graphene composites with good electromagnetic microwave absorbing performances

Author’s Accepted Manuscript Hydrothermal Fe3O4/graphene electromagnetic performances

synthesis of magnetic composites with good microwave absorbing

Lingyu Zhu, Xiaojun Zeng, Xiaopan Li, B. Yang, Ronghai Yu www.elsevier.com/locate/jmmm

PII: DOI: Reference:

S0304-8853(16)32427-1 http://dx.doi.org/10.1016/j.jmmm.2016.11.063 MAGMA62138

To appear in: Journal of Magnetism and Magnetic Materials Received date: 2 October 2016 Revised date: 13 November 2016 Accepted date: 14 November 2016 Cite this article as: Lingyu Zhu, Xiaojun Zeng, Xiaopan Li, B. Yang and Ronghai Yu, Hydrothermal synthesis of magnetic Fe 3O4/graphene composites with good electromagnetic microwave absorbing performances, Journal of Magnetism and Magnetic Materials, http://dx.doi.org/10.1016/j.jmmm.2016.11.063 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Hydrothermal synthesis of magnetic Fe3O4/graphene composites with good electromagnetic microwave absorbing performances Lingyu Zhu1, Xiaojun Zeng1, Xiaopan Li, B. Yang*, Ronghai Yu* School of Materials Science and Engineering, Beihang University, Beijing 100191, China

[email protected] [email protected] *

Corresponding Author.

ABSTRACT The Fe3O4 sub-microspheres have been embedded uniformly into the reduced graphene oxide (rGO) to form a new-type Fe3O4/rGO composites through a one-pot solvothermal method. The dielectric properties for these magnetic Fe3O4/rGO composites can be greatly tuned by their different rGO additions. A good impedance matching from the balanced dielectric and magnetic loss is achieved in the Fe3O4/rGO composites with 4 wt% rGO addition, which dominates their excellent microwave absorbing performances including the minimum reflection loss (RL) value of -45 dB at a frequency of 8.96 GHz with a sample thickness of 3.5 mm and an effective absorption bandwidth of 3.2 GHz (below -10 dB) superior to those of the most magnetic materials and carbon-based composites. The controlled Fe3O4/rGO composite structure also exhibits high chemical stability and low density, which shows

1

great

potential

application

in

These authors contributed equally to this work. 1

high-performance

electromagnetic

microwave-absorbing materials. Keywords: Fe3O4/rGO composites; One-pot solvothermal method; Dielectric properties; Excellent microwave absorbing performances; Magnetic hysteresis

1. Introduction The electromagnetic (EM) microwave absorption materials have always attracted much research interests because of their wide applications in numerous technical fields including wireless data communication, radar system and local area networks [1,2]. Nowadays, the increasing problems occurring in various EM devices due to the material limits further promote the research of new EM microwave absorption materials [3]. The ferrite-based materials have been widely used as EM microwave absorption materials by virtue of their proper microwave absorption abilities. It has been reported that the optimal minimum reflection loss (RL) value of Fe3O4 nanowires can reach -17.2 dB at 6.2 GHz with a sample thickness of 5.5 mm [4] and the RL value for a conductive PANI/MnFe2O4 nanocomposite can be improved to be -15.3 dB at 10.4 GHz with a thickness of 1.4 mm [5]. As is known, the ideal EM microwave absorption materials should meet the requirements of the strong absorption, wide absorption bandwidth, thin thickness, light weight and high thermal stability [6,7], however, all of which can be hardly realized simultaneously in single-component materials. The carbon-based magnetic composites for EM microwave absorption materials 2

have received intensive study due to their good magnetic and dielectric properties along with lightweight and chemical stability [8,9]. Many preparation methods such as solvothermal method [10] physical mixing [11], chemical synthesis [12], CVD [13] and arc discharge [14] have been developed to prepare various carbon-based composite materials. It has been reported that the graphene as a typical two-dimensional carbon material shows excellent electronic, thermal and mechanical properties and can be used as an effective part to construct various carbon-based composites applied in several technical areas such as the transistors, supercapacitors, gas sensors and energy storage [15,16]. Recently, several graphene-based magnetic nanocomposites have been reported to show good microwave absorbing properties [17,18]. Typically, the rGO/Fe2O3 composites prepared by solution phase technique have been found to exhibit the RL value of about -33.5 dB at 7.12 GHz with a thickness of 5 mm [9]. Moreover, the graphene/Fe nanocomposites have been reported to show a minimum RL value of about -31.5 dB at 14.2 GHz with a thickness of 2.5 mm [14]. However, it is still necessary to develop the effective methods for fabricating new carbon-based magnetic composites with desired structure and excellent wave absorbing properties to meet the requirements for their actual application. In this work, we have reported a one-pot solvothermal method to synthesize magnetic Fe3O4/rGO composites exhibiting good microwave absorbing performances. The high-purity Fe3O4 sub-microspheres can be embedded uniformly into the rGO sheets to form a new-type conducting Fe3O4/rGO 3D networks. The dielectric 3

