CoFe2O4 Nanostructures for High

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Sandwich CoFe2O4/RGO/CoFe2O4 Nanostructures for High-performance Electromagnetic Absorption Kun Zhang, Junjian Li, Fan Wu, Mengxiao Sun, Yilu Xia, and Aming Xie ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b01927 • Publication Date (Web): 19 Dec 2018 Downloaded from http://pubs.acs.org on December 19, 2018

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ACS Applied Nano Materials

Sandwich

CoFe2O4/RGO/CoFe2O4

Nanostructures

for

High-performance

Electromagnetic Absorption Kun Zhang,†,§ Junjian Li,‡ Fan Wu,*,† Mengxiao Sun,† Yilu Xia,§ and Aming Xie*,† †

School of Mechanical Engineering, Nanjing University of Science & Technology, Nanjing

210094, China ‡ Key

Laboratory of Tropical Biological Resources of Ministry Education, State Key Laboratory of

Marine Resource Utilization in South China Sea, Hainan University, Haikou 570228, China § School

of Chemical Engineering, Nanjing University of Science & Technology, Nanjing 210094,

China Abstract：The rational design of specific nanostructures with desirable combination of electrical conductivity and magnetism is of significant importance in the field of electromagnetic absorption. To date, it is still difficult to uniformly coat magnetic composition on reduced graphene oxide (RGO) surface, especially through a metal organic frameworks (MOFs) -pyrolyzation strategy, just because of facing dificulty in evenly deposition of MOFs on graphene oxide (GO). Herein, we successfully deposit MOFs on GO to form sandwich MOFs/GO/MOFs, through the addition of Fe3+ to MOFs precursor. Then, we adopt a temperature-controlled pyrolysis strategy to transform MOFs/GO/MOFs into sandwich CoFe2O4/RGO/CoFe2O4. The nanomaterial exhibits remarkable electromagnetic absorption (EMA) performance, where its maximum effective width reaches 7.08 GHz under 2.6 mm. It is thought that the synergy of electric loss, magnetic loss, and impedance match is ascribed to high-perforamnce EMA of this sandwich nanostructure. Keywords: Metal organic frameworks (MOFs), Graphene oxide (GO), Nanostructure, Pyrolysis, Electromagnetic absorption 1. Introduction With the increasingly widespread application of modern electronics equipped with highly integrated circuits, electromagnetic pollution is being inevitably generated, as a result, causes adverse influence on advanced electronic equipment and human health.1-4 To solve this problem, significant efforts have focused on the design of high-performance electromagnetic absorption (EMA) materials that can eliminate electromagnetic radiation based on absorbing mechanism.5-9 The EMA performance of a material relies critically on its permittivity and permeability, which are greatly influenced by the aspect ratio, electrical conductivity, magnetic property as well as the combination

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of electric active component and magnetic component.10,11

It is expected to furnish high EMA

performance by the design of a material with both high aspect ratio and rational combination of conductive component and magnetic component. During the past decade, reduced graphene oxide (RGO), prepared from the reduction of graphene oxide (GO) precursor, has been paid great attention and extensively explored in a broad range of fields including energy, catalysis, environment, medicine, and biology, due to its superior electronic, mechanical, optical, and biocompatible properties.12-18 However, pure RGO cannot be always regarded as a good EMA material, because its high electric conductivity usually leads to high reflection to incident electromagnetic radiation rather than absorption.19,20 One of the most common method to enhance the EMA performance of RGO is surficial modification. For example, benefiting from nanotechnology, enhanced EMA performance can be frequently obtained by the decoration of RGO with various nanomaterials, such as vertically aligned CuS nanoflakes,21 wrapped ZnO hollow spheres,22 polypyrrole,23 MoS2 nanosheets,24 carbon nanotubes,25 MOF constrained ZnO,26 and their combination.27 Normally, RGO microscopically appears as a two-dimensional (2D) nano-structure possessing a large aspect ratio as well as large specific surface area.13 The in-plane electrical conductivity of RGO is very high, and thus leads to dominant electromagnetic reflection.19,20 An efficient strategy to improve EMA capacity is the decrease of surficial impedance, which may be desirably solved by the surficial introduction of magnetic component.28-31 Through this strategy, for instance, the EMA performance of RGO can be efficiently tuned by various magnetic nanomaterials, such as MnFe2O4 nanoparticles,28 Fe3O4 nanorod arrays,29 Ni nanocrystals,30 and CoS2 nanocrystals.31 However, when it comes to these composites, there are some inadequacies, including nonuniform distribution of magnetic component on RGO surface and interruption between magnetic particles which may lead to insufficient hetero interface or effective surficial impedance regulation. Metal organic frameworks (MOFs) is porous materials possessing high surface areas, has earned a significant attention for potential applications in catalysis,32,33 photo-degradation,34 gases storage,35 and battery.36 More importantly, Co-based MOFs precursor containing metal element can be in situ transformed to magnetic metal oxides/carbides/nitrides, which may be of distinct EMA performance.37 However, it is difficult to coat these magnetic compositions uniformly on the surface of RGO, thus leading to weakened interfacial function between metal oxides/carbides/nitrides and


