3D architecture reduced graphene oxide-MoS2 composite: Preparation and excellent electromagnetic wave absorption performance

3D architecture reduced graphene oxide-MoS2 composite: Preparation and excellent electromagnetic wave absorption performance

Composites: Part A 90 (2016) 424–432 Contents lists available at ScienceDirect Composites: Part A journal homepage: www.elsevier.com/locate/composit...

3MB Sizes 0 Downloads 21 Views

Composites: Part A 90 (2016) 424–432

Contents lists available at ScienceDirect

Composites: Part A journal homepage: www.elsevier.com/locate/compositesa

3D architecture reduced graphene oxide-MoS2 composite: Preparation and excellent electromagnetic wave absorption performance Xiao Ding a, Ying Huang a,⇑, Suping Li a, Na Zhang a, Jianguo Wang b a Department of Applied Chemistry and the Key Laboratory of Space Applied Physics and Chemistry, Ministry of Education, School of Science, Northwestern Polytechnical University, Xi’an 710072, PR China b School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, PR China

a r t i c l e

i n f o

Article history: Received 24 February 2016 Received in revised form 5 August 2016 Accepted 6 August 2016 Available online 9 August 2016 Keywords: A. Graphene B. Microstructures D. Microstructural analysis

a b s t r a c t High-performance electromagnetic absorbers with wide absorption band, strong absorption and lightweight are necessary for industry and military application. To obtain the desired materials, twodimensional (2D) atomic layers structure nanosheets, such as graphene and graphene-like, were adopted due to its unique structure and properties. Here, 3D architecture reduced graphene oxide-molybdenum disulfide (RGO-MoS2) composite was prepared by one-pot hydrothermal reaction. MoS2 generated on graphene oxide intercalation through hydrothermal process and rGO is obtained in the meanwhile. 3D architecture RGO-MoS2 composite can effectively prevent two-dimensional nanosheets re-stacked and can be applied in electromagnetic wave absorption field. In this paper, composites consist of RGO and various MoS2 were prepared and their electromagnetic performances were investigated for the first time. Maximum absorption bandwidth (RL < 10 dB) is 5.92 GHz with thickness of 2.5 mm. We may reasonably conclude that RGO-MoS2 composite can serve as excellent light-weight electromagnetic wave absorbers and can be widely used in practice. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction With the development of electronic devices and communication facilities and increasingly electromagnetic pollution, the electromagnetic wave absorption materials have been paid more and more attention all over the world. The most commonly used materials, such as metal and metal oxide nanoparticles materials, ferrite, polymer, inorganic nonmetallic materials, have made significant progress. Nanostructured 3D CeO2 were synthesized by using PEG 2000 assisted simple hydrothermal technique and minimum reflection loss with 19.3 dB was observed at 15.8 GHz with the thickness of 2.0 mm [1]. Wu et al. [2] reported preparation method of core-shell structured ɤ[email protected] nanorod-carbon sphere composites and the minimum reflection loss is 8.11 dB at 3.92 GHz. Zhang and co-workers [3] synthesized Co0.5Ni0.5Fe2O4/carbon nanotubes/polyimide and the thermostability was preserved up to 500 °C, the maximum reflection loss (RL) value of nanocomposites containing 0.75 wt% modified MWNTs was 24.37 dB and the frequency range where the RL value was less than 10 dB was 5.1 GHz from 7.8 to 12.9 GHz.

⇑ Corresponding author. E-mail address: [email protected] (Y. Huang). http://dx.doi.org/10.1016/j.compositesa.2016.08.006 1359-835X/Ó 2016 Elsevier Ltd. All rights reserved.

Since researchers extracted graphene from graphite using ordinary adhesive tape in 2004, it has developed at an astonishing speed in many areas during the past decade. As a new class and the thinnest material in the carbon family [4], graphene possesses not only a stable structure but also a large specific surface areas, high mechanical properties, charge carrier mobility, thermal conductivity and excellent electronic conductivity [5]. To date, graphene-based materials have great potential application in many fields due to its unique physical and chemical properties, such as electronic materials [6–8], catalyst [9], photocatalysts [10], lithium-ion batteries [11], microwave attenuation [12] and super capacitor [13]. Graphene oxide may be the best candidates for obtaining higher loss tangent and high efficiency EMI shielding due to abundant defects and hydroxyl, epoxy, and carboxyl groups [4] on the nanosheets. In the field of absorbing microwave, Zhang et al. [14] fabricate electrically conductive polymethylmethacrylate (PMMA) nanocomposite by using graphene sheets as the conducting filler and then to make the brittle nanocomposite ductile by foaming with the aid of subcritical CO2 foaming technique. Chen and co-workers [15] fabricated an ultra-lightweight and highly conductive graphene/polymer foam composite and its EMI shielding effectiveness is as high as 30 dB for a very low graphene loading of <0.8 wt%. Highly porous poly(dimethyl siloxane) (PDMS)