properties for Fe3O4/rGO composites can be tuned by the different rGO additions so as to regulate their absorbing performances. The correlation between the microstructure, magnetic properties and microwave absorbing performances for these Fe3O4/rGO composites were also investigated systematically.

2. Experimental section 2.1. Synthesis of Fe3O4/rGO The main raw materials including ferric chloride hexahydrate (FeCl3·6H2O), sodium acetate (NaAc), sodium dodecylbenzenesulfonate (SDBS), potassium persulfate (K2S2O8), phosphorus pentoxide (P2O5), sodium nitrate (NaNO3), potassium permanganate (KMnO4) and ethylene glycol (EG) were purchased from Sinopharm Chemical Reagent Co., Ltd. The graphite powders (200 mesh) were purchased from Alfa Aesar. All the chemicals used in the experiment receive no further purification. Firstly, the initial GO sheets were prepared from the graphite powders by a modified Hummers method [18]. Then, the Fe3O4/rGO nanocomposites with high-purity Fe3O4 sub-microspheres embedded uniformly in the rGO sheets have been synthesized by a facile hydrothermal method. Typically, the SDBS (0.33 g) was added into EG (32 mL) to form a homogeneous solution under magnetic stirring at room temperature. A certain amount of GO sheets was added into the above solution with stirring for 5 min and then the mixture was treated ultrasonically for 20 min. Afterwards, a suitable amount of FeCl3·6H2O (1.08 g) and NaAc (1.97 g) were added 4

into the newly treated solution with vigorous stirring for 15 min to form a homogeneous solution. The obtained solution was transferred into a Teflon-lined stainless steel autoclave and then maintained at 180 °C for 8 h in an oven. After cooling the cave, the black precipitates were collected and washed with deionized water and ethanol for several times. The final products were obtained by drying the wet precipitates in a vacuum oven at 40 °C for 12 h. For investigating the different effects of the rGO additions on the absorbing properties for the products, several Fe3O4/rGO composites with varying the rGO contents from 0 to 5 wt% were prepared through the same route described above. 2.2. Characterization The phase structure of the Fe3O4/rGO composites was characterized by X-ray diffraction (XRD) using a Rigaku D/max 2500PC X-ray diffractometer with Cu Kα radiation. The microstructure of the samples was observed by a field emission scanning electron microscopy (FESEM, JSM-7500F, JEOL) and a transmission electron microscopy (TEM, JEM-2100, JEOL). The room temperature magnetic properties of the samples were measured by a vibrating sample magnetometer (VSM, Lakeshore 7307) under a maximum magnetic field of 10 kOe. 2.3. Wave absorbing measurements The measured samples for microwave absorption measurements were prepared by mixing the products (50 wt%) and the paraffin wax (50 wt%) to get a uniform composites and then compressing them into a toroidal sample (Φin = 3 mm and Φout = 7 mm) with thickness of 2.5−3.5 mm. The EM parameters including complex 5

effective permittivity (εr) and permeability (μr) for the toroidal samples were measured by an Agilent N5230C network analyzer at the frequency range of 2−18 GHz. The RL values for the samples can be calculated from their measured effective εr and μr at the given frequency and the absorber thicknesses according to the transmission line theory as following equations [19]: Zin = Z0(μr/εr)1/2tanh[j(2πfd/c)(μrεr)1/2]

(1)

RL = 20log(Zin − Z0)/(Zin + Z0)

(2)

where Zin is the input impedance for the absorber, Z0 is the free-space impedance, μr and εr are the effective relative complex permeability and permittivity, f is the frequency of EM wave, d is the absorber thickness, and c is the light velocity.

