Hybrid of MoS2 and Reduced Graphene Oxide - ACS Publications

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Hybrid of MoS2 and Reduced Graphene Oxide: A Lightweight and Broadband Electromagnetic Wave Absorber Yanfang Wang,†,‡ Dongliang Chen,† Xiong Yin,‡ Peng Xu,‡ Fan Wu,*,§ and Meng He*,‡ †

College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing 100029, P. R. China CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience and Technology, Beijing 100190, P. R. China § State Key Laboratory for Disaster Prevention & Mitigation of Explosion & Impact, PLA University of Science and Technology, Nanjing 210007, P. R. China ‡

S Supporting Information *

ABSTRACT: Electromagnetic wave absorbing materials that can exhibit effective absorption in a broad bandwidth at a thin thickness are strongly desired due to their widespread applications in electronic devices. In this study, hybrids of MoS2 and reduced graphene oxide (RGO) were prepared and their microwave absorption performance was investigated for the first time. It was found that a thin sample consisting of 10 wt % MoS2/RGO hybrid in the wax matrix exhibited an effective microwave absorption bandwidth of 5.72 GHz at the thickness less than 2.0 mm. The highest reflection loss of −50.9 dB was observed at 11.68 GHz for a sample with a thickness of 2.3 mm. Results obtained in this study indicate that hybrids of MoS2 and RGO are promising microwave absorbing materials, which can exhibit broad effective absorption bandwidth at low filler loading and thin thickness. KEYWORDS: MoS2, reduced graphene oxide, composite, electromagnetic properties, microwave absorber frequency band of 4.32 GHz with a thickness of 4 mm.14 The microstructure of graphene or RGO based materials is critical for electromagnetic wave absorption performance. For examples, graphene foams, which are 3D interconnected graphene networks, exhibited a good electromagnetic wave absorption performance in a broad bandwidth of more than 60 GHz when compressed.17 Remarkable electromagnetic wave shielding effectiveness was also demonstrated by alternatively stacked multilayers of graphene and poly(methyl methacrylate) (PMMA)16 and other well designed graphene based radar absorbing materials.15,18 Modifying graphene or RGO with other nanoparticles, such as Fe2O3 or Fe3O4,19−21 MnFe2O4,22 ZnO hollow spheres or nanoparticles,23,24 poly(3,4-ethylenedioxythiophene) (PEDOT),25 polypyrrole (PPy)1 and CNTs,26,27 also resulted in improved electromagnetic wave absorption performance, as evidenced by the stronger absorption in a broader bandwidth at the reduced thickness of the composites. Furthermore, nanoparticles of core− shell structures, for example, Fe3O4@ZnO,28 SiO2@Fe3O4,29 and Fe3O4@Fe,30 can also be applied to modify RGO for enhanced electromagnetic wave absorption performance. Molybdenum disulfide (MoS2), as a transition metal dichalcogenide with a layered structure similar to that of graphite,

1. INTRODUCTION With the rapid development of wireless communications and high frequency devices, electromagnetic wave absorbing materials have attracted more and more attention all over the world. An ideal electromagnetic wave absorbing material should be lightweight and exhibit high absorption efficiency in a broad frequency band at a low filler loading ratio.1 Traditionally, electromagnetic wave absorbing materials are mainly based on metal oxides. With the development of nanotechnology, nanosized dielectric or magnetic materials have been fabricated to improve the electromagnetic wave absorption performance, such as ZnO (cagelike-structure,2 nanorod3), CuS,4 α-MnO2,5 and dendrite-like Fe3O4, γ-Fe2O3, and Fe.6 Composites of nanoparticles were also developed to further improve electromagnetic wave absorption performance, such as NiO/SiC,7,8 Fe3O4@ TiO2,9 CoFe2O4/Co3Fe7,10 CdS/α-Fe2O3,11 FexOy@SiO2,12 and [email protected] Benefiting from the nanoscale dimensions, the above-mentioned materials showed superior electromagnetic wave absorption performance with a modest filler loading ratio in composites. In recent years, significant effort has been devoted to the development of electromagnetic wave absorbing materials based on graphene and reduced graphene oxide (RGO) due to their impressive properties.14−18 A composite consisting of RGO nanosheets dispersed in polyvinylidene fluoride (PVDF) matrix exhibited effective electromagnetic wave absorption in a © 2015 American Chemical Society

