Efficient and Lightweight Electromagnetic Wave Absorber Derived

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Efficient and Lightweight Electromagnetic Wave Absorber Derived from Metal Organic Framework-Encapsulated Cobalt Nanoparticles Haicheng Wang,*,† Long Xiang,† Wei Wei,† Jing An,‡ Jun He,‡ Chunhong Gong,§ and Yanglong Hou∥ †

National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing 100083, China Institute of Functional Materials, Central Iron & Steel Research Institute, Beijing 100081, P. R. China § College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, Henan, P. R. China ∥ Beijing Key Laboratory for Magnetoelectric Materials and Devices (BKLMMD), BIC-EAST, Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, China ‡

S Supporting Information *

ABSTRACT: Porous-carbon-based nanocomposites are gaining tremendous interest because of good compatibility, lightweight, and strong electromagnetic wave absorption. However, it is still a great challenge to design and synthesize porous-carbon-based composites with strong absorption capability and broad frequency bandwidth. Herein, a facile and effective method was developed to synthesize Co magnetic nanoparticles/metal organic framework (MOF) (Co NPs/ ZIF-67) nanocomposites. Co NPs/porous C composites were subsequently obtained by annealing Co NPs/ZIF-67 nanocomposites at different temperatures under an inert atmosphere. The carbonized nanocomposites showed highly efficient electromagnetic wave absorption capability. Specifically, the optimal composite (i.e., Co/C-700) possessed a maximum reflection loss (RL) value of −30.31 dB at 11.03 GHz with an effective absorption bandwidth (RL ≤ −10 dB) of 4.93 GHz. The electromagnetic parameters and the absorption performance of the composites are readily tunable by adjusting the carbonization temperature and the concentration of Co NPs in the composites. Because of the combination of good impedance matching, dualloss mechanism, and the synergistic effect between Co NPs and porous carbon composites, these Co NPs/MOF-derived composites are attractive candidates for electromagnetic wave absorbers. KEYWORDS: nanoparticles, metal organic frameworks, electromagnetic wave absorber, lightweight, impedance matching

1. INTRODUCTION Electromagnetic (EM) waves have been widely applied in defense research, civil commercial products, and daily life applications. Although EM waves are fundamentally and practically important in these applications, efficient methods need to be established to circumvent the disadvantages of EM radiation. Besides possible physiological damage to human bodies, there are also concerns about information security and electromagnetic disturbance.1−4 To address these increasingly serious problems, many scientists had paid much attention to developing highly efficient EM wave absorbers in the past decades.5−8 In general, the performance of EM wave absorbing materials depends on EM attenuation capability and impedance matching characteristics. Complex permittivity (εr = ε′ − jε″) and permeability (μr = μ′ − jμ″) are the critical factors for measuring the attenuation abilities of EM wave absorbing materials.9,10 Traditional electromagnetic wave absorption materials, such as ferromagnetic metals,11,12 carbons,13 ceramics,14 and conducting polymers,15 can be used for absorbing EM waves. However, it is hard for any one of these materials to meet the requirements © 2017 American Chemical Society

thoroughly owing to their high density and poor stability when applied as a single EM wave absorbing material.16−18 Therefore, developing lightweight composite materials with less thickness, strong absorption capability, and broad absorption frequency bandwidth is a possible solution to tackle this problem.19−23 Many efforts have been made to improve the electromagnetic properties of the absorbers. For instance, Liu et al. prepared the composites of CoNi@SiO2@TiO2 core−shell−shell structures and obtained a reflection loss (RL) value of −58.2 dB with only 2.1 mm thickness.24 Our group had synthesized cobalt/ polypyrrole nanocomposites with a maximum RL value of −33 dB at 13.6 GHz, and the absorption bandwidth for Co/PPy (30 wt %) was 4.77 GHz.25 Most recently, metal organic framework (MOF)-derived porous carbon materials have received extensive interest owing to their large specific surface area, high porosity, and lightweight. Lv et al. proposed the preparation of porous Co@C nanocomposites derived from MOF, which leads to Received: September 11, 2017 Accepted: November 13, 2017 Published: November 13, 2017 42102

DOI: 10.1021/acsami.7b13796 ACS Appl. Mater. Interfaces 2017, 9, 42102−42110

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ACS Applied Materials & Interfaces