3. Results and discussion 3.1. Characterization of the samples Fig. 1 shows the XRD patterns of the as-synthesized products without and with different rGO contents of 3 wt%, 4 wt% and 5 wt%. As shown in Fig. 1(a), all the diffraction peaks for the sample without rGO addition can be only indexed to the face-centered cubic (fcc) Fe3O4 phase (JCPDS card no. 79-0419), which indicates that well-crystallized Fe3O4 phase with high purity can be formed through a hydrothermal synthesis. However, for the other three samples with different rGO contents, besides the sharp diffraction peaks for fcc-Fe3O4 phase, another broad peak at around 23° can be observed in their XRD patterns shown in Fig. 1(b)−(d), which can be assigned to the (002) plane of rGO in the composites [20]. 6

Fig. 1. The XRD patterns of pure Fe3O4 sample (a) and Fe3O4/rGO composites with different rGO contents of 3 wt% (b), 4 wt% (c) and 5 wt% (d).

Fig. 2 shows the representative SEM images of pure Fe3O4 sample and the Fe3O4/rGO composites with different rGO contents. As shown in Fig. 2(a), the pure Fe3O4 sample exhibits uniform spherical morphologies with particle size ranging from 250 nm to 350 nm, which can be ascribed to the modulating effect of SDBS addition as surfactant during the preparation [21]. Fig. 2(b)−(d) illustrate the obvious Fe3O4/rGO composite structure with Fe3O4 sub-microspheres embedded uniformly on the surface of rGO sheets. It can be found that the rGO sheets provide a large contact surface for the growth of Fe3O4 phase on their both sides and prevent the agglomeration of Fe3O4 particles, which also avoids the stacking of the rGO sheets. So the uniform Fe3O4 distribution on the rGO sheets can be also observed. Moreover, these Fe3O4 sub-microspheres present a rough surface, which can promote their adhesion to the rGO sheets so as to improve the conductivity for the Fe3O4/rGO composites and further enhance their EM wave absorbing performances discussed below.

7

Fig. 2. The SEM images of pure Fe3O4 sample (a) and Fe3O4/rGO composites with different rGO contents of 3 wt% (b), 4 wt% (c) and 5 wt% (d).

Fig. 3 shows the representative TEM images for the four samples to further investigate their microstructures. As shown in Fig. 3(a), a good dispersion of pure Fe3O4 sub-microspheres is confirmed by their TEM images. Furthermore, Fe3O4/rGO composites with different rGO contents shows almost the same composite microstructures shown in the Fig. 3(b)−(d), which indicates the rGO additions show no effects on the growth of Fe3O4 phase. It can be concluded that the formation of Fe3O4 in the Fe3O4/rGO composites is mainly determined by the hydrothermal conditions, which is the same as those for preparing pure Fe3O4 phase and promote the high chemical stability for the composites. It is worth pointing out that these Fe3O4/rGO composites also exhibit very low density along with large specific area 8

due to the existence of the rGO sheets [22], which promotes their potential application in high-performance EM microwave absorption materials discussed later.

Fig. 3. The TEM images of pure Fe3O4 sample (a) and Fe3O4/rGO composites with different rGO contents of 3 wt% (b), 4 wt% (c) and 5 wt% (d).

3.2. Formation mechanism of Fe3O4/rGO composites Based on the reaction process described in preparation method and the above microstructural investigation for Fe3O4/rGO composites, their schematic formation can be illustrated in Fig. 4. The chemical reactions for the formation of Fe3O4/rGO composites can be analyzed as follows: GO + EG → rGO

(3)

Fe3+ + EG → Fe2+

(4)

NaAc + H2O ↔ HAc + NaOH

(5)

Fe3+ + Fe2+ + 5OH− → Fe(OH)3 + Fe(OH)2

(6)

2Fe(OH)3 + Fe(OH)2 + rGO → Fe3O4/rGO+ 4H2O

(7)

9

Firstly, the graphite powders are converted to GO sheets due to a variety of residual defects resulting from the treatment with concentrated H2SO4 and KMnO4, which also results in several functional groups including −COOH, −OH, epoxy and ketone [23,24]. Then, the rGO sheets with abundant surface oxygen-containing groups can be easily formed by vigorous stirring and ultrasonic treatment in a stable colloidal solution under the effect of SDBS addition. The FeCl3·6H2O can be dissolved in the EG solution to generate Fe3+ ions and pure H2O. After adding the GO sheets in the reaction system simultaneously, the EG can show reducibility with the presence of OH− ions and serve as a strong reducing agent to reduce part of GO and Fe3+ ions to rGO and Fe2+ ions, respectively. This alkaline condition further promotes the co-precipitation of original Fe3+ ions and the generated Fe2+ ions to form Fe(OH)3 and Fe(OH)2 (Eq. (6)), which can be decomposed simultaneously to form pure Fe3O4 phase under suitable condition [25,26]. It is worthy to investigate the growth process for Fe3O4 sub-microspheres on the surface of rGO sheets. As shown in Fig. 4, firstly, the Fe3+ and Fe2+ ions can favorably bind with the oxygen-containing groups of rGO sheets via electrostatic interactions resulting in the growth of Fe3O4 nucleuses on the surface of rGO sheets. As the reaction is proceeding, the initially formed Fe3O4 crystals will anchor on the surface of rGO sheets [27] and grow immediately to be spherical morphologies through a dissolution-recrystallization process under the hydrothermal conditions [28]. Finally, the 3D Fe3O4/rGO monolithic networks can be obtained by decorating the monodispersed Fe3O4 sub-microspheres on the rGO sheets. 10