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RGO. 26,38 It is reasonably considered that the crucial step to solve this problem is how to uniformly deposit MOFs on GO surface. Herein, we first constructed a MOFs/GO/MOFs (MGM) sandwich nanosheet through the introduction of Fe3+ during the formation of Co-based MOFs. Under this condition, the MOFs phase are uniformly bound to the GO surface. Then, a temperature-controlled pyrolysis was used to transform MGM to sandwich CoFe2O4/RGO/CoFe2O4 (CRC), which exhibits highly broadband EMA performance. A synergy of electric loss, magnetic loss, and impedance match is thought to be the reason behind the remarkable EMA capacity of this sandwich nanomaterial. 2. Experimental 2.1 Materials CoCl2·6H2O (AR, Aladdin), Fe(NO3)3·9H2O (AR, Aladdin), methanol (99 %, Energy Chemical) and 2-methylimidazole (2-MIM) (97 %, AlfaAesar) were purchased, and employed without further purification. GO nanosheets (piece diameter ＞ 5 um, layer number < 10 was purchased from XFNANO. 2.2 Synthesis of CRC nanosheets The MGM precursor was synthesized as follow. Firstly, 50 mg of GO nanosheets39 was dispersed in a mixture of Fe(NO3)3·9H2O (1.21 g) and CoCl2·6H2O (0.36 g) in 40 ml of methanol. Then, a mixture of 2-methylimidazole (2.8 g) in methanol (10 ml) was poured into the GO mixture, and stirred for 5~8 hours at ambient temperature to furnish sandwich MGM. The MGM was collected, and gradually heated to 500 °C in a tube furnace at a heating rate of 3 °C/minute under Ar atmosphere and kept for 5 h to furnish CRC nanosheets. As comparisons, MOFs was prepared without GO nanosheets and pyrolyzed to furnish calcined MOFs (C-MOFs) without RGO according to a similar process. 2.3 Characterizations and Measurements Fourier Transfor Infrared (FT-IR) spectra were obtained from a Nicolet iS10 FT-IR instrument (Thermo Fisher Scientiﬁc, USA). The micro-morphologies of samples were observed on a scanning electron microscope (SEM, S4800, Hitachi) with spray gold and a high-resolution transmission electron microscope (HR-TEM, Tecnai G2 F20, FEI) equipped with an energy dispersive spectrometer (EDS). The crystal structure was identified via an X-ray diffractometer (XRD, X’ Pert Pro, Philips), using Cu Kα (λ = 1.54 Å) radiation source (40.0 kV, 30.0 mA). X-ray photoelectron



spectroscopy (XPS) was measured on an apparatus (ESCALABTM 250Xi, Thermo Fisher Scientific). Raman spectroscopy was obtained on a Renishaw in Via Raman Microscope, equipped with a 514 nm laser. The thermo-gravimetric analysis was carried out on an instrument (SDT Q600, TA) from room temperature to 800 °C at a heating rate of 20 °C/min under Ar atmosphere. The samples for EMA test were prepared via the hot mixing of 20 wt.% of samples in wax which were then pressed into cylindrical specimens (inner diameter: 3.04 mm, outer diameter: 7.00 mm). The complex permeability (μr =μ′−jμ″) and complex permittivity (εr=ε′−jε″) were recorded via a vector network analyzer (VNA, N5242A PNA-X, Agilent) in a frequency range of from 2 to 18 GHz. 3. Results and Discussions The preparation route of CRC nanosheets is showed in Scheme 1. As is well known, there are a number of -OH, -COOH, and -O- groups on the surface of GO, which furnish a great number of surficial negative sites.13 The positive Co2+ and Fe3+ will be bound by these negative sites through an electrostatic interaction. After the addition of organic-ligand (2-MIM), Co2+ and Fe3+ rich sites prefer to nucleate to form bimetallic MOFs layer on GO surface to form a sandwich MGM. On account of that coordinate bonds between metal ions and 2-MIM cannot provide efficient charge transfer, the formed MOFs layer cannot be electrical active or magnetic. MOFs shows a low stability under high humidity and relative high temperature. In addition, GO layer displays low electrical conductivity. To make up for these inadequacies, a temperature-controlled pyrolysis was adopted to transform precursor MGM to CRC nanosheets. Scheme 1. The preparation route of CRC nanosheets.

We firstly used SEM technology to investigate the micro-morphologies. As is shown in Figure


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1a, relative smooth surface is observed for pure GO. Generally, the growth of MOFs on GO surface prefers to form separate polyhedrons with a size of several hundreds of nanometers.26,38 But it is quite different from the previous condition that the GO surface in this study was covered by a rough and compact MOFs shell (Figure 1b and c). It indicates that the introduction of Fe3+ and Co2+leads to the formation of crushed MOFs rather than regular polyhedral MOFs (See Figure 1 in supporting information).26 It is observed from Figure 1d that CRC prepared from heat-treated MGM precursor still appears as 2D nanosheets. The MOFs coated on GO was retained but roughened during the pyrolysis process (Figure 1e and f).

Figure 1. The SEM images of GO (a), MGM (b, c), CRC nanosheets (d-f). HR-TEM was employed to further investigated the prepared MGM and CRC nanosheets. It is observed from Figure 2a-c that MGM looks like stacking thick papers with rough surface. None obvious crystal lattice was seen on the magnified HR-TEM image (Figure 2d), indicating that this MGM may belong to amorphous solid. It is demonstrated from the element mapping analysis that C, N, O, Fe and Co elements are distributed homogeneously in MOFs (Figure 2e-i). Besides, the intensity distribution of Fe element mapping signal is quite similar to that of Co element (Figure 2h and i), implying Fe and Co atoms may uniformly participate the formation of MOFs. It may indicate the existence of absorbed oxygen, evidenced by the O element mapping (Figure 2g).



