real part (e0 ) gradually declines from 17.08 at 2.0 GHz to 10.09 at 18.0 GHz, and the value of imaginary part (e00 ) decreases from 7.63 at 2.0 GHz to 5.31 at 6.6 GHz and then shows a slight fluctuation between 4.54 and 5.31 from 6.6 GHz to 18.0 GHz. From the complex permeability of Ni@CNOs
shown in Fig. 3b, it can be seen that the real part (l0 ) exhibits a fluctuation between 0.99 and 1.03 in the whole frequency range, and the imaginary part (l00 ) presents a fluctuation between 0.017 and 0.007 from 2.0 GHz to 12.0 GHz and an abrupt decrease from 0.005 at 12.0 GHz to 0.079 at 18.0 GHz. Fig. 3c shows the frequency dependence of dielectric loss tangent and magnetic loss tangent of Ni@CNOs/paraffin composite. It is obvious that dielectric loss is larger than magnetic loss from 2 GHz to 15.3 GHz, and dielectric loss is less than magnetic loss
Fig. 3. The complex permittivity (a), complex permeability (b), dielectric loss tangent and magnetic loss tangent (c), and microwave reflection losses (d) of the Ni@CNOs/paraffin composite with 50 wt% Ni@CNOs.
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from 15.3 GHz to 18 GHz. Moreover, multiple resonances are observed and the peaks of dielectric loss tangent and the negative peak of magnetic loss tangent appear in pairs at the same frequency, implying an energy conversion between complex permittivity and complex permeability [5]. Demonstrated in Fig. 3d are the microwave reflection losses of Ni@CNOs/paraffin composite, deduced from transmission line theory according to measured complex permittivity and complex permeability data [10]. It is clear that the maximum reflection loss is 29.0 dB at 15.7 GHz. Once the reflection loss is over 10 dB, the response bandwidth will become dominant factor for an efficient EM absorber. It can be seen from Fig. 3d that the bandwidth over 10 dB for the sample is from 3.4 to 18.0 GHz when the thickness of samples ranged from 1.5 to 5.0 mm. Particularly, the bandwidth over 10 dB for the sample with a thickness of 1.5 mm is ranged from 13.5 to 18 GHz. In comparison with those Ni@C-based absorbers reported previously [11], the arc-discharged Ni@CNOs demonstrate the following advantageous features. (a) Its complex permittivity is much larger than that of Ni@CA and Ni@CE, indicative of enhanced dielectric loss capacity; (b) Three dielectric resonant and three magnetic antiresonant peaks are detected, indicating multiple energy transformations between permeability and permittivity. In contrast, only one dielectric resonant and one magnetic antiresonant peaks are observed for Ni@CA and Ni@CE; (c) Its RL values exceed 10 dB when its thickness is above 1.5 nm, while the RL values of Ni@CA and Ni@CE are larger than 10 dB when their thicknesses are larger than 2.1 and 5.1 nm, respectively; (d) Its RLmax reached 29 dB at 15.7 GHz when t(RLmax) and fEt are 1.5 nm and 4.5 GHz, respectively, showing smaller t(RLmax) and larger fEt than Ni@CA and Ni@CE. 4. Conclusions In summary, arc-discharged Ni@CNOs are proved to be of many enhanced microwave absorption performances, making them a good candidate for lightweight and wide band microwave absorption. It is believed that the curvature of the carbon shells could not only increase the introduction of electromagnetic waves, but also offer abundant polarization center to stimulate multiple dielectric resonances. CRediT authorship contribution statement Lei Zhang: Conceptualization, Methodology, Investigation, Writing - original draft, Writing - review & editing. Qin Zhou: Methodology, Writing - original draft, Writing - review & editing. Hongtao Zhao: Investigation. Chao Ruan: Methodology, Writing