Received: September 8, 2015 Accepted: November 5, 2015 Published: November 17, 2015 26226

DOI: 10.1021/acsami.5b08410 ACS Appl. Mater. Interfaces 2015, 7, 26226−26234

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ACS Applied Materials & Interfaces has received a great deal of attention because of its semiconducting properties.31 Composites of MoS2/RGO have found potential applications in the area of energy storage and transformation,32−35 hydrogen evolution.36−38 Nevertheless, to the best of our knowledge, the dielectric properties and electromagnetic wave absorption performance of MoS 2 /RGO composite have never been reported. In this study, the composite of MoS2/RGO was prepared and its superior electromagnetic wave absorption performance was evidenced. With the filler loading of MoS2/RGO hybrid as low as 10.0 wt % in a wax matrix, the composites with the thicknesses of 1.9 and 2 mm exhibited an effective electromagnetic wave absorption bandwidth of 5.72 GHz. With the thickness of 2.3 mm, the highest reflection loss reaches −50.9 dB at 11.68 GHz. These results indicate that MoS2/RGO hybrid is a very promising electromagnetic wave absorbing material, which can exhibit broad effective absorption bandwidth at low filler loading and thin thickness.

Scheme 1. Synthetic Process of the MoS2/RGO Hybrid

2. EXPERIMENTAL SECTION 2.1. Materials. All reagents were of analytical grade and used without further purification. Sodium molybdate dihydrate (Na2MoO4·2H2O), carbon disulfide (CS2) and graphite were obtained from Aladdin Industrial Inc. Sulfuric acid, KMnO4, H2O2 (30%) were supplied by Sinopharm Chemical Reagent Co. Ltd. Distilled water was obtained from Direct-Q3 UV, Millipore. 2.2. Synthesis and Purification of GO. Graphite oxide was synthesized by a modified Hummers method.39 In brief, 2.0 g of graphite was first mixed with a solution of 100 mL of H2SO4 in an ice bath for 3 h. Then, 8.0 g of KMnO4 was slowly added to the solution. After stirring for 2 h, 200 mL of distilled water was added drop by drop under water bath. After an additional 30 min stirring, 10 mL of H2O2 (30%) was slowly added to the abovementioned solution, and a bright yellow dispersion of graphite oxide appeared during this process. The graphite oxide was filtered with a dialysis bag (MD 34, MW 7000, USA) in distilled water and the water was changed every 12 h. After 1 week, all the impurities had been removed. Then, the gel-like graphite oxide was freeze-dried at −50 °C for 24 h to obtain graphite oxide powder. The graphite oxide powder was dispersed in distilled water and centrifuged at 10 000 rpm for 30 min to remove all the agglomerate sheets. The GO was obtained from the supernatant and dried at 50 °C. 2.3. Synthesis of MoS2/RGO Hybrid. For the synthesis of the MoS2/RGO hybrid, 80 mg of Na2MoO4·2H2O was added to a solution of prepared GO (4 mg/mL, 10 mL). The mixed solution was sonicated for 0.5 h to obtain a homogeneous dispersion, which was then freeze-dried at −50 °C for 48 h to get GO/Na2MoO4 hybrid powder. The powder was transferred to a tube furnace, and then heated to 650 °C at a rate of 10 °C/min. The powder was held at 650 °C for 2 h to react with CS2 vapor, which was introduced by carrying an Ar flow at the rate of 100 sccm (standard-state cubic centimeter per minute). After the reaction, the tube furnace was turned off, and the product was cooled to room temperature naturally in flowing Ar. The as prepared MoS2/RGO hybrid was washed with distilled water and dried into fluffy powder for further use. This synthetic process has been summarized in Scheme 1. 2.4. Characterization and Measurement. The morphology of MoS2/RGO hybrid was characterized with a field emission scanning electron microscope (FE-SEM, S-4800, Hitachi) and a field emission high resolution transmission electron microscope (FE-HRTEM, Tecnai G2 F20UTwin, FEI). Powder diffraction data of the as-synthesized samples were collected from 5° to 80°

