Microwave Electromagnetic and Absorption Properties of N-Doped

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Microwave Electromagnetic and Absorption Properties of N-Doped Ordered Mesoporous Carbon Decorated With Ferrite Nanoparticles Guozhu Shen, Buqing Mei, Hongyan Wu, Hongyu Wei, Xumin Fang, and Yewen Xu J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b10906 • Publication Date (Web): 27 Jan 2017 Downloaded from http://pubs.acs.org on January 31, 2017

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The Journal of Physical Chemistry

Microwave Electromagnetic and Absorption Properties of N-Doped Ordered Mesoporous Carbon Decorated with Ferrite Nanoparticles †

†

†

‡

§

Guozhu Shen,† Buqing Mei,† Hongyan Wu,† Hongyu Wei,‡ Xumin Fang,§ and §

Yewen Xu*,§

†

School of Physics and Optoelectronic Engineering, Nanjing University of

Information Science & Technology, Nanjing 210044, China ‡

College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics

and Astronautics, Nanjing 210016, China §

Science and Technology on Near-Surface Detection Laboratory, Wuxi 214035,

China

1

ACS Paragon Plus Environment


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ABSTRACT: Lightweight nitrogen-doped ordered mesoporous carbon (NOMC) with high specific surface area and pore volume have been prepared through self-assembly and subsequent heat treatment route. The spherical NOMC particles are decorated with CoFe2O4 nanoparticles via co-precipitation method to enhance their microwave absorption

property. The

electromagnetic

parameters

of the

NOMC

and

CoFe2O4/NOMC composites are measured and the microwave reflection loss properties are evaluated in the frequency range of 0.5-18 GHz. The results show that both real part and imaginary part of permittivity of NOMC totally decline and real part of permeability increases with the introduction of ferrite. However, the negative values of imaginary part of complex permeability appear for the CoFe2O4/NOMC composites, which may be caused by enhanced eddy current effect due to the introduction of ferrite. The reflection loss results exhibit that the CoFe2O4/NOMC composites have excellent microwave absorption performances. The absorption bandwidth less than -10 dB reaches 5.0 GHz (11.9-16.9 GHz) for 40-F/NOMC composite (40 wt% ferrite) with 1.5 mm of thickness and the minimum reflection loss value is up to -38.3 dB at 3.9 GHz for 30-F/NOMC composite with 4.0 mm of thickness. The excellent absorption properties derive from the synergistic effect between dielectric loss of NOMC and magnetic loss of ferrite and better impendence matching at air and ferrite/NOMC composite interface. Thus the lightweight ferrite/NOMC composites exhibit their great potential as microwave absorbing materials.

■ INTRODUCTION 2


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Recently, electromagnetic (EM) wave absorbers have been paid more and more attention due to the deterioration of electromagnetic environment and the military requirement of stealth technology. Conventional EM absorbing materials mainly include magnetic loss materials such as ferrite,1-4 magnetic metal powders,5-7 and dielectric loss materials such as ZnO,8-10 MnO2,11,12 BaTiO3,13,14 etc. Furthermore, carbonceous materials acted as absorbers have been generally investigated because of their advantages of high dielectric loss and environmental stability.15 It is well known that the absorption properties of absorbers are determined by their complex permittivity, permeability and impendence matching at the air and absorbers interface. Therefore, to meet the demand of strong absorption in a wide frequency range, carbon materials are usually prepared to composites with magnetic materials, such as magnetic carbon fibers,16,17 carbon nanotubes,18,19 graphenes,20,21 carbon spheres22-24 and porous carbon composites.25,26 Among these carbon materials, ordered mesoporous carbons (OMC) and their composites as microwave absorbers exhibit great potential because of their lightweight, larger functionalized surfaces and tunable complex permittivity.27 Various ways have been developed to obtain OMC28-31 and their composites.32-34 In particular, Zeng et al.35,36 fabricated the MoO2-OMC and Ge/GeO2-OMC nanocomposites respective using OMC as nanoreactor, thus some oxides nanoparticles were confined in the mesopores of OMC. For OMC microwave absorbers, Wang et al.37 introduced magnetic Fe3O4 nanoparticles into the mesochannels of OMC by reduction process. The resultant magnetic carbon composite exhibited maximum reflection loss of -32 3



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dB at 11.3 GHz and a bandwidth less than -10 dB of 2 GHz. Yuan et al.38 fabricated 3D ordered arrays of core-shell microshperes with Fe3O4 cores and OMC shells by a confined interface coassembly coating strategy. The core-shell structures indicated the maximum reflection loss of -57 dB at 8 GHz and absorption bandwidth less than -10 dB of 6.4 GHz. Furthermore, compared with OMC, improved surface polarity and electric conductivity can be obtained by nitrogen doping,39,40 which will enhance the dielectric loss of OMC in the microwave region. In our previous research, magnetic cobalt coated nitrogen-doped ordered mesoporous carbons have been prepared by low temperature hydrothermal and electroless plating method.41 However, the electroless plating is high-cost due to the low efficiency of reduction reaction from metal ions to metals. In this research, spherical NOMC particles with the diameters of 130-210 nm were prepared by self-assembly and subsequent heat treatment process. Then, the NOMC particles were decorated with CoFe2O4 nanoparticles via co-precipitation method. Finally, microwave electromagnetic and absorption properties of the lightweight ferrite/NOMC composites were studied.