- review & editing. Yujin Wang: Investigation. Zhigang Li: Investigation. Yongfu Lian: Conceptualization, Writing - original draft, Writing - review & editing, Funding acquisition, Supervision. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work is supported by National Natural Science Foundation of China (51572071) and Distinguished Young Scholars Fund of Heilongjiang Academy of sciences (2018WL001). References [1] Z. Xu, M. Liang, X. He, Q. Long, J. Yu, K. Xie, et al., The preparation of carbonized silk cocoon-Co-graphene composite and its enhanced electromagnetic interference shielding performance, Composites Part A 119 (2019) 111–118. [2] F. Wang, N. Wang, X. Han, D. Liu, Y. Wang, L. Cui, et al., Core-shell FeCo@carbon nanoparticles encapsulated in polydopamine-derived carbon nanocages for efficient microwave absorption, Carbon 145 (2019) 701–711. [3] C. Wang, V. Murugadoss, J. Kong, Z. He, X. Mai, Q. Shao, et al., Overview of carbon nanostructures and nanocomposites for electromagnetic wave shielding, Carbon 140 (2018) 696–733. [4] L.W. Jiang, Z.H. Wang, D.Y. Geng, Y.M. Lin, Y. Wang, J. An, et al., Structure and electromagnetic properties of both regular and defective onion-like carbon nanoparticles, Carbon 95 (2015) 910–918. [5] Z.H. Wang, Z. Han, D.Y. Geng, Z.D. Zhang, Synthesis, characterization and microwave absorption of carbon-coated Sn nanorods, Chem. Phys. Lett. 489 (2010) 187–190. [6] D. Liu, R. Qiang, Y. Du, Y. Wang, C. Tian, X. Han, Prussian blue analogues derived magnetic FeCo alloy/carbon composites with tunable chemical composition and enhanced microwave absorption, J. Colloid Interface Sci. 514 (2018) 10– 20. [7] C. Ruan, Y. Lian, Purification of carbon nano-onions fabricated by arc discharge, Fuller. Nanotub. Car. N. 23 (2015) 488–493. [8] A. Heckmann, O. Fromm, U. Rodehorst, P. Münster, M. Winter, T. Placke, New insights into electrochemical anion intercalation into carbonaceous materials for dual-ion batteries: impact of the graphitization degree, Carbon 131 (2018) 201–212. [9] K. Bogdanov, A. Fedorov, V. Osipov, T. Enoki, K. Takai, T. Hayashi, et al., Annealing-induced structural changes of carbon onions: high-resolution transmission electron microscopy and Raman studies, Carbon 73 (2014) 78– 86. [10] D. Ding, Y. Wang, X. Li, R. Qiang, P. Xu, W. Chu, et al., Rational design of coreshell Co@C microspheres for high-performance microwave absorption, Carbon 111 (2017) 722–732. [11] Z. Li, X. Ding, F. Li, X. Liu, S. Zhang, H. Long, Enhanced dielectric loss induced by the doping of SiC in thick defective graphitic shells of Ni@C nanocapsules with ash-free coal as carbon source for broadband microwave absorption, J. Phys. D Appl. Phys. (2017;50.).
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
The arc-discharged Ni-cored carbon onions with enhanced microwave absorption performances Lei Zhang a, Qin Zhou a, Hongtao Zhao b, Chao Ruan c, Yujin Wang d, Zhigang Li b, Yongfu Lian a,⇑ a
Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, China Institute of Technical Physics, Heilongjiang Academy of Sciences, Harbin 150009, China c Jiangxi Copper Technology Research Institute Co., LTD., Nanchang, China d Institute for Advanced Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150080, China b
a r t i c l e
i n f o
Article history: Received 4 September 2019 Received in revised form 3 January 2020 Accepted 21 January 2020 Available online 28 January 2020 Keywords: Ni-cored carbon onions Microwave absorption Carbon materials Defects Polarization relaxation sites
a b s t r a c t Carbon-based microwave absorbers are important for the rapid development of electronic devices. Herein Ni-cored carbon onions with wide particle size distribution were prepared via arc discharge method, and their structures were characterized by electron microscope, X-ray diffraction, Raman spectroscopy. The three-dimension porous structure, thick carbon shell and large number of defects endows Ni-cored carbon onions with various polarization centers that can stimulate multiple dielectric resonances, leading to wide response frequency bandwidth and multiple strong microwave absorption features. It was evidenced that the bandwidths over 10 dB were from 3.4 to 18.0 GHz when the thickness of samples ranged from 1.5 to 5.0 mm. Ó 2020 Elsevier B.V. All rights reserved.
