Cubic MnFe2O4 particles decorated reduced graphene oxide with excellent microwave absorption properties

Cubic MnFe2O4 particles decorated reduced graphene oxide with excellent microwave absorption properties

Materials Letters 231 (2018) 209–212 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue C...

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Materials Letters 231 (2018) 209–212

Contents lists available at ScienceDirect

Materials Letters journal homepage: www.elsevier.com/locate/mlblue

Cubic MnFe2O4 particles decorated reduced graphene oxide with excellent microwave absorption properties Gengyuan Zhang, Ruiwen Shu ⇑, Yan Xie, Haitao Xia, Ying Gan, Jianjun Shi, Jie He School of Chemical Engineering, Anhui University of Science and Technology, Huainan 232001, PR China

a r t i c l e

i n f o

Article history: Received 7 June 2018 Received in revised form 13 July 2018 Accepted 10 August 2018 Available online 11 August 2018 Keywords: Reduced graphene oxide Manganese ferrite Carbon materials Nanocomposites Microwave absorption

a b s t r a c t Herein, we have fabricated the reduced graphene oxide/manganese ferrite (RGO/MnFe2O4) hybrid composites by a facile one-pot hydrothermal method. The obtained MnFe2O4 particles exhibited the uniquely cubic morphology with an average particle size of 100.6 nm, which were uniformly attached to the surface of RGO sheets. Results demonstrated that both the ratio of RGO to MnFe2O4 and filling ratio had notable effects on the microwave absorption performance of the as-prepared hybrid composites. Moreover, the hybrid composites showed the characteristics of thin thickness, broad bandwidth and strong absorption. Significantly, the hybrid composite with a filling ratio of 70 wt% (S2) exhibited the best microwave absorption performance, i.e. the minimum reflection loss reached 47.5 dB and effective absorption bandwidth (less than 10 dB) was 5.2 GHz for a thickness of only 1.7 mm. Therefore, the RGO/ MnFe2O4 hybrid composites could be potential candidates for application in microwave absorption. Ó 2018 Elsevier B.V. All rights reserved.

1. Introduction Electromagnetic interference and pollution problems have become increasingly serious due to the extensive use of electronic devices and equipment, therefore it is urgent to design and develop new types of microwave absorbing materials [1–3]. MnFe2O4, an important kind of spinel ferrites, has been used as microwave absorbers owing to its remarkable properties such as good chemical stability, outstanding magnetic loss characteristic and moderate saturation magnetization [4,5]. However, its shortcomings as microwave absorber such as high density, bad impedance matching characteristic as well as sole magnetic loss mechanism toward microwave attenuation cannot be ignored. These drawbacks limit the practical application of MnFe2O4 in the field of microwave absorption. Owing to the characteristics of low density, high specific surface areas, residual defects and high dielectric loss, reduced graphene oxide (RGO) has been extensively investigated as microwave absorbers [2,4,6–8]. According to the electromagnetic theory, the two principles of impedance matching and maximum microwave attenuation should be considered [2,6,7]. Recent studies showed that the hybridization of dielectric RGO with magnetic ferrites could be an effective way to enhance the microwave absorption [4,6,7]. For example, Zhang et al. fabricated NiFe2O4-RGO nanohy⇑ Corresponding author. E-mail address: [email protected] (R. Shu). https://doi.org/10.1016/j.matlet.2018.08.055 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.

brids by a facile confined growth method and found that the minimum reflection loss (RLmin) reached 58 dB at 11.52 GHz and effective absorption bandwidth (less than 10 dB) was 4.08 GHz for a thickness of 2.7 mm [6]. However, there are few reports on the facile preparation and microwave absorption performance study of RGO/MnFe2O4 hybrid composite. In this work, RGO/MnFe2O4 hybrid composites were fabricated by a facile one-pot hydrothermal route. Moreover, the effects of additive amount of GO and filling ratio on the microwave absorption performance were investigated. Our results demonstrate that the obtained hybrid composites could be used as ideal microwave absorbers.