Figure 1. (a, b) SEM images of MoS2/RGO hybrid.

in 2θ using an X-ray diffractometer (XRD, D/MAX TTRIII, Rigaku) with Cu Kα (λ = 1.5418 Å) radiation. Raman spectroscopy was carried out on a Renishaw in Via Raman Microscope equipped with a 514 nm laser. X-ray photoelectron spectra (XPS) were recorded using a Thermo Scientific ESCALAB 250Xi X-ray photoelectron spectrometer equipped with a monochromatic Al Kα X-ray source (1486.6 eV). The relative complex permittivity (εr) and permeability (μr) were measured by a vector network analyzer (VNA, N5242A PNA-X, Agilent) in the frequency range 2−18 GHz. The measured samples were prepared by uniformly mixing 3, 5, 10, and 15 wt % of MoS2/RGO hybrid with a wax matrix at 85 °C. The mixture was then pressed into toroidal shaped samples with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. In a coaxial wire analysis, εr of the dielectric material has been calculated from the experimental scattering parameters S11 (or S22) and S21 (or S12) using the standard Nicolson−Ross−Weir (NRW) algorithm.40,41 26227


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Figure 4. Raman spectrum of MoS2/RGO hybrid.

Figure 2. (a, b) TEM images, (c) the corresponding SAED pattern, and (d) HRTEM image of a RGO plate with MoS2 nanosheets attached to it. (e) TEM image of an agglomerate of MoS2 nanosheets. (f) HRTEM image of a MoS2 nanosheet in the agglomerate.

Figure 3. X-ray powder diffraction pattern of MoS2/RGO hybrid (upper) and the calculated data of MoS2 reported in PDF 65-0160 (bottom).

3. RESULTS AND DISCUSSION Typical SEM images of the as-prepared MoS2/RGO hybrid are presented in Figure 1. Both flexible two-dimensional sheet-like structures and three-dimensional granular particles are found in the hybrid. The flexible sheets with dimensions of several micrometers are supposed to be RGO, whereas the granular particles are thought to be the agglomerate of MoS2 nanosheets. This assumption is confirmed by TEM characterizations. As shown in Figure 2a,b, electron beam transparent two-dimensional flexible sheets are observed by TEM, together with small dark particles attached to them. The corresponding selected area electron diffraction (SAED) pattern is given in Figure 2c. Diffraction rings in the SAED pattern result from (110) and (100) planes of graphene sheets and MoS2 (indicated with G and M, respectively,

Figure 5. XPS survey spectrum (a) and core level spectra of Mo 3d (b), S 2p (c), and C 1s (d) of the hybrid of MoS2/RGO. (e) Core level spectrum of C 1s in GO.

in Figure 2c). The absence of hkl with l ≠ 0 in the SAED pattern is due to the fact that the c axis of both RGO and MoS2 sheets attached to them are nearly parallel with the electron beam. Shown in Figure 2d is the HRTEM image of particles attached to the graphene sheet. The Fourier transform of the area marked with a white square is given as an inset of Figure 2d. The Fourier transform can be well indexed with the lattice parameters of MoS2, further confirming that the particles attached to graphene sheets are MoS2. Consistent with SEM observations, agglomerates of MoS2 nanosheets are also found by TEM. A typical TEM 26228


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Figure 6. Real part (a, c) and imaginary part (b, d) of relative complex permittivity of MoS2/RGO−wax composites with filler loadings ranging from 3 wt % to 15 wt %.

