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Enhanced electromagnetic absorption properties of reduced graphene oxide–polypyrrole with NiFe2O4 particles prepared with simple hydrothermal method
Materials Letters 120 (2014) 143–146
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Enhanced electromagnetic absorption properties of reduced graphene oxide–polypyrrole with NiFe2O4 particles prepared with simple hydrothermal method Panbo Liu, Ying Huang n, Xiang Zhang Key Laboratory of Space Applied Physics and Chemistry, Ministry of Education, School of Science, Northwestern Polytechnical University, Xi0 an 710129, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 26 November 2013 Accepted 11 January 2014 Available online 21 January 2014
The ternary composites of reduced graphene oxide–polypyrrole–NiFe2O4 (RGO–PPy–NiFe2O4) were synthesized via a two-step method and the electromagnetic absorption properties were investigated. The average diameter of NiFe2O4 particles on RGO–PPy ranged from 10 to 20 nm. The results revealed that the electromagnetic absorption properties and the absorption bandwidth of RGO–PPy–NiFe2O4 are much better than RGO–PPy. The maximum reflection loss of RGO–PPy–NiFe2O4 is 44.7 dB at 14.9 GHz and the absorption bandwidth with the reflection loss below 10 dB is 4.7 GHz with a thickness of 1.75 mm. Furthermore, our strategy provides a feasible method to obtain the ternary composites with excellent electromagnetic absorption properties and wide absorption bandwidth for future investigators. & 2014 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Polymers Nanoparticles Dielectrics Electromagnetic absorption properties
1. Introduction
2. Experimental
Reduced graphene oxide (RGO) has attracted much attention due to its fascinating properties [1,2]. High dielectric loss and low density enable it to be used as electromagnetic wave absorbers. However, the maximum reflection loss is only 6.9 dB [3]. Based on the impedance matching strategy, one of the effective ways to reduce the problem is to couple RGO with Fe3O4 [4,5], Co3O4 [6] and NiFe2O4 nanoparticles [7]. Recently, the ternary composites of EG/PANI/CF [8] and PANI/graphene/Fe3O4 [9] have been synthesized, but they exhibit weak absorption properties. Polypyrrole (PPy) is one of the most promising conducting polymers with excellent chemical and physical properties. PPy with magnetic nanoparticles also can be used as electromagnetic wave absorbers [10]. In our recent study, we have studied the electromagnetic absorption properties of RGO– PPy–Co3O4, but the synthesis procedure requires multiple steps [11]. Until now, to the best of our knowledge, the electromagnetic absorption properties of the ternary composites consisting of RGO, PPy and NiFe2O4 particles have never been reported. In this paper, we have synthesized RGO–PPy–NiFe2O4 via a twostep method. Structural and morphological properties of RGO–PPy– NiFe2O4 also have been investigated. The maximum reflection loss of the ternary composites is 44.7 dB and the bandwidth exceeding 10 dB is 4.7 GHz.
Graphene oxide (GO) was synthesized by Hummers method [12]. Firstly, pyrrole monomer (0.2 mL) with H2SO4 (2 mL) and (NH4)2S2O8 (APS, 0.95 g) dissolved in GO solution (100 mL) by sonication treatment, then the solution was cooled down to 0 1C and stirred for 12 h. The precipitate was washed with distilled water. Secondly, Ni(NO3)2 6H2O (0.3 g) and Fe(NO3)3 9H2O (0.8 g) were added into the solution and stirred, then NH3H2O was used to adjust the pH value. The mixture was transferred to a Teflonlined autoclave and maintained at 180 1C for 12 h. The obtained product was washed with water and dried. The crystal structure was characterized on X-ray diffraction (D/max 2550 V, Cu Kα radiation). The chemical states were investigated by X-ray photoelectron spectroscopy (XPS, PHI 5300X). The morphology was characterized by field emission transmission electron microscope (FETEM: Tecnai F30G2). The electromagnetic parameters were measured in a HP8753D vector network analyzer.
n
Corresponding author. Tel.: þ 86 29 88431636. E-mail address: [email protected] (Y. Huang).
