Nano Bimetallic@Carbon Layer on Porous Carbon Nanofibers with

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Nano Bimetallic@Carbon Layer on Porous Carbon Nanofibers with Multiple Interfaces for Microwave Absorption Applications Xiaohui Liang, Bin Quan, Jiabin Chen, Weihua Gu, Baoshan Zhang, and Guangbin Ji ACS Appl. Nano Mater., Just Accepted Manuscript • Publication Date (Web): 14 Sep 2018 Downloaded from http://pubs.acs.org on September 14, 2018

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ACS Applied Nano Materials

Nano Bimetallic@Carbon Layer on Porous Carbon Nanofibers with Multiple Interfaces for Microwave Absorption Applications Xiaohui Lianga, b, Bin Quana, Jiabin Chena, Weihua Gua, Baoshan Zhangb, *, Guangbin Jia,*

a

College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211100, P. R. China.

b

School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, P. R. China.

a,*

Corresponding Author:

Prof. Dr. Guangbin Ji. Tel: +86-25-52112902; Fax: +86-25-52112626 E-mail: [email protected] b,*

Corresponding Author:

Prof. Dr. Baoshan Zhang. Tel: +86-25-83597192 E-mail: [email protected]

ACS Paragon Plus Environment

ACS Applied Nano Materials 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

ABSTRACT Porous carbon fibers (FeCo@C-PCFs) hybrids are fabricated by a two-step process involving the electro-spinning followed by heat treatment, in which several steps are involved including the reduction of polyvalent metal ions, the produced alloy nanoparticles are encapsulated into porous carbon substrate, yielding the FeCo-Polyacrylonitrile networks (FeCo-PAN) that are formed in situ and function as the building blocks. After altering feeding proportion of Co2+ and Fe3+, the formation of FeCo@C-PCF compounds could be controlled. More importantly, FeCo alloys seem stable chemical character due to the protection of carbon fibers. With different graphitization degree, FeCo@C-PCF compounds were proved to be outstanding microwave (MW) absorbent including thickness, effective bandwidth and reflection loss (RL). The maximum RL achieved -56 dB at 1.85 mm and broadest band width was 8.3 GHz. KEYWORDS: carbon fiber; electro-spinning; FeCo; porous; MW absorbent


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1. INTRODUCTION Carbon/carbon compounds matrixes caused far-ranging concern in many applications [1-8]. In these, electro-spinning carbon nanofibers (CNFs) fascinating traits such as high surface area, good stability and low density, CNFs are deemed as super-duper candidates for effective absorption. Remarkably, three-dimensional networks could be formed by electro-spinning CNFs [9-11]. Nevertheless, the poor electrical conductivity of pure CNFs unavoidably leads to weak MW absorption and inferior interfacial impedance matching [12-14]. Therefore, coating dielectric or magnetic composites with well-adjusted, increasing conductivity on electro-spinning CNFs is going to produce outstanding lightweight absorbents [15-17]. Among magnetic/carbon composites, Fe, Co, Ni and their alloys with higher Snoek limit and saturation magnetization coated carbon fibers were very fascinating due to their large aspect ratio, outstanding microwave absorbing properties, simple large-scale synthesis and low manufacturing cost [18-19]. However, these nanocomposites are possible to be oxidized in air, which will lead to electromagnetic characteristics degrading. Hence, their applications may be hindered [20-22]. In this work, the (FeCo alloy)@Carbon particles via the electro-spinning and subsequent in-situ grow in CNFs were obtained. We find that the carbonization process is very important for the final FeCo alloys@carbon and porous carbon fibers (PCFs). Within the void stacked volume, the specific carbon is the suitable candidacy as light absorbent [23-24]. The lower electric conductivity of FeCo alloy could availably recede skin effect of porous carbon fibers via the collection of each other.



Due to the better graphitization of the carbon species, PAN changes into turbostratic graphite structure after high temperature treatment. Hence, conductivity of PCFs is further improved. Furthermore, after integration of PCFs and FeCo alloy, some extra MW loss mechanisms were also produced, covering more polarization of FeCo@C which often happened in hetero junction structures because of accumulation that charges at interfaces and formation of dipoles on particles, as well as multiple interfacial polarizations [25]. The prepared hybrids present wonderful MW wave absorption property compared with mechanically mixing materials and pure species. In addition, the effect of FeCo dosage, the paraffin and porous carbon structure on the microwave absorption performance is also investigated. The study proved FeCo@C-PCF compounds are outstanding absorbents as well as thin thicknesses, wide bandwidth and strong absorption ability. At same time, the works also start fresh way for the design of porous alloy@carbon nanofibers with target functionalities. 2. EXPERIMENTAL SECTION 2.1 Materials Polyacrylonitrile (PAN, Mw=150,000, Aldrich Co.), Iron(III) acetylacetonate (C15H21FeO6), cobalt acetylacetonate (Co(acac)2) and dimethylformamide (DMF) are acquired from Sinopharm Chemical Reagent Co. 2.2 Preparation of FeCo@C-PCF hybrids FeCo/C PCFs were compounded by electro-spinning. Firstly, 937 mg of PAN, 352 mg (1 mmol) C15H21FeO6 and 250 mg (1 mmol) Co(acac)2 were dissolved in 10 mL DMF.


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The mixture was throw into plastic syringe of 10 mL after being stirred in oil bath at 50 oC for 2 h. Using typical electro-spinning instruments, prepared solution was electro-spun into nanofibers which contained Co(acac)2 and C15H21FeO6. The trapped nanofibers were treated at 250 oC in air for 2 h following by carbonization for 2 h at 700 oC with a Nitrogen atmosphere to acquire FeCo@C-PCFs-2. For comparison, metal salt of 0.5 and 1.5 mmol and pure carbon nanofibers were also synthesized by the same synthetic route, which were named FeCo@C-PCFs-1, FeCo@C-PCFs-3 and CFs, respectively. 2.3 Structural characterization Inductively Coupled Plasma Techniques (ICP, Optimal 5300 DV) measured ratio of Fe and Co. Morphology was determined by transmission electron microscopy (TEM, Tecnai G2 F30 S-TWIN). Bruker D8 Advanced X-ray diffractometer (Cu Kα radiation) characterizing structural properties of samples. Raman spectroscopy was conducted with a Raman spectrometer (RenishawInVia). The X-ray photoelectron spectroscopy technique (XPS) detected chemical states and elemental compositions. Automated area and pore size analyzer (Micrometrics ASAP 2010) determined the BET specific surface areas. The magnetic properties were detected by the vibrating sample magnetometer (VSM, Lakeshore, Model 7400 series). Agilent PNA N5244A vector network analyzer was detected electromagnetic parameters. Mixtures were compounded via mixing samples and paraffin with 30 wt% [26]. 3. RESULTS AND DISCUSSION