image of the agglomerate of MoS2 nanosheets is given in Figure 2e, whereas a HRTEM image of MoS2 nanosheets is shown in Figure 2f, in which the layered structure of MoS2 is clearly visible. X-ray powder diffraction pattern of the as-prepared MoS2/ RGO hybrid is given in Figure 3. The diffraction data of MoS2 reported in PDF 65-0160 is also presented for comparison. The consistency between them confirms the existence of MoS2 in the hybrid. Signals of RGO can hardly be detected from the powder pattern, due to the weak scattering power and low crystallinity of RGO. Nevertheless, RGO in the hybrid can be readily identified by Raman spectroscopy (Figure 4). Two strong peaks appeared at 1346 and 1587 cm−1, respectively, as well as the band appeared in the range 2500−3000 cm−1 are characteristic Raman signals of RGO.42 Additionally, weak E2g and A1g peaks of MoS2 are also observed at 377 and 404 cm−1, respectively.43 The as-prepared MoS2/RGO hybrid was also characterized with XPS. As expected, only signals of Mo, S, C, and O were detected in the survey spectrum (Figure 5a). The atomic percent contents of Mo, S, C, and O deduced from the survey spectrum are 15.68%, 31.61%, 50.57%, and 2.14%, respectively. The ratio of Mo/S is very close to 1:2, and the low content of O indicates that GO has been well reduced to RGO in the preparation process. Core level spectra of Mo and S shown in Figure 5b,c are very consistent with the presence of MoS2. In comparison with the C 1s core level spectrum of GO (shown in Figure 5e), signals resulting from O-bonded C have been significantly removed in the C 1s spectrum of the hybrid, in good agreement with its low O content. Figure 6 shows the complex permittivity of the as-fabricated MoS2/RGO−wax composites. These composites present typical frequency dependent permittivity, the values of real (ε′) permittivity are found to decrease with the frequency in the tested region (Figure 6a). On the basis of the Debye theory, ε′ and ε″ can be described as1 ε′ = ε∞ +

ε″ =

2 2

1+ωτ

ωτ +

σac ωε0

(2)

where εs is the static permittivity, ε∞ is the relative dielectric permittivity at the high-frequency limit, ω is angular frequency, τ is polarization relaxation time, σac is the alternative conductivity, and ε0 is the dielectric constant in vacuum (ε0 = 8.854 × 10−12 F m−1). According to eq 1, in the frequency range investigated, the decrease in ε′ is attributed to the increase in ω. This phenomenon can probably be considered as the polarization relaxation in the lower frequency. With the increase of MoS2/RGO loading (from 3 wt % to 15 wt %), significant enhancement was achieved in both real (ε′) and imaginary (ε″) permittivity (Figure 6c,d). The increment of ε′ may be attributed to the fact that the increasing loading ratio of MoS2/RGO increases the dipolar polarization.1,44 The tangent of dielectric loss angle (δε) of the material can be expressed as tan δε =

ε″ ε′

(3)

Figure 7 shows tan δε of the composites versus frequency at different loading levels of MoS2/RGO. In general, the values of ε″ (Figure 6b) and tan δε both increase with the filler loading ratio, and several relaxation peaks can be found for each curve in the tested frequency range. When the second part of the eq 2 is not taken into account, the relationship between ε′ and ε″ can be written as εs + ε∞ ⎞2 ⎛ ⎛ εs − ε∞ ⎞2 2 ⎜ε′ − ⎟ + (ε ″ ) = ⎜ ⎟ ⎝ ⎝ 2 ⎠ 2 ⎠

(4)

It corresponds to a circle centered at ((εs + ε∞)/2, 0), which is characteristic for Debye relaxation process. As shown in Figure 8, each Cole−Cole curve of the MoS2/ RGO−wax composite is very complicated, containing many individual semicircles, due to the multirelaxations dielectric properties. These multirelaxations can be well explained by the mechanism proposed by Cao et al.8 They are supposed to

εs − ε∞ 1 + ω 2τ 2

εs − ε∞

(1) 26229


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originate from (1) the defect polarization of MoS2 nanocrystals, (2) the defect polarization of the oxygen-containing groups and the imperfect carbon structures in RGO, and (3) the multiple interfacial polarizations in MoS2/RGO hybrids (Scheme 2). Because the frequency range is 2−18 GHz, the source-toshield distance is greater than the free-space wavelength. Thus, the measurements are considered under the condition of far field.45 According to the transmission line theory,46 the input impedance (Zin) on the interface can be expressed as Z in = Z0

⎛ 2πfd ⎞ tanh⎜j εrμr ⎟ ⎝ c ⎠ εr μr

(5)

where Z0 is the impedance of free space, μr is the complex permeability, μr = μ′ − jμ″, εr is the complex permittivity,

Figure 7. Dielectric loss tangents of MoS2/RGO−wax composites with filler loadings ranging from 3% to 15%.