425

X. Ding et al. / Composites: Part A 90 (2016) 424–432

composites containing cellular-structured microscale graphene foams (GFs) and conductive nanoscale carbon nanotubes (CNTs) are fabricated [16]. The applications of graphene-based materials also triggered the recent flood of research on single- and few-layer of twodimensional nanosheets. Molybdenum disulfide (MoS2), a transition metal sulfide consists of S-Mo-S atomic layers stacked together by van der Walls interactions, can be exfoliated to single- or few-layer nanosheets [17,18]. Owing to the similar layered structure of MoS2 like graphene, MoS2 nanosheets have great potential to replace graphene [18]. Furthermore, graphene-MoS2 architecture nanosheets which combined graphene oxides with MoS2 may be provided unexpected performances [19]. But until now, few researches have considered this kind simple dielectric material. In the present work, 3D reduced graphene oxide-MoS2 architecture nanosheets (RGO-MoS2) were synthesized for light-weight electromagnetic wave absorption. The influence of each component contents in RGO-MoS2 composites on the electromagnetic wave absorption properties was studied. Graphene oxide was synthesized by Hummers’ method. 3D RGO-MoS2 architecture heterostructure were prepared through a simple hydrothermal process in this work. Compared with reported literatures, RGO-MoS2 composites exhibit excellent electromagnetic wave absorption performance, as shown in Table 1. Such a heterostructure averts the adjacent layers restacked together under van der Walls force and emergence of multiple interfaces is beneficial to

enhance the electromagnetic wave absorbing properties of the product.

2. Results and discussion The synthetic procedure of 3D architecture RGO-MoS2 composites is illustrated in Fig. 1. Graphite oxide was firstly produced by the modified Hummer’s method [28] from flake graphite and then dissolved in water to form the graphene oxide solution. Sodium molybdate (Na2MoO4) and thioacetamide (C2H5NS) were added into water and dissolved by agitating magnetically. Sodium molybdate and thioacetamide were chosen as the precursor for molybdenum and sulfur source, respectively. The resulting solutions were then mixed to co-assemble at temperature of 220 °C for 24 h in a Teflon-lined autoclave. 3D architecture RGO-MoS2 composites were prepared via one-pot hydrothermal method. During the hydrothermal process, C2H5NS reacts with water to generate hydrogen sulfide and then MoO2 4 anions were reduced by hydrogen sulfide under high temperature condition, forming MoS2 [18]. To optimize the absorption performance of the composites, the ratio of MoS2 to GO nanosheets was changed from 1:3 to 3:7, 1:2, and 2:3 by tuning the amount of Na2MoO4 in the synthesis process on condition that the content of thioacetamide is excessive. The synthesized composites were denoted as RGO-MoS2-0.25, RGO-MoS2-0.30, RGO-MoS2-0.33, and RGO-MoS2-0.40, respectively.

Table 1 Electromagnetic wave absorption properties of the RGO-MoS2 composites obtained in this work and graphene-based composite reported in literatures. Absorber

Method

Loading (wt%)

Max RL/thickness (dB/mm)

Bandwidth/thickness (<10 dB, GHz/mm)

3D rGOthis work work 3D MoSthis 2 3D rGO-MoS2-0.25this 3D rGO-MoS2-0.30this 3D rGO-MoS2-0.33this 3D rGO-MoS2-0.40this MoS2/RGO [20] 3D G-Fe3O4 [21] G-porous Fe3O4 [22] rGO-Hollow Fe3O4 [23] [email protected] ZnO [24] [email protected] [25] G/[email protected]/ZnO [26] RGO/Ni [27]

Hydrothermal Hydrothermal Hydrothermal Hydrothermal Hydrothermal Hydrothermal 650 °C/CS2 Hydrothermal Hydrothermal Hydrothermal 650 °C/Ar Hydrothermal 650 °C/Ar/H2 Hydrothermal

10 10 10 10 10 10 10 10 30 30 50 30 20 30

21.14/3.5 10.31/4.0 44.84/3.7 49.45/2.4 39.90/2.2 23.86/2.1 50.90/2.3 27.0/4.0 20.0/2.0 24.0/2.0 45.05/2.2 38.0/5.0 38.10/5.0 32.1/2.0

0.88/3.5 0.08/4.0 4.88/2.3 5.68/2.3 6.56/2.4 6.24/2.3 5.72/2.0 3.72/4.0 4.5/2.0 4.96/2.0 3.3/2.2 2.4/5.0 6.0/2.5 4.50/2.0

Fig. 1. Schematic illustration for the preparation of RGO-MoS2 composites. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