■ EXPERIMENTAL SECTION Preparation of NOMC. The spherical NOMC particles are synthesized as reported in our earlier study.42 Pluronic F127 (6.60 g), 3-aminophenol (3.30 g), hexamethylenetetramine (4.20 g) and aqueous ammonia (6.0 mL) were added into a reaction flask with 620 mL of deionized water. After continuous stirring for 1 h, the solution was sealed and heated to 80 ℃ and sustain the temperature for 2 days. The 4


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resultant brown suspension was centrifugated, washed and dried at 80 ℃. The as-prepared product was denoted as NOMC-as. Finally, the sample NOMC-as was heated at 350 ℃ for 3 h, subsequently pyrolyzed at 800 ℃ for 5 h with a heating rate of 1 ℃/min under H2O/N2. The resultant black product was denoted as NOMC. The H2O/N2 was generated through pumping the nitrogen flow via a gas-washing bottle with water. Preparation of CoFe2O4/NOMC Composites. Cobalt ferrite (CoFe2O4)/NOMC composites were prepared via co-precipitation method. The preparative details are as following: Fe(NO3)3·9H2O (1.48 g) and CoCl2·2H2O (0.44 g) were dissolved in 147 mL of deionized water. Then, 1.00 g of NOMC was dispersed in the above solution by ultrasonication for 30 min. After the above mixture was heated to 80 ℃ in an oil bath under continuous stirring, 3.7 mL of ammonia solution was then poured into the above suspension and the suspension was stirred continuously for 2 h using a mechanical stirrer. Finally, the precipitate was centrifuged and thoroughly washed three times with deionized water and dried at 80 ℃ overnight. The obtained powder composite was denoted as 30-F/NOMC, which means that the weight percent of ferrite was 30 wt% in the composite. Other two samples named 40-F/NOMC and 50-F/NOMC were synthesized by altering the dosages of NOMC, and all preparative procedures were the same as that of the above sample 30-F/NOMC. Characterizations. Powder X-ray diffraction (XRD) measurements were carried out using a Thermo ARL X’TRA Diffractometer with Cu-Kα radiation. Transmission electron microscope (TEM) and scanning electron microscope (SEM) images were 5



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taken on Phillips Tecnai 12, G2 F30 and Hitachi SU3500 electron microscopes, respectively. Nitrogen sorption experiments were conducted at 77 K by a Tristar II Surface Area and Porosity Analyser (Micromeritics). An Agilent E8363C vector network analyzer (VNA) was applied to determine the relative complex permittivity (εr=ε’-jε”) and permeability (µr=µ’-jµ”). Before measurement, the powder samples were uniformly mixed with paraffin wax at 30% weight fraction and pressed into a toroidal shape with 7.0 mm of outer diameter and 3.0 mm of inner diameter.

■ RESULTS AND DISCUSSION

Figure 1. XRD patterns of NOMC and ferrite/NOMC composites.

Characterization of samples. XRD patterns of the prepared NOMC and its composites are illustrated in Figure 1. Two wide diffraction peaks of the NOMC are found at about 2θ = 24.3 and 44.1°, which indicate the (002) and (101) planes of graphite, respectively. Compared with the diffraction peaks of (002) at 2θ = 26.23° and (101) at 2θ = 44.34° for graphite (JCPDS 89-7373), calculations show that the d002 and d101 values of the NOMC are larger than those of graphite, indicating the synthesized NOMC is amorphous. The XRD patterns of 30-F/NOMC, 40-F/NOMC and 50-F/NOMC confirm the formation of ferrite CoFe2O4 crystal phase in the 6


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composites, whose diffraction peaks can be well indexed to face-centered cubic cobalt ferrite (CoFe2O4) phase (JCPDS 22-1086) with a space group of Fd3m.

Figure 2. TEM (a, c, d, f, h and j) and SEM (b, e, g, i and k) images of NOMC-as (a and b), NOMC (c, d and e), 30-F/NOMC (f and g), 40-F/NOMC (h and i) and 50-F/NOMC (j and k).