Figure 1. Synthetic route of Co NPs/ZIF-67 composites. 2.2. Synthesis of Co NPs and ZIF-67. Co NPs were synthesized by a modified method.35 In detail, cobalt acetate (1 mmol) and oleic acid (1 mmol) were dissolved in benzyl ether (30 mL) under an Ar atmosphere. Triphenylphosphine (3 mmol) was injected into this solution with constant stirring when the temperature reached 100 °C. Subsequently, lithium triethylborohydride was injected when the mixture was heated up to 200 °C with continuous magnetic stirring. The reaction temperature was maintained at 200 °C for 30 min with subsequent cooling to room temperature. On completion, the precipitate were extracted, centrifuged, and then redispersed in 15 mL of hexane with 200 μL of oleic acid for improving the stability. ZIF-67 was synthesized according to a modified conventional method.26 In detail, Co(NO3)2 (1 mmol dm−3) and mIM (4 mmol dm−3) were dissolved in the methanol (50 mL) solution and stirred under argon for 24 h at room temperature, during which the pink solution turned purple gradually. After centrifugation, the acquired purple precipitate was washed by ethanol several times and then dried at 80 °C for 24 h for future use. 2.3. Synthesis of Co NPs/ZIF-67 Nanocomposites and Co/C. Cobalt NPs were mixed with poly(vinylpyrrolidone) (PVP) (1 g) in the methanol (40 mL) solution for 24 h under an Ar atmosphere. After adding hexane, the particles were precipitated and extracted by following centrifugation. Then, Co(NO3)2 (1 mmol dm−3) and Co NPs modified by PVP and mIM (4 mmol dm−3) were blended in a 50 mL methanol solution with stirring for 24 h. Subsequently, the products were centrifuged, washed with alcohol several times, and then dried for 24 h for use. After being kept at different temperatures (500, 600, 700, 800 °C) for 5 h, the porous Co/C products, denoted Co/C-500, Co/C-600, Co/C-700, and Co/C-800, respectively, were eventually obtained. 2.4. Characterization. The crystal phase of the Co NPs/ZIF-67 nanoparticles was determined by X-ray diffraction (XRD) (PW 3040X’Pert Pro, Cu Kα radiation). A physical property measurement system (Quantum Design, SQUID-VSM 7 T) was adopted to measure the magnetic properties of the samples. Thermogravimetry (TG) profiles of the samples were investigated on an SDT Q600 thermal gravimetric analyzer in N2 or air flow at a temperature range from 30 to 800 °C and at a heating rate of 10 °C min−1. Nitrogen adsorption−desorption isotherms were tested at 77 K on a QUADRASORB SI (Quantachrome) sorption analyzer. The specific surface area was measured by the Brunauer−Emmett−Teller (BET) method. 2.5. Electromagnetic Parameters Measurements. A cylindrical sample, which has 3.00 mm inner diameter, 7.00 mm outer diameter, and 2.00 mm thickness, was prepared by homogeneously mixing a paraffin matrix with Co NPs/ZIF-67 (25 wt %) nanocomposites and pressed into cylindrical compacts. Complex permeability (μr = μ′ − jμ″)

excellent EM wave absorption with a maximum reflection loss of −35.3 dB at 5.80 GHz, and the effective absorption bandwidth was from 8.40 to 14.20 GHz at a thickness of 2.5 mm.26 Zhang et al. synthesized core−shell Co@NPC@TiO2 and multi-interfaced yolk−shell C-ZIF-67@TiO2 composites. The CoNi@ SiO2@TiO2 absorbers showed a significant microwave absorption enhancement at an optimal RL of −58.2 dB with only 2.1 mm thickness. Meanwhile, the absorption bandwidth covered the frequency from 8 to 16.1 GHz.27 Although important progress has been achieved with these composites, optimization of impedance matching and lightweight materials with enhanced attenuation abilities are still not widely available.28−30 In this work, nanoporous Co/C composites were obtained by a thermal carbonization process using Co NPs/ZIF-67 composites as starting materials. The schematic diagram of Co/C nanocomposites is illustrated in Figure 1. The Co NPs are embedded in the porous ZIF-67 matrix. These structures have several advantages for EM wave absorbing materials. First, cobalt is chosen as a magnetic component due to its tunable size, crystal structure, and favorable magnetic properties.31−34 More importantly, Co NPs can effectively reduce the complex permittivity of porous carbon and optimize the impedance matching, thereby enhancing the absorption performance. Moreover, the porous cobalt NPs/graphite interface likely leads to more interface dipoles and interface relaxation polarization, which will be beneficial for the dielectric loss to EM wave. Finally, the electromagnetic property of composites is tunable by adjusting the process parameters and the component concentration. By virtue of all of these properties, the absorption capabilities of these composites are expected to be controllable.

2. EXPERIMENTAL SECTION 2.1. Reagents. Cobalt acetate (99%), triphenylphosphine (99%), benzyl ether (99%), oleic acid (>97%), lithium triethylborohydride (1 M in tetrahydrofuran), cobalt nitrate hexahydrate (Co(NO3)2·6H2O, 99%), 2-methylimidazole (mIM, 99%), poly(vinylpyrrolidone) (PVP), ethanol (99.7%), and methanol (99.9%) were purchased from Acros. Other reagents were purchased from Beijing Chemical Reagent Corporation. All chemicals were used without further purification unless otherwise stated. 42103