0167-577X/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2014.01.054
3. Results and discussion The formation mechanism of RGO–PPy–NiFe2O4 is depicted in Fig. 1a. Firstly, pyrrole monomer absorbs on the surfaces of GO by electrostatic attraction, then initiates to polymerize after adding concentrated H2SO4 and APS. Secondly, the reduction of GO and the crystallization of NiFe2O4 happen in one step by the hydrothermal method. In our experiments, NH3H2O is selected
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P. Liu et al. / Materials Letters 120 (2014) 143–146
Fig. 1. Schematic illustration (a), XRD patterns of GO and RGO–PPy–NiFe2O4 (b), XPS spectrum (c), N 1s (d), Ni 2p (e) and Fe 2p (f) spectra of RGO–PPy–NiFe2O4.
to accomplish the two functions: (1) NH3H2O plays an important role in the formation of NiFe2O4 particles; (2) NH3H2O is a reducing agent for the reduction reaction of GO. XRD patterns of GO and RGO–PPy–NiFe2O4 are shown in Fig. 1b. For GO, the strong peak at 9.81 corresponding to the interlayer spacing of 0.90 nm, which is due to the formation of the oxygen functionalities groups between the layers of GO. For RGO–PPy–NiFe2O4, the disappearance of the peak at 9.81 indicates the reduction of GO. Furthermore, six diffraction peaks can be assigned to the (220), (311), (400), (422), (511) and (440) planes of NiFe2O4 (JCPDS card no. 10-0325), suggesting the formation of NiFe2O4 particles. The relatively weak intensities demonstrate that NiFe2O4 particles are small. XPS spectra (Fig. 1c) indicate the presence of C, N, O, Fe and Ni elements in RGO–PPy–NiFe2O4. In Fig. 1d, N 1s XPS spectra can be deconvoluted into three peaks. The peaks at 398.2, 399.7 and 401.3 eV are attributed to the quinoid imine (¼ N–), the benzenoid amine (–NH–) and the cationic nitrogen atoms (–N þ –), respectively. The presence of these peaks suggests the formation of PPy [13]. In Fig. 1e, Ni 2p spectra exhibit two peaks at 854.7 and 872.6 eV, which are assigned to the binding energy of Ni 2p3/2 and Ni 2p1/2, respectively. As shown in Fig. 1f, the peaks of Fe 2p3/2 and Fe 2p1/2 are located at 710.6 and 724.5 eV, respectively. These results indicate the assembly of NiFe2O4 particles onto RGO–PPy. The morphology of the samples is shown in Fig. 2. Fig. 2a shows that RGO sheets are transparent and appear as silky waves, except for some wrinkles at the edges. In Fig. 2b, after decoration with PPy, the surface of RGO becomes rough and some wrinkles uniformly cover on RGO. The SAED pattern (inset in Fig. 2b) indicates that RGO–PPy has no obvious crystalline character, which is due to the perfect coverage of PPy. From Fig. 2c, we can see that large-scale NiFe2O4 particles with a relatively uniform size distribute on the surface of RGO–PPy, as indicated by the red arrows. In Fig. 2d, it can be observed that the average diameter of NiFe2O4 particles is in the range of 10–20 nm. The SAED patterns (inset in Fig. 2d) obtained from this region clearly demonstrate the
crystalline feature of NiFe2O4 particles. In order to verify the crystalline structure of NiFe2O4 particles, we present the HRTEM image of RGO–PPy–NiFe2O4 in Fig. 2e. All NiFe2O4 particles show a well-defined lattice plane with perfect crystallinity, and the crystal lattice fringe with a spacing of 0.25 nm (inset in Fig. 2e) can be assigned to the (311) plane of NiFe2O4 particles. Fig. 2f shows the EDS analysis of RGO–PPy–NiFe2O4. The results show the presence of C, N, O, Ni and Fe elements in the composites, which is consistent with the results of XPS. Furthermore, the atomic ratio of Ni and Fe (inset in Fig. 2f) is approximately 1:2, the result is consistent with the stoichiometry of NiFe2O4, indicating the particles are NiFe2O4. Fig. 3a shows the real part (ε0 ) and imaginary part (ε00 ) of the