The TEM and SEM images of samples NOMC-as, NOMC and ferrite/NOMC composites are shown in Figure 2. It can be found that the NOMC-as particles are spherical with the diameters of the isolated spheres from 160 to 260 nm, and the 7



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mesostructure is clearly observed from the TEM image in Figure 2a. The NOMC particles carbonized at 800 ℃ keep the spherical morphology and mesostructure, however, the particles size shrink to 130-210 nm, as shown in Figure 2c. Moreover, an enlarged HRTEM image of NOMC particles is shown in Figure 2d. The morphology and size of the spherical NOMC-as and NOMC particles can be also identified by SEM (Figure 2b and e). The EM images of ferrite/NOMC composites (Figure 2f-k) indicate that the particles are still spherical, however, the mesopores are difficult to be found from the TEM images as shown in Figure 2f, h and j. The size of the spherical particles is slightly larger than that of NOMC. These results imply the CoFe2O4 particles are uniformly deposited on NOMC particles.

Figure 3. N2 adsorption-desorption isotherms (a) and the corresponding pore size distribution curve (b) of NOMC.

Nitrogen adsorption-desorption isotherms of the sample NOMC (Figure 3a) show a type Ⅳ curve according to the IUPAC classification, indicating that the carbon material is mesoporous. This can also be confirmed by the pore size distribution analysis via Barrett-Joyner-Halenda (BJH) method, revealing a pore size of 3.1 nm as shown in Figure 3b. The BET surface area and pore volume are calculated to be 1158 8


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m2/g and 0.73 cm3/g, respectively. The high specific surface area and pore volume benefit from the steam activation as mentioned in our previous study.41

Figure 4. Frequency dependence of electromagnetic parameters: real part (a) and imaginary part (b) of permittivity, real part (c) and imaginary part (d) of permeability

Electromagnetic Parameters Analysis. Figure 4 shows the frequency dependence of the electromagnetic parameters of samples NOMC and CoFe2O4/NOMC composites measured by VNA in the frequency range of 0.5-18 GHz. The real part ε’ of NOMC significantly declines from 35.5 to 20.2 with the frequency increasing from 0.5 to 6.1 GHz, then gradually decreases to 13.7 at 18.0 GHz, as shown in Figure 4a. For CoFe2O4/NOMC composites, the ε’ indicates similar variation trend as that of NOMC, and overall decreased with the increase of loading amount of ferrite, which implies that the ε’ of CoFe2O4/NOMC composites is mainly dominated by NOMC 9



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material. From Figure 4b, it can be found that the values of ε” of NOMC decrease from 64.9 to 13.2 with the frequency increasing from 0.5 to 6.0 GHz, and then keep an approximate constant in following frequency range. However, for every ferrite/NOMC sample, peaks of ε” can be found from Figure 4b. The value and location of the peaks are shown in table 1. It also shows the NOMC has the highest imaginary part ε” values nearly at every frequency point for the four samples from Figure 4b. This may be explained by the Debye relaxation equation, where the real and imaginary part of complex permittivity is shown as25,43,44

εs − ε∞ 1 + (2πf ) 2τ 2

(1)

2πfτ (ε S − ε ∞ ) σ + 2 2 1 + (2πf ) τ 2πfε 0

(2)

ε '= ε∞ + ε"=

Where εS and ε∞ are static permittivity and permittivity at infinite frequency, respectively, f is frequency, τ is polarization relaxation time, ε0 is the permittivity of free space and σ is the conductivity. The higher conductivity corresponds to the higher ε” value according to eqn (2). Here, the NOMC has higher conductivity than those ferrite/NOMC composites, and the conductivity of ferrite/NOMC composites declines with the increase of loading amount of ferrite. Furthermore, according to eqn (2) and (3), if the contribution of conductivity to ε” would not be considered, the above Debye relaxation equation can be deduced as follows after removal of frequency f,

(ε' − ε ∞ )2 + (ε" )2 = (ε S - ε ∞ )2

(3)

Thus the plot of ε’ versus ε” is a single semicircle (Cole-Cole semicircle) in theory. Figure 5 indicates the curves of ε’ versus ε” of the four samples. Multiple semicircles 10


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can be clearly observed for three ferrite/NOMC samples and partly overlapped semicircles can be found with the increase of loading amount of ferrite (samples 40-F/NOMC and 50- F/NOMC), which suggests that multiple Debye relaxation processes occurred in these composites. Additionally, as shown in Figure 5, the Cole-Cole semicircles are distorted for these ferrite/NOMC composites, implying that other loss may contribute to the permittivity spectra besides dipolar relaxation, such as conductance loss, interfacial polarization among carbon, ferrite and paraffin. Table 1. Value and location of the ε” peaks for samples NOMC and ferrite/NOMC composites. Samples

NOMC

30-F/NOMC

40-F/NOMC

50-F/NOMC

Value of 1st peak

—

7.2

9.3

8.3

Location of 1st peak/GHz

—

6.4

6.2

8.8

Value of 2nd peak

—

11.8

11.5

7.0

Location of 2nd peak/GHz

—

9.7

10.1

11.1

Figure 5. Cole-Cole semicircles for samples NOMC and ferrite/NOMC composites.