Fig. 4. The schematic formation process for Fe3O4/rGO composites.

3.3. Magnetic properties of Fe3O4/rGO composites Fig. 5 shows the room-temperature hysteresis loops for the pure Fe3O4 sample and Fe3O4/rGO composites with different rGO contents. It can be seen that all the samples exhibit typical magnetic hysteresis behaviors with good intrinsic magnetic properties including high saturation magnetization (Ms) and low coercivity (Hc). The pure Fe3O4 sample shows a highest Ms value of 75.8 A·m2 kg–1 among the four samples, slightly lower than that of bulk Fe3O4 (about 92 A·m2 Kg–1) owing to their nanoscale sizes [29]. However, the three Fe3O4/rGO composites exhibit relatively lower Ms values of 61.0−64.7 A·m2 kg–1 and decrease slightly with increasing rGO content due to the nonmagnetism of the rGO sheets. Very low iHc value of 8.3 Oe is observed in pure Fe3O4 sample, which can be ascribed to its high purity and spherical morphologies. However, the coercivity for the Fe3O4/rGO composites increases slightly from 15.4 to 22.2 Oe with increasing the rGO contents from 3 to 5 wt%, which can be ascribed to their similar high particle symmetry of Fe3O4 phase in the three composites.

11

Fig. 5. The room-temperature hysteresis loops of the pure Fe3O4 sample and Fe3O4/rGO composites with different rGO contents.

3.4. Microwave absorbing performances of the Fe3O4/rGO composites The three-dimensional RL values at the frequency range of 2−18 GHz for the pure Fe3O4 sample and the Fe3O4/rGO composites are shown in Fig. 6. It can be seen that the pure Fe3O4 product shows weak wave absorption abilities with the minimum RL value of around -23.4 dB at 3.84 GHz with a sample thickness of 8.4 mm. However, the rGO additions lead to the greatly enhanced microwave absorption performances for the Fe3O4/rGO composites. The minimum RL value of -39.9 dB at 6.56 GHz with a sample thickness of 5.25 mm can be obtained in rGO/Fe3O4 composites with the 3 wt% rGO addition. Moreover, the optimal minimum RL value for the composites with the 4 wt% rGO content can be increased to -45 dB at 8.96 GHz with a sample thickness of 3.5 mm, which is superior to those of the most of carbon-based composites recently reported in the literature listed in Table 1. However, with increasing the rGO content to 5 wt% for the Fe3O4/rGO composites, their minimum RL value is slightly decreased to -40.8 dB at 9.04 GHz with a sample thickness of 4.6 mm. The influences of different rGO contents on the wave absorption abilities for the 12

Fe3O4/rGO composites can be ascribed to their different impedance matching characteristics discussed below.

Fig. 6. The three-dimensional RL of the pure Fe3O4 sample (a) and Fe3O4/rGO composites with different rGO contents of 3 wt% (b), 4 wt% (c) and 5 wt% (d).

13

Table 1 The microwave absorbing properties of some carbon-based composites reported in the literature.

Sample

Weight fraction (wt%)

RLmin (dB)

Sample thickness (mm)

Bandwidth (<-10dB) GHz

Ref.