Figure 8. Cole−Cole plots of MoS2/RGO−wax composites: (a) 3 wt %; (b) 5 wt %; (c) 10 wt %; (d) 15 wt %.

Scheme 2. Illustrations of Dipole Polarizations in the MoS2/RGO Hybrid: (a) Defect Dipole Polarization of MoS2; (b) Defect Dipole Polarization of RGO; (c) Multiple Interfacial Polarizations in the MoS2/RGO Hybrid

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Figure 9. RL curves and 3D plots of MoS2/RGO−wax composites with filler loadings of 3 wt % (a), 5 wt % (b), 10 wt % (c), and 15 wt % (d) at thicknesses ranging from 1.5 to 4.0 mm in the frequency range 2−18 GHz.

εr = ε′ − jε″, f is the frequency, d is the thickness of material, and c is the speed of light. Considering the weak magnetic properties of RGO−MoS2, μr is taken as 1. On the basis of the model of metal backplane, the reflection loss (RL) of a sample is determined by Z0 and Zin according to the following equation RL (dB) = 20 lg

Z in − Z0 Z in + Z0

frequency range can be considered as an effective absorption bandwidth. The effect of the thickness of MoS2/RGO−wax composite on the electromagnetic wave absorption performance was investigated, and the results are shown in Figure 9. It can be found that the electromagnetic wave absorption performance improves gradually with the increase of filler loading from 3 to 10 wt % (Figure 9a−c). Nevertheless, degraded electromagnetic wave absorption performance was observed for the sample with the filler loading ratio of 15.0 wt % (Figure 9d). According to the fundamental mechanism of electromagnetic wave absorption, the most effective absorption is exhibited when the impedance

(6)

When the RL is lower than −10 dB, more than 90% of the electromagnetic energy is absorbed, implying that this 26231


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Figure 10. (a) RL curves of MoS2/RGO−wax composites with the filler loading of 10 wt % at various thicknesses. At thicknesses of 1.9 mm (b) and 2.0 mm (c), this sample can reach an effective absorption band of 5.72 GHz. At the thickness of 2.3 mm (d), this sample can get the maximum value of RL (−50.9 dB).

Table 1. Electromagnetic Wave Absorption Properties of Typical Materials Reported in This Work and Recent Literatures

a

filler

matrix

loading ratio (wt %)

thickness (mm)

frequency rangea (GHz)

effective bandwidtha (GHz)

ref

MoS2/RGO MoS2/RGO RGO RGO/γ-Fe2O3 RGO/Fe3O4 RGO/α-Fe2O3 RGO/MnFe2O4 RGO/ZnO RGO/ZnO RGO/PEDOT RGO/CNTs RGO/CNTs RGO/hematite RGO/Co3O4 RGO/NiO RGO/Ni

wax wax PVDFb wax wax wax wax wax wax wax wax wax PVDFb wax wax wax

10 10 3 50 10 8 5 50 10 10 5 5 5 20 8 30

1.9 2.0 4.0 2.5 3.0 3.0 3.0 2.2 2.5 2.0 2.75 3 2.0 2.5 3.0 2.0

12.28−18.00 11.72−17.44 8.48−12.80 9.00−12.00 9.20−15.00 10.80−17.20 8.00−12.88 8.80−12.10 11.60−18.00 11.50−16.50 unknown 7.10−10.40 11.28−17.28 5.50−16.00 10.20−16.90 10.90−15.40

5.72 5.72 4.32 3.00 5.80 6.4 4.88 3.30 6.40 5.00 3.50 3.30 6.00 10.50 6.70 4.50

this work this work 14 19 20 21 22 23 24 25 26 27 50 51 52 53

Reflection loss below −10 dB. bPolyvinylidene fluoride.