From Figure 4c, it can be observed that the real part µ’ of NOMC nearly sustain a constant over the whole frequency range. For all ferrite/NOMC composites, µ’ slightly decreases before 8.2 GHz, and then increases with fluctuations and the peaks are found. The µ’ values of each ferrite/NOMC sample are higher than those of nonmagnetic NOMC over the whole frequency range. The maximum value of µ’ is 11



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1.8 at 14.1 GHz for 30-F/NOMC, 1.5 at 16.1 GHz for 40-F/NOMC and 1.4 at 16.0 GHz for 50-F/NOMC, respectively. As shown in Figure 4d, the imaginary part µ” of NOMC is close to zero over the whole frequency range. However, for the ferrite/NOMC composites, negative µ” values and resonance peaks can be found at high frequency, indicating the eddy current effect and strong magnetic resonance loss in the microwave region for these composites.37 For the ferrite/NOMC composites, the eddy current can be easily formed due to low resistivity and porous structure of NOMC as shown in Figure 6, and then conversely induces new magnetic field.45,46 Therefore, the negative µ” values can be considered as induced magnetic energy going out of the absorber as interpreted by Wu et al,47 meanwhile, the incident electromagnetic energy is consumed in the absorber because of eddy current loss. The eddy current loss contribution to µ” can be expressed as following48

µ" ≈ 2 πµ 0 ( µ' ) 2 d 2 fσ / 3

(4)

Where σ, d and µ0 are conductivity, diameter of particles and permeability of free space, respectively. The value of µ”(µ’)-2f-1 (=2πµ0d2σ/3) would be constant over the whole frequency range if µ” results only from eddy current loss. Figure 7 shows the frequency dependence of µ”(µ’)-2f-1 of NOMC and ferrite/NOMC composites. It is observed that the µ”(µ’)-2f-1 values dramatically decline before 2.0 GHz, and then keep an approximate constant from 2.0 to 8.9 GHz, and then fluctuated in following frequency range for three ferrite/NOMC samples. Remarkably, an obvious peak is found at 15.6 GHz for 30-F/NOMC. This implies that the magnetic loss may be caused by other loss mechanism such as natural resonance.49-51 12


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Figure 6. Forming mechanism of eddy current.

Figure 7. Variation of µ” (µ’)-2f-1 of the samples with frequency.

Figure 8. Variation of dielectric loss factor (a) and magnetic loss factor (b) of the samples with frequency.

To better understand the microwave loss mechanism of ferrite/NOMC composites, the calculated dielectric loss factor (tanδe=ε”/ε’) and magnetic loss factor (tanδm=µ”/µ’) are shown in Figure 8. As shown in Figure 8a, the tanδe decreases with the frequency increasing from 0.5 to 6.0 GHz, and then keeps a constant from 6.0 to 12.3 GHz, then increases in following frequency range for NOMC. For ferrite/NOMC composites, the multi-loss peaks can be observed. These loss peaks mainly result from orientational polarization of dipoles and interfacial polarization among ferrite, NOMC and binder matrix. From Figure 8b, it can be observed that the variation trend of tanδm is just inverse to that of tanδe, which can be interpreted by the LRC equivalent circuit 13



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model,25 where L, R and C are the inductance, resistance and capacitance, respectively. The close to zero of tanδm of NOMC means that the NOMC has almost no magnetic loss. As analyzed in complex permeability, negative values of tanδm can be found due to the introduction of ferrite and the resonance peaks can be observed at high frequency for the ferrite/NOMC composites. Especially, a strong resonance peak is found at 15.3 GHz for 30-F/NOMC.

Figure 9. RL curves of NOMC (a), 30-F/NOMC (b), 40-F/NOMC (c) and 50-F/NOMC (d) composites with different layer thickness d.