Figure 1. Schematic illustration of the synthesis of FeCo@C-PCFs (a); SEM images of PAN precursors (b), CFs (c), FeCo@C-PCFs-1, FeCo@C-PCFs-2 and FeCo@C-PCFs-3 (d-f); EDS of FeCo@C-PCFs-2 composites. Schematic diagram of fabrication process of FeCo@C-PCFs and electro-spinning equipment is presented in Figure 1a. After electro-spinning process, precursor nanofibers including metallic origin salts and PAN were obtained. Then, porous carbon fibers were obtained after carbonization at 700 oC for 2 h. There are some FeCo@C balls outside and inside the nanofibers, which are shown in the Fig. 1a. Figure 1b presents SEM image of one-dimensional (1D) PAN precursor nanofibers


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via electro-spinning process. Clearly, the nanofibers present uniform and smooth surface (diameter ranging from 150 to 500 nm). Significantly, after carbonized at 700 o

C (Fig. 1c), one-dimensional structure is complete kept. The surface has become

more and more rough with the addition Fe3+ and Co2+. In addition, after carbonization, the carbon nanofibers surface are some short protrusions (Figure 1d-1f). Furthermore, the short protrusions are also increasing with the addition mole ratio of Fe3+ and Co2+ increasing. Result in Fig. 1gdemonstrates that composites only include C, Fe and Co elements. Based on EDS, the ratio of Fe: Co is approximately 1:1, closed to ICP analysis (1.05:1.03). XRD measurement was presented in Fig. 2. For pure CFs (Fig. 2a), a wide peak is discovered, which suggested carbon obtained could be disordered feature. For FeCo@C-PCFs (Fig. 2b), sharp and strong peaks at 2θ values of 44.8o, 65.3o and 82.7o correspond to the (110), (200) and (211) crystal planes of FeCo alloy (JCPDS No: 49-1568). Additionally, peak at 2θ=26.3o corresponding to crystal plane (002) of the graphite indicated that the present of graphite-like carbon. Forming of graphite could be the results of existence of FeCo alloy that enhanced PAN graphitization during treating in N2 atmosphere [22].

b

(211)

(200)

FeCo@C-PCF-3

Intensity (a.u.)

CF

(110)

a Intensity (a.u.)

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


FeCo@C-PCF-2

FeCo@C-PCF-1

10

20

30

40

50

60

70

80

90

10

20

30

40

50

60

2θ (degree)

2θ (degree)


70

80

90


Figure 2. XRD patterns of pure carbon fibers (a) and FeCo@C porous carbon fibers (b). Similar phenomena could also be found in TEM images. The quantity of FeCo@C particles enhanced with increasing mole ratio of Fe3+ and Co2+ (Fig. 3a-c). As exhibited in Figure 3, FeCo particles are essentially sphere-like, which are well distributed on the fiber surfaces and inside the nanofibers, which is beneficial for electromagnetic properties [27]. Formation of alloy could be mainly because of carbon derived from PAN during the carbonized course, which could decrease relative metal oxides into metallic phase [20]. Obviously, there are many microporous in the carbon nanofibers (Fig. 3b and the insert of Fig. 3b), which is corresponding with the Fig. 1a. These microporous germinated on magnetic carbon based nanofibers networks formed a distinctive layered construction. Developing of porous structure may ascribe catalytic effect of metallic FeCo, which is still under investigation [28]. From the Figure 3d, in-situ forming of FeCo particles may package mainly with ordered graphite layers, which is akin to magnetic nanoparticles/graphite in microstructure, which would contribute to microwave absorption [29]. That could prevent magnetic alloy exposed to the air directly and maintain interfacial stabilization effectively. The interplanar spacing of 0.202 nm can be well assigned to the (110) planes FeCo alloy (insert of Fig. 3d) [30]. The metal elements (Co, Fe, C) (Fig. 3e) distribute for FeCo@C-PCF-2 are basically the same with carbon within measurement range that validates FeCo alloys were uniformly dispersed into carbon fibers.


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Figure 3. TEM images of FeCo@C-PCF-1 (a), FeCo@C-PCF-2 (b) and FeCo@C-PCF-3 (c); HRTEM image of FeCo@C (d); Corresponding EDS elemental mapping images of FeCo@C-PCF-2 (e).

b 0.08 dV/dD Pore Volume (cm3/g/nm)

a Quantity Absorbed (cm3/g STP)

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


FeCo@C-PCF-1 FeCo@C-PCF-2 FeCo@C-PCF-3

200 150 100 50 0


0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 -0.01

0.0

0.2

0.4

0.6

0.8

1.0

0

1

2

Relative pressure (P/P0)

3

4

5

6

7

8

9

10

Pore diameter (nm)

Figure 4. (a) Nitrogen sorption isotherms and (b) pore size distribution of FeCo@C-PNF. Furthermore, the FeCo@C-PCFs composites also possess inner connected structures. The nitrogen adsorption isotherms are shown in Fig. 4a. The BET surface areas of the samples are extremely high due to well-defined microporous structure of PCFs caused by the graphitization of amorphous carbon [31]. For three samples, the BET surface areas are 23.19, 121.02 and 300.58 m2g−1, respectively. From FeCo@C-PCF-1 to FeCo@C-PCF-3 specific surface areas increased that confirm the



increase of FeCo content in the composites could improve pore structures, which also indirectly proved a successful regulation of the porous structure by FeCo alloy. Fig. 4b of all samples presents a number of disordered nanopores and pore size distributing from 1 to 10 nm. Distinct peaks centered at 1.2 nm. The large amounts of micropores contributed to the higher surface area, which offer more active sites for scattering and reflection of MW, enhancing MW repeated absorption process more effectively [30]. a

C=C C1s

C1s

b

pyridinic-N

N1s

300

400

500

600

700

800

C-N

C-O

N ic ro l py r cN

200

O1s

gr ap hi ti

N1s

Intensity (a.u.)

Intensity (a.u.)

Fe2p Co2p

C=O 294

292

290

288

286

284

282

280

410

Binding energy (eV)

c

d

Co2p

405

400

395

Binding energy (eV) Fe2p

Intensity (a.u.)

Intensity (a.u.)

