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CoFe2O4 composite and its excellent microwave absorption properties
Materials Letters 114 (2014) 52–55
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
One-pot hydrothermal synthesis of RGO/CoFe2O4 composite and its excellent microwave absorption properties Meng Zong, Ying Huang n, Haiwei Wu, Yang Zhao, Qiufen Wang, Xu Sun 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
art ic l e i nf o
a b s t r a c t
Article history: Received 28 July 2013 Accepted 28 September 2013 Available online 7 October 2013
Reduced graphene oxide (RGO)/CoFe2O4 composite was synthesized by a one-pot hydrothermal route, which avoided the usage of chemical reducing agent. The reduction of graphene oxide (GO) and the crystallization of CoFe2O4 crystals happened in a one step process by the hydrothermal method. The RGO/CoFe2O4 composite shows remarkably improved electromagnetic performance in comparison with CoFe2O4 NPs and reported pure RGO. Not only a larger reflection loss ( 47.9 dB at 12.4 GHz), but also a wider absorption band (less than 10 dB from 12.4 to 17.4 GHz) has been achieved in the frequency range of 2–18 GHz. It is believed that such composites could be used as a candidate microwave absorber. & 2013 Elsevier B.V. All rights reserved.
Keywords: Carbon materials RGO Nanocomposites XPS Magnetic materials Microwave absorbing
1. Introduction Much attention has been paid to microwave absorbing materials owing to the expanded electromagnetic interference problems [1]. But the traditional microwave absorbing materials cannot meet all of the requirements such as being strong, wide, lightweight and thin at the same time [2]. Over the past decade, considerable efforts have been made to develop novel microwave absorbing materials [3]. Carbon based composite materials show outstanding microwave absorption properties. They also have other technical requirements for effective and practical microwave absorption applications such as being light-weight, having high complex permittivity values, etc. [4]. Graphene becomes a potential nanoscale building block for new composite materials due to its special surface properties and layered structure [5]. Recent research shows that inorganic nanoparticles (NPs), such as Fe3O4 [5,6], Co3O4 [7], NiFe2O4 [8] etc., could be attached to graphene to form composite materials, which have application in microwave absorbing field. However, to the best of our knowledge, there have been few reports on studying the microwave absorption property of RGO combined with CoFe2O4. Currently, reducing agents such as hydrazine [9] and NaBH4 [6] are widely used for the chemical reduction of GO to graphene. Some studies found that supercritical water can play the role of
n
Corresponding author. Tel.: þ 86 29 88431636. E-mail addresses: [email protected] (M. Zong), [email protected] (Y. Huang). 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.09.113
reducing agent in hydrothermal conditions and offers a green chemistry alternative to organic solvents [10,11]. Herein, RGO/ CoFe2O4 composite was synthesized by a facile hydrothermal route, which avoided the usage of chemical reducing agent. The reduction of GO and the crystallization of CoFe2O4 crystals happened in a one step process by the hydrothermal method. The morphology, structure and electromagnetic properties of asprepared composite were investigated.
2. Experimental GO was prepared by Hummer's method [12]. In a typical procedure, 50 mg GO was dispersed in 150 mL of deionized water and ultrasonicated for 1 h. 62 mg Co(NO3)2 6 H2O and 171 mg Fe (NO3)3 9H2O were added to the suspension of GO. The solution was stirred for 1 h. 1 M NaOH aqueous solution was added to the suspension until pH ¼11. The solution was stirred for 10 min, followed by a hydrothermal treatment at 180 1C for 10 h. The black products were washed with deionized water and ethanol, and then dried at 60 1C in vacuum. For comparison purposes, pure CoFe2O4 NPs were also prepared by similar procedures. The crystal structure was determined by X-ray diffraction (XRD, Rigaku, model D/max-2500 system at 40 kV and 100 mA of Cu Kα). XPS analysis was characterized by an X-ray photoelectron spectrometer (K-α; Thermo Fisher Scientific (SID-Elemental), USA). The morphology and the size of synthesized samples were characterized by transmission electron microscopy (TEM, Tecnai F30 G2, FEI,
M. Zong et al. / Materials Letters 114 (2014) 52–55
53
Fig. 1. (a) Illustration of synthesis process of RGO/CoFe2O4 and (b) XRD patterns of GO, RGO/CoFe2O4 and CoFe2O4 and XPS spectra: (c) wide scan and (d) C 1s spectrum of RGO/CoFe2O4.