2. Experimental The synthesis of graphite oxide was based on the improved Hummers0 method as mentioned in our previous work [9]. RGO/ MnFe2O4 hybrid composites were prepared by a facile one-pot hydrothermal strategy. Briefly, aqueous graphene oxide (GO) dispersions with different concentration were firstly obtained by ultrasonication of a certain amount of graphite oxide (10, 20 and 40 mg, respectively) in 30 mL deionized water for 30 min and vigorous stirring for 2 h. Then, MnCl24H2O (0.2 mmol) and Fe (NO3)39H2O (0.4 mmol) were dissolved in the obtained GO dispersion by vigorous stirring for 1.5 h, respectively. Ammonium solution was added drop-wise into the mixed dispersion to adjust the pH equal to 11. Thereafter, the mixture was transferred to a

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Teflon-lined stainless-steel autoclave (50 mL) and maintained at 180 °C for 24 h. Finally, after centrifuging and washed with deionized water, the product was dried in a vacuum oven at 60 °C for 24 h. For simplicity, the RGO/MnFe2O4 hybrid composites with different additive amounts of GO were labeled as S1 (10 mg), S2 (20 mg), and S3 (40 mg), respectively. The structure, morphology, electromagnetic parameters and microwave absorption properties of the as-prepared hybrid composites are characterized by various analytical techniques, as shown in supplementary materials.

3. Results and discussion The crystalline structure of graphite oxide and the sample of S2 were analyzed by XRD. The XRD patterns of Fig. 1(a) prove that MnFe2O4 does exist in the composite due to all the diffraction

(b)

D G

Intensity (a.u.)

(440)

(422) (511)

(400)

(311)

S2

(001)

Intensity (a.u.)

(220)

(a)

peaks of the S2 can be assigned to the face-centered cubic structure of MnFe2O4 (JCPDS No. 10-0319) [4]. Meanwhile, we could not observe the peak at 9.7° corresponding to (0 0 1) crystal planes of graphite oxide in the composite, which indicates that GO is reduced to RGO. The XRD pattern of S2 also shows no diffraction peak at 26°, which further indicates there is no agglomeration of RGO sheets in the composite [4]. Raman spectroscopy is used to further analyze the structural characteristics of the sample of S2. In Fig. 1(b), the GO and S2 both show two prominent peaks appearing at 1330 cm1 named D-band and 1580 cm1 named G-band [4,7], which stands for the vibration of sp3 defects and vibration of sp2 hybridization, respectively. The intensity ratio of D band to G band (ID/IG) of S2 is equal to 1.22, which is much higher than that of GO. The higher ID/IG values indicate that more defects and disorders are introduced during the hydrothermal process [4,7]. Besides, the Raman scattering peak at 622 cm1 is assigned to the A1g mode of MnFe2O4 [4].

S2

ID/IG=1.22

ID/IG=0.89

GO

Graphite oxide 0

10

20

30

40

50 o

2 ()

60

70

80

0

500 1000 1500 2000 2500 3000 3500 4000 -1

Raman shift (cm )

Fig. 1. (a) XRD patterns of graphite oxide and the sample of S2, (b) Raman spectra of GO and the sample of S2.

Fig. 2. TEM images with different magnifications: (a) and (b), HRTEM image (c), particle size distribution histogram of MnFe2O4 nanoparticles (d) of the sample of S2.

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-5

d / mm 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

-10 -15 -20 -25 -30

(b)

S1

0

Reflection Loss (dB)

Reflection Loss (dB)

(a)

2

4

6

8

Frequency (GHz)

Reflection Loss (dB)

(c)

-20 -30 -40

2

4

6

8

10 12 14 16 18 20 22

Frequency (GHz)

S3

0 -2

d / mm 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

-4 -6 -8 -10 -12 -14

d / mm 1.0 1.5 1.7 2.0 2.5 3.0 3.5 4.0 4.5 5.0

-10

-50

10 12 14 16 18 20 22

S2

0

2

4

6

8

10 12 14 16 18 20 22

Frequency (GHz) Fig. 3. Frequency-dependent reflection loss of the hybrid composites at different thicknesses with a filling ratio of 70 wt%: (a) S1, (b) S2 and (c) S3; (d) 3D representation of reflection loss curve of S2.