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

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820

810

800

790

780

Binding energy (eV)

770

740

730

720

710

700

Binding energy (eV)

Figure 5. XPS high-resolution C1s (a), N 1s (b), Co 2p(c) and Fe 2p (d) spectra of the as-prepared FeCo@C-PCF-2 hybrids. Additionally, survey scan of prepared FeCo@C-PCF-2 hybrids samples is presented in insert of Fig. 5a. Obvious characteristics peaks of Fe, Co, N and C elements could be seen in Fig. 5. C1s spectrum can be divided into several peaks (Fig. 5a) that are corresponding to C-O, C=O and C-C/C=C groups. Peak at 285.5 eV (Figure 5a) could be C-N groups. Meanwhile, the profile of N 1s could be divided


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into three peaks (Figure 5b). Peaks at 398.4, 400.2 and 401.4 eV were divided to pyridinic N, pyrrolic N and graphitic N, respectively, which indicated N-doping in the carbon [32-33]. Peak at 778.3 eV in the Co 2p3/2 spectra could be assigned to metallic Co (Fig. 5c). In the Fig. 5d, the characteristic peak at 710.3 eV should be in Fe 2p3/2 region, and the binding energy at 724.8 eV is the characteristic chemical shift of Fe 2p1/2 [34]. b

CF FeCo@C-PCF-1 FeCo@C-PCF-2 FeCo@C-PCF-3

60 50 40 30 20 10

40 30 20 10 0

0 2

4

6

8

10

12

14

16

CF FeCo@C-PCF-1 FeCo@C-PCF-2 FeCo@C-PCF-3

50

Imaginary part of Permittivity

Real part of Permittivity

a

2

18

4

6

20.22

-1


14.68

11.06

6.44

0.81 1.15

S

1.51 1.88

C

2.062.42

X

10

12

14

16

18

d


Intensity (a.u.)

c

8

Frequency (GHz)

Frequency (GHz)

σ/S•cm

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


2.66 2.71

Ku

500

1000

1500

2000

2500

-1

Raman shift (cm )

Figure 6. (a) Frequency dependence of the real part (ε′) and (b) imaginary part (ε′′) of permittivity; (c) Conductivity of all samples and (d) Raman spectra. The electromagnetic parameters of the FeCo@C-PCF were mainly determined by their µr=µ′-jµ″ (complex permeability) and εr=ε′-jε″ (complex permittivity) [35]. The ε′ and µ′ stand for storage ability for electric and magnetic energy, and ε″ and µ″ represent dissipation of electric and magnetic energy [36-37]. Fig. 6a-6c presents real, imaginary portions of permittivity and electrical conductivity of all compounds,



respectively. It can be seen that content of FeCo and porous carbon have significant influence on electromagnetic parameters. From equation ε″ = ωτ(εs-ε∞)/(1+ω2τ2) + σ/ωε0, where εs, ε∞, ω, τ, and σ represent static permittivity, relative dielectric permittivity at the high-frequency limit, angular frequency, polarization relaxation time and electrical conductivity, respectively. Due to innate parameters of materials including εs, ω, ε∞ and τ, σ is dominated factor affecting value of ε″. Significantly, FeCo@C and porous carbon nanofibers could form conductive networks that fetch higher σ value. Therefore, FeCo@C-PCF-3 is of higher ε″ values that means higher loss of electric energy. It’s worth noting that the ε″ value is increasing with the increase of FeCo alloy particles (Fig. 6b). It is known to all, dielectric property of materials is determined by conductivity and polarization. FeCo@C-PCF-3 sample exhibit a higher complex permittivity values with high electrical conductivity and more polarization effect. Besides, electrical conductivity (Figure 6c) calculated by the equation of σ AC = ε 0ε ' ' w = ε 0ε ' '2πf [38-39], prove strong connection between ε′′ value and conductivity that is also consistent with analysis of Fig. 6b. Furthermore, we could deduce that with enhanced ε″ values electrical conductivity gradually added. Raman was provided to evaluate quality of composites. Generally, Raman of carbon materials includes of D-band and G-band peaks at 1335 cm-1 and 1587 cm-1, respectively [40]. ID / IG values are on behalf of disorder structure carbon. On this occasion, ID/IG values of FeCo@C-PCF-1, FeCo@C-PCF-2 and FeCo@C-PCF-3 are 1.04, 1.14 and 0.93, respectively. Demonstrating that majorities of nanofibers are amorphous carbon that fitting with XRD consequences. We can see that with


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increasing of FeCo alloy, intensity of D and G band changes higher, suggesting the presence of FeCo alloy enhances the graphitization of PAN [41]. The pre-oxidation of PAN nanofibers acts an important part in carbon nanofibers. At pre-oxidation process, molecular structure changes and oxygen content of nanofibers increases [42]. At higher temperature, deoxidization makes the PAN changing into turbostratic graphite structure is very important to carbonization course. From Fig. 1d-1f, as carbon composites with excellent crystallization some carbon nanotubes are concerned, which are good to better graphitization of carbon a certain level. Therefore, conductivity of PCFs is further improved. a 0.09

b 6.0

FeCo-PCF-1 FeCo-PCF-2 FeCo-PCF-3

0.08 0.07

FeCo-PCF-1

5.5 5.0

0.06

tan δε

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


4.5

0.05 0.04

ε″ 4.0

0.03

3.5

0.02

3.0

0.01 2.5 2

4

6

8

10

12

14

16

18

5

6

7

8

Frequency (GHz)

d 55

c 10

FeCo-PCF-2

9

ε″

50

8

45

7

40

6

9

10

11

12

ε′ FeCo-PCF-3

35

5

ε″ 30

4

25

3

20

2

15

1 5

6

7

8

9

10

11

12

13

10

20

ε′

30

40

ε′

50

60

Figure 7. (a) Frequency dependence of dielectric loss tangent of three samples; Cole-Cole curves of FeCo@C-PCF-1 (b), FeCo@C-PCF-2 (c) and FeCo@C-PCF-3 (d). Fig. 7a presents dielectric loss factor (tan δe = ε″/ε′). High tangent loss can enhance microwave absorption abilities [43]. Fig. 7a displays that the tanδe value of FeCo@C-PCF-3 sample is lowest in frequency scope of 2-18 GHz. Tangent dielectric



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loss of FeCo@C-PCF-2 is higher than FeCo@C-PCF-1 sample. Based on the above analysis, FeCo@C-PCF-2 sample is functioned as dielectric absorbents. In addition, in dielectric loss, interface polarization unavoidably acts an important part. Equation describing relative complex permittivity is as follows [44],

εr = ε∞ +

εs − ε∞ = ε '− jε '' 1 + j 2π f τ

(1)

Where εs, ε∞, τ and f are static permittivity, relative dielectric permittivity at high-frequency limit, polarization relaxation time and frequency. Thus, following equations about ε′ and ε″ are follows [45-46].