Figure 2. HR-TEM images (a-c), and element mapping analysis (d-i) of MGM. MOFs is normally composed of various coordination bonds, and thus is not stabble at relatively high temperature.37 The nature of coordinate bonds enable MOFs to have both poor electrical and magnetic activity. To improve the electromagnetic properties, we adopted a heat-treatment process to transform MGM to CRC nanosheets. According to thermo-gravimetric analysis (TGA), the weight of MGM gradually reduces under argon. Until at 500 °C, the weight keeps stable with no obvious loss (See Figure S2 in supporting information). Based on TGA, we investigated the pyrolysis of MGM at 500 °C under argon. It is obvious that GO layer must be transformed to RGO. As shown in Figure 3a-c, there are a large number of nanoparticles sticking to RGO surface. It indicates that a number of magnetic nanoparticles simultaneously formed at the same time of magnetic coating forming from the pyrolysis of MOFs layer. The amplified HR-TEM image shows clear crystal lattice of magnetic nanoparticles, displaying three main d-spacings of 0.21, 0.25 and 0.3 nm (Figure 3d). The element mapping analysis indicates that C, N, O, Co, and Fe elements are also existed in the CRC nanosheets and distributed evenly (Figure 3e-i).


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Figure 3. HR-TEM images (a-c), and element mapping analysis (d-i) of CRC nanosheets. XRD technology was adopted to identify the crystal structure of MGM and CRC nanosheets. The XRD pattern of MGM exhibits no characteristic signal (Figure 4a), further indicating amorphous form of MGM. The XRD pattern of CRC nanosheets shows obviously the signal at 35.4° (Figure 4b), which may correspond to the (311) crystal plane of CoFe2O4 (PDF 22-1086). The (311) crystal plane also can be proved by the d-spacing of 0.25 nm in HR-TEM image (Figure 3d). The d-spacings of 0.21 and 0.3 nm in HR-TEM images correspond to the (400) and (220) crystal planes of CoFe2O4 (Figure 3d and 4b).



Figure 4. XRD patterns of MGM (a), and CRC nanosheets (b). To further determine the compositions, XPS was employed and clearly shows C, N, O, Co, and Fe elements in MGM and CRC (Figure 5a-c). The atomic percentages of Co, Fe and N in MGM are 2.00 %, 4.00 % and 6.25 %. Accordingly, the [Co]: [Fe]: [N] ratio is 1: 2: 3.12, consistent with the atom ratio (1:1) of metal and N in Co-based MOFs,40 indicating that Fe participates in the formation of MOFs. The [Co]: [Fe] ratio in CRC increases to 1: 2.39, which is close to the stoichiometric CoFe2O4, further demonstrate the formation of CoFe2O4 phase. The Co 2p3/2 peak with binding energy of 781.5 eV can be attributed to the Co2+ tetrahedral site (Figure 5b).41 The Fe 2p spectrum contains satellite peaks with binding energy of 724.8 and 710.9 eV, respectively (Figure 5c), suggesting the valence of Fe is +3, which is consistent with the valence of Fe in CoFe2O4.42,43 It is sufficiently demonstrated by these evidences that CoFe2O4 form during the pyrolysis process. The O and C atomic percentages are very high, due to the existence of GO, RGO, and adsorbed oxygen.41 To investigate the transformation of 2-methylimidazole and GO during the pyrolysis process, C 1s core-level spectra are measured (Figure 5d and e). It is found that the O-C=O peak with binding energy of 288.4 eV disappears in CRC, implying that a decarboxylation reaction takes place during pyrolysis. The imidazole rings cannot keep invariability during pyrolysis, and may decompose into more stable compositions, such as graphitized carbon, evidenced by the serious weakened signal standing for C=N/C=O bonds.


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Figure 5. XPS survey curves of MGM and CRC (a), core-level spectra of Co 2p (b) and Fe 2p (c), Core-level spectra of C 1s in MGM (d) and in MGM (e). In addition, FTIR and Raman spectra were adopted to elucidate the chemical structure of MGM and CRC nanosheets. As exhibited in Figure 6a, the broad band around 3280 cm-1 is assigned to the O-H vibration, stems from H-O-H groups, indicating existence of bound water and free water in the MOFs and MGM. The peaks at 1581 and 1633 cm-1 are corresponded to the stretching mode of C=N and C=C bonds in 2-MIM, respectively. The peak observed at 1343 cm-1 can be seemed as the stretching vibration in imidazole ring.44 After heat-treatment, the broadband around 3280 cm-1, the peaks at 1581, 1633, and 1343 cm-1 all disappear, accompanying with emerging peaks at 2120, 1985 and 1870 cm-1. The peaks at 2120 and 1985 cm-1 may be attributed to formed expanded conjugated bonds. The peaks at 1870 cm-1 is ascribed to the residual -COOH or C=O. It further demonstrates the decomposition of imidazole ring and the formation of conjugated bonds. According to the literature, it may also indicate that some carbon component forms from the decomposition of organic ligand under the pyrolysis condition.38 However, it is difficult to confirm the reduction of GO during the pyrolysis process by FT-IR, on account of the similar FT-IR spectrum of CRC to that of CMOFs. As presented in Figure 6b, the peaks at 214, 271 and 383 cm-1 are characteristic vibrational involving Co and Fe species in MOFs,45,46 which may be assigned to the coordinate bond between Fe, Co and N. When combined GO with MOF, typical Raman spectra peaks around 1580 and 1350 cm-1 appear, which stand for the characteristic signals of C-sp2 and C-sp3 of GO/carbon,



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respectively. It is also difficult to distinguish RGO from carbon by similar Raman spectra of CMOFs and CRC. After heat-treatment at 500 ℃, the peaks at 1580 and 1350 cm-1 enhance obviously, indicating the retainment of C-sp2 and C-sp3 in both C-MOFs and CRC.38 Therefore, it is demonstrated by the above results that the prepared CRC nanosheets is constructed by a conductive layer (RGO layer) and a magnetic coating layer (CoFe2O4 layer).