426

X. Ding et al. / Composites: Part A 90 (2016) 424–432

Fig. 2. (a) X-ray powder diffraction patterns of MoS2 and RGO-MoS2, (b) Raman spectra of graphite oxide (1), RGO-MoS2-0.25 (2), RGO-MoS2-0.30 (3), RGO-MoS2-0.33 (4), RGO-MoS2-0.40 (5). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

The X-ray powder diffraction (XRD) images of as-prepared MoS2 and RGO-MoS2 are shown in Fig. 2a. As for the prepared MoS2, the diffraction peaks of (0 0 2), (1 0 0), (1 0 6) and (1 1 0) planes can be indexed to the hexagonal phase MoS2 (JCPDS card No. 37-1492) [29]. Graphite oxide delivers a sharp and strong diffraction peak at 2h = 9.38° [30] which caused by oxidization of sp2-boned carbon in graphite nanosheets. However, the peak becomes weak in RGO-MoS2 composites due to the GO nanosheets could be easily reduced to RGO by H2S under hydrothermal conditions [31]. Diffraction peak of (0 0 2) plane located at about 25° did not diffract very well due to the reduction degree is not high. Raman spectroscopy of graphite oxide and RGO-MoS2 composites with various ratios of MoS2 are shown in Fig. 2b. It revealed the characteristic peaks of MoS2 at 382 cm1 and 407 cm1 (corresponding to the Eg and Ag vibration modes [32]) and the G and D bands of graphite oxide in the 3D architecture composites. The ID/IG value of RGO-MoS2 composites is higher than that of pure graphite oxide confirming the reduction reaction of graphene oxide in composites occurs during high temperature and pressure condition. The D peak position of the RGO-MoS2 composites exhibit slight left shifting compared to graphite oxide, frequency difference of two characteristic peaks (D and G band of RGO) is marked as 4. The 4 values were calculated to be 226 cm1, 237 cm1, 245 cm1, 234 cm1 and 251 cm1 for graphite oxide, RGO-MoS2-0.25, RGO-MoS2-0.30, RGO-MoS2-0.33, RGO-MoS2-0.40, respectively. This phenomenon provides evidence of the interface between MoS2 and graphite oxide [33,34] and the charger transfer [35,36] between the interface of rGO and MoS2 nanoshheets. Thus, the frequency difference of two characteristic peaks demonstrates the surface spacing of reduced graphene oxide increase with the addition of molybdenum disulfide. It is known that the position of Raman peak illustrates the existence of a certain group and the shift of peak position is affected by the adjacent groups. For RGO-MoS2 composites, the distribution of electron cloud of reduced graphene oxide nanosheets changed due to the addition of molybdenum disulfide (the generation of C-S/Mo, as shown in Fig. 3), so the locations of the characteristic peaks of reduced graphene oxide are shift. X-ray photoelectron spectroscopy (XPS) also provides the evidence on reduction of GO to RGO and the formation of MoS2 during hydrothermal process. The survey scan spectrum of RGO-MoS2-0.33 in Fig. 3b indicates that the prepared composite consists of C, O, Mo and S elements. The high-resolution C 1s spectrum of RGO-MoS2-0.33 (Fig. 3c) shows four peaks by typical curve fitting. The strong peak centered at 284.6 cm1 can be assigned to CAC/[email protected] (sp2-hybridized carbon atoms [37]) in GO nanosheets. The peak located at 285.6 cm1 is attributed to CAS/Mo (carbon atoms not bound to sulfur [38]) and the peaks at 286.5 cm1 and