Fig. 2. TEM image (a), (b) HRTEM image (c) and SAED pattern (d) of RGO/CoFe2O4.
54
M. Zong et al. / Materials Letters 114 (2014) 52–55
USA). Electromagnetic (EM) parameters were measured by a vector network analyzer (VNA, HP8720ES) in the range of 2–18 GHz.
3. Results and discussions The formation of the RGO/CoFe2O4 composite is described in Fig. 1a. Graphite was treated with H2SO4 and KMnO4 and obtained GO contained a variety of functional groups, including OH, COOH, epoxy and ketone [13]. In our work, Co2 þ and Fe3 þ were dispersed in a suspension of GO with a mole ratio of 1:2 and adsorbed onto the surface of GO by electrostatic attraction. Ions were transformed into Co(OH)2 and Fe(OH)3 by adding NaOH. Then the reduction of GO and the crystallization of CoFe2O4 crystals happened in a one step process by the hydrothermal method. The overall reaction can be described by the following equations: Co2 þ þ 2OH -CoðOHÞ2
ð1Þ
Fe3 þ þ 3OH -FeðOHÞ3
ð2Þ
GO þ CoðOHÞ2 þ 2FeðOHÞ3
hydrothermally
⟹
RGO=CoFe2 O4 þ 4H2 O
ð3Þ
Fig. 1b shows the XRD patterns of GO, RGO/CoFe2O4 and CoFe2O4. It can be observed that GO exhibits a strong peak at 11.11, corresponding to the (001) reflection. For RGO/CoFe2O4, seven peaks at 18.41, 30.31, 35.61, 43.31, 53.61, 57.11 and 62.81 are observed, which are very similar to those of the pure CoFe2O4 NPs and could be indexed as the characteristic (111), (220), (311), (400),
(422), (511) and (440) reflections, respectively, of the cubic spinel crystal structure of CoFe2O4 (JCPDS no. 22-1086). Notably, no obvious diffraction peaks for RGO can be observed in the RGO/ CoFe2O4 composite, which might be due to the relatively low diffraction intensity of RGO in the composite [4]. Further evidence for the chemical composition of the RGO/ CoFe2O4 composite was obtained by XPS (Fig. 1c and d). The C 1s, O 1s, Co 2p, and Fe 2p core photoionization signals and Fe LMM, O KLL Auger signals [14] are clearly displayed in the survey spectrum (Fig. 1c). To assess the oxidation states of cobalt and iron, the Co 2p and Fe 2p spectra were investigated as shown in Fig. 1c. Two peaks of an Fe 2p level with binding energies of 710.9 and 724.7 eV were assigned to Fe 2p3/2 and Fe 2p1/2, respectively [6]. In addition, the Co 2p spectrum exhibits two main peaks at 780.3 eV and 795.8 eV, corresponding to the Co 2p3/2 and Co 2p1/2, respectively [7], suggesting the formation of CoFe2O4 NPs. Compared with those of GO reported previously [15], the relative contribution of the components associated with oxygenated functional groups decreased conspicuously, indicating that GO was reduced well by the hydrothermal method. The morphology of RGO/CoFe2O4 composite was investigated by TEM. As seen from the low magnification TEM images of RGO/ CoFe2O4 composite (Fig. 2a and b), the graphene nanosheets are well loaded by CoFe2O4 NPs with diameters from 15 nm to 25 nm, which deposit on the nanosheets evenly. The HRTEM image shown in Fig. 2c also reveals the crystalline structure of the CoFe2O4 NPs, and the lattice fringes with an interplanar distance of 0.293 nm can be assigned to the (220) planes of the cubic spinel crystal CoFe2O4. The selected-area electron diffraction pattern (SAED;
Fig. 3. Frequency dependence of (a) the complex permittivity and the complex permeability, (b) the loss tangent, (c) the reflection loss of RGO/CoFe2O4 composite, and (d) the reflection loss of CoFe2O4 NPs.