Figure 6. FT-IR spectra (a) and Raman spectra (b) of MOFs, MGM, C-MOFs and CRC nanosheets. The EMA performances can be evaluated by reflection loss (RL) values. More than 90 % of microwave is absorbed if the RL value is lower than −10 dB. The frequency range can be seen as an effective EMA bandwidth. RL value can be written as equation (1) and (2).47 𝑅𝐿 = 20𝑙𝑔 𝑍=

𝑍𝑖𝑛 𝑍0

|𝑍𝑍 ―+ 11|

=

𝜇𝑟

(1)

𝜀𝑟 𝑡𝑎𝑛ℎ

(𝑗2𝜋𝑓𝑑 𝑐

)

𝜀𝑟𝜇𝑟

(2)

where Z0 is the impedance in free space, f stands for the tested frequency, d is sample thickness, and c is the light speed in free space. Figure 7 exhibits RL curves in the frequency range of from 2 to 18 GHz. The RL values of both MOFs and MGM are higher than -1 dB in the tested frequency range, demonstrating low EMA performances (Figure 7a and b). After heat-treatment at 500 ℃ under argon for 5 h, the RL value of C-MOFs decreases apparently, but still shows poor EMA performance (Figure 7c). CRC nanosheets


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shows remarkable EMA performance with broadband of RL value that are lower than -10 dB (Figure 7d). It is found that the maximal EMA position shifts from high frequency to low frequency, with the increasing of sample thickness, intensively implying that the EMA performance can be regulated by the thickness (Figure 7e). This can be well explained by the transmission line theory. According to equation 2, f is inversely proportional to d if other parameters are constant. The effective EMA bandwidth of CRC nanosheets reaches 7.08 GHz at 2.6 mm from 10.92 to 18 GHz (Figure 7f). Under the same thickness, the maximal absorption reaches -53.3 dB at 13.92 GHz. Compared with most reported RGO- or MOFs-based EMA materials (Table 1), CRC nanosheets exhibits a remarkable superiority, indicating its huge potential in the application of electromagnetic radiation elimination.



Figure 7. RL curves of MOFs (a), MGM (b), C-MOFs (c) and CRC Nanosheets (d) with fillerloading-ratio of 20 wt % in wax; 3D plot (e) and RL curve under 2.6 mm (f) of CRC Nanosheets with filler-loading-ratio of 20 wt% in wax.


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Table 1 EMA performance of reported RGO- or MOF-based materials a Loading

Thickness

Effective EMA

ratio(wt. %)

(mm)

RGO/α-Fe2O3

8

RGO/γ-Fe2O3

Bandwidth(GHz)

Minimum RL (dB)

Reference

3.0

6.76

-33.5

48

45

2.5

3.00

-59.6

49

RGO/CuS

20

2.5

4.50

-54.5

21

RGO/MoS2

10

2.0

5.72

-50.9

24

RGO/MOF-5

40

2.6

7.20

-50.5

26

RGO/MOF-67

6

3.2

7.72

-52.0

38

RGO/MOF-53

-

2.0

5.90

-25.8

50

Porous MOF-67

40

2.5

5.80

-35.3

37

FeⅢ-MOF-5

60

1.5

4.96

-30.4

51

Co/MOF-67

25

3.0

4.93

-30.3

52

SiC/MOF-67

10

2.0

5.92

-47.0

53

MOF (Co, Zn)

30

2.0

5.30

-59.7

54

20

1.8

4.08

-20.3

55

20

2.6

7.08

-53.3

This work

Filler

MCNTs/MOF67 CRC Nanosheets The matrix is wax.

a

εr and μr are used to explore EMA mechanism. Theoretically, real parts (ε′ and μ′) represent the electromagnetic energy storage ability, while imaginary parts (ε″ and μ″) stand for electromagnetic energy loss.56,57 The dielectric dissipation factors (tan δε = ε″/ε′) and magnetic dissipation factors (tan δμ = μ″/μ′) reflect the dielectric and magnetic loss of an absorber, respectively.56,57 It is obviously found that both ε′ and ε″ values of MOFs are too low to furnish obvious electrical energy storage and energy loss, which is consistent with the RL value of MOFs (Figure 8a, b and 7a). The insertion of GO nanosheets as the core cannot enlarge the permittivity of MOFs (Figure 8a and b), because of the low charge mobility of destroyed aromatic rings in GO. After a heat-treatment, C-MOFs shows increased permittivity (ε′ and ε″), but also exhibits low EMA performance (Figure 8a, b and 7c). However, for CRC nanosheets, both the ε′ and ε″ values increase remarkably (Figure 8a and b). More clearly, the tan δε value of CRC nanosheets increases distinctly,



and are much larger than that of MOFs, C- MOFs and MGM, leading to good dielectric loss of electromagnetic energy (Figure 8c). It is reasonably thought that this remarkable enhancement of dielectric loss can be attributed to that the formation of RGO or graphited carbon in CRC leads to increased electrical conductivity (See Figure S4 in the supporting information).