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Figure 2. (a) XRD patterns of the ZIF-67 and (b) porous Co/C composites. and permittivity (εr = ε′ − jε″) were measured by a coaxial reflection/ transmission method using an Agilent N5230C vector network analyzer at the frequency range of 1−18 GHz. Transmission line theory was adopted to characterize the absorption property, which was designated as RL. The RL value of the sample is determined by the following equations

in N2 compared to that in air. For the case in air, the initial decline of the TG curve below 100 °C can be ascribed to the mass loss of absorbed water in the composite, and then a drastic decomposition of ZIF-67 from 300 to 375 °C results in a total weight loss of 85.08%. However, for the case in N2, ZIF-67 is stable at even 400 °C. As the temperature further increased, the quick weight loss of ZIF-67 starts at 500 °C and ends at 600 °C. The total weight loss (52.32%) is equal to 8.92 + 43.4% for the range from room temperature to 600 °C. Because this weight loss value is lower than the theoretical values after a transformation of ZIF-67 to metallic Co (73.3%) and to its oxides Co3O440 (63.7%) or CoO (66.1%), it can be deduced that some mixture of carboncontaining materials, metallic Co, or its oxides might be produced during the carbonization process of ZIF-67 under an inert atmosphere. Therefore, we deliberately performed the carbonization process of as-prepared samples under a flow of extrapure N2 (99.99%) to avoid the formation of Co oxides. To investigate the influence of carbonization temperature on the magnetic property and wave absorbing performance, the samples were carbonized at 500, 600, 700, and 800 °C. The morphologies of the Co NPs/ZIF-67 and Co NPs/Co@C composites at different carbonization temperatures (Figure 4a,b) demonstrate that Co NPs/ZIF-67 exhibits rhombic dodecahedral morphology and metallic particles are embedded in ZIF-67, from high-angle annular dark-field scanning transmission electron microscopy (STEM) images. Figure 4c−f indicates that the skeleton of Co NPs/ZIF-67 shrinks after carbonization and tends to collapse with the increase in the carbonation temperature up to 700 °C. Moreover, nearly most of the skeleton collapses and the original skeleton structure cannot be distinguished as the carbonization temperature reached 800 °C. This behavior might destroy the porous framework of ZIF67, which will be unfavorable to the attenuation ability to the electromagnetic wave. Additionally, the cobalt cation in ZIF-67 has been turned into metallic cobalt particles wrapped by a carbon shell, as shown in Figure 4g,h. This structure is suppressing the skin effect of cross-linked Co networks and improving for effective attenuation of the incident electromagnetic wave, which can not only effectively regulate the complex permittivity of Co/C microspheres by introducing polarization relaxations but also reduce the aggregation of Co nanoparticles, suppressing the effect of cross-linked Co networks on skin and improving the magnetic loss of Co/C.41 The magnetic properties of Co/C-500−800 are illustrated in Figure 5. The saturation magnetization (Ms) values of Co/C500, Co/C-600, Co/C-700, and Co/C-800 are 4.14, 35.26, 38.78, and 65.21 emu g−1, respectively. Although these are lower than those of bulk Co (164.8 emu g−1 at T = 300 K, 155.2 emu

Z in = Z0(μr /εr)−1/2 tanh[j(2πfd /c)(με )−1/2 ] r r RL = 20 log|(Z in − Z0)/(Z in + Z0)| where Zin, d, and μ are the normalized input impedance, thickness, and permeability of the material, respectively; c is the light velocity in vacuum; and f is the microwave frequency.36,37 It is generally accepted that RL smaller than −10 dB indicates that 90% of incident microwaves can be absorbed. The relevant frequency range corresponding with the RL smaller than −10 dB is defined as the effective absorption bandwidth.

3. RESULTS AND DISCUSSION The phase structure of Co-MOF (ZIF-67) was characterized by X-ray diffraction. It can be seen from Figure 2a that the diffraction peaks are identical to those of the simulated ZIF-67 phase structure.38 The crystalline structure of ZIF-67 carbonization products is shown in Figure 2b. Three primary diffraction peaks appeared at 44.2, 51.5, and 75.9° should be assigned to the metallic cobalt with a face-centered cubic structure (JCPDS 894307), and no peak of CoO was observed. In addition, a broad peak at approximately 25° can be seen from the XRD patterns, and it may be the (002) peak of graphitic carbon materials.39 To obtain high-quality microporous Co/C composites, it is crucial to appropriately control the atmosphere and temperature during the carbonization process. The TG curves of ZIF-67 measured in air and N2 are shown in Figure 3. From the curves, it can be concluded that the stability of ZIF-67 is greatly improved

Figure 3. TG curves of the Co-MOF precursors measured in air and N2. 42104


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Figure 4. Transmission electron microscopy (TEM) characterization of the samples. (a) TEM bright field images of Co NPs/ZIF-67. (b) STEM images of as-prepared samples. (c−f) TEM bright field images of Co/C under different carbonization temperatures (500−800 °C). (g, h) High-resolution transmission electron microscopy images of Co NPs/Co@C (metallic cobalt wrapped by a carbon shell).

g−1 at T = 412 K), the typical ferromagnetic hysteresis loop could be ascribed to the existence of metallic Co nanoparticles.42−44 The lower Ms of the as-prepared Co/C samples is mainly

originated from the small size effect of nanomaterials and the amorphous carbon wrapped on the surface of Co. According to the M−H curve, the saturation magnetization of samples 42105