288.8 cm1 can be viewed as stretching vibration of CAO and [email protected], respectively. In comparison with the C 1s spectrum of GO (shown in Fig. 3a), the content of CAO in the composite decreased rapidly and the result illustrates that oxygencontaining functional group has been significantly removed in the composite and the reduction of GO to RGO. The binding energies of Mo 3d5/2 and Mo 3d3/2 peaks in the composite are located at 229.0 eV and 232.2 eV, respectively, suggesting the formation of Mo4+. The peaks of S 2p spectrum located at 161.9 eV and 163.1 eV are attributed to S 2p3/2 and S 2p1/2, respectively. Core level spectra of Mo and S shown in Fig. 3d and e proves the presence of MoS2. The morphology and microstructure of the as-synthesized MoS2 and the 3D architecture RGO-MoS2-0.33 composite were investigated by field-emission scanning electron microscopy. Fig. 4a shows the prepared two-dimensional nano materials MoS2 selfaggregated to form clusters. Furthermore, it indicates large amount of uniform MoS2 nanosheets can be synthesized by hydrothermal process [18]. During the hydrothermal condition, 3D architecture RGO-MoS2 composite was successfully prepared while adding 2D graphene oxide nanosheets and MoS2 nanosheets as the building block, as shown in Fig. 4b. Moreover, 3D architecture structure can efficiently hamper aggregation and possess interconnected pores which are benefited for the multiple reflection of electromagnetic wave. Further microstructure information about the prepared samples was obtained via transmission electron microscopy (TEM). Fig. 5a shows GO nanosheets are transparent lamellar nanostructure with a few wrinkles on the surface. For pure MoS2, the structure of nanosheets likes flower and the morphology mimics exactly that of a single graphene oxide nanosheet with wrinkles and scrolling, as shown in Fig. 5b and c. In addition, compare with graphene oxide nanosheets, the MoS2 are more rigid and pure MoS2 architecture cannot be built by using MoS2 nanosheets alone. However, the inherent flexibility of graphene oxide originated from the defective structures generated from the preparation process and the functional groups are crucial for constructing the 3D architecture composite [19]. Fig. 5d and e is low-magnification TEM images of RGO-MoS2-0.33 composite. The thin MoS2 nanosheets are evenly dispersed in GO nanosheets, forming the 3D nanosheets network. The HRTEM image in Fig. 5f shows the crystallite structure of the composite and the distance were calculated to be 0.60 nm which can be assigned to the (0 0 2) interplanar distance of MoS2 crystalline structure in the hybrid architecture. The electromagnetic wave absorption properties of the RGO-MoS2–paraffin composite containing 10 wt% RGO-MoS2 composites were investigated in the frequency range of 2–18 GHz. According to the transmit-line theory, the reflection loss (RL) can

X. Ding et al. / Composites: Part A 90 (2016) 424–432

427

Fig. 3. XPS spectra of C 1s of GO (a), survey scan (b), C 1s (c), Mo 3d (d), S 2p and (e) spectrum of RGO-MoS2-0.33. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4. Typical FESEM images of MoS2 (a) and RGO-MoS2-0.33 composite (b).

be calculated from the relative permeability (lr), relative permittivity (er) and the thickness (d) of circular ring sample by the following equations [39].

  Z in  1   RL ðdBÞ ¼ 20 log  Z in þ 1 Z in ¼

qffiffiffiffiffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffiffiffi lr =er tan h½jð2pfd=cÞ er lr

ð1Þ ð2Þ

er ¼ e1 þ

es  e1 ¼ e0  e00 1 þ j2pf s

ð3Þ

where Zin is the input impedance of the composite, f is the frequency of incident electromagnetic waves, c is the velocity of light in free space. Fig. 6 shows the RL curves and 3D plots of the RGO-MoS2 composites with the thickness of 1.5–4.0 mm. For RGO-MoS2-0.25, the maximum RL value of 41.53 dB is observed at 11.36 GHz with the thickness of 3.0 mm. The maximum RL value

428

X. Ding et al. / Composites: Part A 90 (2016) 424–432

Fig. 5. Low-magnification TEM images of Graphene oxide (a), MoS2 (b and c), and 3D architecture RGO-MoS2-0.33 composite (d and e). High-resolution TEM image of RGO-MoS2-0.33 composite. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

of RGO-MoS2-0.30-paraffin composite, RGO-MoS2-0.33-paraffin composite and RGO-MoS2-0.40-paraffin composite with the thickness of 2.0 mm is 36.28 dB, 32.91 dB and 23.57 dB, respectively. The maximum absorption bandwidth (RL values below 10 dB, 90% attenuation of the electromagnetic energy) of the RGO-MoS2 composites is different and the maximum value is 5.92 GHz with 2.5 mm thickness. From the above we can conclude that the electromagnetic wave absorption performance of the composite can be controlled by changing the dosage of MoS2. Moreover, the electromagnetic wave absorption properties of both reduced graphene oxide and molybdenum disulfide were investigated in the frequency range of 2–18 GHz. For reduced graphene oxide, the maximum reflection loss is 21.14 dB with the thickness of 3.5 mm and the corresponding bandwidth is 0.88 GHz, as shown in Fig. 7a. It can be seen in Fig. 7b, the maximum reflection loss of molybdenum disulfide is 10.31 dB when the thickness is 4.0 mm. Therefore, 3D architecture RGO-MoS2 composites exhibit enhanced electromagnetic wave absorption properties in terms of both the maximum absorption bandwidth and the reflection loss. The increased interfaces existed in 3D architecture RGO-MoS2 composites extended the transmission path of electromagnetic wave and it is beneficial to reflected EMW and attenuate EM energy. In addition, compared with other graphene-based composites such as graphene-wrapped ZnO hollow spheres [24], graphenecarbonyl iron [40], RGO-Fe3O4 [41], [email protected] [25] and G/[email protected]/ZnO [26], RGO-MoS2 composites exhibit excellent electromagnetic wave absorption properties. More it is worth mentioning that RGO-MoS2 composites can be used as light-weight absorbing materials due to the added weight of these composites in the paraffin matrix is only 10 wt%. For example, the RL values of G/[email protected]/ZnO are larger than 39 dB and the corresponding bandwidth is about 3.0 GHz as the thickness is 5.0 mm when the quaternary composite weight in paraffin matrix is 20 wt% [26]. When the weight ratio of RGO-Fe3O4 and paraffin is 2:3, the maximum value is 26.4 dB and the bandwidths corresponding to the