Figure 8. ε′ value (a), ε″ value (b), tan δε (c), μ′ value (d), μ″ value (e), and tan δμ (f) of MOFs, MGM, C-MOFs, and CRC nanosheets. Besides, the magnetic loss of these materials should be taken into consideration. As shown in Figure 8d and e, both MOFs and MGM display negligible complex permeabilities, as a result, resulting ignorable magnetic loss. But the C-MOFs exhibits an abruptly increased permeability (Figure 8d and e). The μ′ value of C-MOFs decreases from 1.15 at 2 GHz to 1.02 at 6.5 GHz, and then fluctuated around 1, while the μ″ value declined from 0.13 at 2 GHz to 0.02 at 18 GHz. It is indicated by this tendency that the C-MOFs has a low-frequency EMA potential, which can be further evidenced by the tan δμ value (Figure 8f). The permeability of CRC nanosheets appears a similar tendency to that of C-MOFs, intensively demonstrates that the main contribution of magnetic loss is the magnetic component derived from pyrolysis of MOFs (Figure 8d-f).


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MOFs and MGM have no magnetism, therefore generate no magnetic resonance phenomenon (See Figure S3 in supporting information). After a heat-treatment, the magnetism of C-MOF increases significantly, due to the formation of magnetic CoFe2O4. The existence of RGO pulls down the magnetism of CRC nanosheets (See Figure S3 in supporting information), fully explaining good magnetic storage and loss. However, C-MOF only shows poor EMA performance (Figure 7c). It is demonstrated that magnetic loss contribution to EMA is rather limited. Impedance match is an important factor that has obvious influence on EMA performance of a material, because it determines how much electromagnetic wave can enter into absorbents.52-55 Impedance matching ratio value (Zr) can be used to reveal the impedance matching of an absorbent, which can be expressed as Equation (3).26 𝑍𝑟 =

𝜇𝑟 𝜀𝑟

(3)

If εr = μr, the Zr will be equal to 1. Under this condition, the front surface of an absorbent can gain zero-reflection toward incident electromagnetic waves. It is obvious that higher Zr leads to better impedance matching. MOFs, MGM and C-MOFs show better impedance matching than CRC (Figure 9a). Meanwhile, the propagation loss of electromagnetic waves in absorbent can be evaluated by α, which is expressed as equation (4).26 α=

2πf 𝑐

(𝜇′′ε′′ ― 𝜇′ε′) + (𝜇′′ε′′ ― 𝜇′ε′)2 + (𝜇′′ε′ ― 𝜇′ε′′)2



It is obvious that high μ′ and ε′ values lead to high α values. As shown in Figure 9b, the α value of CRC is much larger than those of MOFs, MGM and C-MOFs. This is why CRC shows lower impedance matching but higher EMA performance.

Figure 9. Zr curves (a), and α curves (b), of MOFs, MGM, C-MOFs, and CRC composites. Based on the above analysis, it is considered that dielectric loss plays a predominant role in the EMA of CRC nanosteets. The insertion of RGO nanosheets enhances the dielectric loss of magnetic CoFe2O4. Meanwhile, the coating with magnetic layer endows RGO with optimal impedance and



noteworthy magnetic loss. Therefore, appropriate combination of dielectric loss and magnetic loss is crucial for the design of high-performance EMA materials. In short, we have developed an efficient route to construct sandwich-like CRC nanosheets, referring a growth of MOFs with multicomponent metal ion and a pyrolysis process under inert atmosphere. Due to the existence of Fe3+, the MOFs appears as a uniform layer on GO surface rather than regular polyhedrons, leading to a sandwich-like MGM precursor. Under a heat-treatment at 500 oC, the precursor was transformed into an CRC nanosheets, where the MOFs was decomposed into magnetic layer while GO was reduced to RGO. This synthetic strategy is so effective that we consider it will be expanded to the construction of other CRC nanostructures or magnetic/conductive core-shell nanostructures. In addition, this CRC nanosheets displays excellent broadband EMA performance. Under 2.6 mm, the maximum effective width of CRC nanosheets reaches 7.08 GHz which has obvious superiority to most RGO-based and MOFs-based EMA materials. The combination of high dielectric loss by RGO layer, and impedance match and remarkable magnetic loss by magnetic component layer is considered to be the main reason for the high EMA performance of CRC nanosheets. It is believed that this work will provide a valuable guidance to the rational design of CRC nanostructure for electromagnetic absorbing materials. ASSOCIATED CONTENT Supporting Information Supporting Information shows Figures S1−S4, including the SEM image, TGA analysis, and hysteresis loop of relative materials. AUTHOR INFROMATION Corresponding Authors * E-mail: [email protected] (Fan Wu) * E-mail: [email protected] (Aming Xie) ACKNOWLEDGMENT This work is financially supported by the National Natural Science Foundation of China (NSFC: 51702161) which is gratefully acknowledged. References (1) Genc, O.; Bayrak, M.; Yaldiz, E. Analysis of the Effects of GSM Bands to the Electromagnetic Pollution in the RF Spectrum. Prog. Electromagn. Res. 2010, 101, 17-32.