relative complex permittivity of the ternary composites. It can be found that the values of ε0 and ε00 are in the range of 6.4–16.4 and 2.2–11.3 respectively. Both ε0 and ε00 values decrease gradually with several fluctuations. Fig. 3b shows the real part (m0 ) and imaginary part (m00 ) of the relative complex permeability. It reveals that the values of m0 are in the range of 0.9–1.1 and the m00 values are less than 0.4 over 2–18 GHz. From Fig. 3c, it can be found that tan δμ are largely lower than those of tan δε, indicating that the electromagnetic attenuation mechanism of the ternary composites is mainly dependent on dielectric loss. Furthermore, it demonstrates that RGO–PPy–NiFe2O4 have better complementarities between dielectric loss and magnetic loss at 13.5–15.1 GHz, which suggests that they have excellent electromagnetic wave absorption properties at this region. To compare the electromagnetic absorption properties of RGO– PPy and RGO–PPy–NiFe2O4, the reflection loss (RL) is calculated by the following equations: Z 1 RL ðdBÞ ¼ 20 log in ð1Þ Z in þ 1 Z in ¼
pffiffiffiffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffiffi μr =εr tanh jð2πf d=cÞ εr μr
ð2Þ
P. Liu et al. / Materials Letters 120 (2014) 143–146
145
Fig. 2. TEM images of RGO (a) and RGO–PPy (b), TEM images (c and d), HRTEM image (e) and EDS spectra (f) of RGO–PPy–NiFe2O4. (For interpretation of the references to color in this figure the reader is referred to the web version of this article.)
Fig. 3. The complex relative dielectric permittivity (a), the complex relative magnetic permeability (b) and the loss tangent (c) of RGO–PPy–NiFe2O4.
where Zin is the input impedance of the absorber, c is the velocity of electromagnetic waves in free space, f is the frequency and d is the layer thickness. In Fig. 4a, it can be seen that RGO–PPy exhibits poor electromagnetic absorption properties when the thickness ranges from 1.5 to 4 mm, the maximum RL is only 6.7 dB with a thickness of 1.5 mm. In order to show that the electromagnetic absorption properties of RGO–PPy can be greatly enhanced by adding NiFe2O4, the RL curves of RGO–PPy–NiFe2O4 with different thicknesses are presented in Fig. 4b. It can be observed that the maximum RL of RGO–PPy–NiFe2O4 is 44.7 dB at 14.9 GHz and the absorption bandwidth with the RL below 10 dB is 4.7 GHz (from 12.6 to 17.3 GHz) with a thickness of 1.75 mm. The results demonstrate that RGO–PPy–NiFe2O4 exhibits excellent electromagnetic absorption properties than RGO [3], RGO–PPy and previous reports, such as Fe3O4/PPy [10], PPy/Ag/NanoG [14] and PPy–RGO–Co3O4 [11]. The reasons for the excellent electromagnetic absorption properties can be concluded as follows: Firstly, RGO and PPy are dielectric loss absorbents, NiFe2O4 particles have
outstanding magnetic characteristics, the complementarities between RGO, PPy and NiFe2O4 particles play an important role in increasing the electromagnetic absorption properties. Secondly, dipole polarizations are presented in NiFe2O4 particles, the small particles size will increase the dipole polarizations, which can be contributed to the dielectric loss. In addition, the multi-functional electrical polarization between RGO, PPy and NiFe2O4 particles generates interface scattering, leading to better electromagnetic absorption. The introduction of NiFe2O4 particles improves the electromagnetic absorption properties of RGO–PPy, which can be used as an attractive candidate for the new type of EM wave absorptive materials.
4. Conclusions In summary, we have synthesized the ternary composites of RGO–PPy–NiFe2O4 via a simple two-step method. TEM
146
P. Liu et al. / Materials Letters 120 (2014) 143–146
results indicate that the ternary composites can be used as an attractive candidate for electromagnetic absorption materials.