reflection losses below 10 dB are 2 GHz with the thickness is 4.0 mm [41]. As we all know, the real part and imaginary part represent the storage and loss of electric energy, respectively. Fig. 8a and b shows the frequency dependence of e0 and e00 at the given frequency. The real part (e0 ) values of RGO-MoS2-0.25 paraffin composite declines from 8.04 to 5.01 with the increasing frequency in 2–18 GHz except several fluctuations in the frequency range of 8–9 GHz and 11–16 GHz. The real part (e0 ) values of paraffin composite containing 10 wt% RGO-MoS2-0.30, RGO-MoS2-0.33, RGO-MoS2-0.40 are in the range of 9.32–4.65, 9.45–4.55, 9.08–4.53, respectively. The imaginary part (e00 ) values of the RGO-MoS2 composites are in the range of 6.15–2.01, 10.04–2.24, 10.19–2.58, 12.78–3.07 in the 2–18 frequency range. As shown in Fig. 8c, dielectric loss tangent (tan de = e00 /e0 ) values are in the range of 0.78–0.37 (RGO-MoS2-0.25), 1.08–0.44 (RGO-MoS2-0.30), 1.09–0.49 (RGO-MoS2-0.33), 1.40–0.58 (RGO-MoS2-0.40). The electrical conductivities of the samples were measured by four probe conductivity meter. The conductivity of RGO-MoS2-0.25, RGO-MoS2-0.30, RGO-MoS2-0.33 and RGO-MoS2-0.40 are 65.53 S/m, 91.66 S/m, 113.3 S/m and 333.4 S/m, respectively. According to the free electric theory, relative permittivity is related to the electrical conductivity: e00 = r(2pfe0)1, where r is the electrical conductivity of absorber, e0 is the permittivity of free space, f is the frequency of the electromagnetic wave. Thus, the higher e00 values may be determined by its high conductivity. Electrical conductivity of RGO-MoS2 composites is mainly caused by reduced graphene oxide due to the conductivity of molybdenum disulfide is poor. With the increase amount of thioacetamide, more hydrogen sulfide gas produced and the bigger degree of reduction of graphene oxide nansheets are obtained in the hydrothermal process. Absorbing performance is determined by the dielectric loss due to magnetic materials does not exist in the composite. For RGO-MoS2 composites, dielectric loss is the only factor that affects the absorbing performance. In order to investigate and

X. Ding et al. / Composites: Part A 90 (2016) 424–432

429

Fig. 6. Reflection loss curves and 3D plots of G-MoS2-0.25 (a), G-MoS2-0.30 (b), G-MoS2-0.33 (c) and G-MoS2-0.40 (d) with filler loading of 10 wt% composite samples in paraffin wax matrix. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 7. Reflection loss curves of reduced graphene oxide (a) and molybdenum disulfide (b). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

430

X. Ding et al. / Composites: Part A 90 (2016) 424–432

Fig. 8. The frequency dependence of the real part (a), imaginary part (b) and dielectric loss tangent (c) of relative permittivity of the RGO-MoS2-paraffin composite. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

better understand the possible mechanism of the enhanced electromagnetic wave absorption properties of G-MoS2 composite, Cole–Cole semicircle curves are presented in Fig. 9. Cole–Cole semicircle curves illustrate the phenomena of dielectric relaxation exist in the composite. As for the Debye dipolar relaxation, the semicircles can be explained according to the following equation:



e0 

es þ e1 2 2

2

þ ðe00 Þ ¼

e  e 2 s 1 2

ð4Þ

where es is the relative dielectric permittivity at the high frequency limit and e1 is static permittivity. Each semicircle represents one Debye relaxation process.