Microwave absorption properties. To evaluate the microwave absorption properties of the composites, the reflection loss (RL) based on transmission-line theory can be calculated as following equations

RL(dB) = 20 lg

Z in − Z 0 Z in + Z 0

(5)

where Z0 (377 Ω) is characteristic impedance of free space, and Zin is input impedance 14


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of absorber at absorber surface, which is given by

Z in = Z 0

µr  2 πfd  tanh j  µrε r εr c  

(6)

where d is the thickness of absorber, f is the frequency and c is the velocity of light in free space. The calculated RL of NOMC and ferrite/NOMC composites with d = 1.5-4.0 mm is shown in Figure 9. It is found that the RL characteristics are sensitive to the thickness. The loss peak (minimum RL value) shifts to lower frequency with thickness increasing for all samples. The locations of loss peaks are related to the set thickness, frequency and electromagnetic parameters of absorbers. It can be explained by the formula7

dm =

λm 4

=

c

(7)

4 f m ε r µr

where dm is the matching thickness of absorber, which is equal to λm/4. λm and fm are the wavelength and frequency located in RL peak. As shown in Figure 9a, the minimum RL value (RLmin) is -7.9 dB at 11.7 GHz for NOMC with d = 1.5 mm. For 30-F/NOMC composite (Figure 9b), the RLmin reaches -38.3 dB at 3.9 GHz (d = 4.0 mm), and another strong peak value is -35.2 dB at 12.1 GHz, and effective absorption bandwidth (RL ≤ -10 dB) is up to 3.2 GHz (10.8-14.0 GHz) when thickness d = 1.5 mm. For 40-F/NOMC composite (Figure 9c), the RLmin is -25.1 dB at 7.9 GHz (d = 2.5 mm) and the largest effective absorption bandwidth reaches 5.0 GHz (11.9-16.9 GHz) with d = 1.5 mm. For 50-F/NOMC composite (Figure 9d), the RLmin is -33.2 dB at 8.0 GHz (d = 2.5 mm) and the largest effective absorption bandwidth is 2.8 GHz 15



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(7.2-10.0 GHz) with d = 2.5 mm.

Figure 10. Variation of relative input impendence with frequency.

Compared the RL peak values of NOMC with those of ferrite/NOMC composites, one can find that peak value of NOMC is the largest（weak absorption）among the composites with the same thickness. For the four samples, NOMC has the highest dielectric loss factor in the frequency range of 0.5-8.7 GHz and ferrite/NOMC composites show negative magnetic loss factor in the medium frequency range as shown in Figure 8a and b, thus the excellent reflection loss properties of ferrite/NOMC composites should attribute to their not only magnetic loss but also better impendence matching at the air/absorber interface. According to eqn (5), the nonreflecting condition is Zin=Z0, accordingly, excellent reflection loss can happen when the relative input impedance Zin/Z0 is nearer to 1. Here, an example of frequency dependence of Zin/Z0 of all samples with thickness d = 2.0 mm is given in Figure 10. The results exhibit that the ferrite/NOMC composites show better impendence match than NOMC in the frequency range of 5.2-16.2 GHz. 16


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■ CONCLUSIONS In summary, spherical ferrite/NOMC composite particles with excellent microwave absorption properties have been successfully synthesized via organic-organic self-assembly and co-precipitation process. The microwave absorption results exhibit that the ferrite/NOMC composites have more excellent absorption properties than NOMC. For 30-F/NOMC and 40-F/NOMC composites, the absorption bandwidth less than -10 dB reaches 3.2 GHz (10.8-14.0 GHz) and 5.0 GHz (11.9-16.9 GHz) with only 1.5 mm of thickness, respectively. The enhanced microwave absorption properties are mainly derived from effective complementarities between dielectric loss of NOMC and magnetic loss of ferrite and better impendence matching at air and ferrite/NOMC composite interface. The dielectric loss can attribute to the polarization relaxation and proper conductivity of NOMC materials and the magnetic loss should originate from the natural resonance of ferrite materials and eddy current loss induced by alternating magnetic field. The lightweight ferrite/NOMC composites can become a promising candidate for microwave absorption.

■ AUTHOR INFORMATION Corresponding Authors *Y.W. Xu: e-mail, [email protected]

Notes The authors declare no competing financial interest.

■ ACKNOWLEDGMENTS This work has been supported by Science and Technology on Near-Surface 17



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Detection Laboratory, Natural Science Foundation-Outstanding Youth Foundation of Jiangsu Province of China (Grant No. BK20160091) and the Funds of National Natural Science Foundation of China (Grant No. 21601089 and 51405242).