Acknowledgments This work was supported by the Spaceflight Foundation of the People0 s Republic of China (NBXW0001), the Spaceflight Innovation Foundation of China (NBXT0002) and the Doctorate Foundation of Northwestern Polytechnical University (CX201328). References [1] Wu JS, Pisula W, Mullen K. Chem Rev 2007;107:718–47. [2] Park S, Suk JW, An J, Oh J, Lee S, Lee W, et al. Carbon 2012;50:4573–8. [3] Wang C, Han XJ, Xu P, Zhang XL, Du YC, Hu SR, et al. Appl Phys Lett 2011;98:072906-1–3. [4] Sun X, He JP, Li GX, Tang J, Wang T, Guo YX, et al. J Mater Chem C 2013;1:765–77. [5] Li XH, Yi HB, Zhang JW, Feng J, Li FS, Xue DS, et al. J Nanopart Res 2013;15:1472. [6] Liu PB, Huang Y, Wang L, Zong M, Zhang W. Mater Lett 2013;107:166–9. [7] Fu M, Jiao QZ, Zhao YJ. Mater Chem A 2013;1:5577–86. [8] Chen KY, Xiang C, Li LC, Qian HS, Xiao QS, Xu FJ. Mater Chem 2012;22:6449–55. [9] Singh K, Ohlan A, Pham VH, Balasubramaniyan R, Varshney S, Jang J, et al. Nanoscale 2013;5:2411–20. [10] Li YB, Chen G, Li QH, Qiu GZ, Liu XH. J Alloys Compd 2011;509:4104–7. [11] Liu PB, Huang Y, Wang L, Zhang W. J Alloys Compd 2013;573:151–6. [12] Hummers WS, Offeman RE. J Am Chem Soc 1958;80:1339. [13] Zhang JT, Zhao XS. J Phys Chem C 2012;116:5420–6. [14] Yang YQ, Qi SH, Zhang XX, Qin YC. Mater Lett 2012:229–32.
Fig. 4. The reflection loss of RGO–PPy (a) and RGO–PPy–NiFe2O4 (b).
results indicate that the average diameter of NiFe2O4 particles on RGO–PPy is in the range of 10–20 nm. The electromagnetic absorption properties indicate that the maximum RL of RGO– PPy–NiFe2O4 is 44.7 dB at 14.9 GHz and the absorption bandwidth exceeding 10 dB is 4.7 GHz with a thickness of 1.75 mm. The
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Enhanced electromagnetic absorption properties of reduced graphene oxide–polypyrrole with NiFe2O4 particles prepared with simple hydrothermal method Panbo Liu, Ying Huang n, Xiang Zhang Key Laboratory of Space Applied Physics and Chemistry, Ministry of Education, School of Science, Northwestern Polytechnical University, Xi0 an 710129, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 26 November 2013 Accepted 11 January 2014 Available online 21 January 2014
The ternary composites of reduced graphene oxide–polypyrrole–NiFe2O4 (RGO–PPy–NiFe2O4) were synthesized via a two-step method and the electromagnetic absorption properties were investigated. The average diameter of NiFe2O4 particles on RGO–PPy ranged from 10 to 20 nm. The results revealed that the electromagnetic absorption properties and the absorption bandwidth of RGO–PPy–NiFe2O4 are much better than RGO–PPy. The maximum reflection loss of RGO–PPy–NiFe2O4 is 44.7 dB at 14.9 GHz and the absorption bandwidth with the reflection loss below 10 dB is 4.7 GHz with a thickness of 1.75 mm. Furthermore, our strategy provides a feasible method to obtain the ternary composites with excellent electromagnetic absorption properties and wide absorption bandwidth for future investigators. & 2014 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Polymers Nanoparticles Dielectrics Electromagnetic absorption properties
1. Introduction
2. Experimental
Reduced graphene oxide (RGO) has attracted much attention due to its fascinating properties [1,2]. High dielectric loss and low density enable it to be used as electromagnetic wave absorbers. However, the maximum reflection loss is only 6.9 dB [3]. Based on the impedance matching strategy, one of the effective ways to reduce the problem is to couple RGO with Fe3O4 [4,5], Co3O4 [6] and NiFe2O4 nanoparticles [7]. Recently, the ternary composites of EG/PANI/CF [8] and PANI/graphene/Fe3O4 [9] have been synthesized, but they exhibit weak absorption properties. Polypyrrole (PPy) is one of the most promising conducting polymers with excellent chemical and physical properties. PPy with magnetic nanoparticles also can be used as electromagnetic wave absorbers [10]. In our recent study, we have studied the electromagnetic absorption properties of RGO– PPy–Co3O4, but the synthesis procedure requires multiple steps [11]. Until now, to the best of our knowledge, the electromagnetic absorption properties of the ternary composites consisting of RGO, PPy and NiFe2O4 particles have never been reported. In this paper, we have synthesized RGO–PPy–NiFe2O4 via a twostep method. Structural and morphological properties of RGO–PPy– NiFe2O4 also have been investigated. The maximum reflection loss of the ternary composites is 44.7 dB and the bandwidth exceeding 10 dB is 4.7 GHz.