Micromorphology and structure of the sample of S2 were observed by TEM, as shown in Fig. 2. Generally, the MnFe2O4 particles are evenly anchored on the RGO sheets without obvious agglomeration and show cubic morphology (Fig. 2(a) and (b)). The diagram of particle size distribution shows that the average particle size of MnFe2O4 is 100.6 nm (Fig. 2(d)). In Fig. 2(c), the high-resolution TEM (HRTEM) image clearly shows the interplane distance of fringes is 0.3 nm, corresponding to the (2 2 0) crystal planes of MnFe2O4. This finding is in good agreement with the results of XRD characterization. The microwave absorption properties of RGO/MnFe2O4 hybrid composites are further studied by calculating the reflection loss (RL) values according to the measured complex permittivity and permeability. The calculation formula of RL is as follows [7,10–12]:

  Z in  Z 0   RLðdBÞ ¼ 20lg Z in þ Z 0 

ð1Þ

Where Zin is the input characteristic impedance of absorber, which can be expressed as follows [7,10–12]:

rffiffiffiffiffi Zin ¼ Z 0

   lr 2pfd pffiffiffiffiffiffiffiffiffi lr er tanh j c er

ð2Þ

Where er and lr are the relative complex permittivity and permeability of the absorber, respectively. Z0 is the impedance of free space, f is the frequency, d is the thickness of the absorber and c is the velocity of light in free space. Fig. 3(a)–(c) show the RL values of S1, S2 and S3 at different thicknesses with a filling ratio of 70 wt% in the frequency range of 2–18 GHz. The results demonstrate that the additive amount of GO (i.e. the ratio of RGO to MnFe2O4) indeed greatly affects the microwave absorption performance of the hybrid composites. Specifically, the S1 shows the RLmin of 27.5 dB with a thickness of 4.5 mm and effective absorption bandwidth (less than 10 dB) of 3.6 GHz with a thickness of 3.0 mm, the S2 exhibits the RLmin

of 47.5 dB and effective absorption bandwidth of 5.2 GHz with a thickness of only 1.7 mm. However, the S3 presents the RLmin of only 11.8 dB with a thickness of 1.5 mm. Therefore, the S2 exhibits the best microwave absorption performance among the three samples. Moreover, the microwave absorption performance of the hybrid composites could be facilely optimized by changing the ratio of RGO to MnFe2O4. Fig. 3(d) depicts the threedimensional (3D) representation of RL of S2, which indicates that the RLmin gradually appearing at different frequencies can be achieved by controlling the thickness of microwave absorber. Fig. S1 in supplementary materials shows the frequencydependent reflection loss of the sample of S2 with different thicknesses and filling ratios. It is clear that the filling ratio has notable effect on the microwave absorption performance. Specifically, the RLmin values of S2 are 7.4 dB, 9.8 dB, 19.3 dB, 43.3 dB and 47.5 dB, corresponding to the filling ratios of 30 wt%, 40 wt%, 50 wt%, 60 wt% and 70 wt%, respectively. Therefore, the microwave absorption strength enhances with the increasing of filling ratio and the S2 presents the best microwave absorption performance with the characteristics of strong absorption, thin thickness and broad bandwidth for the filling ratio of 70 wt%. Besides, the possible microwave absorption mechanism of the hybrid composites could be attributed to the synergistic effect of dielectric loss and magnetic loss and the multiple interfacial polarization between RGO and MnFe2O4. 4. Conclusions We have successfully prepared the RGO/MnFe2O4 hybrid composites by a facile one-pot hydrothermal strategy. Results demonstrated that both the ratio of RGO to MnFe2O4 and filling ratio had significant effects on the microwave absorption performance of the hybrid composites. Moreover, the microwave absorption performance could be facilely tuned by changing the thickness of absor-

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ber. The as-prepared hybrid composite (S2) with a filling ratio of 70 wt% exhibited the best microwave absorption properties with the RLmin of 47.5 dB and effective absorption bandwidth of 5.2 GHz for a thickness of only 1.7 mm. In addition, the possible microwave absorption mechanism of the hybrid composite was also proposed. Therefore, it was believed that the obtained hybrid composites were potential candidates for microwave absorption application. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (Grant No. 51507003), the Program of Innovation and Entrepreneurship for Undergraduates of Anhui Province (Grant No. 201710361261), the Lift Engineering of Young Talents and Doctor’s Start-up Research Foundation (Grant No. ZY537) of Anhui University of Science and Technology. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.matlet.2018.08.055.

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