■ REFERENCES (1) Zhu W. M.; Wang L.; Zhao R.; Ren J. W.; Lu G. Z.; Wang Y. Q. Electromagnetic and microwave-absorbing properties of magnetic nickel ferrite nanocrystals. Nanoscale, 2011, 3, 2862-2864. (2) Gu X.; Zhu W. M.; Jia C. J.; Zhao R.; Schmidt W. G.; Wang Y. Q. Synthesis and microwave absorbing properties of highly ordered mesoporous crystalline NiFe2O4. Chem. Commun. 2011, 47, 5337-5339. (3) Ren X. H.; Xu G. L. Electromagnetic and microwave absorbing properties of NiCoZn-ferrites doped with La3+. J. Magn, Magn, Mater. 2014, 354, 44-48. (4) Mosleh Z.; Kameli P.; Poorbaferani A.; Ranjbar M.; Salamati H. Structural, magnetic and microwave absorption properties of Ce-doped barium hexaferrite. J. Magn, Magn, Mater. 2016, 397, 101-107. (5) Liu Q. H.; Cao Q.; Zhao X. B.; Bi H.; Wang C.; Wu D. S.; Che R. C. Insights into size-dominant magnetic microwave absorption properties of CoNi microflowers via off-axis electron holography. ACS Appl. Mater. Interfaces 2015, 7, 4233-4240. (6) Kim S. T.; Kim S. S. Microwave absorbing properties of hollow microspheres plated with magnetic metal films. J. Appl. Phys. 2014, 115, 17A528-1-3. (7) Liu C.; Yuan Y.; Jiang J. T.; Gong Y. X.; Zhen L. Microwave absorption properties of FeSi flaky particles prepared via a ball-milling process. J. Magn. Magn. 18


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Mater. 2015, 395, 152-158. (8) Wu G. L.; Cheng Y. H.; Xie Q.; Jia Z. R.; Xiang F.; Wu H. J. Facile synthesis of urchin-like ZnO hollow spheres with enhanced electromagnetic wave absorption properties. Mater. Lett. 2015, 144, 157-160 (9) Hu Q.; Tong G. X.; Wu W. H.; Liu F. T.; Qian H. S.; Hong D. Y. Selective preparation

and

enhanced

microwave

electromagnetic

characteristics

of

polymorphous ZnO architectures made from a facile one-step ethanediamine-assisted hydrothermal approach. CrystEngComm 2013, 15, 1314-1323. (10) Zhou R. F.; Wang Y. N.; Yan D.; Li S. K.; Liu Y.; Wang F. Y. One-step synthesis and excellent microwave absorption of hierarchical tree-like ZnO nanostructures. Mater. Lett. 2014, 117, 34-36. (11) Duan Y. P.; Liu Z.; Jing H.; Zhang Y. H.; Li S. Q. Novel microwave dielectric response of Ni/Co-doped manganese dioxides and their microwave absorbing properties. J. Mater. Chem. 2012, 22, 18291-18299. (12) Wang G. S.; He S.; Luo X.; Wen B.; Lu M. M.; Guo L.; Cao M. S. Synthesis and growth mechanism of 3D α–MnO2 clusters and their application in polymer composites with enhanced microwave absorption properties. RSC Adv. 2013, 3, 18009-18015. (13) Zhang M.; Zheng J.; Liang L.; Jiang F.; Wang Y. Preparation and microwave absorption properties of Ag-doped BaTiO3 nanocomposites. J. Magn. Magn. Mater.

2014, 368, 198-201. (14) Yang J.; Zhang J.; Liang C. Y.; Wang M.; Zhao P. F.; Liu M. M.; Liu J. W.; Che 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 26

R. C. Ultrathin BaTiO3 nanowires with high aspect ratio: A simple one-step hydrothermal synthesis and their strong microwave absorption. ACS Appl. Mater. Interfaces 2013, 5, 7146-7151. (15) Qin F.; Brosseau C. A review and analysis of microwave absorption in polymer composites filled with carbonaceous particles. J. Appl. Phys. 2012, 111, 031301-1-23 (16) Shah A.; Wang Y. H.; Huang H.; Zhang L.; Wang D. X.; Zhou L.; Duan Y. P.; Dong X. L.; Zhang Z. D. Microwave absorption and flexural properties of Fe nanoparticle/carbon fiber/epoxy resin composite plates. Compos. Struct. 2015, 131, 1132-1141. (17) Shah A.; Ding A. Wang Y. H.; Zhang L.; Wang D. X.; Muhammad J.; Huang H.; Duan Y. P.; Dong X. L.; Zhang Z. D. Enhanced microwave absorption by arrayed carbon fibers and gradient dispersion of Fe nanoparticles in epoxy resin composites. Carbon 2016, 96, 987-997. (18) Cao M. S.; Yang J.; Song W. L.; Zhang D. Q.; Wen B.; Jin H. B.; Hou Z. L.; Yuan J. Ferroferric oxide/multiwalled carbon nanotubes vs polyaniline/ferroferric oxide/multiwalled carbon nanotube multiheterostructures for highly effective microwave absorption. ACS Appl. Mater. Interfaces 2012, 4, 6949-6956. (19) Li G.; Sheng L. M.; Yu L. M.; Ren W.; Zhao X. L. Electromagnetic and microwave absorption properties of single-walled carbon nanotubes and CoFe2O4 nanocomposites. Mater. Sci. Eng. B 2015, 193, 153-159. (20) Zhang X. J.; Wang G. S.; Cao W. Q.; Wei Y. Z.; Liang J. F.; Guo L.; Cao M. S. Enhanced