M. Zong et al. / Materials Letters 114 (2014) 52–55
Fig. 2d) clearly shows the ring pattern arising from the cubic spinel crystal CoFe2O4, further confirming the crystalline nature of CoFe2O4 NPs. Fig. 3a shows the real part and imaginary part of the relative complex permittivity (εr ¼ ε' jε′′) and the relative complex permeability (μr ¼ μ' jμ′′) in the range of 2–18 GHz for RGO/CoFe2O4 composite. The values of ε′ and ε′′ are in the range of 7.2–12.0 and 0.9–6.5, respectively, over the 2–18 GHz frequency range, which are relatively higher than those of CoFe2O4 NPs. Both ε′ and ε′′ values decrease gradually with several small fluctuations, while the μ′ and μ′′ remain around 1 and 0 in the whole frequency range, respectively. We have also calculated both the dielectric tangent loss (tan δE ¼ ε′′/ε′) and the magnetic tangent loss (tan δM ¼ μ′′/μ′) of the composite, as shown in Fig. 3b. The values of tan δE are larger than 0.2 at almost 2–18 GHz, indicating that the dielectric loss occurs at in entire frequency range. Meanwhile, the values of tan δM are lower than tan δE at almost 2–18 GHz. It indicates that the values of the magnetic loss are considerably lower than those of the dielectric loss for the RGO/CoFe2O4 composite. Thus, the microwave attenuation mechanism of RGO/CoFe2O4 composite is mainly dependent on the dielectric loss. According to the transmission-line theory, the reflection loss (RL) can be calculated by the following equations: RL ðdBÞ ¼ 20 log ðZ in 1Þ=ðZ in þ 1Þ ð4Þ qffiffiffiffiffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffiffiffi Z in ¼ μr =εr tanh ½jð2π f d=cÞ εr μr
ð5Þ
where Zin is the input impedance of the absorber, μr and εr are respectively the relative complex permeability and permittivity, ƒ is the frequency of microwaves, d is the thickness of the absorber, and c is the velocity of electromagnetic waves in free space. The calculated results are shown in Fig. 3c, which indicate that the maximum RL reaches 47.9 dB at 12.4 GHz and the bandwidth corresponding to RL at 10 dB can reach 4.9 GHz (from 10.9 to 15.8 GHz) for a layer of 2.3 mm thickness. In addition, the bandwidth corresponding to RL at 10 dB can reach 5.0 GHz (from 12.4 to 17.4 GHz) for the thickness of 2.0 mm. Since the absorber with RL values less than 10 dB can be designed to attenuate microwave [6], the RGO/CoFe2O4 composite is very promising for new types of microwave absorption materials. The electromagnetic parameters of the pure CoFe2O4 NPs were also measured, and the calculated RL with a thickness of 2–5 mm is shown in Fig. 3d.