Graphene oxide (GO) was synthesized by Hummers method [12]. Firstly, pyrrole monomer (0.2 mL) with H2SO4 (2 mL) and (NH4)2S2O8 (APS, 0.95 g) dissolved in GO solution (100 mL) by sonication treatment, then the solution was cooled down to 0 1C and stirred for 12 h. The precipitate was washed with distilled water. Secondly, Ni(NO3)2 6H2O (0.3 g) and Fe(NO3)3 9H2O (0.8 g) were added into the solution and stirred, then NH3H2O was used to adjust the pH value. The mixture was transferred to a Teflonlined autoclave and maintained at 180 1C for 12 h. The obtained product was washed with water and dried. The crystal structure was characterized on X-ray diffraction (D/max 2550 V, Cu Kα radiation). The chemical states were investigated by X-ray photoelectron spectroscopy (XPS, PHI 5300X). The morphology was characterized by field emission transmission electron microscope (FETEM: Tecnai F30G2). The electromagnetic parameters were measured in a HP8753D vector network analyzer.
n
Corresponding author. Tel.: þ 86 29 88431636. E-mail address: [email protected] (Y. Huang).
0167-577X/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2014.01.054
3. Results and discussion The formation mechanism of RGO–PPy–NiFe2O4 is depicted in Fig. 1a. Firstly, pyrrole monomer absorbs on the surfaces of GO by electrostatic attraction, then initiates to polymerize after adding concentrated H2SO4 and APS. Secondly, the reduction of GO and the crystallization of NiFe2O4 happen in one step by the hydrothermal method. In our experiments, NH3H2O is selected
144
P. Liu et al. / Materials Letters 120 (2014) 143–146
Fig. 1. Schematic illustration (a), XRD patterns of GO and RGO–PPy–NiFe2O4 (b), XPS spectrum (c), N 1s (d), Ni 2p (e) and Fe 2p (f) spectra of RGO–PPy–NiFe2O4.
to accomplish the two functions: (1) NH3H2O plays an important role in the formation of NiFe2O4 particles; (2) NH3H2O is a reducing agent for the reduction reaction of GO. XRD patterns of GO and RGO–PPy–NiFe2O4 are shown in Fig. 1b. For GO, the strong peak at 9.81 corresponding to the interlayer spacing of 0.90 nm, which is due to the formation of the oxygen functionalities groups between the layers of GO. For RGO–PPy–NiFe2O4, the disappearance of the peak at 9.81 indicates the reduction of GO. Furthermore, six diffraction peaks can be assigned to the (220), (311), (400), (422), (511) and (440) planes of NiFe2O4 (JCPDS card no. 10-0325), suggesting the formation of NiFe2O4 particles. The relatively weak intensities demonstrate that NiFe2O4 particles are small. XPS spectra (Fig. 1c) indicate the presence of C, N, O, Fe and Ni elements in RGO–PPy–NiFe2O4. In Fig. 1d, N 1s XPS spectra can be deconvoluted into three peaks. The peaks at 398.2, 399.7 and 401.3 eV are attributed to the quinoid imine (¼ N–), the benzenoid amine (–NH–) and the cationic nitrogen atoms (–N þ –), respectively. The presence of these peaks suggests the formation of PPy [13]. In Fig. 1e, Ni 2p spectra exhibit two peaks at 854.7 and 872.6 eV, which are assigned to the binding energy of Ni 2p3/2 and Ni 2p1/2, respectively. As shown in Fig. 1f, the peaks of Fe 2p3/2 and Fe 2p1/2 are located at 710.6 and 724.5 eV, respectively. These results indicate the assembly of NiFe2O4 particles