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Information (SI)). After carbonization under 700 °C, Co/C-700 shows a mixture of microporous with mesoporous structures according to the pore size distribution. This can be explained by the fact that much larger pores occurred in this composite with the improvement of crystallinity and increasing size of cobalt. On the basis of the principle of electromagnetic energy conversion,28 the reflection and attenuation characteristics of electromagnetic wave absorbers are correlated with relative complex permittivity (εr = ε′ − jε″), relative complex permeability (μr = μ′ − jμ′), and proper impedance matching. The real parts, ε′ and μ′, represent the stored electrical and magnetic energy within the medium, whereas the imaginary parts, ε″ and μ″, stand for the dissipation (or loss) of electrical and magnetic energy. The dielectric and magnetic dissipation factors, tan δE = ε″/ε′ and tan δM = μ″/μ′, respectively, provide a way to measure the power loss in a material relative to the amount of stored power.40−44 The frequency dependence of the electromagnetic parameters of paraffin composites filled with 25 wt % Co/C obtained at different temperatures is illustrated in Figure 6. The ε′ value of the four samples tends to decrease continuously throughout the measured frequency. Specifically, the ε′ value dropped from 2.61 to 2.51 for Co/C-500, from 5.78 to 3.99 for Co/C-600, from 10.63 to 5.38 for Co/C-700, and from 19.26 to 8.71 for Co/C-

Figure 5. M−H curves of Co/C-500−800 measured at room temperature.

increases as the carbonization temperature rises, which could be partially because of the higher crystallinity of the samples and larger magnetic Co nanoparticles due to higher carbonization temperature.26 In addition, the enhancement of Ms is resulted from the quick increase in the Co mass percentage in the whole composite. Therefore, Co/C-800 has the highest Ms. From the Brunauer−Emmett−Teller (BET) method, Co NPs/ZIF-67 displays a typical type-IV isotherm and possesses a relatively high surface area of 1613 m2 g−1 (Figure S1, Supporting

Figure 6. Frequency dependence of complex permittivity and complex permeability of the samples annealed at different temperatures: (a) the real part (ε′), (b) imaginary part (ε″), (c) dielectric loss (tan δE), (d) real part (μ′), (e) imaginary part (μ″), and (f) magnetic loss (tan δM). 42106


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ACS Applied Materials & Interfaces 800. Similarly, the ε″ value decreases from 0.05 to 0, from 1.08 to 0.65, from 4.01 to 2.73, and from 13.45 to 3.81 for the corresponding four samples. In general, the higher metal content will show a good electrical conductivity. With an increase in the carbonization temperature, the crystallinity of Co will be higher and the dielectric constant will increase. Dielectric loss mainly includes conductivity loss and polarization loss. The high carbonization temperature could result in an improvement of graphitization of the carbonaceous skeleton in Co/C composites. This can lead to a higher conductivity and thus effective contribution to the complex permittivity based on the free electron theory ε ≈ σ/2πε0 f.45 Polarization loss mainly includes ion polarization, electron polarization, dipole orientation polarization, and interface polarization (space charge polarization). Ion polarization and electron polarization usually occur in the higher-frequency region (103−106 GHz) and can be excluded directly.46 Dipole polarization is usually caused by the redirection of the dipole and the interaction of electromagnetic field, whereas interfacial polarization is caused by the space charge distribution of the heterogeneous interface. Co/C-700 and Co/C-800 exhibit a typical frequency dispersion behavior (the electromagnetic parameter varies with frequency), which is usually related to the dipole-polarized electromagnetic energy loss. In comparison, the imaginary part of the complex permittivity in Co/C-500 and Co/C-600 nearly levels out over the given frequency range, indicating an insufficient dipolar orientation polarization. Charge transfer between the metal and carbon shell can result in the formation of electric dipoles at the interface of the Co core and the graphite layers and leads to the generation of interface polarization loss to the electromagnetic wave. With the increasing carbonization temperature, the dipoles will be increased accordingly, which will be beneficial to the dielectric loss. In addition, electric dipoles may generate from defects in metal cores and strongly curved graphite layers, which leads to other types of polarization losses at different frequencies.47−49 Therefore, it can be concluded that the main mechanism of dielectric loss of Co/C composites is dipole-oriented polarization and interfacial polarization. Figure 6c demonstrates the dielectric dissipation factors (tan δE) of Co/C composites. It can be seen that tan δE enhanced with an increase in the carbonization temperature. Figure 6d,e shows that the imaginary parts (μ″) of the complex permeability increase with the increasing carbonation temperature. In addition to dielectric loss, magnetic loss is another key factor in the absorption of electromagnetic waves.50 Magnetic loss mainly includes hysteresis loss, domain wall resonance loss, natural ferromagnetic resonance loss, and eddy current loss. Generally, hysteresis loss and domain wall resonance loss occur at low frequencies (MHz).51 With regard to eddy current losses, Figure 7 shows that the C0 of the Co/C composite varies from 0 to 0.04 in the range of 1.0−18.0 GHz. It is known that C0 (C0 = μ″(μ′)−2f−1) should be constant if the magnetic loss of the material comes mainly from the eddy current loss. An obvious peak, emerging at about 2.7 GHz, corresponds to the natural resonance loss of the sample. In the frequency range of 4−18 GHz, there is still a small peak, which may be caused by the exchange resonance of the material.25 Thus, it can be concluded that the natural ferromagnetic resonance loss of the material is the main part of the magnetic loss at 1−4 GHz. Moreover, in the frequency range of 4−18 GHz, the magnetic loss includes the eddy current loss and exchange resonance loss, among which the eddy current loss is dominant.