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(2) Yang, Y.; Gupta, M. C.; Dudley, K. L.; Lawrence, R. W. Novel Carbon Nanotube-Polystyrene Foam Composites for Electromagnetic Interference Shielding. Nano Lett. 2005, 5, 2131-2134. (3) Singh, K.; Ohlan, A.; Pham, V. H.; Balasubramaniyan, R.; Varshney, S.; Jang, J.; Kong, B. S. Nanostructured Graphene/Fe3O4 Incorporated Polyaniline as a High-performance Shield Against Electromagnetic Pollution. Nanoscale 2013, 5, 2411-2420. (4) Shen, B.; Zhai, W.; Tao, M.; Ling, J.; Zheng, W. Lightweight, Multifunctional Polyetherimide/graphene@Fe3O4 Composite Foams for Shielding of Electromagnetic Pollution. ACS Appl. Mater. Interfaces 2013, 5, 11383-11391. (5) Zhang, Y.; Huang, Y.; Zhang, T.; Chang, H.; Xiao, P.; Chen, H.; Huang, Z.; Chen, Y. Broadband and Tunable High‐performance Microwave Absorption of an Ultralight and Highly Compressible Graphene Foam. Adv. Mater. 2015, 27, 2049-2053. (6) Zhang, W. L.; Jiang, D.; Wang, X.; Hao, B. N.; Liu, Y. D.; Liu, J. Growth of Polyaniline Nanoneedles on MoS2 Nanosheets, Tunable Electro-response, and Electromagnetic Wave Attenuation Analysis. J. Phys. Chem. C 2017, 121, 4989-4998. (7) Han, M.; Yin, X.; Li, X.; Anasori, B.; Zhang, L.; Cheng, L.; Gogotsi, Y. Laminated and TwoDimensional Carbon-Supported Microwave Absorbers Derived from MXenes. ACS Appl. Mater. Interfaces 2017, 9, 20038-20045. (8) Liang, C.; Wang, Z. Controllable Fabricating Dielectric-Dielectric SiC@C Core-Shell Nanowires for High-Performance Electromagnetic Wave Attenuation. ACS Appl. Mater. Interfaces 2017, 9, 40690-40696. (9) Tian, X; Meng, F.; Meng, F.; Chen, X.; Guo, Y.; Wang, Y., Zhu, W.; Zhou, Z. Synergistic Enhancement of Microwave Absorption Using Hybridized Polyaniline@helical CNTs with Dual Chirality. ACS Appl. Mater. Interfaces 2017, 9, 15711-15718. (10)Yu, H. L.; Wang, T. S.; Wen, B.; Lu, M. M.; Xu, Z.; Zhu, C. L.; Chen, Y. J.; Xue, X. Y.; Sun, C. W.; Cao, M. S. Graphene/polyaniline Nanorod Arrays: Synthesis and Excellent Electromagnetic Absorption Properties. J. Mater. Chem. 2012, 22, 21679-21685. (11) Wang, T. S.; Liu, Z. H.; Lu, M. M.; Wen, B; Ouyang, Q. Y.; Chen, Y. J.; Zhu, C. L.; Gao, P.; Li, C. Y.; Cao, M. S.; Qi, L. H. Graphene-Fe3O4 Nanohybrids: Synthesis and Excellent Electromagnetic Absorption Properties. J. Appl. Phys. 2013, 113, 024314. (12)Tkachev, S. V.; Buslaeva, E. Yu.; Naumkin, A. V.; Kotova, S. L.; Laure, I. V.; Gubin, S. P.



Reduced Graphene Oxide. Inorg. Mater. 2012, 48, 796-802. (13) Zhu, Y.; Murali, S.; Cai, W.; Li, X.; Suk, J. W.; Potts, J. R.; Ruoff, R. S. Graphene and Graphene Oxide: Synthesis, Properties, and Applications. Adv. Mater. 2010, 22, 3906-3924. (14) Compton, O. C.; Nguyen, S. T. Graphene Oxide, Highly Reduced Graphene Oxide, and Graphene: Versatile Building Blocks for Carbon‐based Materials. Small 2010, 6, 711-723. (15) Zhang, L.; Xia, Z. Mechanisms of Oxygen Reduction Reaction on Nitrogen-doped Graphene for Fuel Cells. J. Phys. Chem. C 2011, 115, 11170-11176. (16) Zhu, X.; Zhu, Y.; Murali, S.; Stoller, M. D.; Ruoff, R. S. Nanostructured Reduced Graphene Oxide/Fe2O3 Composite as a High-performance Anode Material for Lithium Ion Batteries. ACS Nano 2011, 5, 3333-3338. (17) Li, Y.; Gao, W.; Ci, L.; Wang, C.; Ajayan, P. M. Catalytic Performance of Pt Nanoparticles on Reduced Graphene Oxide for Methanol Electro-oxidation. Carbon 2010, 48, 1124-1130. (18) Robinson, J. T.; Perkins, F. K.; Snow, E. S.; Wei, Z.; Sheehan, P. E. Reduced Graphene Oxide Molecular Sensors. Nano Lett. 2008, 8, 3137-3140. (19)Chen, Z.; Xu, C.; Ma, C.; Ren, W.; Cheng, H. M. Lightweight and Flexible Graphene Foam Composites for High-Performance Electromagnetic Interference Shielding. Adv. Mater. 2013, 25, 1296-1300. (20)Wen, B.; Cao, M.; Lu, M.; Cao, W.; Shi, H.; Liu, J.; Wang, X.; Jin, H.; Fang, X.; Wang, W.; Yuan, J. Reduced Graphene Oxides: Light-weight and High-efficiency Electromagnetic Interference Shielding at Elevated Temperatures. Adv. Mater. 2014, 26, 3484-3489. (21)Liu, P.; Huang, Y.; Yan, J.; Yang, Y.; Zhao, Y. Construction of CuS Nanoflakes Vertically Aligned on Magnetically Decorated Graphene and Their Enhanced Microwave Absorption Properties. ACS Appl. Mater. Interfaces 2016, 8, 5536-5546. (22)Han, M.; Yin, X.; Kong, L.; Li, M.; Duan, W.; Zhang, L.; Cheng, L. Graphene-wrapped ZnO Hollow Spheres with Enhanced Electromagnetic Wave Absorption Properties. J. Mater. Chem. A 2014, 2, 16403-16409. (23)Wu, F.; Xie, A.; Sun, M.; Wang, Y. and Wang, M. Reduced Graphene Oxide (RGO) Modified Spongelike Polypyrrole (PPy) Aerogel for Excellent Electromagnetic Absorption. J. Mater. Chem. A 2015, 3, 14358-14369. (24)Wang, Y.; Chen, D.; Yin, X.; Xu, P.; Wu, F.; He, M. Hybrid of MoS2 and Reduced Graphene