ε ' = ε∞ +

ε '' =

εs − ε∞ 1 + (2π f )2τ 2

(2)

2π f τ (ε s − ε ∞ ) 1 + (2π f )2τ 2

(3)

On account of equation (4) and (5), ε′ and ε″ could be shown as:

(ε '− ε ∞ ) 2 + (ε '') 2 = (ε s − ε ∞ ) 2

(4)

The semicircles in Fig. 7b-d were Cole-Cole semicircle. Besides, one Debye relaxation process is described by every semicircle, and the rising slash at high frequency is often the results of conduction affect. On this occasion, on interfaces between carbon nanofibers, FeCo metal, air and paraffin, interfacial polarization occurred

[47].

Comparing

with

FeCo@C-PCF-1,

FeCo@C-PCF-2

and

FeCo@C-PCF-3 exhibit evident resonance peaks as shown in Fig. 7a, indicating relaxation dielectric property is possible major originates from interfacial polarizations of FeCo@carbon composites. If the permittivity mainly results from polarization processes, εr values would be ordered as FeCo@C-PCF-3 >


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FeCo@C-PCF-2 > FeCo@C-PCF-1 (As can be seen from Figure 7a-c, the more semicircles, the more dielectric polarization processes). As shown in Fig. 7b-d, due to stronger interface polarization affect, more Cole-Cole semicircles exist in all samples that are good for dielectric loss. 40

b 1.2


30 20 10 0

10

-10

5 B

-20

0

-30

µ′

1.0

Permeability

a M (emu/g)

0.8 FeCo@C-PCF-3 FeCo@C-PCF-2 FeCo@C-PCF-1

0.6 0.4

µ″

0.2

-5 -10 -1500-1000 -500

-40 -10000

-5000

0

0

500 1000 1500

5000

10000

0.0 0

2

4

H (K Oe)

c 0.25

d 0.04

FeCo@C-PCF-2

0.20

µ″

0.15

0.03

0.10

0.02

0.05

6

8

10 12 14 16 18 20

Frequency (GHz)

C0

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


FeCo@C-PCF-2

0.01

0.00 0.00

-0.05

-0.01

-0.10 0

2

4

6

8

10 12 14 16 18 20

0

2

4

Frequency (GHz)

6

8

10 12 14 16 18 20

Frequency (GHz)

Figure 8. (a) The M-H loops; (b) real part of permeability of all the samples, (c) resonance peaks in µ′′ and (d) eddy current loss of the FeCo@C-PCF-2. Magnetic loss has also been investigated by relevant analysis and characterization. Usually, hysteresis loss, residual loss and eddy current loss are three modalities in magnetic loss [48-49]. Figure 6a presents measurements of magnetization versus of FeCo@C-PCF hybrids. Because of massive carbon matrix in hybrids, saturation magnetization (Ms) values of FeCo@C-PCF-1, FeCo@C-PCF-2 and FeCo@C-PCF-3, (13.5 emu/g, 26 emu/g and 35 emu/g) are less than some FeCo alloys reported. The µ-M equation is as follows [50]:



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µ ' = 1 + ( M H ) cos σ

(5)

µ ' ' = 1 + ( M H ) sin σ

(6)

where M is magnetization, H stands for intensity of external magnetic field, σ is phase lag angle of magnetization. Values of µ′ (Fig. 8b) are homologous to values of Ms, because of crystalline grain size, domain wall resonance and spin rotation relaxation, mismatching is existent at some frequency. As is known to all, at high frequency range magnetic absorbents (magnetic alloy) invariably present weak absorption behavior, which caused by the Snoek limit. Additionally, Ms restricts Snoek limit, thus, enhancing magnetization is very important to promote magnetic loss abilities. At the study, FeCo nanoparticles are provided the magnetic loss, and the Ms values of FeCo@C-PCF hybrids enhance with adding FeCo contents. The consequences indicate that obtained FeCo@C-PCF absorbents are desired materials to increase resonance frequency by simply adjusting contents of FeCo in FeCo@C-PCF hybrids. Besides, Hc values of FeCo@C-PCF-1, FeCo@C-PCF-2 and FeCo@C-PCF-3 are 693, 500 and 472 kOe, respectively, which are due to the shape anisotropy and crystalline anisotropy. The eddy current losses are as well as vital for magnetic attenuation, which are relative to electric conductivity (σ) and thickness (d) of absorbent [26]: C 0 = µ ' ' ( µ ' ) −2 f

−1

= 2πµ 0 d 2σ

(7)

It can be known the C0 value should be a constant with increased frequency if the magnetic losses just result from the eddy current. Figure 8d show C0 values of FeCo@C-PCF composites, which at low frequency shrink forcefully and only at high


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frequency eddy current loss keep constant. At high frequency the eddy current losses play a regnant part that is in accordance with its larger electric conductivity. Generally, dimension resonance, domain wall resonance, nature resonance and exchange resonance and so on result in residual loss. Domain wall resonance major lies in less than 2 GHz [51], thus the absorbents can be excluded worked at gigahertz range. Figure 8c shows two resonance peaks in curves of imaginary part of permeability. Generally, nature resonance usually happed in low frequency, however, at high frequency exists exchange resonance [52]. Therefore, resonances peak less than 10 GHz could be attributed to exchange resonances at high frequency and nature resonance.

Figure 9. Reflection loss values of three-dimensional for (a) FeCo@C-PCF-1, (b) FeCo@C-PCF-2, (c) FeCo@C-PCF-3 samples; 3D plots of effective frequency band width evaluation (d).