Figure 7. C0 curves of Co/C at different carbonization temperatures.

The electromagnetic wave absorption property is illustrated in Figure 8, where the RL values are calculated from the relative permeability and permittivity at various absorber thicknesses throughout the given frequency range. The RL curves of Co/C500, Co/C-600, Co/C-700, and Co/C-800 with different thicknesses at 2−18 GHz are shown in Figure 8a−d, respectively. Figure 8e−h shows the corresponding three-dimensional (3D) contour maps. Figure 8a shows the reflection loss curve of Co/C500, and nearly no absorptive properties could be seen. For Co/ C-600, the maximum RL is only −8.31 dB at 8.65 GHz with a thickness of 4.5 mm. For Co/C-700, an optimal maximum RL value of −30.31 dB is achieved at 11.03 GHz with a thickness of 3 mm, as well as an effective absorption bandwidth (RL ≤ −10 dB) of 4.93 GHz (from 8.31 to 13.24 GHz). For Co/C-800, the maximum RL is just −13.87 dB at 12.90 GHz with a thickness of 2 mm, and the effective absorption bandwidth (RL ≤ −10 dB) is only 3.91 GHz. It can also be seen from Figure 6f that the magnetic dissipation factor (tan δM) increases with the increasing carbonization temperature. The absorption performance could be controlled by tuning the carbonization temperature. A comparison with other state-of-the-art absorbents reported by other published papers has been given (Table S1 in SI). The incorporation of controllable magnetic Co NPs can effectively reduce the complex permittivity, optimize impedance matching,52 enhance the magnetic loss, and finally result in excellent electromagnetic wave absorption.

4. CONCLUSIONS Structurally and compositionally controllable Co NPs/porous C composites were synthesized by a facile chemical solution method followed by thermal annealing under an inert atmosphere. The Co/C-700 composite with filler loading of only 25 wt % in paraffin matrix exhibited remarkable properties of electromagnetic wave absorption. The maximum RL is −30.31 dB at 11.03 GHz with a thickness of 3 mm, and the effective absorption bandwidth was 4.93 GHz (8.31−13.24 GHz). The main mechanism of dielectric loss of Co/C composites is dipole polarization and interfacial polarization. The magnetic loss is mainly caused by the natural ferromagnetic resonance loss and eddy current loss. Porous carbides derived from ZIF-67 exhibit good properties, including high porosity, lightweight, and tunable conductivity and dielectric loss. These metallic magnetic NPs/porous carbon nanocomposites with well-designed constituents and porous structures are attractive candidates for electromagnetic wave absorbers that show good impedance matching and strong EM attenuation capability because of the dual-loss mechanism and synergistic effect of the components. It is expected that this work can lay the foundation for a class of 42107


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Figure 8. Calculated reflection loss of samples with various thicknesses: (a) Co/C-500, (b) Co/C-600, (c) Co/C-700, and (d) Co/C-800 samples; (e− h) corresponding 3D contour maps.

lightweight and high-performance electromagnetic wave absorbing materials.

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ASSOCIATED CONTENT

S Supporting Information *

properties of our samples with those of the other stateof-the-art absorbents reported in the literature (PDF)

AUTHOR INFORMATION

Corresponding Author

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b13796. N2 adsorption−desorption isotherms of Co NPs/ZIF-67, Co/C-700, and corresponding pore size distribution curves and tabulated comparison of the absorption