At least two Cole–Cole semicircles are clearly found in the e0 -e00 curves of the RGO-MoS2 composites, which represented multidielectric relaxation processes and demonstrated the contribution of the Debye relaxation process to the enhanced dielectric properties of the RGO-MoS2 composites [20,42]. The dielectric loss is mainly due to interfacial polarization and polarization in the electromagnetic frequency range [43,44]. And large part of electromagnetic energy is attenuated due to the resistance of reduced graphene oxide and molybdenum disulfide. In the 3D architecture composite, the presence of interfaces between GO and MoS2 nanosheets and the accumulation of charges at the interface generates interfacial polarization. In addition, the defects on reduced

Fig. 9. Typical Cole–Cole semicircle curve of G-MoS2-0.25 (a), G-MoS2-0.30 (b), G-MoS2-0.33 (c) and G-MoS2-0.40 (d). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

X. Ding et al. / Composites: Part A 90 (2016) 424–432

graphene oxide nanosheets act as the dipole center and bring out dipole polarization [45]. However, the distorted semicircle may be due to other loss mechanisms (conductance loss, oxygen defects and interfacial polarization) existed except the dielectric relaxation mechanism [42]. Meanwhile, the synergy effect of two components in RGO-MoS2 composites may play a very important role for attenuation electromagnetic energy. 3. Conclusion In summary, 3D architecture RGO-MoS2 composites with various amount of MoS2 were prepared by one-pot hydrothermal reaction. The formation of molybdenum disulfide and reduction of graphene oxide happens during hydrothermal process. RGO-MoS2 composite exhibits excellent electromagnetic wave absorption properties in terms of both maximum reflection loss value and absorption bandwidth when evaluated as electromagnetic wave absorbers. For paraffin composite with 10 wt% filler loading of RGO-MoS2-0.33, the maximum reflection loss value reaches 31.57 dB and the maximum absorption bandwidth (RL < 10 dB) is 5.92 GHz with thickness of 2.5 mm. As stated above, it is believed that 3D architecture RGO-MoS2 composite can serve as excellent light-weight electromagnetic wave absorbers. 4. Experimental section Chemicals: sodium molybdate (Na2MoO42H2O), thioacetamide (C2H5NS) were purchased from Aladdin Industrial Inc. All chemicals are of analytical grade and used without further purification. The aqueous solutions were freshly prepared using high purity water (resistivity of >18 MX cm). Synthesis of RGO-MoS2 nanosheets: 66 mg Na2MoO42H2O and 132 mg C2H5NS were dissolved in 25 mL water to form a transparent solution by agitating magnetically. Then 45 mL GO solution (2 mg/mL) was added into the above solution and stirred for 6 h. the solution was transferred to an 80 mL Teflon-lined stainless steel autocalve and hydrothermally treated in an electric oven at 220 °C for 24 h. As-prepared black precipitates were harvested after centrifugation and freeze-dried to get RGO-MoS2 composite, denoted as (G-MoS2-0.33). Using the same procedures, G-MoS20.25, G-MoS2-0.30 and G-MoS2-0.40 were prepared with varying amount of MoS2. Characterization: Powder X-ray diffraction patterns were recorded on a powder diffractometer (Rigaku, model D/max-2500 system) at 40 kV and 100 mA of Cu Ka. The morphology and microstructure were investigated by Field emission scanning electron microscopy (FESEM, SuPRA 55, German ZEISS) equipped with an energy dispersive spectroscopy system and transmission electron microscopy (TEM, Tecnai F30 G2, FEI, USA). The Raman spectra of the composites were collected on Laser Raman spectrometer (InVia Reflex; Renishaw Company, London, England). X-ray photoelectron spectroscopy was characterized by X-ray photoelectron spectrometer (XPS, ESCALAB 250, Thermofisher Co). The electromagnetic parameters (relative complex permittivity, er and relative complex permeability, lr) were measured by a vector network analyzer (NA, HP8720ES, Agilent) in the frequency range of 2– 18 GHz. In a coaxial wire analysis, the measured composites mixed with paraffin matrix in a certain proportion and pressed into toroidal shaped samples (uout: 7.00 mm; uin: 3.04 mm). Acknowledgements This work was financially supported by the Aerospace Innovation Fund of the P.R. China (2014KC11023) and the Spaceflight Support Technology Fund of China (No. 2014-HT-XGD).