onto RGO–PPy. The morphology of the samples is shown in Fig. 2. Fig. 2a shows that RGO sheets are transparent and appear as silky waves, except for some wrinkles at the edges. In Fig. 2b, after decoration with PPy, the surface of RGO becomes rough and some wrinkles uniformly cover on RGO. The SAED pattern (inset in Fig. 2b) indicates that RGO–PPy has no obvious crystalline character, which is due to the perfect coverage of PPy. From Fig. 2c, we can see that large-scale NiFe2O4 particles with a relatively uniform size distribute on the surface of RGO–PPy, as indicated by the red arrows. In Fig. 2d, it can be observed that the average diameter of NiFe2O4 particles is in the range of 10–20 nm. The SAED patterns (inset in Fig. 2d) obtained from this region clearly demonstrate the
crystalline feature of NiFe2O4 particles. In order to verify the crystalline structure of NiFe2O4 particles, we present the HRTEM image of RGO–PPy–NiFe2O4 in Fig. 2e. All NiFe2O4 particles show a well-defined lattice plane with perfect crystallinity, and the crystal lattice fringe with a spacing of 0.25 nm (inset in Fig. 2e) can be assigned to the (311) plane of NiFe2O4 particles. Fig. 2f shows the EDS analysis of RGO–PPy–NiFe2O4. The results show the presence of C, N, O, Ni and Fe elements in the composites, which is consistent with the results of XPS. Furthermore, the atomic ratio of Ni and Fe (inset in Fig. 2f) is approximately 1:2, the result is consistent with the stoichiometry of NiFe2O4, indicating the particles are NiFe2O4. Fig. 3a shows the real part (ε0 ) and imaginary part (ε00 ) of the relative complex permittivity of the ternary composites. It can be found that the values of ε0 and ε00 are in the range of 6.4–16.4 and 2.2–11.3 respectively. Both ε0 and ε00 values decrease gradually with several fluctuations. Fig. 3b shows the real part (m0 ) and imaginary part (m00 ) of the relative complex permeability. It reveals that the values of m0 are in the range of 0.9–1.1 and the m00 values are less than 0.4 over 2–18 GHz. From Fig. 3c, it can be found that tan δμ are largely lower than those of tan δε, indicating that the electromagnetic attenuation mechanism of the ternary composites is mainly dependent on dielectric loss. Furthermore, it demonstrates that RGO–PPy–NiFe2O4 have better complementarities between dielectric loss and magnetic loss at 13.5–15.1 GHz, which suggests that they have excellent electromagnetic wave absorption properties at this region. To compare the electromagnetic absorption properties of RGO– PPy and RGO–PPy–NiFe2O4, the reflection loss (RL) is calculated by the following equations: Z 1 RL ðdBÞ ¼ 20 log in ð1Þ Z in þ 1 Z in ¼
pffiffiffiffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffiffi μr =εr tanh jð2πf d=cÞ εr μr
ð2Þ
P. Liu et al. / Materials Letters 120 (2014) 143–146
145
Fig. 2. TEM images of RGO (a) and RGO–PPy (b), TEM images (c and d), HRTEM image (e) and EDS spectra (f) of RGO–PPy–NiFe2O4. (For interpretation of the references to color in this figure the reader is referred to the web version of this article.)
Fig. 3. The complex relative dielectric permittivity (a), the complex relative magnetic permeability (b) and the loss tangent (c) of RGO–PPy–NiFe2O4.