Page 18 of 23

Page 19 of 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


Oxide: a Lightweight and Broadband Electromagnetic Wave Absorber. ACS Appl. Mater. Interfaces 2015, 7, 26226-26234. (25)Kong, L.; Yin, X. W.; Yuan, X. Y.; Zhang, Y. J.; Liu, X. M.; Cheng, L. F.; Zhang, L. T. Electromagnetic Wave Absorption Properties of Graphene Modified with Carbon Nanotube/poly (dimethyl siloxane) Composites. Carbon 2014, 73, 185-193. (26)Liang, X.; Quan, H. B.; Ji, G. B.; Liu, W.; Zhao, H. Q.; Dai, S. S.; Lv, J. and 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. (27)Ren, Y. L.; Wu, H. Y.; Lu, M. M.; Chen, Y. J.; Zhu, C. L.; Gao, P. and Ouyang, Q. Y. Quaternary Nanocomposites Consisting of Graphene, Fe3O4@Fe Core@Shell, and ZnO Nanoparticles: Synthesis and Excellent Electromagnetic Absorption Properties. ACS Appl. Mater. Interfaces 2012, 4, 6436-6442. (28)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

Graphene

Oxide

(RGO)-MnFe2O4

Nanocomposites and Polyvinylidene Fluoride. ACS Appl Mater Interfaces 2014, 28, 7471-7478. (29)Zhang, H.; Zhu, C.; Chen, Y.; Gao, H. Growth of Fe3O4 Nanorod Arrays on Graphene Sheets for Application in Electromagnetic Absorption Fields. Chemphyschem 2014, 15, 2261-2266. (30)Chen, T.; Deng, F.; Zhu, J.; Chen, C.; Sun, G.; Ma, S.; Yang, X. Hexagonal and Cubic Ni Nanocrystals Grown on Graphene: Phase-Controlled Synthesis, Characterization and Their Enhanced Microwave Absorption Properties. J. Mater. Chem. 2012, 22, 15190-15197. (31)Zhang, C.; Wang, B.; Xiang, J.; Su, C.; Mu, C.; Wen, F.; Liu, Z. Microwave Absorption Properties of CoS2 Nanocrystals Embedded into Reduced Graphene Oxide. ACS Appl. Mater. Interfaces 2017, 9, 28868-28875. (32)Chen, G. J.; Wang, J. S.; Jin, F. Z.; Liu, M. Y.; Zhao, C. W.; Li, Y. A.; Dong, Y. B. Pd@Cu(II)MOF-Catalyzed Aerobic Oxidation of Benzylic Alcohols in Air with High Conversion and Selectivity. Inorg. Chem. 2016, 55, 3058-3064. (33)Deng, Z. W.; Chen, M.; Gu, G. X.; Wu, L. M. A Facile Method to Fabricate ZnO Hollow Spheres and Their Photocatalytic Property. J. Phys. Chem. B. 2008, 112, 16-22. (34)Dua, J.J.; Yuan, Y. P.; Sun, J.X.; Peng, F. M.; Jiang, X.; Qiu, L.G.; Xie, A. J.; Shen, Y. H.; Zhu, J. F.; New Photocatalysts Based on MIL-53 Metal–Organic Frameworks for the Decolorization