match between absorbers and free space is achieved.1,47,48 The RL values of MoS2/RGO (10 wt %)−wax composites with the thickness varying from 1.5 to 4 mm are shown in Figure 10a. The highest effective absorption bandwidth of 5.72 GHz is achieved for the composite at the thicknesses of 1.9 mm (12.28−18 GHz) and 2 mm (11.72−17.44 GHz), respectively (Figure 10b,c). The maximum reflection loss of −50.9 dB is observed at 11.68 GHz for a MoS2/RGO (10 wt %)−wax composite with a thickness of 2.3 mm (Figure 10d). In contrast to the high performance demonstrated by MoS2/ RGO (10 wt %)−wax composites, only weak electromagnetic wave absorption was exhibited by the composites of wax and pure RGO (10 wt %) (Figure S1). This implies that the introduction of MoS2 nanosheets into the RGO−wax composites has played a key role in improving the electromagnetic wave absorption

performance. It was found that the introduction of MoS2 nanosheets resulted in a significant decrease of the imaginary part of the permittivity of the composites (Figure 6 and S2), indicating the lowering of conductivity.49 We also noted that no characteristic of Debye relaxation was observed in the Cole− Cole plot of the RGO (10 wt %)−wax composite (Figure S3). This is in sharp contrast to that observed in the case of MoS2/ RGO (10 wt %)−wax composite (Figure 8c). Clearly, it is the multirelaxation that improves the electromagnetic wave absorption performance of the MoS2/RGO−wax composites. The electromagnetic wave absorption properties of MoS2/ RGO hybrid absorber together with other RGO-based materials reported in recent literatures were summarized in Table 1. In comparison with the recently reported other RGO-based materials, MoS2/RGO−wax composites exhibited superior performance at 26232


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(4) Wei, Y.; Wang, G.; Wu, Y.; Yue, Y.; Wu, J.; Lu, C.; Guo, L. Bioinspired Design and Assembly of Platelet Reinforced Polymer Films with Enhanced Absorption Properties. J. Mater. Chem. A 2014, 2, 5516− 5524. (5) Zhou, M.; Zhang, X.; Wei, J.; Zhao, S.; Wang, L.; Feng, B. Morphology-Controlled Synthesis and Novel Microwave Absorption Properties of Hollow Urchinlike α-MnO2 Nanostructures. J. Phys. Chem. C 2011, 115, 1398−1402. (6) Sun, G.; Dong, B.; Cao, M.; Wei, B.; Hu, C. Hierarchical DendriteLike Magnetic Materials of Fe3O4, γ-Fe2O3, and Fe with High Performance of Microwave Absorption. Chem. Mater. 2011, 23, 1587−1593. (7) Yang, H.; Cao, M.; Li, Y.; Shi, Z.; Hou, Z.; Fang, X.; Jin, H.; Wang, W.; Yuan, J. Enhanced Dielectric Properties and Excellent Microwave Absorption of SiC Powders Driven with NiO Nanorings. Adv. Opt. Mater. 2014, 2, 214−219. (8) Yang, H.; Cao, W.; Zhang, D.; Su, T.; Shi, H.; Wang, W.; Yuan, J.; Cao, M. NiO Hierarchical Nanorings on SiC: Enhancing Relaxation to Tune Microwave Absorption at Elevated Temperature. ACS Appl. Mater. Interfaces 2015, 7, 7073−7077. (9) Zhu, C.; Zhang, M.; Qiao, Y.; Xiao, G.; Zhang, F.; Chen, Y. Fe3O4/ TiO2 Core/Shell Nanotubes: Synthesis and Magnetic and Electromagnetic Wave Absorption Characteristics. J. Phys. Chem. C 2010, 114, 16229−16235. (10) Li, W.; Wang, L.; Li, G.; Xu, G. Hollow CoFe2O4-Co3Fe7 Microspheres Applied in Electromagnetic Absorption. J. Magn. Magn. Mater. 2015, 377, 259−266. (11) Shi, X.; Cao, M.; Yuan, J.; Zhao, Q.; Kang, Y.; Fang, X.; Chen, Y. Nonlinear Resonant and High Dielectric Loss Behavior of CdS/α-Fe2O3 Heterostructure Nanocomposites. Appl. Phys. Lett. 2008, 93, 183118. (12) Zheng, J.; Yu, Z.; Ji, G.; Lin, X.; Lv, H.; Du, Y. Reduction Synthesis of FexOy@SiO2 Core-shell Nanostructure with Enhanced MicrowaveAbsorption Properties. J. Alloys Compd. 2014, 602, 8−15. (13) Zhao, B.; Shao, G.; Fan, B.; Zhao, W.; Zhang, R. Investigation of the Electromagnetic Absorption Properties of Ni@TiO2 and Ni@SiO2 Composite Microspheres with Core-Shell Structure. Phys. Chem. Chem. Phys. 2015, 17, 2531−2539. (14) Zhang, X.; Wang, G.; Cao, W.; Wei, Y.; Cao, M.; Guo, L. Fabrication of Multi-functional PVDF/RGO Composites via a Simple Thermal Reduction Process and Their Enhanced Electromagnetic Wave Absorption and Dielectric Properties. RSC Adv. 2014, 4, 19594−19601. (15) Huang, X.; Hu, Z.; Liu, P. Graphene based Tunable Fractal Hilbert Curve Array Broadband Radar Absorbing Screen for Radar Cross Section Reduction. AIP Adv. 2014, 4, 117103. (16) Batrakov, K.; Kuzhir, P.; Maksimenko, S.; Paddubskaya, A.; Voronovich, S.; Lambin, P.; Kaplas, T.; Svirko, Y. Flexible Transparent Graphene/Polymer Multilayers for Efficient Electromagnetic Field Absorption. Sci. Rep. 2014, 4, 7191. (17) 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 Altralight and Highly Compressible Graphene Foam. Adv. Mater. 2015, 27, 2049. (18) Balci, O.; Polat, E. O.; Kakenov, N.; Kocabas, C. GrapheneEnabled Electrically Switchable Radar-Absorbing Surfaces. Nat. Commun. 2015, 6, 6628. (19) 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. (20) Hu, C.; Mou, Z.; Lu, G.; Chen, N.; Dong, Z.; Hu, M.; Qu, L. 3D Graphene-Fe3O4 Nanocomposites with High-Performance Microwave Absorption. Phys. Chem. Chem. Phys. 2013, 15, 13038−13043. (21) Zhang, H.; Xie, A.; Wang, C.; Wang, H.; Shen, Y.; Tian, X. Novel rGO/α-Fe2O3 Composite Hydrogel: Synthesis, Characterization and High Performance of Electromagnetic Wave Absorption. J. Mater. Chem. A 2013, 1, 8547−8552. (22) Zhang, X.; Wang, G.; Cao, W.; Wei, Y.; Liang, J.; Guo, L.; Cao, M. Enhanced Microwave Absorption Property of Reduced Graphene Oxide