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To demonstrate MW absorption characteristic of all samples, based on the transmission line theory we calculated 3D plots of reflection loss values, which is as follows [53-54]: RL = 20 log ( Z in − Z 0 ) /( Z in + Z 0 )

(8)

µr 2πfd tanh( j µrε r ) c εr

(9)

Z in = Z 0

Z0 stands for impedance of free space, Zin is input characteristic impedance, µr and εr are complex permeability and complex permittivity, c is velocity of light and d is absorbent thickness. Figure 9a-c present that FeCo@C-PCF-1 and FeCo@C-PCF-2 hybrids at thin thickness present super MW absorbing abilities and maximum RL values are all less than -30 dB. For the FeCo@C-PCF-3, the RL values are not reached -10 dB. As everyone knows, a perfect MW absorbent should have characteristics of thin thickness, wide bandwidth, as well as low density besides a strong absorption. Comparison of the effective frequency band peak width for FeCo@C-PCF-1 and FeCo@C-PCF-2 composites is presented in Figure 9d to have detailed comprehending of MW absorbing characteristics. By Figure 3b, at 17.7 GHz FeCo@C-PCF-2 presents maximum RL value of -56 dB with thickness of 1.85 nm. After comparison (Figure 9d), it can be found out that FeCo@C-PCF-1 reveal widest effective bandwidth reaches 8.6 GHz at 2.5 mm. Obviously, at a relatively low thickness the as-prepared FeCo@C-PCF-2 also possesses the merits of strong absorption and broad absorption bandwidth. Since for three samples the FeCo@C-PCF-2 could be act as ideal absorbing composites.


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Constant α

1200


1000 800 600 400 200

0.15

Zr

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


0.10 0.05 0.00 0

2

4

6

8

10

12

14

16

18

20

Frequency (GHz)

Figure 10. Frequency dependence of impedance matching ratio (Zr) and attenuation constant (α) of FeCo@C-PCF composites. Energy conservation and impedance matching are enduring theme in MW absorption areas [55]. An optimal MW absorbent should have not only strong dissipation capacity but also high impedance matching. However, when balancing these two factors in reality it is a contradictory spot. In line with impedance matching [55], Z = |Zin/Z0|

(10)

if εr is close to µr, ideal impedance matching obtained, and super impedance matching could be gained on occasion that εr =µr. At this point we assign impedance matching ratio Zr = Z/Z0. If Zr = 1, at the front surface of the absorbents, incident microwave could reach zero-reflection. More microwave can be introduced into the interior of absorbent when Z value is Higher. Hence, εr and µr are main factors affecting impedance matching. Conversely, based on transmission line theory the MW dissipation ability is dominated by attenuation constant α [26], α = 21/2Πf ((µ″ε″ - µ′ε′) + ((µ″ε″ -µ′ε′)2 + (µ′ε″ +µ″ε′)2)1/2)1/2/c


(11)


The ε″ values are proportional to attenuation ability. Higher ε″ will bring stronger attenuation ability. Figure 10 reveals representative correlation comparison between impedance matching ratio (Zr) and attenuation constant (α) of all the samples. Discussed above and MW parameter of three composites (Fig. 6), FeCo@C-PCF-3 composites present a higher complex permittivity than FeCo@C-PCF-2 and FeCo@C-PCF-1. It is not hard to find (Fig. 10) that α value of FeCo@C-PCF-3 hybrids is higher than both of FeCo@C-PCF-2 and FeCo@C-PCF-1, but the Zr value is just the opposite. RL values of FeCo@C-PCF-2 and FeCo@C-PCF-1 exhibit distinct advantage compared with FeCo@C-PCF-3 (Fig. 9). Hence we could conclude that the higher impedance matching is more important than dissipation ability in a specific range.


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0 -10

RL (dB)

-20 -30

1.85 mm 2.75 mm 3.65 mm 4.55 mm

-40

2.15 mm 3.05 mm 3.95 mm 4.85 mm

2.45 mm 3.35 mm 4.25 mm

-50 -60 10

8

tm/mm

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


6

••

4

• •

• • •

•

2 2

4

6

8

10

12

•

• 14

• 16

18

Frequency (GHz)

Figure 11. Comparison of various absorbent thicknesses (tm) at the frequency for FeCo@C-PCF-2 samples with ë/4 conditions of maximum RL values (fm). Usually, except dielectric loss and magnetic loss, MW could be assimilated via “geometrical effect” too [55]. If tm at fm conforms to equation: tm = nc/(4fm(|µr||εr|)1/2) (n = 1, 3, 5…)

(12)

|µr| and |εr| are module of µr and εr, at the air-absorbent interface reflected and incident waves in absorbents bring about cancellation of each other, c stands for velocity of light in free. In order to clear why at the thickness of 1.85 mm maximum RL value appears, we perform a simulation of tm under λ/4 occasions for FeCo@C-PCF-2 hybrids (Fig. 11). Black dots stand for experimental matching



thickness (texpm) at fm and gray curve is simulation thickness (tfitm) using the quarter wavelength rules. We can found the value of texpm at 1.85 mm is strong consistency with simulation tfitm, however, at other thicknesses the texpm deviate from the tfitm to various degrees. Therefore, geometrical effect can account for this phenomenon. Attenuation loss ability and combination of moderate impedance matching character benefit to greatest MW absorption property. Furthermore, except magnetic, dielectric loss and quarter-wave rules, interference cancellation is another vital dissipation element in thickness design of MW absorbent.

Figure 12. Schematic representation of MW wave absorption for FeCo@C-PCF composites. In Figure 12, three sides and portion of loss schematics presented associated mechanisms for enhanced MW absorption properties. (i) Dielectric loss. Porous carbon nanofibers form conductive network, which act as important parts in dielectric loss that is due to more conductive ways could add


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Page 23 of 34 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


exciting hopping electron to attenuate electromagnetic wave [55]. Meanwhile, porous carbon nanofibers could also offer immediate route for charge transport. (ii) Magnetic loss. In Figure 8 we have discussed, at applied field the FeCo@C-PCF composites have hysteresis loss that is good for promoting MW absorption. At high frequency, in FeCo@C-PCF hybrids eddy current loss takes place. Additionally, exchange resonances and nature resonance act vital parts in MW attenuation. (iii) Porous effect. Inside the absorbent, porous structure could availably enhance impedance matching and alter permittivity. On basis of Maxwell-Garnett theory, effective permittivity (εeff) of porous absorbent could be described as following equation if porous materials were regarded as compound of solid media and air [56]:

ε effMG = ε 1

(ε 2 + 2ε 1 ) + 2 p(ε 2 − ε 1 ) (ε 2 + 2ε 1 ) − p(ε 2 − ε 1 )

(13)

That ε2 and ε1 are dielectric constant of gas and solid state, respectively. Evidently, εeff was interrelated to porous structure. Moreover, mixing logarithmic law illustrated relationship between permittivity and porous structure [57]:

ln ε = Va ln ε a + Vb ln ε b + Vc ln ε c

(14)