microwave

absorption

property

of

reduced

20


graphene

oxide

Page 21 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(RGO)-MnFe2O4 nanocomposites and polyvinylidene fluoride. ACS Appl. Mater. Interfaces 2014, 6, 7471-7478. (21) Hu C. G.; Mou Z. Y.; Lu G. W.; Chen N.; Dong Z. L.; Hu M. J.; Qu L. T. 3D graphene-Fe3O4 nanocomposites with high-performance microwave absorption. Phys. Chem. Chem. Phys. 2013, 15, 13038-13043. (22) Khani O.; Shoushtari M. Z.; Jazirehpour M.; Shams M. H. Effect of carbon shell thickness on the microwave absorption of magnetite-carbon core-shell nanoparticles. Ceram. Int. 2016, 42, 14548-14556. (23) Li N.; Hu C. W.; Cao M. H. Enhanced microwave absorbing performance of CoNi alloy nanoparticles anchored on a spherical carbon monolith. Phys. Chem. Chem. Phys. 2013, 15, 7685-7689. (24) Wu G. L.; Cheng Y. H.; Ren Y. Y.; Wang Y. Q.; Wang Z. D.; Wu H. J. Synthesis and characterization of γ–Fe2O3@C nanorod-carbon sphere composite and its application as microwave absorbing materials. J. Alloy. Comp. 2015, 652, 346-350. (25) Guo S. L.; Wang L. D.; Wu H. J. Facile synthesis and enhanced electromagnetic wave absorption of thorny-like Fe-Ni alloy/ordered mesoporous carbon composite. Adv. Powder Technol. 2015, 25, 1250-1255. (26) Zhou H.; Wang J. C.; Zhuang J. D.; Liu Q. A covalent route for efficient surface modification of ordered mesoporous carbon as high performance microwave absorbers. Nanoscale, 2013, 5, 12502-12511. (27) Du Y. C.; Liu T.; Yu B.; Gao H. B.; Xu P.; Wang J. Y.; Wang X. H.; Han X. J. The electromagnetic properties and microwave absorption of mesoporous carbon. 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 26

Mater. Chem. Phys. 2012, 135, 884-891. (28) Meng Y.; Gu D.; Zhang F. Q.; Shi Y. F.; Cheng L.; Feng D.; Wu Z. X.; Chen Z. X.; Wan Y.; Stein A.; Zhao D. Y. A family of highly ordered mesoporous polymer resin and carbon structures from organic-organic self-assembly. Chem. Mater. 2006, 18, 4447-4464. (29) Fang Y.; Gu D.; Zou Y.; Wu Z. X.; Li F. Y.; Che R. C.; Deng Y. H.; Tu B.; Zhao D. Y. A low-concentration hydrothermal synthesis of biocompatible ordered mesoporous carbon nanospheres with tunable and uniform size. Angew. Chem. Int. Ed.

2010, 49, 7987-7991. (30) Kailasam K.; Jun Y. S.; Kateomol P.; Epping J. D.; Hong W. H.; Thomas A. Mesoporous melamine resins by soft templating of block-co-polymer mesophases. Chem. Mater. 2010, 22, 428-434. (31) Liu R. L.; Shi Y. F.; Wan Y.; Meng Y.; Zhang F. Q.; Gu D.; Chen Z. X.; Tu B.; Zhao D. Y. Triconstituent co-assembly to ordered mesostructured polymer-silica and carbon-silica nanocomposites and large-pore mesoporous carbons with high surface areas. J. Am. Chem. Soc. 2006, 128, 11652-11662. (32) Lin Y.; Wang X. Y.; Qian G.; Watkins J. J. Additive-driven self-assembly of well-ordered

mesoporous

carbon/iron

oxide

nanoparticle

composites

for

supercapacitors. Chem. Mater. 2014, 26, 2128-2137. (33) Yang Y.; Gao G.; Zhang X.; Li F. W. Facile fabrication of composition-tuned Ru-Ni bimetallics in ordered mesoporous carbon for levulinic acid hydrogenation. ACS Catal. 2014, 4, 1419-1425. 22