where Zin is the input impedance of the absorber, c is the velocity of electromagnetic waves in free space, f is the frequency and d is the layer thickness. In Fig. 4a, it can be seen that RGO–PPy exhibits poor electromagnetic absorption properties when the thickness ranges from 1.5 to 4 mm, the maximum RL is only 6.7 dB with a thickness of 1.5 mm. In order to show that the electromagnetic absorption properties of RGO–PPy can be greatly enhanced by adding NiFe2O4, the RL curves of RGO–PPy–NiFe2O4 with different thicknesses are presented in Fig. 4b. It can be observed that the maximum RL of RGO–PPy–NiFe2O4 is 44.7 dB at 14.9 GHz and the absorption bandwidth with the RL below 10 dB is 4.7 GHz (from 12.6 to 17.3 GHz) with a thickness of 1.75 mm. The results demonstrate that RGO–PPy–NiFe2O4 exhibits excellent electromagnetic absorption properties than RGO [3], RGO–PPy and previous reports, such as Fe3O4/PPy [10], PPy/Ag/NanoG [14] and PPy–RGO–Co3O4 [11]. The reasons for the excellent electromagnetic absorption properties can be concluded as follows: Firstly, RGO and PPy are dielectric loss absorbents, NiFe2O4 particles have
outstanding magnetic characteristics, the complementarities between RGO, PPy and NiFe2O4 particles play an important role in increasing the electromagnetic absorption properties. Secondly, dipole polarizations are presented in NiFe2O4 particles, the small particles size will increase the dipole polarizations, which can be contributed to the dielectric loss. In addition, the multi-functional electrical polarization between RGO, PPy and NiFe2O4 particles generates interface scattering, leading to better electromagnetic absorption. The introduction of NiFe2O4 particles improves the electromagnetic absorption properties of RGO–PPy, which can be used as an attractive candidate for the new type of EM wave absorptive materials.
4. Conclusions In summary, we have synthesized the ternary composites of RGO–PPy–NiFe2O4 via a simple two-step method. TEM
146
P. Liu et al. / Materials Letters 120 (2014) 143–146
results indicate that the ternary composites can be used as an attractive candidate for electromagnetic absorption materials.
Acknowledgments This work was supported by the Spaceflight Foundation of the People0 s Republic of China (NBXW0001), the Spaceflight Innovation Foundation of China (NBXT0002) and the Doctorate Foundation of Northwestern Polytechnical University (CX201328). References [1] Wu JS, Pisula W, Mullen K. Chem Rev 2007;107:718–47. [2] Park S, Suk JW, An J, Oh J, Lee S, Lee W, et al. Carbon 2012;50:4573–8. [3] Wang C, Han XJ, Xu P, Zhang XL, Du YC, Hu SR, et al. Appl Phys Lett 2011;98:072906-1–3. [4] Sun X, He JP, Li GX, Tang J, Wang T, Guo YX, et al. J Mater Chem C 2013;1:765–77. [5] Li XH, Yi HB, Zhang JW, Feng J, Li FS, Xue DS, et al. J Nanopart Res 2013;15:1472. [6] Liu PB, Huang Y, Wang L, Zong M, Zhang W. Mater Lett 2013;107:166–9. [7] Fu M, Jiao QZ, Zhao YJ. Mater Chem A 2013;1:5577–86. [8] Chen KY, Xiang C, Li LC, Qian HS, Xiao QS, Xu FJ. Mater Chem 2012;22:6449–55. [9] Singh K, Ohlan A, Pham VH, Balasubramaniyan R, Varshney S, Jang J, et al. Nanoscale 2013;5:2411–20. [10] Li YB, Chen G, Li QH, Qiu GZ, Liu XH. J Alloys Compd 2011;509:4104–7. [11] Liu PB, Huang Y, Wang L, Zhang W. J Alloys Compd 2013;573:151–6. [12] Hummers WS, Offeman RE. J Am Chem Soc 1958;80:1339. [13] Zhang JT, Zhao XS. J Phys Chem C 2012;116:5420–6. [14] Yang YQ, Qi SH, Zhang XX, Qin YC. Mater Lett 2012:229–32.
Fig. 4. The reflection loss of RGO–PPy (a) and RGO–PPy–NiFe2O4 (b).
results indicate that the average diameter of NiFe2O4 particles on RGO–PPy is in the range of 10–20 nm. The electromagnetic absorption properties indicate that the maximum RL of RGO– PPy–NiFe2O4 is 44.7 dB at 14.9 GHz and the absorption bandwidth exceeding 10 dB is 4.7 GHz with a thickness of 1.75 mm. The