GO/Fe3O4@ZnO

30

-40

5

5.5(9.5~14)

[2]

Carbon@Fe@Fe3O4

50

-40

1.5

5.2(8.6~13.8)

[6]

50

-29

5

5(13~18)

[8]

GO/Fe3O4

50

-40

4.5

3.2(5.8~9)

[30]

rGO/MCNTs/Fe3O4

−

-36

2

4.1(11.5~15.6)

[31]

Fe3O4/GCs

30

-32

3.5

4.5(7.5~12)

[32]

GO/Fe3O4/Fe

−

-23.1

4

3.9(7.4~11.3)

[33]

Fe3O4/rGO

50

-45

3.5

3.2(7.76~10.96)

This work

Fe3O4@Carbon

As is known, the EM microwave absorbing properties for an absorber is mainly determined by its EM parameters including complex effective permittivity (εr = ε' − jε") and permeability (μr = μ' − jμ"), where the real parts (ε' and μ') and the imaginary parts (ε" and μ") represent the storage capability and loss capability of the EM microwave energies, respectively [34]. Fig. 7 shows the frequency-dependent εr, μr, dielectric loss tanδε and magnetic loss tanδμ curves for the pure Fe3O4 sample and Fe3O4/rGO composites with different rGO contents at the frequency range of 2−18 GHz. As shown in Fig. 7(a) and (b), the values of ε' and ε" for the Fe3O4/rGO composites decrease rapidly with increasing the applied frequency, which is similar with frequency-dependent dielectric dispersion occurring in some carbon-based composites [9,35]. Moreover, the absolute εr values for the composites are increased

14

obviously with increasing their rGO contents from 0 to 5 wt%, which indicates that both storage capability and dielectric loss for the composites can be enhanced with more rGO additions. It can be concluded that dielectric properties for the Fe3O4/rGO composites can be tuned by different rGO additions due to high conductivity of rGO sheets. It is should be pointed that the composites with 4 wt% rGO content show a highest ε' value among the four samples in the frequency range of 8−18 GHz, which can be ascribed to the reduction of dielectric dipole occurring in the composites with the excessive rGO sheets connecting to each other [36]. As shown in Fig. 7(c) and (d), the different rGO additions in Fe3O4/rGO composites show slight effects on their complex effective permeability. The absolute μr values along with their variation are very similar for the composite samples, which indicates their similar storage capacity of magnetic energies and magnetic loss. In general, the permeability of magnetic materials can be calculated by the following equation [37]: μi = (Ms2)/(akiHcMs + bλξ)

(8)

where Ms is the saturation magnetization, iHc is the coercive field, a and b are two constants determined by the material composition, λ is the magnetostriction constant, ξ is an elastic strain parameter of the crystal, and k is a proportion coefficient. From the hysteresis loops shown in Fig. 5, the three Fe3O4/rGO composites show a similar value of Ms and iHc so as to result in their similar permeability according to Eq. (8). Fig. 7(e) and (f) further show the dielectric loss tanδε (ε"/ε') and magnetic loss tanδμ (μ"/μ') of the products at the frequency range of 2−18 GHz. It can be obviously found 15

that the Fe3O4/rGO composites possess higher tanδε values than that of pure Fe3O4 sample, which can be attributed to the interfacial polarizations between Fe3O4 phase and rGO sheets [30] and thus improve their microwave absorbing performances discussed above. However, as shown in Fig. 7(f), the slight difference between the tanδμ values for the four samples indicating their similar magnetic loss, which agrees well with the above magnetic investigation. It can be concluded that the dielectric loss dominates the total loss for the Fe3O4/rGO composites in their microwave absorbing measurements.

16

Fig. 7. The frequency-dependent εr (a and b), μr (c and d), dielectric loss tanδε (e) and magnetic loss tanδμ (f) curves for the pure Fe3O4 sample and Fe3O4/rGO composites with different rGO contents.

It has been reported that excellent microwave absorbing performances can be originated from the EM wave attenuation resulting from dielectric and magnetic loss along with a good impedance matching [38]. As discussed above, the three Fe3O4/rGO composites exhibit different dielectric properties due to different rGO contents. 17

However, the similar magnetic loss for the composite samples probably contributes equally to their EM wave attenuation. So the suitable rGO additions in the Fe3O4/rGO composites may balance their dielectric and magnetic properties to a proper level so as to reach a better impedance matching [39,40]. Therefore, it is very important to investigate the impedance matching characteristics for three Fe3O4/rGO composites. Generally, the impedance matching characteristics can be evaluated by the frequency-dependent value of Z = |Zin/Zo| calculated from Eq. (1), where the Z values closer to 1 mean the better impedance matching [41]. Fig. 8 shows the Z-f curves for the pure Fe3O4 sample and Fe3O4/rGO composites with different rGO contents. It can be obviously seen that the Z values on the broad peak in Z-f curves for the Fe3O4/rGO composites with 4 wt% rGO content approach much near to 1 than those for the pure Fe3O4 sample and the other two composites, which indicates that a better impedance matching occurs in this composites and resulting in their enhanced microwave absorbing performances. In summary, the good microwave absorbing performances for the Fe3O4/rGO composites can be mainly attributed to the synergistic effects from their high dielectric loss and better impedance matching from the conductive 3D Fe3O4/GO networks due the suitable rGO additions.