*E-mail: [email protected]. ORCID

Haicheng Wang: 0000-0002-8238-8728 Yanglong Hou: 0000-0003-0579-4594 42108


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(15) Joo, J.; Lee, C. Y. High Frequency Electromagnetic Interference Shielding Response of Mixtures and Multilayer Films Based on Conducting Polymers. J. Appl. Phys. 2000, 88, 513−518. (16) Motojima, S.; Noda, Y.; Hoshiya, S.; Hishikawa, Y. Electromagnetic Wave Absorption Property of Carbon Microcoils in 12−110 GHz Region. J. Appl. Phys. 2003, 94, 2325−2330. (17) Wang, A.; Wang, W.; Long, C.; Li, W.; Guan, J.; Gu, H.; Xu, G. Facile preparation, Formation Mechanism and Microwave Absorption Properties of Porous Carbonyl Iron Flakes. J. Mater. Chem. C 2014, 2, 3769−3776. (18) Huang, X.; Zhang, J.; Lai, M.; Sang, T. Preparation and Microwave Absorption Mechanisms of the NiZn Ferrite Nanofibers. J. Alloys Compd. 2015, 627, 367−373. (19) Chen, Y. J.; Xiao, G.; Wang, T. S.; Ouyang, Q.-Y.; Qi, L. H.; Ma, Y.; Gao, P.; Zhu, C. L.; Cao, M. S.; Jin, H. B. Porous Fe3O4/Carbon Core/Shell Nanorods: Synthesis and Electromagnetic Properties. J. Phys. Chem. C 2011, 115, 13603−13608. (20) Wen, B.; Cao, M. S.; Lu, M. M.; Cao, W. Q.; Shi, H. L.; Liu, J.; Wang, X. X.; Jin, H. B.; Fang, X. Y.; Wang, W. Z.; Yuan, J. Reduced Graphene Oxides: Light-Weight and High-Efficiency Electromagnetic Interference Shielding at Elevated Temperatures. Adv. Mater. 2014, 26, 3484−3489. (21) Zhao, B.; Zhao, W.; Shao, G.; Fan, B.; Zhang, R. Corrosive synthesis and enhanced electromagnetic absorption properties of hollow porous Ni/SnO2 hybrids. Dalton Trans. 2015, 44, 15984− 15993. (22) Sui, J. H.; Zhang, C.; Li, J.; Yu, Z. L.; Cai, W. Microwave absorption and catalytic activity of carbon nanotubes decorated with cobalt nanoparticles. Mater. Lett. 2012, 75, 158−160. (23) Liu, Q. L.; Zhang, D.; Fan, T. X. Electromagnetic wave absorption properties of porous carbon/Co nanocomposites. Appl. Phys. Lett. 2008, 93, No. 013110. (24) Liu, Q.; Cao, Q.; Bi, H.; Liang, C.; Yuan, K.; She, W.; Yang, Y. J.; Che, R. C. CoNi@SiO2@TiO2 and CoNi@Air@TiO2 Microspheres with Strong Wideband Microwave Absorption. Adv. Mater. 2016, 28, 486−490. (25) Wang, H.; Ma, N.; Yan, Z. R.; Deng, L.; He, J.; Hou, Y. L.; Jiang, Y.; Yu, G. H. Cobalt/polypyrrole nanocomposites with controllable electromagnetic properties. Nanoscale 2015, 7, 7189−7196. (26) Lü, Y.; Wang, Y.; Li, H.; Lin, Y.; Jiang, Z.; Xie, Z.; Kuang, Q.; Zheng, L. MOF-Derived Porous Co/C Nanocomposites with Excellent Electromagnetic Wave Absorption Properties. ACS Appl. Mater. Interfaces 2015, 7, 13604−13611. (27) Zhang, X. M.; Ji, G. B.; Liu, W.; Zhang, X. X.; Gao, Q. W.; Li, Y. C.; Du, Y. W. A novel Co/TiO2 nanocomposite derived from a metalorganic framework: synthesis and efficient microwave absorption. J. Mater. Chem. C 2016, 4, 1860−1870. (28) Aijaz, A.; Masa, J.; Rösler, C.; Xia, W.; Weide, P.; Botz, A. J. R.; Fischer, R. A.; Schuhmann, W.; Muhleret, M. Co@Co3O4 Encapsulated in Carbon Nanotube-Grafted Nitrogen-Doped Carbon Polyhedra as an Advanced Bifunctional Oxygen Electrode. Angew. Chem., Int. Ed. 2016, 55, 4087−4091. (29) Mahmood, A.; Zou, R.; Wang, Q.; Xia, W.; Tabassum, H.; Qiu, B.; et al. Nanostructured electrode materials derived from metal-organic framework xerogels for High-Energy-Density Asymmetric Supercapacitor. ACS Appl. Mater. Interfaces 2016, 8, 2148−2157. (30) Gadipelli, S.; Patel, H. A.; Guo, Z. X. An ultrahigh pore volume drives up the amine stability and cyclic CO2 capacity of a solid-amine@ carbon sorbent. Adv. Mater. 2015, 27, 4903−4909. (31) Michael, A. Z.; Michael, L. V.; Judy, S. R.; Martin, S.; Timothy, G. S. P. Structural and magnetic properties of cobalt nanoparticles encased in siliceous shells. Chem. Mater. 2007, 19, 6597−6604. (32) Puntes, V. F.; Krishnan, K. M.; Alivisatos, A. P. Colloidal nanocrystal shape and size control: the case of cobalt. Science 2001, 291, 2115−2117. (33) Puntes, V. F.; Gorostiza, P.; Aruguete, D. M.; Bastus, N. G.; Alivisatos, P. Collective behaviour in two-dimensional cobalt nanoparticle assemblies observed by magnetic force microscopy. Nat. Mater. 2004, 3, 263−268.

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L.X. and H.C.W. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS H.W. thanks Tao Xu at Southeast University for performing TEM. H.W. acknowledges financial support from the National Natural Science Foundation of China (51101013) and the Fundamental Research Funds for the Central Universities (FRFTP-14-012A2, FRF-TP-15-007A3). Y.H. acknowledges financial support from the National Natural Science Foundation of China (51590882, 51631001) and the State key Project of Research and Development of China (2017YFA0206301).