431

References [1] Wu GL, Cheng YH, Xiang F, Jia ZR, Xie Q, Wu GQ, Wu HJ. Morphology-controlled synthesis, characterization and microwave absorption properties of nanostructured 3D CeO2. Mater Sci Semicon Proc 2016;41:6–11. [2] Wu GL, Cheng YH, Ren YY, Wang YQ, Wang ZD, Wu HJ. Synthesis and characterization of [email protected] nanorod-carbon sphere composite and its application as microwave absorbing material. J Alloy Compd 2015;652:346–50. [3] Zhang L, Shi CS, Rheec KY, Zhao NQ. Properties of Co0.5Ni0.5Fe2O4/carbon nanotubes/polyimide nanocomposites for microwave absorption. Composites A 2012;12:2241–8. [4] Wen B, Cao M, Lu M, Cao W, Shi H, Liu J, Wang X, Jin H, Fang X, Wang X, Yuan J. Reduced graphene oxides: light-weight and high-efficiency electromagnetic interference shielding at elevated temperatures. Adv Mater 2014;26:3484–9. [5] Cao M, Wang X, Cao W, Yuan J. Ultrathin graphene: electrical properties and highly efficient electromagnetic interference shielding. J Mater Chem C 2015;3:6589. [6] Kim KS, Zhao Y, Jang H, Lee SY, Kim JM, Kim KS, Ahn JH, Kim P, Choi JY, Hong BH. Large-scale pattern growth of graphene films for stretchable transparent electrodes. Nature 2009;457:706–10. [7] Eda G, Fanchini G, Chhowalla M. Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material. Nat Nanotechnol 2008;3:270–4. [8] Wang X, Zhi L, Müllen K. Transparent, conductive graphene electrodes for dyesensitized solar cells. Nano Lett 2008;1:323–7. [9] Liang Y, Li Y, Wang H, Zhou J, Wang J, Regier T, Dai H. Co3O4 nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction. Nat Mater 2011;10:780–6. [10] Williams G, Seger B, Kamat PV. TiO2-graphene nanocomposites. UV-assisted photocatalytic reduction of graphene oxide. ACS Nano 2008;7:1487–91. [11] Paek S, Yoo E, Honma I. Enhanced cyclic performance and lithium storage capacity of SnO2/graphene nanoporous electrodes with three-dimensionally delaminated flexible structure. Nano Lett 2009;1:72–5. [12] Wang L, Huang Y, Sun X, Huang H, Liu P, Zong M, Wang Y. Synthesis and microwave absorption enhancement of [email protected]@[email protected] nanosheet hierarchical structures. Nanoscale 2014;6:3157–64. [13] Wang Y, Shi Z, Huang Y, Ma Y, Wang C, Chen M, Chen Y. Supercapacitor devices based on graphene materials. J Phys Chem C 2009;30:13103–7. [14] Zhang HB, Yan Q, Zheng WG, He ZX, Yu ZZ. Tough graphene-polymer microcellular foams for electromagnetic interference shielding. ACS Appl Mater Interfaces 2011;3:918–24. [15] Chen ZP, Xu C, Ma CQ, Ren WC, Cheng HM. Lightweight and flexible graphene foam composites for high-performance electromagnetic interference shielding. Adv Mater 2013;25:1296–300. [16] Sun XY, Liu X, Shen X, Wu Y, Wang ZY, Kim JK. Graphene foam/carbon nanotube/poly(dimethyl siloxane) composites for exceptional microwave shielding. Composites A 2016;85:199–206. [17] Zhou W, Yin Z, Du Y, Huang X, Zeng Z, Fan Z, Liu H, Wang J. Synthesis of fewlayer MoS2 nanosheet-coated TiO2 nanobelt heterostructures for enhanced photocatalytic activities. Small 2013;9:140–7. [18] Chen Y, Song B, Tang X, Lu L, Xue J. Ultrasmall Fe3O4 nanoparticle/MoS2 nanosheet composites with superior performances for lithium ion batteries. Small 2014;10:1536–43. [19] Gong Y, Yang S, Zhan L, Ma L, Vajtai R, Ajayan PM. A bottom-up approach to build 3D architectures from nanosheets for superior lithium storage. Adv Funct Mater 2014;24:125–30. [20] Wang YF, Chen DL, Yin X, Xu P, Wu F, He M. Hybrid of MoS2 and reduced graphene oxide: a lightweight and broadband electromagnetic wave absorber. ACS Appl Mater Interfaces 2015;7:26226–34. [21] Hu CG, Mou ZY, Lu GW, Chen N, Dong ZL, Hua MJ, Qu LT. 3D graphene–Fe3O4 nanocomposites with high-performance microwave absorption. Phys Chem Chem Phys 2013;15:13038. [22] Sun DP, Zou Q, Qian GQ, Sun C, Jiang W, Li FS. Controlled synthesis of porous Fe3O4-decorated graphene with extraordinary electromagnetic wave absorption properties. Acta Mater 2013;61:5829–34. [23] Xu HL, Bi H, Yang RB. Enhanced microwave absorption property of bowl-like Fe3O4 hollow spheres/reduced graphene oxide composites. J Appl Phys 2012;111:07A522. [24] Han MK, Yin XW, Kong L, Li M, Duan WY, Zhang LT, Cheng LF. Graphenewrapped ZnO hollow spheres with enhanced electromagnetic wave absorption properties. J Mater Chem A 2014;2:16403–9. [25] Sun DP, Zou Q, Wang YP, Wang YJ, Jiang W, Li FS. Controllable synthesis of porous [email protected] sphere decorated graphene for extraordinary electromagnetic wave absorption. Nanoscale 2014;6:6557–62. [26] Ren YL, Wu HY, Lu MM, Chen YJ, Zhu CL, Gao P, Cao MS, Li CY, Ouyang QY. Quaternary nanocomposites consisting of graphene, [email protected] [email protected], and ZnO nanoparticles: synthesis and excellent electromagnetic absorption properties. ACS Appl Mater Interfaces 2012;4:6436–42. [27] Liu G, Jiang W, Sun D, Wang YP, Li FS. One-pot synthesis of urchinlike Ni nanoparticles/RGO composites with extraordinary electromagnetic absorption properties. Appl Surf Sci 2014;314:523–9. [28] Hummers WS, Offema RE. Preparation of graphitic oxide. J Am Chem Soc 1958;80:1339.