1. Introduction With the need for solving the issues caused by expanded electromagnetic interface, electromagnetic wave (EMW) absorbing materials have attracted considerable attention [1]. Ideal EM wave absorbers should be thin in thickness, light in weight, wide in absorption band and strong in absorption capacity. Among the applicable candidates [1,2], carbon materials are the most attractive because of their relatively low density, multiple and controllable structures, easy preparation and low cost. In the past decade, carbon nanotubes, carbon nanofibers, mesoporous carbon and graphene have been investigated in the field of microwave absorption [3]. Recently, researchers paid much attention to carbon onions (CNOs), since their onion-like shells might contribute greatly to EMW absorption. Jiang et al. [4] ascribed the good EMW absorption properties of the defective CNOs to their various polarizations in carbon shells, and the encapsulation of metal particles in CNOs leaded to the improvement of impedance matching. Wang et al. [5] proposed that the core–shell interfacial architecture at nanoscale could not only broaden the response frequency bandwidth
⇑ Corresponding author. E-mail address: [email protected] (Y. Lian). https://doi.org/10.1016/j.matlet.2020.127408 0167-577X/Ó 2020 Elsevier B.V. All rights reserved.
but also enhance the absorption intensity of CNOs. Recently, it was reported that some metal encapsulated CNOs (M@CNOs) demonstrated excellent EMW absorption properties [2,6]. Herein we applied DC arc discharge to the preparation of Ni-cored CNOs, in which nickel particles might play a role of nucleation centres for the growth of Ni@CNOs. The as-prepared sample showed a wide absorption band at high frequency, indicative of the potential application of such obtained Ni@CNOs in EM absorption.
2. Experimental 2.1. The preparation of Ni@CNOs The Ni@CNOs with wide particle size distribution were prepared in an arc discharge chamber [7]. In brief, graphite and nickel powder were mixed and filled into a graphite rod with a hole drilled in the centre, and the content of nickel powder was approximately 10% (wt/wt) in the composite graphite rod. The composite graphite rod was employed as anode while another graphite block as cathode, and an arc was generated with a current of 110A in a helium atmosphere of 450 Torr. The as-prepared Ni@CNOs were collected after the chamber was cooled down to room temperature.
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2.2. The characterization of Ni@CNOs The morphology of Ni@CNOs was observed by a field-emission scanning electron microscope (SEM, QUANTA 200S, FEI, Holland) and a transmission electron microscope (TEM, JEM2100, JEOL, Japan), and the structure of Ni@CNOs was investigated by X-ray diffraction (XRD, D8 Advance, Bruker, German) and Raman scattering recorded on a confocal Raman spectroscopic system (Renishaw, In Via) excited with a laser of 633 nm. The relative permeability and permittivity of Ni@CNOs were determined on an Agilent N5230A vector network analyzer (Agilent, USA) within the frequency range of 2–18 GHz, and the reflection loss was calculated in line with the achieved data of the relative permeability and permittivity. The sample for microwave absorption measurement was a composite of Ni@CNOs and paraffin in a weight ratio of 1:1, which was pressed into a ring with outer diameter, inner diameter and thickness of 7, 3 and 2 mm, respectively.
3. Results and discussion Shown in Fig. 1 are the SEM and TEM images of the as-prepared Ni@CNOs. It can be seen from Fig. 1a and b that the as-prepared Ni@CNOs are aggregated nanoparticles and the measured size ranges from 10 to 80 nm, which are spherically stacked into a three-dimension (3D) porous structure. It is believed that such
kind of 3D porous structures are important for the transmission and dissipation of microwaves. From the TEM image shown in Fig. 1c, it is observable that Ni@CNOs are of a shell/core structure composed of a crystalline core and a coating onion-like shell. The diameter distribution of nickel core is 3–50 nm and the thickness of carbon shell is 3–15 nm. Demonstrated in Fig. 1d is a typical TEM image of a Ni@CNO with a diameter about 18 nm. The diameter of the nickel nanoparticle core is about 10 nm, and the onionlike shell is made up of a dozen of carbon layers with an interval spacing of about 0.34 nm, corresponding to the [0 0 2] lattice plane of graphite layers. Shown in Fig. 2 are the powder X ray diffraction (XRD) pattern, Raman spectrum of the as-prepared Ni@CNOs. The XRD peaks observable in Fig. 2a are assigned to crystalline graphite or the single-phase fcc-Ni lattice planes. In comparison with that of [1 1 1] Ni, the intensity of [0 0 2] graphite plane is not extremely high, indicates a relative medium degree of graphitization for the carbon shells. According to Mering-Maire equation [8], the degree of graphitization was calculated to be 58.1%. On the other hand, four Raman dominated bands are observed in Fig. 2b, which can be assigned to the D peak, G peak, G0 peak and D + G combined peak, respectively. The ID/IG ratio was calculated to be 1.15, also reflecting a medium degree graphitization for carbon shells. Moreover, the relative high intensity of D peak along with the presence of D + G combined peak indicates that the in-plane hexagonal carbon layers was destroyed to some extent by the introduction of
Fig. 1. The SEM (a, b) and TEM (c, d) images of the as-prepared Ni@CNOs.