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REFERENCES

(1) Wang, G.; Wu, Y.; Zhang, X.; Li, Y.; Guo, L.; Cao, M. Controllable Synthesis of Uniform ZnO Nanorods and Their Enhanced Dielectric and Absorption Properties. J. Mater. Chem. A 2014, 2, 8644−8651. (2) Yuan, K.; Che, R. C.; Cao, Q.; Sun, Z.; Yue, Q.; Deng, Y. Designed Fabrication and Characterization of Three-Dimensionally Ordered Arrays of Core−Shell Magnetic Mesoporous Carbon Microspheres. ACS Appl. Mater. Interfaces 2015, 7, 5312−5319. (3) Lv, H.; Liang, X. H.; Cheng, Y.; Zhang, H. Q.; Tang, D. M.; Zhang, B. S.; Ji, G. B.; Du, Y. W. Coin-like α-Fe2O3@CoFe2O4 Core-Shell Composites with Excellent Electromagnetic Absorption Performance. ACS Appl. Mater. Interfaces 2015, 7, 4744−4750. (4) Saini, P.; Arora, M.; Gupta, G.; Gupta, B. K.; Singh, V. N.; Choudhary, V. High Permittivity Polyaniline-Barium Titanate Nanocomposites with Excellent Electromagnetic Interference Shielding Response. Nanoscale 2013, 5, 4330−4346. (5) Saini, P.; Choudhary, V.; Dhawan, S. K. Improved Microwave Absorption and Electrostatic Charge Dissipation Efficiencies of Conducting Polymer Grafted Fabrics Prepared via in situ Polymerization. Polym. Adv. Technol. 2012, 23, 343−349. (6) Yang, Y.; Gupta, M. C.; et al. Novel Carbon Nanotube-Polystyrene Foam Composites for Electromagnetic Interference Shielding. Nano Lett. 2005, 5, 2131−2134. (7) Kong, L.; Yin, X.; Yuan, X.; Zhang, Y.; Liu, X.; Cheng, L.; Zhang, L. Electromagnetic wave absorption properties of graphene modified with carbon nanotube/poly (dimethyl siloxane) composites. Carbon 2014, 73, 185−193. (8) Zhang, A. B.; Cao, X. F.; Tang, M.; Zheng, Y. P.; Lu, Z. B.; Shen, Y. T. The effect of modifier contents of polyvinyl pyrrolidone on the enhanced dielectric and microwave absorbing properties of multiwalled carbon nanotubes. J. Appl. Polym. Sci. 2014, 131, No. 41007. (9) Qing, Y. C.; Zhou, W. C.; Luo, F.; Zhu, D. M. Epoxy-silicone filled with multi-walled carbon nanotubes and carbonyl iron particles as a microwave absorber. Carbon 2010, 48, 4074−4080. (10) Wen, F. S.; Zhang, F.; Liu, Z. Y. Investigation on Microwave Absorption Properties for Multiwalled Carbon Nanotubes/Fe/Co/Ni Nanopowders as Lightweight Absorbers. J. Phys. Chem. C 2011, 115, 14025−14030. (11) Xiang, J.; Li, J. L.; Zhang, X. H.; Ye, Q.; Xu, J. H.; Shen, X. Q. Magnetic carbon nanofibers containing uniformly dispersed Fe/Co/Ni nanoparticles as stable and high-performance electromagnetic wave absorbers. J. Mater. Chem. A 2014, 2, 16905−16914. (12) Zhao, H. B.; Fu, Z. B.; Chen, H. B.; Zhong, M. L.; Wang, C. Y. Excellent Electromagnetic Absorption Capability of Ni/Carbon Based Conductive and Magnetic Foams Synthesized via a Green One Pot Route. ACS Appl. Mater. Interfaces 2016, 8, 1468−1477. (13) Wang, J. C.; Xiang, C. S.; Liu, Q.; Pan, Y. B.; Guo, J. K. Ordered mesoporous carbon/fused silica composites. Adv. Funct. Mater. 2008, 18, 2995−3002. (14) Yan, L.; Wang, J. B.; Han, X. H.; Ren, Y.; Liu, Q. F.; Li, F. S. Enhanced microwave absorption of Fe nanoflakes after coating with SiO2 nanoshell. Nanotechnology 2010, 21, No. 095708. 42109