55
It can be found that that the maximum RL is larger than 3.5 dB. The result demonstrates that the RGO plays a significant role in the microwave absorption properties of the RGO/CoFe2O4 composite. 4. Conclusion In summary, the RGO/CoFe2O4 composite was synthesized by a simple hydrothermal route. The maximum RL of the RGO/CoFe2O4 composite is 47.9 dB at 12.4 GHz for the thickness of 2.3 mm, and the absorption bandwidth with the RL below 10 dB is up to 5.0 GHz (from 12.4 to 17.4 GHz) for a thickness of 2.0 mm. The introduction of RGO signal enhanced microwave absorption performance of the CoFe2O4 NPs. It is believed that such composites will find their wide applications in microwave absorbing area. Acknowledgments This work was supported by the Spaceflight Foundation of China (No. 2011XW110001C110001) and the Spaceflight Innovation Foundation of China (No. 2011XT110002C110002). References [1] Yu HL, Wang TS, Wen B, Lu MM, Xu Z, Zhu CL, et al. Journal of Materials Chemistry 2012;22:21679–85. [2] Zhu CL, Zhang ML, Qiao YJ, Xiao G, Zhang F, Chen YJ. Journal of Physical Chemistry C 2010;114:16229–35. [3] Guo XH, Deng YH, Gu D, Che RC, Zhao DY. Journal of Materials Chemistry 2009;19:6706–12. [4] Zhang H, Xie AJ, Wang CP, Wang HS, Shen YH, Tian XY. Journal of Materials Chemistry A 2013;1:8547–52. [5] Ma EL, Li JJ, Zhao NQ, Liu EZ, He CN, Shi CS. Materials Letters 2013;91:209–12. [6] Zong M, Huang Y, Zhao Y, Wang L, Liu PB, Wang Y, et al. Materials Letters 2013;106:22–5. [7] Liu PB, Huang Y, Wang L, Zong M, Zhang W. Materials Letters 2013;107:166–9. [8] Fu M, Jiao Q, Zhao Y. Journal of Materials Chemistry A 2013;1:5577–86. [9] Guo HL, Wang XF, Qian QY, Wang FB, Xia XH. ACS Nano 2009;3:2653–9. [10] Zhou Y, Bao QL, Tang LAL, Zhong YL, Loh KP. Chemistry of Materials 2009;21:2950–6. [11] Xu YX, Sheng KX, Li C, Shi GQ. ACS Nano 2010;4:4324–30. [12] Hummers WS, Offeman RE. Journal of the American Chemical Society 1958;80:1339. [13] Kassaee MZ, Motamedi E, Majdi M. Chemical Engineering Journal 2011;172:540–9. [14] Li NW, Zheng MB, Chang XF, Ji GB, Lu HL, Xue LP, et al. Journal of Solid State Chemistry 2011;184:953–8. [15] Liu PB, Huang Y, Wang L. Materials Letters 2013;91:125–8.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
One-pot hydrothermal synthesis of RGO/CoFe2O4 composite and its excellent microwave absorption properties Meng Zong, Ying Huang n, Haiwei Wu, Yang Zhao, Qiufen Wang, Xu Sun 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
art ic l e i nf o
a b s t r a c t
Article history: Received 28 July 2013 Accepted 28 September 2013 Available online 7 October 2013
Reduced graphene oxide (RGO)/CoFe2O4 composite was synthesized by a one-pot hydrothermal route, which avoided the usage of chemical reducing agent. The reduction of graphene oxide (GO) and the crystallization of CoFe2O4 crystals happened in a one step process by the hydrothermal method. The RGO/CoFe2O4 composite shows remarkably improved electromagnetic performance in comparison with CoFe2O4 NPs and reported pure RGO. Not only a larger reflection loss ( 47.9 dB at 12.4 GHz), but also a wider absorption band (less than 10 dB from 12.4 to 17.4 GHz) has been achieved in the frequency range of 2–18 GHz. It is believed that such composites could be used as a candidate microwave absorber. & 2013 Elsevier B.V. All rights reserved.