18

Fig. 8. The frequency-dependent Z-f curves for the pure Fe3O4 sample and Fe3O4/rGO composites with different rGO contents.

4. Conclusions The 3D Fe3O4/rGO composite networks with the uniform Fe3O4 sub-microspheres embedded on the surface of the rGO sheets have been fabricated by a one-pot solvothermal method. The different rGO additions in the Fe3O4/rGO composites show great influences on their dielectric properties due to high conductivity of the rGO sheets but slight effects on their magnetic properties. The 4 wt% rGO addition in the Fe3O4/rGO composites can balance their dielectric and magnetic loss to a proper level reaching a better impedance matching so as to result in their excellent microwave absorbing performances including the minimum RL value of -45 dB and an effective absorption bandwidth of 3.2 GHz. These Fe3O4/rGO composites also exhibit the high chemical stability and low density, which promises their big potential application for high-performance EM microwave absorption materials.

Acknowledgements 19

This work was supported by Beijing Natural Science Foundation under Grant no. 2132039 and the National Natural Science Foundation of China under Grant nos. 51101007, 51171007 and 51271009.

References [1] H.J. Wu, G.L. Wu, Y.Y. Ren, L. Yang, L.D. Wang, X.H. Li, Co2+/Co3+ ratio dependence of electromagnetic wave absorption in hierarchical NiCo2O4-CoNiO2 hybrids, J. Mater. Chem. C 3 (2015) 7677−7690. [2] D.P. Sun, Q. Zou, Y.P. Wang, Y.J. Wang, W. Jiang, F.S. Li, Controllable synthesis of porous Fe3O4@ZnO sphere decorated graphene for extraordinary electromagnetic wave absorption, Nanoscale 6 (2014) 6557−6562. [3] A. Mallick, A.S. Mahapatra, A. Mitra, P.K. Chakrabarti, Soft magnetic property and enhanced microwave absorption of nanoparticles of Co0.5Zn0.5Fe2O4 incorporated in MWCNT, J. Magn. Magn. Mater. 416 (2016) 181−187. [4] B. Qu, C.L. Zhu, C.Y. Li, X.T. Zhang, C.J. Chen, Coupling hollow Fe3O4-Fe nanoparticles with graphene sheets for high-performance electromagnetic wave absorbing material, ACS Appl. Mater. Inter. 8 (2016) 3730−3735. [5] Z.J. Wang, L.N. Wu, J.G. Zhou, B.Z. Shen, Z.H. Jiang, Enhanced microwave absorption of Fe3O4 nanocrystals after heterogeneously growing with ZnO nanoshell, RSC Adv. 3 (2013) 3309−3315. [6] H.L. Lv, G.B. Ji, W. Liu, H.Q. Zhang, Y.W. Du, Achieving hierarchical hollow 20

carbon@Fe@Fe3O4 nanospheres with superior microwave absorption properties and lightweight features, J. Mater. Chem. C 3 (2015) 10232−10241. [7] P.M. Sudeep, S. Vinayasree, P. Mohanan, P.M. Ajayan, T.N. Narayanan, M.R. Anantharaman, Fluorinated graphene oxide for enhanced S and X-band microwave absorption, Appl. Phys. Lett. 106 (2015) 221603. [8] Y.C. Du, W.W. Liu, R. Qiang, Y. Wang, X.J. Han, J. Ma, P. Xu, Shell thickness-dependent microwave absorption of core-shell Fe3O4@C composites, ACS Appl. Mater. Inter. 6 (2014) 12997−13006. [9] H. Zhang, A.J. Xie, C.P. Wang, H.S. Wang, Y.H. Shen, X.Y. Tian, Novel rGO/α-Fe2O3 composite hydrogel: synthesis, characterization and high performance of electromagnetic wave absorption, J. Mater. Chem. A. 1 (2013) 8547−8552. [10] R. Kumar, R.K. Singh, J. Singh, R.S. Tiwari, O.N. Srivastava, Synthesis, characterization

and

optical

properties

of

graphene

sheets-ZnO

multipod

nanocomposites, J. Alloy. Compd. 526 (2012) 129−134. [11] N. Campo, A. M. Visco, Incorporation of carbon nanotubes into ultra high molecular weight polyethylene by high energy ball milling, Int. J. Pol. Anal. Ch. 15 (2010) 438−449. [12] H. Hekmatara, M. Seifi, K. Forooraghi, S. Mirzaee, Synthesis and microwave absorption characterization of SiO2 coated Fe3O4-MWCNT composites, Phys. Chem. Chem. Phys. 16 (2014) 24069−24075. [13] P.N. Mbuyisa, F. Rigoni, L. Sangaletti L, S. Ponzoni, S. Pagliara, A. Goldoni, M. Ndwandwe, C. Cepek, Growth of hybrid carbon nanostructures on iron-decorated 21