That Va, Vb and Vc stand for volume fraction of FeCo particles, carbon and air, εa, εb and εc present complex permittivity. Pore structure can tune the complex permittivity of fixed porous carbon absorbent. At the same time, under an alternating MW field microwave plasma could be induced by interspaces in porous structure. Moreover, propagated MW would be reflected inside void stacked volume. After long way in



narrow void, MW can be absorbed and exhausted. CONCLUSION In summary, FeCo@Carbon porous carbon fibers were successfully prepared via a simple electro-spinning in-situ method. The as-prepared FeCo@C-PCF hybrids present outstanding MW absorption ability due to thorough dielectric/magnetic dissipation. In addition, interfacial and dipolar polarization were also happened. For instance, FeCo@C-PCF-2-paraffin-30, effective bandwidth of 8.3 GHz achieves at 2.5 mm and the maximum RL value reaches -56 dB at 1.85 mm. This study not only illustrates vital part of architecture design in MW dissipation, but also offers a simple in-situ way to synthesize the binary hybrids. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (G. B. J.) *E-mail: [email protected] (B. S. Z.) Author Contributions All authors written through the manuscript and approved the final version of the manuscript. Notes Authors declare no competing financial interest.

ACKNOWLEDGMENT Financial supports from the Aeronautics Science Foundation of China (2017ZF52066), the National Nature Science Foundation of China (No. 11575085, 11475086), the Postgraduate Research & Practice Innovation of Jiangsu Province (KYCX18_0277) and Six talent peaks project in Jiangsu Province (No.XCL-035) are highly


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acknowledged.

REFERENCE [1] Chen, W. J.; Özdemir, S. K.; Zhao, G. M.; Wiersig, J.; Yang, L. Exceptional Points Enhance Sensing in an Optical Micro Cavity. Nature 2017, 548, 192-196. [2] Hu, H.; Zhao, Z. B.; Zhou, Q.; Gogotsi, Y.; Qiu, J. S. The Role of Microwave Absorption on Formation of Graphene from Graphite Oxide. Carbon 2012, 50, 3267-3273. [3] He, X. J.; Geng, Y. J.; Qiu, J. S.; Zheng, M. D.; Long, S.; Zhang, X. Y. Effect of Activation

Time

on

the

Properties

of

Activated

Carbons

Prepared

by

Microwave-Assisted Activation for Electric Double Layer Capacitors. Carbon 2010, 48, 1662-1669. [4] Yan, D. X.; Pang, H.; Li, B.; Vajtai, R.; Xu, L.; Ren, P. Structured Reduced Graphene

Oxide/Polymer

Composites

for

Ultra-Efficient

Electromagnetic

Interference Shielding. Adv. Funct. Mater. 2015, 25, 559-566. [5] He, X. J.; Li, R. C.; Qiu, J. S.; Xie, K.; Ling, P. H.; Yu, M. X.; Zhang, X. Y.; Zheng, M. D. Synthesis of Mesoporous Carbons for Supercapacitors from Coal Tar Pitch by Coupling Microwave-Assisted KOH Activation with a MgO Template. Carbon 2012, 50, 4911-4921. [6] Liang, X. H.; Quan, B.; Ji, G. B.; Liu, W.; Zhao, H. Q.; Dai, S. S.; Lv, J.; Du, Y. W. Tunable

Dielectric

Performance

Derived

from

the

Metal-Organic

Framework/Reduced Graphene Oxide Hybrid with Broadband Absorption. ACS



Sustainable Chem. Eng. 2017, 5, 10570-10579. [7] He, X. J.; Geng, Y. J.; Qiu, J. S.; Zheng, M. D.; Zhang, X. Y.; Shui, H. F. Influence of KOH/Coke Mass Ratio on Properties of Activated Carbons Made by Microwave-Assisted Activation for Electric Double-Layer Capacitors. Energy Fuels 2010, 24, 3603-3609. [8] Panigrahi, R.; Srivastava, S. K. Trapping of Microwave Radiation in Hollow Polypyrrole Microsphere through Enhanced Internal Reflection: A Novel Approach. Sci. Rep. 2015, 5, 7638-7643. [9] Cho, J. S.; Hong, Y. J.; Kang, Y. C. Design and Synthesis of Bubble-Nanorod-Structured Fe2O3-Carbon Nanofibers as Advanced Anode Material for Li-Ion Batteries. ACS Nano 2015, 9, 4026-4035. [10] Zhang, B.; Yu, Y.; Huang, Z. D.; He, Y. B.; Jang, D.; Yoon, W. S.; Mai, Y. W.; Kang, F. Y.; Kim, J. Y. Exceptional Electrochemical Performance of Free Standing Electrospun Carbon Nanofiber Anodes Containing Ultrafine SnOx Particles. Energy Environ. Sci. 2012, 5, 9895-9902. [11] Kim, C.; Yang, K. S.; Kojima, M.; Yoshida, K.; Kim, Y. J.; Kim, Y. A.; Endo, M. Fabrication of Electrospinning-Derived Carbon Nanofiber Webs for the Anode Material of Lithium-Ion Secondary Batteries. Adv. Funct. Mater. 2006, 16, 2393-2397. [12] Zhang, Y.; Huang, Y.; Zhang, T. F.; Chang, H. C.; Xiao, P. S.; Chen, H. H.; Huang, Z. Y.; Chen, Y. S. Broad Band and Tunable High-Performance Microwave Absorption of an Ultralight and Highly Compressible Graphene Foam. Adv. Mater.


Page 26 of 34

Page 27 of 34 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


2015, 27, 2049-2053. [13] Wang, L.; Huang, Y.; Sun, X.; Huang, H. J.; Liu, P. B.; Zong, M.; Wang, Y. Synthesis

and

Microwave

Absorption

Enhancement

of

Graphene@Fe3O4@SiO2@NiO Nanosheet Hierarchical Structures. Nanoscale 2014, 6, 3157-3164. [14] Shahzad, F.; Alhabeb, M.; Hatter, C. B.; Anasobi, B.; Hong, S. M.; Koo, C. M.; Gogotsi, Y. Electromagnetic Interference Shielding with 2D Transition Metal Carbides (MXenes). Science 2016, 353, 1137-1140. [15] Sun, G. B.; Dong, B. X.; Cao, M. H.; Wei, B. Q.; Hu, C. W. Hierarchical Dendrite-Like Magnetic Materials of Fe3O4, γ-Fe2O3, and Fe with High Performance of Microwave Absorption. Chem. Mater. 2011, 23, 1587-1593. [16] Liu, J.; Cao, W. Q.; Jin, H. B.; Yuan, J.; Zhang, D. Q.; Cao, M. S. Enhanced Permittivity and Multi-Region Microwave Absorption of Nanoneedle-Like ZnO in the X-Band at Elevated Temperature. J. Mater. Chem. C 2015, 3, 4670-4677. [17] Wang, S.; Xiao, N.; Zhou, Y.; Ling, Z.; Li, M. Y.; Qiu, J. S. Lightweight Carbon Foam from Coal Liquefaction Residue with Broad-Band Microwave Absorbing Capability. Carbon 2016, 105, 224-226. [18] Wang, L.; He, F.; Wan, Y. Z. Facile Synthesis and Electromagnetic Wave Absorption Properties of Magnetic Carbon Fiber Coated with Fe-Co Alloy by Electroplating. J. Alloys Compd. 2011, 509, 4726-4730. [19] Park, K. Y.; Han, J. H.; Lee, S. B.; Yi, J. W. Microwave Absorbing Hybrid Composites Containing Ni-Fe Coated Carbon Nanofibers Prepared by Electroless