Keywords: Carbon materials RGO Nanocomposites XPS Magnetic materials Microwave absorbing
1. Introduction Much attention has been paid to microwave absorbing materials owing to the expanded electromagnetic interference problems [1]. But the traditional microwave absorbing materials cannot meet all of the requirements such as being strong, wide, lightweight and thin at the same time [2]. Over the past decade, considerable efforts have been made to develop novel microwave absorbing materials [3]. Carbon based composite materials show outstanding microwave absorption properties. They also have other technical requirements for effective and practical microwave absorption applications such as being light-weight, having high complex permittivity values, etc. [4]. Graphene becomes a potential nanoscale building block for new composite materials due to its special surface properties and layered structure [5]. Recent research shows that inorganic nanoparticles (NPs), such as Fe3O4 [5,6], Co3O4 [7], NiFe2O4 [8] etc., could be attached to graphene to form composite materials, which have application in microwave absorbing field. However, to the best of our knowledge, there have been few reports on studying the microwave absorption property of RGO combined with CoFe2O4. Currently, reducing agents such as hydrazine [9] and NaBH4 [6] are widely used for the chemical reduction of GO to graphene. Some studies found that supercritical water can play the role of
n
Corresponding author. Tel.: þ 86 29 88431636. E-mail addresses: [email protected] (M. Zong), [email protected] (Y. Huang). 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.09.113
reducing agent in hydrothermal conditions and offers a green chemistry alternative to organic solvents [10,11]. Herein, RGO/ CoFe2O4 composite was synthesized by a facile hydrothermal route, which avoided the usage of chemical reducing agent. The reduction of GO and the crystallization of CoFe2O4 crystals happened in a one step process by the hydrothermal method. The morphology, structure and electromagnetic properties of asprepared composite were investigated.
2. Experimental GO was prepared by Hummer's method [12]. In a typical procedure, 50 mg GO was dispersed in 150 mL of deionized water and ultrasonicated for 1 h. 62 mg Co(NO3)2 6 H2O and 171 mg Fe (NO3)3 9H2O were added to the suspension of GO. The solution was stirred for 1 h. 1 M NaOH aqueous solution was added to the suspension until pH ¼11. The solution was stirred for 10 min, followed by a hydrothermal treatment at 180 1C for 10 h. The black products were washed with deionized water and ethanol, and then dried at 60 1C in vacuum. For comparison purposes, pure CoFe2O4 NPs were also prepared by similar procedures. The crystal structure was determined by X-ray diffraction (XRD, Rigaku, model D/max-2500 system at 40 kV and 100 mA of Cu Kα). XPS analysis was characterized by an X-ray photoelectron spectrometer (K-α; Thermo Fisher Scientific (SID-Elemental), USA). The morphology and the size of synthesized samples were characterized by transmission electron microscopy (TEM, Tecnai F30 G2, FEI,
M. Zong et al. / Materials Letters 114 (2014) 52–55
53
Fig. 1. (a) Illustration of synthesis process of RGO/CoFe2O4 and (b) XRD patterns of GO, RGO/CoFe2O4 and CoFe2O4 and XPS spectra: (c) wide scan and (d) C 1s spectrum of RGO/CoFe2O4.
Fig. 2. TEM image (a), (b) HRTEM image (c) and SAED pattern (d) of RGO/CoFe2O4.
54
M. Zong et al. / Materials Letters 114 (2014) 52–55
USA). Electromagnetic (EM) parameters were measured by a vector network analyzer (VNA, HP8720ES) in the range of 2–18 GHz.
3. Results and discussions The formation of the RGO/CoFe2O4 composite is described in Fig. 1a. Graphite was treated with H2SO4 and KMnO4 and obtained GO contained a variety of functional groups, including OH, COOH, epoxy and ketone [13]. In our work, Co2 þ and Fe3 þ were dispersed in a suspension of GO with a mole ratio of 1:2 and adsorbed onto the surface of GO by electrostatic attraction. Ions were transformed into Co(OH)2 and Fe(OH)3 by adding NaOH. Then the reduction of GO and the crystallization of CoFe2O4 crystals happened in a one step process by the hydrothermal method. The overall reaction can be described by the following equations: Co2 þ þ 2OH -CoðOHÞ2
ð1Þ
Fe3 þ þ 3OH -FeðOHÞ3
ð2Þ
GO þ CoðOHÞ2 þ 2FeðOHÞ3
hydrothermally
⟹
RGO=CoFe2 O4 þ 4H2 O
ð3Þ
Fig. 1b shows the XRD patterns of GO, RGO/CoFe2O4 and CoFe2O4. It can be observed that GO exhibits a strong peak at 11.11, corresponding to the (001) reflection. For RGO/CoFe2O4, seven peaks at 18.41, 30.31, 35.61, 43.31, 53.61, 57.11 and 62.81 are observed, which are very similar to those of the pure CoFe2O4 NPs and could be indexed as the characteristic (111), (220), (311), (400),