ZnO nanorods, Nanotechnology 27 (2016) 145605. [14] Y.J. Chen, Z.Y. Lei, H.Y. Wu, C.L. Zhu, P. Gao, Q.Y. Ouyang, L.H. Qi, W. Qin, Electromagnetic absorption properties of graphene/Fe nanocomposites, Mater. Res. Bull. 48 (2013) 3362−3366. [15] F.S. Wen, W.L. Zuo, H.B. Yi, N. Wang, L. Qiao, F. Li, Microwave-absorbing properties of shape-optimized carbonyl iron particles with maximum microwave permeability, Physica B: Condensed Matter 404 (2009) 3567−3570. [16] S.S.S. Afghahi, A. Shokuhfar, Two step synthesis, electromagnetic and microwave absorbing properties of FeCo@C core-shell nanostructure, J. Magn. Magn. Mater. 370 (2014) 37−44. [17] X.F. Zhang, X.L. Dong, H. Huang, B. Lv, J.P. Lei, C.J. Choi, Microstructure and microwave absorption properties of carbon-coated iron nanocapsules, J. Phys. D: Appl. Phys. 40 (2007) 5383−5387. [18] V.C. Tung, M.J. Allen, Y. Yang, R.B. Kaner, High-throughput solution processing of large-scale graphene, Nat. Nanotechnol. 4 (2009) 25−29. [19] T. Maeda, S. Sugimoto, T. Kagotani, N. Tezuka, K. Inomata, Effect of the soft/hard exchange interaction on natural resonance frequency and electromagnetic wave absorption of the rare earth-iron-boron compounds, J. Magn. Magn. Mater. 281 (2004) 195−205. [20] X. Ding, Y. Huang, S.P. Li, J.G. Wang, Preparation and electromagnetic wave absorption properties of FeNi3 nanoalloys generated on graphene–polyaniline nanosheets, RSC Adv. 6 (2016) 31440−31447. 22

[21] X.Z. Wang, Z.B. Zhao, J.Y. Qu, Z.Y. Wang, J.H. Qiu, Shape-control and characterization of magnetite prepared via a one-step solvothermal route, Cryst. Growth. Des. 10 (2010) 2863−2869. [22] B.J.P. Adohi, D. Bychanok, B. Haidar, C. Brosseau, Microwave and mechanical properties of quartz/graphene-based polymer nanocomposites, Appl. Phys. Lett. 102 (2013) 072903. [23] Y.Q. Zhan, F.B. Meng, Y.J. Lei, R. Zhao, J.C. Zhong, X.B. Liu, One-pot solvothermal synthesis of sandwich-like graphene nanosheets/Fe3O4 hybrid material and its microwave electromagnetic properties, Mater. Lett. 65 (2011) 1737−1740. [24]

M.Z.

Kassaee,

E.

Motamedi,

M.

Majdi,

Magnetic

Fe3O4-graphene

oxide/polystyrene: fabrication and characterization of a promising nanocomposite, Chem. Eng. J. 172 (2011) 540−549. [25] L.S. Zhong, J.S. Hu, H.P. Liang, A.M. Cao, W.G. Song, L.J. Wan, Self-assembled 3D flowerlike iron oxide nanostructures and their application in water treatment, Adv. Mater. 18 (2006) 2426−2431. [26] J.P. Ge, Y.X. Hu, M. Biasini, C. Dong, J.H. Gu, W.P. Beyermann, Y.D. Yin, One-step synthesis of highly water-soluble magnetite colloidal nanocrystals, Chem.-Eur. J. 13 (2007) 7153−7161. [27]

H.K.

He, C.