432

X. Ding et al. / Composites: Part A 90 (2016) 424–432

[29] Li Y, Wang H, Xie L, Liang Y, Hong G, Dai H. MoS2 nanoparticles grown on graphene: an advanced catalyst for the hydrogen evolution reaction. J Am Chem Soc 2011;19:7296–9. [30] Ding X, Huang Y, Wang J, Wu H, Liu P. Excellent electromagnetic wave absorption property of quaternary composites consisting of reduced graphene oxide, polyaniline and [email protected] nanoparticles. Appl Surf Sci 2015;908–914. [31] Chang K, Chen W. Single-layer MoS2/graphene dispersed in amorphous carbon: towards high electrochemical performances in rechargeable lithium ion batteries. J Mater Chem 2011;21:17175–84. [32] Liang Y, Feng R, Yang S, Ma H, Liang J, Chen J. Rechargeable Mg batteries with graphene-like MoS2 cathode and ultrasmall Mg nanoparticle anode. Adv Mater 2011;5:640–3. [33] Lee CG, Yan HG, Brus LE, Heinz TF, James H, Ryu S. Anomalous lattice vibrations of single-and few-layer MoS2. ACS Nano 2010;4:2695–700. [34] Lv HL, Ji GB, Liang XH, Zhang HQ, Du YW. A novel rod-like [email protected] loading on graphene giving excellent electromagnetic absorption properties. J Mater Chem C 2015;3:5056–64. [35] Lv HL, Ji GB, Liu W, Zhang HQ, Du YW. Achieving hierarchical hollow [email protected]@Fe3O4 nanospheres with superior microwave absorption properties and lightweight features. J Mater Chem C 2015;3:10232–41. [36] Gong YJ, Yang SB, Zhan L, Ma LL, Vajtai R, Ajayan PM. A bottom-up approach to build 3D architectures from nanosheets for superior lithium storage. Adv Funct Mater 2014;24:125–30. [37] Qiu W, Jiao J, Xia J, Zhong H, Chen L. A self-standing and flexible electrode of yolk-shell CoS2 spheres encapsulated with nitrogen-doped graphene for highperformance lithium-ion batteries. Chem - Eur J 2015;11:4359–67.

[38] Wiegand BC, Roberts CMF, Roberts JT. Adsorbate thermodynamics as a determinant of reaction mechanism: pentamethylene sulfide on Mo (110). Langmuir 1989;5:1292–8. [39] Yang Y, Xu C, Xia Y, Wang T, Li F. Synthesis and microwave absorption properties of FeCo nanoplates. J Alloy Compd 2010;1–2:549–52. [40] Zhu ZT, Sun X, Xue HR, Guo H, Fan XL, Pan XC, He JP. Graphene–carbonyl iron cross-linked composites with excellent electromagnetic wave absorption properties. J Mater Chem C 2014;2:6582–91. [41] Sun X, He JP, Li GX, Tang J, Wang T, Guo YX, Xue HR. Laminated magnetic graphene with enhanced electromagnetic wave absorption properties. J Mater Chem C 2013;1:765–77. [42] Zong M, Huang Y, Zhao Y, Sun X, Qu C, Luo D, Zheng J. Facile preparation, high microwave absorption and microwave absorbing mechanism of RGO–Fe3O4 composites. RSC Adv 2013;45:23638. [43] Tang X, Hu K. Preparation and electromagnetic wave absorption properties of Fe-doped zinc oxide coated barium ferrite composites. Mater Sci Eng B 2007;2–3:119–23. [44] Ding X, Huang Y, Wang JG. Synthesis of FeNi3 nanocrystals encapsulated in carbon nanospheres/reduced graphene oxide as a light weight electromagnetic wave absorbent. RSC Adv 2015;5:64878–85. [45] Lv H, Ji G, Liu W, Zhang H, Du Y. Achieving hierarchical hollow [email protected]@Fe3O4 nanospheres with superior microwave absorption properties and lightweight features. J Mater Chem C 2015;3:10232–41.