(422), (511) and (440) reflections, respectively, of the cubic spinel crystal structure of CoFe2O4 (JCPDS no. 22-1086). Notably, no obvious diffraction peaks for RGO can be observed in the RGO/ CoFe2O4 composite, which might be due to the relatively low diffraction intensity of RGO in the composite [4]. Further evidence for the chemical composition of the RGO/ CoFe2O4 composite was obtained by XPS (Fig. 1c and d). The C 1s, O 1s, Co 2p, and Fe 2p core photoionization signals and Fe LMM, O KLL Auger signals [14] are clearly displayed in the survey spectrum (Fig. 1c). To assess the oxidation states of cobalt and iron, the Co 2p and Fe 2p spectra were investigated as shown in Fig. 1c. Two peaks of an Fe 2p level with binding energies of 710.9 and 724.7 eV were assigned to Fe 2p3/2 and Fe 2p1/2, respectively [6]. In addition, the Co 2p spectrum exhibits two main peaks at 780.3 eV and 795.8 eV, corresponding to the Co 2p3/2 and Co 2p1/2, respectively [7], suggesting the formation of CoFe2O4 NPs. Compared with those of GO reported previously [15], the relative contribution of the components associated with oxygenated functional groups decreased conspicuously, indicating that GO was reduced well by the hydrothermal method. The morphology of RGO/CoFe2O4 composite was investigated by TEM. As seen from the low magnification TEM images of RGO/ CoFe2O4 composite (Fig. 2a and b), the graphene nanosheets are well loaded by CoFe2O4 NPs with diameters from 15 nm to 25 nm, which deposit on the nanosheets evenly. The HRTEM image shown in Fig. 2c also reveals the crystalline structure of the CoFe2O4 NPs, and the lattice fringes with an interplanar distance of 0.293 nm can be assigned to the (220) planes of the cubic spinel crystal CoFe2O4. The selected-area electron diffraction pattern (SAED;
Fig. 3. Frequency dependence of (a) the complex permittivity and the complex permeability, (b) the loss tangent, (c) the reflection loss of RGO/CoFe2O4 composite, and (d) the reflection loss of CoFe2O4 NPs.
M. Zong et al. / Materials Letters 114 (2014) 52–55
Fig. 2d) clearly shows the ring pattern arising from the cubic spinel crystal CoFe2O4, further confirming the crystalline nature of CoFe2O4 NPs. Fig. 3a shows the real part and imaginary part of the relative complex permittivity (εr ¼ ε' jε′′) and the relative complex permeability (μr ¼ μ' jμ′′) in the range of 2–18 GHz for RGO/CoFe2O4 composite. The values of ε′ and ε′′ are in the range of 7.2–12.0 and 0.9–6.5, respectively, over the 2–18 GHz frequency range, which are relatively higher than those of CoFe2O4 NPs. Both ε′ and ε′′ values decrease gradually with several small fluctuations, while the μ′ and μ′′ remain around 1 and 0 in the whole frequency range, respectively. We have also calculated both the dielectric tangent loss (tan δE ¼ ε′′/ε′) and the magnetic tangent loss (tan δM ¼ μ′′/μ′) of the composite, as shown in Fig. 3b. The values of tan δE are larger than 0.2 at almost 2–18 GHz, indicating that the dielectric loss occurs at in entire frequency range. Meanwhile, the values of tan δM are lower than tan δE at almost 2–18 GHz. It indicates that the values of the magnetic loss are considerably lower than those of the dielectric loss for the RGO/CoFe2O4 composite. Thus, the microwave attenuation mechanism of RGO/CoFe2O4 composite is mainly dependent on the dielectric loss. According to the transmission-line theory, the reflection loss (RL) can be calculated by the following equations: RL ðdBÞ ¼ 20 log ðZ in 1Þ=ðZ in þ 1Þ ð4Þ qffiffiffiffiffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffiffiffi Z in ¼ μr =εr tanh ½jð2π f d=cÞ εr μr
ð5Þ
where Zin is the input impedance of the absorber, μr and εr are respectively the relative complex permeability and permittivity, ƒ is the frequency of microwaves, d is the thickness of the absorber, and c is the velocity of electromagnetic waves in free space. The calculated results are shown in Fig. 3c, which indicate that the maximum RL reaches 47.9 dB at 12.4 GHz and the bandwidth corresponding to RL at 10 dB can reach 4.9 GHz (from 10.9 to 15.8 GHz) for a layer of 2.3 mm thickness. In addition, the bandwidth corresponding to RL at 10 dB can reach 5.0 GHz (from 12.4 to 17.4 GHz) for the thickness of 2.0 mm. Since the absorber with RL values less than 10 dB can be designed to attenuate microwave [6], the RGO/CoFe2O4 composite is very promising for new types of microwave absorption materials. The electromagnetic parameters of the pure CoFe2O4 NPs were also measured, and the calculated RL with a thickness of 2–5 mm is shown in Fig. 3d.