Plating. Compos. Part A 2011, 42, 573-578. [20] Wang, L.; Yu, Y.; Chen, P. C.; Chen, C. H. Electrospun Carbon-Cobalt Composite Nanofiber as an Anode Material for Lithium Ion Batteries. Scr. Mater. 2008, 58, 405-408. [21] Ji, L. W.; Lin, Z.; Medford, A. J.; Zhang, X. W. In-Situ Encapsulation of Nickel Particles in Electrospun Carbon Nanofibers and the Resultant Electrochemical Performance. Chem. Eur. J. 2009, 15, 10718-10722. [22] Barakat, N. A. M.; Abadir, M. F.; Nam, K. T.; Hamza, A. M.; Al-Deyab, S. S.; Baek, W. I.; Kim, H. Y. Synthesis and Film Formation of Iron-Cobalt Nanofibers Encapsulated in Graphite Shell: Magnetic, Electric and Optical Properties Study. J. Mater. Chem. 2011, 21, 10957-10964. [23] Obrova, M.; Chevrier, V. Alloy Negative Electrodes for Li-ion Batteries. Chem. Rev. 2014, 114, 11444-11502. [24] Liang, Y.; Fu, R.; Wu, D. Reactive Template-Induced Self-Assembly to Ordered Mesoporous Polymeric and Carbonaceous Materials. ACS Nano 2013, 7, 1748-1754. [25] Quan, B.; Liang, X. H.; Ji, G. B.; Cheng, Y.; Liu, W.; Ma, J. N.; Zhang, Y. N.; Li, D. R.; Xu, G. Y. Dielectric Polarization in Electromagnetic Wave Absorption: Review and Perspective. J. Alloys Compds. 2017, 728, 1065-1075. [26] Liang, X. H.; Quan, B.; Sun, Y. S.; Ji, G. B.; Zhang, Y. N.; Ma, J. N.; Li, D. R.; Zhang, B. S.; Du, Y. W. Multiple Interfaces Structure Derived from Metal-Organic Frameworks for Excellent Electromagnetic Wave Absorption. Part. Part. Syst. Charact. 2017, 34, 1700006.


Page 28 of 34

Page 29 of 34 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


[27] Che, R. C.; Zhi, C. Y.; Liang, C. Y.; Zhou, X. G. Fabrication and Microwave Absorption of Carbon Nanotubes/CoFe2O4 Spinel Nanocomposite. Appl. Phys. Lett. 2006, 88, 033105. [28] Hou, H. Q.; Reneker, D. H. Carbon Nanotubes on Carbon Nanofibers: A Novel Structure Based on Electrospun Polymer Nanofibers. Adv. Mater. 2004, 16, 69-73. [29] Liang, X. H.; Quan, B.; Ji, G. B.; Liu, W.; Cheng, Y.; Zhang, B. S.; Du, Y. W. Novel Nanoporous Carbon Derived from Metal-Organic Frameworks with Tunable Electromagnetic Wave Absorption Capabilities. Inorg. Chem. Front. 2016, 3, 1516-1526. [30] Ghunaim, R.; Scholz, M.; Damm, C.; Rellinghaus, B.; Klingeler, R.; Büchner, B.; Mertig, M.; Hampel, S. Single-Crystalline FeCo Nanoparticle-Filled Carbon Nanotubes: Synthesis, Structural Characterization and Magnetic Properties. Beilstein J. Nanotechnol. 2018, 9, 1024-1034. [31] Lee, W. C.; Chien, H. T.; Lo, Y.; Chiu, H. C.; Wang, T. P.; Kang, D. Y. Synthesis of Zeolitic Imidazolate Framework Core-Shell Nanosheets Using Zinc-Imidazole Pseudopolymorphs. ACS Appl. Mater. Interfaces 2015, 7, 18353-18361. [32] Zhang, P. F.; Gong, Y. T.; Li, H. R.; Chen, Z. R.; Wang, Y. Solvent-Free Aerobic Oxidation of Hydrocarbons and Alcohols with Pd@N-doped Carbon from Glucose. Nat. Commun. 2013, 4, 1593. [33] Jia, L.; Wang, D. H.; Huang, Y. X.; Xu, A. W.; Yu, H. Q. Highly Durable N-Doped Graphene/CdS Nanocomposites with Enhanced Photocatalytic Hydrogen Evolution from Water under Visible Light Irradiation. J. Phys. Chem. C 2011, 115,



11466-11473. [34] Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W. M.; Gerson, A. R.; Smart, R. St. C. Resolving Surface Chemical States in XPS Analysis of First Row Transition Metals, Oxides and Hydroxides: Cr, Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717-2730. [35] Wu, G.; Cheng, Y.; Xie, Q.; Jia, Z.; Xiang, F.; Wu, H. Facile Synthesis of Urchin-Like ZnO Hollow Spheres with Enhanced Electromagnetic Wave Absorption Properties. Mater. Lett. 2015, 144, 157-160. [36] Huang, Y.; Wang, Y.; Li, Z.; Yang, Z.; Shen, C.; He, C. Effect of Pore Morphology on the Dielectric Properties of Porous Carbons for Microwave Absorption Applications. J. Phys. Chem. C 2015, 118, 26027-26032. [37] Lu, Y.; Wang, Y.; Li, H.; Lin, Y.; Jiang, Z.; Xie, Z.; Kuang, Q.; Zheng, L. S. MOF-Derived Porous Co/C Nanocomposites with Excellent Electromagnetic Wave Absorption Properties. ACS Appl. Mater. Interfaces 2015, 7, 13604-13611. [38] Lee, H. S.; Baek, G. Y.; Jeong, S. Y.; Shin, K.; Jung, C. H.; Choi, J. H. Preparation of Thin Porous Carbon Membranes from Polyacrylonitrile by Phase Separation and Heat Treatment. J. Nanosci. Nanotech. 2017, 17, 5822-5825. [39] Wang, H. C.; Xiang, L.; Wei, W.; An, J.; He, J.; Gong, C. H.; Hou, Y. L. Efficient and Lightweight Electromagnetic Wave Absorber Derived from Metal Organic Framework-Encapsulated Cobalt Nanoparticles. ACS Appl. Mater. Interfaces 2017, 9, 42102-42110. [40] Zeng, M.; Liu, J.; Yue, M.; Yang, H. Z.; Dong, H. R.; Tang, W. K.; Jiang, H,;