a rather thin thickness, indicating the promising perspective of MoS2/RGO hybrid absorber in the development of lightweighted, thin electromagnetic wave absorbing coatings.

4. CONCLUSION In summary, hybrids of MoS2/RGO were prepared and their electromagnetic wave absorption performance was investigated for the first time. The hybrids of MoS2/RGO consist of large RGO plates and small MoS2 nanosheets. The dimensions of RGO plates range from several to more than 10 μm, whereas MoS2 nanoflakes extend two-dimensionally to only several hundred nanometers. The hybrids of MoS2/RGO exhibited superior electromagnetic wave absorption performance with high efficiency and broad bandwidth at thin thicknesses and low filler loadings. Impressively, an effective bandwidth of 5.72 GHz was observed for a wax-based sample containing 10 wt % MoS2/RGO hybrid with a thickness less than 2.0 mm. The highest reflection loss of a sample with the thickness of 2.3 mm reached −50.9 dB at 11.68 GHz. Taking the low cost and high stability into account, we think the hybrids of MoS2/RGO are promising electromagnetic wave absorbers and deserve further detailed investigations.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.5b08410. RL curves, relative complex permittivity, and Cole−Cole plot of RGO−wax composites with the filler loading of 10 wt % (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*F. Wu. E-mail: [email protected]. Tel: +86-25-80825493. *M. He. E-mail: [email protected]. Tel: +86-10-82545555. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No. 51403236), the Major State Basic Research Development Program of China (973 Program) (No. 2011CB932702), and the Opening Project of State Key Laboratory of Disaster Prevention & Mitigation of Explosion & Impact (DPMEIKF201310).

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REFERENCES

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