Page 23 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(34) Wang W.; Zhang L. P.; Liu Y.; Xu H.; Zhong Y.; Mao Z. P. Synthesis and infrared stealth property of ordered mesoporous carbon-aluminum-doped zinc oxide composites. Ind. Eng. Chem. Res. 2013, 52, 15066-15074. (35) Zeng L. X.; Zheng C.; Deng C.L.; Ding X. K.; Wei M. D. MoO2-ordered mesoporous carbon nanocomposites as an anode materials for lithium-ion batteries, ACS Appl. Mater. Interfaces 2013, 5, 2182-2187. (36) Zeng L. X.; Huang X. X.; Chen X.; Zheng C.; Qian Q. R.; Chen Q. H. Wei M. D. Ge/GeO2-ordered mesoporous carbon nanocomposites for rechargeable lithium-ion batteries with a long-term cycling performance. ACS Appl. Mater. Interfaces 2016, 8, 232-239. (37) Wang J. C.; Zhou H.; Zhuang J. D.; Liu Q. Magnetic γ-Fe2O3, Fe3O4, and nanoparticles confined within ordered mesoporous carbon as efficient microwave absorbers. Phys. Chem. Chem. Phys. 2015, 17, 3802-3812. (38) Yuan K. P.; Che R. C.; Cao Q.; Sun Z. K.; Yue Q.; Deng Y. H. Designed fabrication and characterization of three-dimensionally ordered arrays of core-shell magnetic mesoporous carbon microspheres. ACS Appl. Mater. Interfaces 2015, 7, 5312-5319. (39) Wei J.; Zhou D. D.; Sun Z. K.; Deng Y. H.; Xia Y. Y.; Zhao D. Y. A controllable synthesis of rich nitrogen-doped ordered mesoporous carbon for CO2 capture and supercapacitors. Adv. Funct. Mater. 2013, 23, 2322-2328. (40) Chen L. F.; Zhang X. D.; Liang H. W.; Kong M. G.; Guan Q. F.; Chen P.; Wu Z. Y.; Yu S. H. Synthesis of nitrogen-doped porous carbon nanofibers as an efficient 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 26

electrode materials for supercapacitors. ACS Nano 2012, 6, 7092-7102. (41) Shen G. Z.; Xu Y. W.; Liu B.; Du P. Li Y.; Zhu J.; Zhang D. Enhanced microwave absorption properties of N-doped ordered mesoporous carbon plated with metal Co. J. Alloy. Comp. 2016, 680, 553-559. (42) Shen G. Z.; Sun X. R.; Zhang H. W.; Liu Y.; Zhang J.; Meka A.; Zhou L.; Yu C. Z.

Nitrogen-doped

ordered

mesoporous

carbon

single

crystals:

aqueous

organic-organic self-assembly and superior supercapacitor performance. J. Mater. Chem. A 2015, 3, 24041-24048. (43) Lu M. M.; Cao W. Q.; Shi H. L.; Fang X. Y.; Yang J.; Hou Z. L.; Jin H. B.; Wang W. Z.; Yuan J.; Cao M. S. Multi-wall carbon nanotubes decorated with ZnO nanocrystals: Mild solution-process synthesis and highly efficient microwave absorption properties at elevated temperature. J. Mater. Chem. A 2014, 2, 10540-10547. (44) Narayanan T. N.; Sunny V.; Shaijumon M. M.; Ajayan P. M.; Anantharaman M. R. Enhance microwave absorption in nickel-filled multiwall carbon nanotubes in the S band. Electrochem. Solid-State Lett. 2009, 12, K21-K24. (45) Wang C.; Han X.; Xu P.; Wang J.; Du Y.; Wang X.; Qin W.; Zhang T. Controlled

synthesis

of

hierarchical

nickel

and

morphology-dependent

electromagnetic properties. J. Phys. Chem. C 2010, 114, 3196-3203. (46) Markel V. A. Can the imaginary part of permeability be negative?. Phys. Rev. E

2008, 78, 026608-1-5 (47) Wu H. J.; Wang L. D.; Wang Y. M.; Guo S. L.; Shen Z. Y. Enhanced microwave 24


Page 25 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


performance of highly ordered mesoporous carbon coated by Ni2O3 nanoparticles. J. Alloy. Comp. 2012, 525, 82-86. (48) Zong M.; Huang Y.; Zhao Y.; Sun X.; Qu C. H.; Luo D. D.; Zheng J. B. Facile preparation, high microwave absorption and microwave absorbing mechanism of RGO-Fe3O4 composites. RSC Adv. 2013, 3, 23638-23648. (49) Wang T.; Wang H. D.; Chi X.; Li R.; Wang J. B. Systhesis and microwave absorption properties of Fe-C nanofibers by electrospinning with disperse Fe nanoparticles parceled by carbon. Carbon 2014, 74, 312-318. (50) Aharoni A. Exchange resonance modes in a ferromagnetic sphere. J. Appl. Phys. 1991, 69, 7762-7764. (51) Wu H. J.; Wu Q. F.; Wang L. D. Design and wide range microwave absorption of porous Co-Co3O4 hybrid hollow sphere with magnetic multi-resonance mechanisms. Mater. Charact. 2015, 103, 1-10.

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Microwave Electromagnetic and Absorption Properties of N-Doped

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