L. Zhang et al. / Materials Letters 265 (2020) 127408
3
Fig. 2. The XRD pattern (a) and Raman spectrum (b) of the as-prepared Ni@CNOs.
sp3 hybrid carbon atoms and the curvature of onion-like shell [9]. Shown in Fig. 3a is the real and imaginary part of complex permittivity of Ni@CNOs/paraffin composite are in the frequency range of 2–18 GHz. The value of the real part (e0 ) gradually declines from 17.08 at 2.0 GHz to 10.09 at 18.0 GHz, and the value of imaginary part (e00 ) decreases from 7.63 at 2.0 GHz to 5.31 at 6.6 GHz and then shows a slight fluctuation between 4.54 and 5.31 from 6.6 GHz to 18.0 GHz. From the complex permeability of Ni@CNOs
shown in Fig. 3b, it can be seen that the real part (l0 ) exhibits a fluctuation between 0.99 and 1.03 in the whole frequency range, and the imaginary part (l00 ) presents a fluctuation between 0.017 and 0.007 from 2.0 GHz to 12.0 GHz and an abrupt decrease from 0.005 at 12.0 GHz to 0.079 at 18.0 GHz. Fig. 3c shows the frequency dependence of dielectric loss tangent and magnetic loss tangent of Ni@CNOs/paraffin composite. It is obvious that dielectric loss is larger than magnetic loss from 2 GHz to 15.3 GHz, and dielectric loss is less than magnetic loss
Fig. 3. The complex permittivity (a), complex permeability (b), dielectric loss tangent and magnetic loss tangent (c), and microwave reflection losses (d) of the Ni@CNOs/paraffin composite with 50 wt% Ni@CNOs.
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L. Zhang et al. / Materials Letters 265 (2020) 127408
from 15.3 GHz to 18 GHz. Moreover, multiple resonances are observed and the peaks of dielectric loss tangent and the negative peak of magnetic loss tangent appear in pairs at the same frequency, implying an energy conversion between complex permittivity and complex permeability [5]. Demonstrated in Fig. 3d are the microwave reflection losses of Ni@CNOs/paraffin composite, deduced from transmission line theory according to measured complex permittivity and complex permeability data [10]. It is clear that the maximum reflection loss is 29.0 dB at 15.7 GHz. Once the reflection loss is over 10 dB, the response bandwidth will become dominant factor for an efficient EM absorber. It can be seen from Fig. 3d that the bandwidth over 10 dB for the sample is from 3.4 to 18.0 GHz when the thickness of samples ranged from 1.5 to 5.0 mm. Particularly, the bandwidth over 10 dB for the sample with a thickness of 1.5 mm is ranged from 13.5 to 18 GHz. In comparison with those Ni@C-based absorbers reported previously [11], the arc-discharged Ni@CNOs demonstrate the following advantageous features. (a) Its complex permittivity is much larger than that of Ni@CA and Ni@CE, indicative of enhanced dielectric loss capacity; (b) Three dielectric resonant and three magnetic antiresonant peaks are detected, indicating multiple energy transformations between permeability and permittivity. In contrast, only one dielectric resonant and one magnetic antiresonant peaks are observed for Ni@CA and Ni@CE; (c) Its RL values exceed 10 dB when its thickness is above 1.5 nm, while the RL values of Ni@CA and Ni@CE are larger than 10 dB when their thicknesses are larger than 2.1 and 5.1 nm, respectively; (d) Its RLmax reached 29 dB at 15.7 GHz when t(RLmax) and fEt are 1.5 nm and 4.5 GHz, respectively, showing smaller t(RLmax) and larger fEt than Ni@CA and Ni@CE. 4. Conclusions