Research Article

ACS Applied Materials & Interfaces (34) Gao, J.; Gu, H. W.; Xu, B. Multifunctional magnetic nanoparticles: design, synthesis, and biomedical applications. Acc. Chem. Res. 2009, 42, 1097−1107. (35) Sun, S. H.; Murray, C. B. Synthesis of monodisperse cobalt nanocrystals and their assembly into magnetic superlattices. J. Appl. Phys. 1999, 85, 4325−4330. (36) Kong, L.; Yin, X. W.; Zhang, Y. J.; Yuan, X. Y.; Li, Q.; Ye, F.; Cheng, L. F.; Zhang, L. T. Electromagnetic Wave Absorption Properties of Reduced Graphene Oxide Modified by Maghemite Colloidal Nanoparticle Clusters. J. Phys. Chem. C 2013, 117, 19701−19711. (37) Miles, P. A.; Westphal, W. B.; Von Hippel, A. Dielectric spectroscopy of ferromagnetic Semiconductors. Rev. Mod. Phys. 1957, 29, 279−307. (38) Ding, D.; Wang, Y.; Li, X. D.; Qiang, R.; Xu, P.; Chu, W. L.; Han, X. J.; Du, Y. C. Rational design of core-shell Co@C microspheres for high-performance microwave absorption. Carbon 2017, 111, 722−732. (39) Wang, Z. H.; Xiong, X. Q.; Qie, L.; Huang, Y. H. HighPerformance Lithium Storage in Nitrogen-Enriched Carbon Nanofiber Webs Derived from Polypyrrole. Electrochim. Acta 2013, 106, 320−326. (40) Lü, Y.; Zhan, W. W.; He, Y.; Wang, Y. T.; Kong, X. J.; Kuang, Q.; Xie, Z. X.; Zheng, L. S. MOF-Templated Synthesis of Porous Co3O4 Concave Nanocubes with High Specific Surface Area and Their Gas Sensing Properties. ACS Appl. Mater. Interfaces 2014, 6, 4186−4195. (41) Park, K. S.; Ni, Z.; Côté, A. P.; Choi, J. Y.; Huang, R.; Uribe-Romo, F. J.; Chae, H. K.; O’Keeffe, M.; Yaghi, O. M. Exceptional chemical and thermal stability of zeolitic imidazolate Frameworks. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 10186−10191. (42) Yi, H. B.; Wen, F. S.; Qiao, L.; Li, F. S. Microwave Electromagnetic Properties of Multiwalled Carbon Nanotubes Filled with Co Nanoparticles. J. Appl. Phys. 2009, 106, No. 103922. (43) Torad, N. L.; Hu, M.; Ishihara, S.; Sukegawa, H.; Belik, A. A.; Imura, M.; Ariga, K.; Sakka, Y.; Yamauchi, Y. Direct Synthesis of MOFDerived Nanoporous Carbon with Magnetic Co Nanoparticles toward Efficient Water Treatment. Small 2014, 10, 2096−2107. (44) García Prieto, A.; Fdez-Gubieda, M.; Meneghini, C.; GarcíaArribas, A.; Mobilio, S. Microstructural and Magnetic Evolution upon Annealing of Giant Magnetoresistance Melt-Spun Co-Cu Granular Alloys. Phys. Rev. B 2003, 67, No. 224415. (45) Cao, M. S.; Yang, J.; Song, W. L.; Zhang, D. P.; Wen, B.; Jin, H. B.; Hou, Z. L.; Yuan, J. Ferroferric oxide/multiwalled carbon nanotube vs polyaniline/ferroferric oxide/multiwalled carbon nanotube multiheterostructures for highly effective microwave absorption. ACS Appl. Mater. Interfaces 2012, 4, 6949−6956. (46) Tian, C. H.; Du, Y. C.; Xu, P.; Qiang, R.; Wang, Y.; Ding, D.; Xue, J. L.; Ma, J.; Zhao, H. T.; Han, X. J. Constructing Uniform Core−Shell PPy@PANI Composites with Tunable Shell Thickness toward Enhancement in Microwave Absorption. ACS Appl. Mater. Interfaces 2015, 7, 20090−20099. (47) Wang, H.; Dai, Y. Y.; Geng, D. Y.; Ma, S.; Li, D.; An, J.; He, J.; Liu, W.; Zhang, Z. D. CoxNi100-x nanoparticles encapsulated by curved graphite layers: controlled in-situ metal-catalytic preparation and broadband microwave absorption. Nanoscale 2015, 7, 17312. (48) Wang, H.; Dai, Y. Y.; Gong, W. J.; Geng, D. Y.; Ma, S.; Li, D.; Liu, W.; Zhang, Z. D. Broadband microwave absorption of CoNi@C nanocapsules enhanced by dual dielectric relaxation and multiple magnetic resonances. Appl. Phys. Lett. 2013, 102, No. 223113. (49) Wang, H.; Guo, H. H.; Dai, Y. Y.; Geng, D. Y.; Han, Z.; Li, D.; Yang, T.; Ma, S.; Liu, W.; Zhang, Z. D. Optimal electromagnetic-wave absorption by enhanced dipole polarization in Ni/C nanocapsules. Appl. Phys. Lett. 2012, 101, No. 083116. (50) Wen, F. S.; Hou, H.; Xiang, J. Y.; Zhang, X. Y.; Su, Z. B.; Yuan, S. J.; Liu, Z. Y. Fabrication of carbon encapsulated Co3O4 nanoparticles embedded in porous graphitic carbon nanosheets for microwave absorber. Carbon 2015, 89, 372−373. (51) Qiang, R.; Du, Y. C.; Zhao, H. T.; Wang, Y.; Tian, C. H.; Li, Z. G.; Han, X. J.; Xu, P. Metal organic framework-derived Fe/C nanocubes toward efficient microwave absorption. J. Mater. Chem. A 2015, 3, 13426−13434.

(52) Fang, Z. G.; Li, C. S.; Sun, J. Y.; Zhang, H. T.; Zhang, J. S. The electromagnetic characteristics of carbon foams. Carbon 2007, 45, 2873−2879.

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Efficient and Lightweight Electromagnetic Wave Absorber Derived

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