Gao,

Supraparamagnetic,

conductive, and

processable

multifunctional graphene nanosheets coated with high-density Fe3O4 nanoparticles, ACS Appl. Mater. Inter. 2 (2010) 3201−3210. [28] N.N. Guan, Y.T. Wang, D.J. Sun, J. Xu, A simple one-pot synthesis of 23

single-crystalline magnetite hollow spheres from a single iron precursor, Nanotechnology 20 (2009) 105603. [29] L.P. Zhu, H.M. Xiao, W.D. Zhang, G. Yang, S.Y. Fu, One-pot template-free synthesis of monodisperse and single-crystal magnetite hollow spheres by a simple solvothermal route, Cryst. Growth Des. 8 (2008) 957−963. [30] X.L. Zheng, J. Feng, Y. Zong, H. Miao, X.Y. Hu, J.T. Bai, X.H. Li, Hydrophobic graphene nanosheets decorated by monodispersed superparamagnetic Fe3O4 nanocrystals as synergistic electromagnetic wave absorbers, J. Mater. Chem. C 3 (2015) 4452−4463. [31] H. Zhang, M. Hong, P. Chen, A.J. Xie, Y.H. Shen, 3D and ternary rGO/MCNTs/Fe3O4 composite hydrogels: Synthesis, characterization and their electromagnetic wave absorption properties, J. Alloy. Compd. 665 (2016) 381−387. [32] X. Jian, B. Wu, Y.F. Wei, S.X. Dou, X.L. Wang, W.D. He, N. Mahmood, Facile synthesis of Fe3O4/GCs composites and their enhanced microwave absorption properties, ACS Appl. Mater. Inter. 8 (2016) 6101−6109. [33] Y. Ding, L. Zhang, Q.L. Liao, G.J. Zhang, S. Liu, Y. Zhang, Electromagnetic wave absorption in reduced graphene oxide functionalized with Fe3O4/Fe nanorings, Nano Res. 9 (2016) 2018−2025. [34] X.M. Zhang, G.B. Ji, W. Liu, B. Quan, X.H. Liang, C.M. Shang, Y. Cheng, Y.W. Du, Thermal conversion of an Fe3O4@metal-organic framework: A new method for an efficient Fe-Co/nanoporous carbon microwave absorbing material, Nanoscale 7 (2015) 12932−12942. 24

[35] B.J.P. Adohi, V. Laur, B. Haidar, C. Brosseau, Measurement of the microwave effective permittivity in tensile-strained polyvinylidene difluoride trifluoroethylene filled with graphene, Appl. Phys. Lett. 104 (2014) 082902. [36] Y.C. Yin, M. Zeng, J. Liu, W.K. Tang, H.R. Dong, R.Z. Xia, R.H. Yu, Enhanced high-frequency absorption of anisotropic Fe3O4/graphene nanocomposites, Sci. Rep. 2016, DOI: 10.1038/srep25075. [37] R.T. Lv, A. Cao, F.Y. Kang, W.X. Wang, J.Q. Wei, J.L. Gu, K.L. Wang, D.H. Wu, Single-crystalline permalloy nanowires in carbon nanotubes: enhanced encapsulation and magnetization, J. Phys. Chem. C 111 (2007) 11475−11479. [38] Y. Chen, X.Y. Liu, X.Y. Ma, Q.X. Zhuang, Z. Xie, Z.W. Han, γ-Fe2O3– MWNT/poly (p-phenylenebenzobisoxazole) composites with excellent microwave absorption performance and thermal stability, Nanoscale 6 (2014) 6440−6447. [39] X. Sun, J.P. He, G.X. Li, J. Tang, T. Wang, Y.X. Guo, H.R. Xue, Laminated magnetic graphene with enhanced electromagnetic wave absorption properties, J. Mater. Chem. C 1 (2013) 765−777. [40] C. Wang, X.J. Han, P. Xu, X.L. Zhang, Y.C. Du, S.R. Hu, J.Y. Wang, X.H. Wang, The electromagnetic property of chemically reduced graphene oxide and its application as microwave absorbing material, Appl. Phys. Lett. 98 (2011) 072906. [41] J.Y. Fang, T. Liu, Z. Chen, Y. Wang, W. Wei, X.G. Yue, Z.H. Jiang, A wormhole-like porous carbon/magnetic particles composite as an efficient broadband electromagnetic wave absorber, Nanoscale 8 (2016) 8899−8909.

25

Highlights 

Magnetic Fe3O4/rGO composites are fabricated by a facile solvothermal method.



The dielectric properties for the Fe3O4/rGO composites can be tuned.



The Fe3O4/rGO composites exhibits high chemical stability and low density.



Excellent microwave absorption performances for the composites are obtained.

Graphical abstract

26