Page 30 of 34

Page 31 of 34 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


Liu, X. F.; Yu, R. H. High-Frequency Electromagnetic Properties of the Manganese Ferrite Nanoparticles. J. Appl. Phys. 2015, 117, 17B527. [41] Liu, Q.; Cao, S. B.; Qiu, Y. J.; Zhao, L. Bimetallic Fe-Co Promoting One-Step Growth of Hierarchical Nitrogen Doped Carbon Nanotubes/Nanofibers for Highly Efficient Oxygen Reduction Reaction. Mater. Sci. Eng. B 2017, 223, 159-166. [42] Zhao, J.; Zhang, J.; Zhou, T.; Liu, X.; Yuan, Q.; Zhang, A. New Understanding on the Reaction Pathways of the Polyacrylonitrile Copolymer Fiber Preoxidation: Online Tracking by Two-Dimensional Correlation FTIR Spectroscopy. RSC Adv. 2016, 6, 4397-4409. [43] Zhang, X.; Li, Y.; Liu, R.; Rao, Y.; Rong, H.; Qin, G. High-Magnetization FeCo Nanochains with Ultrathin Interfacial Gaps for Broadband Electromagnetic Wave Absorption at Gigahertz. ACS Appl. Mater. Interfaces 2016, 8, 3494-3498. [44] Liang, X. H.; Quan, B.; Chen, J. B.; Tang, D. M.; Zhang, B. S.; Ji, G. B. Strong Electric Wave Response Derived from the Hybrid of Lotus Roots-Like Composites with Tunable Permittivity. Sci. Rep. 2017, 7, 9462. [45] Manna, K.; Srivastava, S. K. Fe3O4@Carbon@Polyaniline Trilaminar Core-Shell Composites as Superior Microwave Absorber in Shielding of Electromagnetic Pollution. ACS Sustainable Chem. Eng. 2017, 5, 10710-10721. [46] Wang, H. C.; Yan, Z. R.; An, J.; He, J.; Hou, Y. L.; Yu, H. Y.; Ma, N.; Yue, G. H.; Sun, D. B. Iron Cobalt/Polypyrrole Nanoplates with Tunable Broadband Electromagnetic Wave Absorption. RSC Adv. 2016, 6, 92152-92158. [47] Lv, H.; Guo, Y.; Wu, G.; Ji, G.; Zhao, Y.; Xu, Z. Interface Polarization Strategy to



Solve Electromagnetic Wave Interference Issue. ACS Appl. Mater. Interfaces 2017, 9, 5660-5668. [48] Xie, S.; Guo, X.; Jin, G.; Guo, X. Carbon Coated Co-SiC Nanocomposite with High-Performance Microwave Absorption. Phys. Chem. Chem. Phys. 2013, 15, 16104-16110. [49] Senapati, S.; Srivastava, S. K.; Singh, S. B.; Kulkarni, A. R. SERS Active Ag Encapsulated Fe@SiO2 Nanorods in Electromagnetic Wave Absorption and Crystal Violet Detection. Environ. Res. 2014, 135, 95-104. [50] Zhang, X. F.; Dong, X. L.; Huang, H.; Liu, Y. Y.; Wang, W. N.; Zhu, X. G.; Lv, B.; Lei, J. P. Microwave Absorption Properties of the Carbon-Coated Nickel Nanocapsules. Appl. Phys. Lett. 2006, 89, 053115. [51] Lv, H.; Ji, G.; Liu, W.; Zhang, H.; Du, Y. Achieving Hierarchical Hollow Carbon@Fe@Fe3O4Nanospheres with Superior Microwave Absorption Properties and Lightweight Features. J. Mater. Chem. C 2015, 3, 10232-10241. [52] Kitao, J.; Takahashi, Y.; Fujiwara, K.; Ahagon, A.; Matsuo, T.; Daikoku, A. Hysteresis Loss Analysis of Laminated Iron Core by Using Homogenization Method Taking Account of Hysteretic Property. IEEE Trans. Magn. 2017, 53, 1-4. [53] Jian, X.; Wu, B.; Wei, Y. F.; Dou, S. X.; Wang, X. L.; He, W. D.; Mahmood, N. Facile Synthesis of Fe3O4/GCs Composites and Their Enhanced Microwave Absorption Properties. ACS Appl. Mater. Interfaces 2016, 8, 6101-6109. [54] Jian, X.; Xiao, X. Y.; Deng, L. J.; Tian, W.; Wang, X.; Mahmood, N.; Dou, S. X. Heterostructured Nanorings of Fe-Fe3O4@C Hybrid with Enhanced Microwave


Page 32 of 34

Page 33 of 34 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


Absorption Performance. ACS Appl. Mater. Interfaces 2018, 10, 9369-9378. [55] Zhu, L.; Zeng, X.; Chen, M.; Yu, R. Controllable Permittivity in 3D Fe3O4/CNTs Network for Remarkable Microwave Absorption Performances. RSC Adv. 2017, 7, 26801-26808. [56] Li, X.; Zhang, B.; Ju, C.; Han, X.; Du, Y.; Xu, P. Morphology-Controlled Synthesis and Electromagnetic Properties of Porous Fe3O4 Nanostructures from Iron Alkoxide Precursors. J. Phys. Chem. C 2011, 115, 12350-12357. [57] Zhang, X.; Ji, G.; Liu, W.; Zhang, X.; Gao, Q.; Li, Y.; Du, Y. A Novel Co/TiO2 Nanocomposite Derived from a Metal-Organic Framework: Synthesis and Efficient Microwave Absorption. J. Mater. Chem. C 2016, 4, 1860-1870.



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Nano Bimetallic@Carbon Layer on Porous Carbon Nanofibers with

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