In summary, arc-discharged Ni@CNOs are proved to be of many enhanced microwave absorption performances, making them a good candidate for lightweight and wide band microwave absorption. It is believed that the curvature of the carbon shells could not only increase the introduction of electromagnetic waves, but also offer abundant polarization center to stimulate multiple dielectric resonances. CRediT authorship contribution statement Lei Zhang: Conceptualization, Methodology, Investigation, Writing - original draft, Writing - review & editing. Qin Zhou: Methodology, Writing - original draft, Writing - review & editing. Hongtao Zhao: Investigation. Chao Ruan: Methodology, Writing
- review & editing. Yujin Wang: Investigation. Zhigang Li: Investigation. Yongfu Lian: Conceptualization, Writing - original draft, Writing - review & editing, Funding acquisition, Supervision. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work is supported by National Natural Science Foundation of China (51572071) and Distinguished Young Scholars Fund of Heilongjiang Academy of sciences (2018WL001). References [1] Z. Xu, M. Liang, X. He, Q. Long, J. Yu, K. Xie, et al., The preparation of carbonized silk cocoon-Co-graphene composite and its enhanced electromagnetic interference shielding performance, Composites Part A 119 (2019) 111–118. [2] F. Wang, N. Wang, X. Han, D. Liu, Y. Wang, L. Cui, et al., Core-shell FeCo@carbon nanoparticles encapsulated in polydopamine-derived carbon nanocages for efficient microwave absorption, Carbon 145 (2019) 701–711. [3] C. Wang, V. Murugadoss, J. Kong, Z. He, X. Mai, Q. Shao, et al., Overview of carbon nanostructures and nanocomposites for electromagnetic wave shielding, Carbon 140 (2018) 696–733. [4] L.W. Jiang, Z.H. Wang, D.Y. Geng, Y.M. Lin, Y. Wang, J. An, et al., Structure and electromagnetic properties of both regular and defective onion-like carbon nanoparticles, Carbon 95 (2015) 910–918. [5] Z.H. Wang, Z. Han, D.Y. Geng, Z.D. Zhang, Synthesis, characterization and microwave absorption of carbon-coated Sn nanorods, Chem. Phys. Lett. 489 (2010) 187–190. [6] D. Liu, R. Qiang, Y. Du, Y. Wang, C. Tian, X. Han, Prussian blue analogues derived magnetic FeCo alloy/carbon composites with tunable chemical composition and enhanced microwave absorption, J. Colloid Interface Sci. 514 (2018) 10– 20. [7] C. Ruan, Y. Lian, Purification of carbon nano-onions fabricated by arc discharge, Fuller. Nanotub. Car. N. 23 (2015) 488–493. [8] A. Heckmann, O. Fromm, U. Rodehorst, P. Münster, M. Winter, T. Placke, New insights into electrochemical anion intercalation into carbonaceous materials for dual-ion batteries: impact of the graphitization degree, Carbon 131 (2018) 201–212. [9] K. Bogdanov, A. Fedorov, V. Osipov, T. Enoki, K. Takai, T. Hayashi, et al., Annealing-induced structural changes of carbon onions: high-resolution transmission electron microscopy and Raman studies, Carbon 73 (2014) 78– 86. [10] D. Ding, Y. Wang, X. Li, R. Qiang, P. Xu, W. Chu, et al., Rational design of coreshell Co@C microspheres for high-performance microwave absorption, Carbon 111 (2017) 722–732. [11] Z. Li, X. Ding, F. Li, X. Liu, S. Zhang, H. Long, Enhanced dielectric loss induced by the doping of SiC in thick defective graphitic shells of Ni@C nanocapsules with ash-free coal as carbon source for broadband microwave absorption, J. Phys. D Appl. Phys. (2017;50.).