55
It can be found that that the maximum RL is larger than 3.5 dB. The result demonstrates that the RGO plays a significant role in the microwave absorption properties of the RGO/CoFe2O4 composite. 4. Conclusion In summary, the RGO/CoFe2O4 composite was synthesized by a simple hydrothermal route. The maximum RL of the RGO/CoFe2O4 composite is 47.9 dB at 12.4 GHz for the thickness of 2.3 mm, and the absorption bandwidth with the RL below 10 dB is up to 5.0 GHz (from 12.4 to 17.4 GHz) for a thickness of 2.0 mm. The introduction of RGO signal enhanced microwave absorption performance of the CoFe2O4 NPs. It is believed that such composites will find their wide applications in microwave absorbing area. Acknowledgments This work was supported by the Spaceflight Foundation of China (No. 2011XW110001C110001) and the Spaceflight Innovation Foundation of China (No. 2011XT110002C110002). References [1] Yu HL, Wang TS, Wen B, Lu MM, Xu Z, Zhu CL, et al. Journal of Materials Chemistry 2012;22:21679–85. [2] Zhu CL, Zhang ML, Qiao YJ, Xiao G, Zhang F, Chen YJ. Journal of Physical Chemistry C 2010;114:16229–35. [3] Guo XH, Deng YH, Gu D, Che RC, Zhao DY. Journal of Materials Chemistry 2009;19:6706–12. [4] Zhang H, Xie AJ, Wang CP, Wang HS, Shen YH, Tian XY. Journal of Materials Chemistry A 2013;1:8547–52. [5] Ma EL, Li JJ, Zhao NQ, Liu EZ, He CN, Shi CS. Materials Letters 2013;91:209–12. [6] Zong M, Huang Y, Zhao Y, Wang L, Liu PB, Wang Y, et al. Materials Letters 2013;106:22–5. [7] Liu PB, Huang Y, Wang L, Zong M, Zhang W. Materials Letters 2013;107:166–9. [8] Fu M, Jiao Q, Zhao Y. Journal of Materials Chemistry A 2013;1:5577–86. [9] Guo HL, Wang XF, Qian QY, Wang FB, Xia XH. ACS Nano 2009;3:2653–9. [10] Zhou Y, Bao QL, Tang LAL, Zhong YL, Loh KP. Chemistry of Materials 2009;21:2950–6. [11] Xu YX, Sheng KX, Li C, Shi GQ. ACS Nano 2010;4:4324–30. [12] Hummers WS, Offeman RE. Journal of the American Chemical Society 1958;80:1339. [13] Kassaee MZ, Motamedi E, Majdi M. Chemical Engineering Journal 2011;172:540–9. [14] Li NW, Zheng MB, Chang XF, Ji GB, Lu HL, Xue LP, et al. Journal of Solid State Chemistry 2011;184:953–8. [15] Liu PB, Huang Y, Wang L. Materials Letters 2013;91:125–8.