of Methylene Blue Dye. J. Hazard. Mater. 2011, 190, 945-951. (35)Li, J. R.; Kuppler, R. J.; Zhou, H. C. Selective Gas Adsorption and Separation in Metal-Organic Frameworks. Chem. Soc. Rev. 2009, 38, 1477-1504. (36) Li, Q.; Xu, P.; Gao, W.; Ma, S.; Zhang, G.; Cao, R.; Cho, J.; Wang, H.; Wu, G. Graphene/Graphene‐Tube Nanocomposites Templated from Cage‐Containing Metal‐Organic Frameworks for Oxygen Reduction in Li–O2 Batteries. Adv. Mater. 2014, 26, 1378-1386. (37)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. (38) Zhang, K.; Xie, A.; Sun, M.; Jiang, W.; Wu, F., Dong, W. Electromagnetic Dissipation on the Surface of Metal Organic Framework (MOF)/Reduced Graphene Oxide (RGO) Hybrids. Mater. Chem. Phys. 2017, 199, 340-347. (39)Hummers, W. S.; Offeman, R. E. Preparation of Graphitic Oxide. J. Am. Chem. Soc. 1958, 80, 1339. (40)Banerjee, R.; Phan, A.; Wang, B.; Knobler, C.; Furukawa, H.; O'keeffe, M.; Yaghi, O. M. HighThroughput Synthesis of Zeolitic Imidazolate Frameworks and Application to CO2 Capture. Science 2008, 319, 939-943. (41)Chen, L.; Ding, D.; Liu, C.; Cai, H.; Qu, Y.; Yang, S.; Gao, Y.; Cai, T. Degradation of Norfloxacin by CoFe2O4-GO Composite Coupled with Peroxymonosulfate: A Comparative Study and Mechanistic Consideration. Chem. Eng. J. 2018, 334, 273-284. (42)Qu, B.; Zhu, C.; Li, C.; Zhang, X.; Chen, Y. Coupling Hollow Fe3O4-Fe Nanoparticles with Graphene Sheets for High-Performance Electromagnetic Wave Absorbing Material. ACS Appl Mater Interfaces 2016, 17, 3730-3735. (43)Zeng, X.; Zhu, L.; Jiang, G.; Wang, C.; Xia, Z.; Yu, R. Template-Free Formation of Uniform Fe3O4 Hollow Nanoflowers Supported on Reduced Graphene Oxide and Their Excellent Microwave Absorption Performances. Phys. Status Solidi A 2018, 215, 1701049. (44)Lin, K. Y. A.; Chang, H. A. Ultra-High Adsorption Capacity of Zeolitic Imidazole Framework67 (ZIF-67) for Removal of Malachite Green from Water. Chemosphere 2015, 139, 624-631. (45)Lv, H.; Zhao, H.; Cao, T.; Qian, L.; Wang, Y.; Zhao, G. Efficient Degradation of High Concentration Azo-dye Wastewater by Heterogeneous Fenton Process with Iron-Based Metal-


Page 20 of 23

Page 21 of 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


Organic Framework. J. Mol. Catal. A: Chem. 2015, 400, 81-89. (46) Lohe, M. R.; Rose, M.; Kaskel, S. Metal–Organic Framework (MOF) Aerogels with High Micro-and Macroporosity. Chem. Commun. 2009, 40, 6056-6058. (47)Naito, Y.; Suetake, K. Application of Ferrite to Electromagnetic Wave Absorber and Its Characteristics. IEEE Trans. Microwave Theory Tech. 1971, 19, 65−72. (48)Zhang, H.; Xie, A.; Wang, C.; Wang, H.; Shen, Y.; Tian, X. Novel rGO/-Fe2O3 Composite Hydrogel: Synthesis, Characterization and High Performance of Electromagnetic Wave Absorption. J. Mater. Chem. A 2013, 30, 8547-8552. (49)Kong, L.; Yin, X.; Zhang, Y.; Yuan, X.; Li, Q.; Ye, F.; Cheng, L.; Zhang, L. Electromagnetic Wave Absorption Properties of Reduced Graphene Oxide Modified by Maghemite Colloidal Nanoparticle Clusters. J. Phys. Chem. C. 2013, 117, 19701-19711. (50)Wang, Y.; Zhang, W. Z.; Wu, X. X.; Luo, C. Y.; Liang, T.; Yan, G. Metal-Organic Framework Nanoparticles Decorated with Graphene: A High-Performance Electromagnetic Wave Absorber, J. Magn. Magn. Mater. 2016, 416, 226-230. (51)Liu, W.; Liu, L.; Ji, G. B.; Li, D. R.; Zhang, Y. N.; Ma, J. N.; Du, Y. W. Composition Design and

Structural

Characterization

of

MOF-Derived

Composites

with

Controllable

Electromagnetic Properties, ACS Sustainable Chem. Eng. 2017, 5, 7961-7971. (52) 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 FrameworkEncapsulated Cobalt Nanoparticles, ACS Appl. Mater. Interfaces 2017, 9, 42102-42110 (53) Zhang, K.; Wu, F.; Xie, A. M.; Sun, M. X.; Dong, W. In Situ Stringing of Metal Organic Frameworks by SiC Nanowires for High-Performance Electromagnetic Radiation Elimination, ACS Appl. Mater. Interfaces 2017, 9, 33041–33048. (54) Feng, W.; Wang, Y. M.; Chen, J. C.; Li, B. Q.; Guo, L. X.; Ouyang, J. H.; Jia D. C.; Zhou, Y. Metal Organic Framework-derived CoZn Alloy/N-doped Porous Carbon Nanocomposites: Tunable Surface Area and Electromagnetic Wave Absorption Properties, J. Mater. Chem. C 2018, 6, 10-18. (55) Zhang, K.; Wu, F.; Li, J., Sun; M., Xie; A.; Dong, W. Networks Constructed by Metal Organic Frameworks

(MOFs)

and

Multiwall

Carbon

Nanotubes

(MCNTs)

Electromagnetic Waves Absorption. Mater. Chem. Phys. 2018, 208, 198-206.


for

Excellent


(56)Zhou, W.; Hu, X.; Bai, X.; Zhou, S.; Sun, C.; Yan, J.; Chen, P. Synthesis and Electromagnetic, Microwave Absorbing Properties of Core-Shell Fe3O4-Poly(3,4-ethylenedioxythiophene) Microspheres. ACS Appl. Mater. Interfaces 2011, 3, 3839-3845. (57) Kong, L. B.; Li, Z. W.; Liu, L.; Huang, R.; Abshinova, M.; Yang, Z. H.; Tang, C. B.; Tan, P. K.; Deng, C. R.; Matitsine, S. Recent Progress in Some Composite Materials and Structures for Specific Electromagnetic Applications. Int. Mater. Rev. 2013, 58, 203-259.


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CoFe2O4 Nanostructures for High

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