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Construction of polyaniline aligned on magnetic functionalized biomass carbon giving excellent microwave absorption properties
Composites Science and Technology 174 (2019) 176–183
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Construction of polyaniline aligned on magnetic functionalized biomass carbon giving excellent microwave absorption properties
T
Qixin Yanga, Yiyuan Shia, Yu Fanga, Yubing Donga, Qingqing Nia,b, Yaofeng Zhua,∗, Yaqin Fua a b
Key Laboratory of Advanced Textile Materials and Manufacturing Technology Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, Zhejiang, 310018, China Interdisciplinary Graduate School of Science and Technology, Shinshu University, Tokida, Ueda, 386-8576, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: A: Hybrid composites B: Magnetic properties B: Interface
A novel ternary nanocomposite of Fe3O4 functionalized porous biomass carbon decorated by aligned polyaniline (A-PANI/Fe3O4/PBC) was successfully fabricated by hydrothermal and in situ oxidative polymerization. The morphology and structure of the composite was characterized by X-ray diffraction, fourier transform infrared spectra, scanning electron microcopy, transmission electron microscopy, X-ray photoelectron spectra and vibrating sample magnetometer. The microwave absorbing properties of A-PANI/Fe3O4/PBC composite were investigated in the frequency of 2–18 GHz. The results indicated that the A-PANI/Fe3O4/PBC composite possess excellent microwave absorbing performance, and the minimum reflection loss can be up to −44.8 dB at 10.67 GHz, effective absorbing bandwidth (RL < −10 dB) reaches 4.69 GHz with a thickness of 2.7 mm. The excellent microwave absorbing performance of composite was mainly related to the multi-loss mechanisms, good impedance matching, synergistic and geometrical effect of porous biomass carbon, magnetic particles and aligned PANI.
1. Introduction Nowadays, electromagnetic wave pollution and interference caused by the explosive development of information technology have severe effect on human health and the normal operation of electronic devices [1,2]. To solve these problems, researchers have devoted much efforts to develop the high-performance microwave absorbing materials (MAMs) enjoying the advantage of the light weight, thin thickness, broad frequency and strong absorption [3,4]. In the past years, carbonaceous materials have been reported used as microwave absorbers for their features of good stability, low density and good electrical conductivity [5], such as graphene [6], carbon nanotubes (CNTs) [7], carbon fibers [8], biomass carbon [9]. Among these carbonaceous materials, biomass carbon materials have attracted more attention for microwave absorption applications because of its advantage properties also including simple fabrication process, low cost and wide variety of sources [10]. Additionally, the unique porous structures and high pore volume of biomass carbon makes it a promising candidate for electromagnetic microwave absorbers [11]. Unfortunately, similar to other carbon materials, the single dielectric loss of biomass carbon materials may result in impedance mismatching, which seriously hinders their practical application as high performance of MAMs. As we know, in the past decades, Fe3O4 nanoparticles have been ∗
used as one of effective components to obtain MAMs with excellent microwave absorption properties, which they exhibit advantages of surface activity, high saturation magnetization and good magnetic loss absorbing properties [12,13]. Therefore, coupling Fe3O4 nanoparticle with carbon materials may contribute the high complex permeability values to composites because of their large saturation magnetization, which give a chance to compensate the high conductivity of carbon materials and further improve its impedance matching effectively. Besides, a recent progress reveals that designing and construction of nanostructure with special geometrical morphologies may be beneficial for electromagnetic wave absorption [14,15]. The rational geometrical morphologies design of composites can induce multiple reflection and scattering under alternated electromagnetic field, which will extent transmission path of electromagnetic wave. Meanwhile, it can also provide large amounts of nano-interfaces to improve interfacial polarization which could balance the strong conductive loss. Polyaniline (PANI) has been promised to be an ideal candidate for constructing reasonable geometrical morphologies of composites due to its geometry can be controlled by rational synthetic routes [16,17]. Moreover, the tunable conductivity of PANI can balance MAM impedance matching and further enhance it attenuate capability. Therefore, combination of PANI with special geometrical morphologies and magnetically decorated porous biomass carbon to construct excellent microwave
Corresponding author. E-mail address: [email protected] (Y. Zhu).
https://doi.org/10.1016/j.compscitech.2019.02.031 Received 25 October 2018; Received in revised form 23 January 2019; Accepted 28 February 2019 Available online 02 March 2019 0266-3538/ © 2019 Elsevier Ltd. All rights reserved.
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of 1 M HClO4 solution with stiring for 10 min. Then, 0.6 mmol of aniline and ammonium persulfate (the molar ratio of aniline/APS was 1:1.25) was added into above suspension solution sequentially, and followed by stirring for 10 h at room temperature. The synthesized products were washed alternately with ethanol and deionized water for 3 times and then dried at 45 °C for 24 h. Finally, the aligned PANI/Fe3O4 functionalized porous biomass carbon composites was denoted as A-PANI/ Fe3O4/PBC.
absorbers are expected and meaningful. In this regard, aligned PANI grown vertically on magnetic Fe3O4 functionalized porous biomass carbon materials (A-PANI/Fe3O4/PBC) have been fabricated by a synthetic method based on simple hydrothermal and in situ polymerization. The morphology, microstructural, and microwave absorption properties of the composite were investigated in detail. The results indicated that the A-PANI/Fe3O4/PBCparaffin wax composite (A-PANI/Fe3O4/PBC absorbers weight fraction = 30 wt%) exhibited superior microwave absorption properties due to the combined action of electric loss, magnetic loss, impedance matching and geometrical effect. Therefore, it is expected that this work will provide a new direction for the preparation of novel microwave absorbing materials.
2.5. Characterizations Scanning electron microscope (SEM, Hitachi S-4800) and transmission electron microscope (TEM, JEOL JEM-2100F) were used to observe the microstructure and morphology of the materials. Fourier Transform Infrared Spectroscopy (FT-IR) was observed by Nicolet 5700 with KBr pellets. The crystal phase structure of the material was analyzed by XRD (Bruker AXS, D8-Discover Cu Kα radiation) and Raman spectrophotometer (LabRAM HR Evolution, Horiba, 785 nm laser). The magnetic properties of the samples were tested by Lake Shore 7047 vibratory magnetometer (VSM) of Lake Shore Company of USA at room temperature. X-ray photoelectron spectroscopy (XPS, K-Alpha) was used to study the chemical composition and chemical binding state of the sample surface. Complex permittivity and permeability of the samples were studied by the vector network analyzer (VNA, Agilent N5224A) in the 2–18 GHz frequency range. The as prepared A-PANI/ Fe3O4/PBC was mixed with wax in a mass ratio of 30 wt%, and then the mixture was pressed into a toroid shape with an outer diameter of 7.0 nm and inner diameter of 3.0 mm.
2. Experimental section 2.1. Materials Ferric trichloride (FeCl3), Ethylene glycol (C2H6O2), Sodium Citrate (Na3C6H5O7), sodium acetate (C2H3NaO2) and Ammonium persulfate (APS) were supplied from Shanghai Macklin Biochemical Co. Ltd. Aniline (AN) was obtained by Aladdin chemistry Co. Ltd. Perchloric acid (HClO4) was purchase by Hangzhou Gaojing Fine chemical industry Co. Ltd. All the reagents were of analytical grade and used as received. 2.2. Preparation of porous biomass carbon The natural loofah used as raw material, the sample was soaked in 1 M KOH solution at 70 °C for 12 h and dried in vacuum oven at 60 °C for 12 h subsequently. Then the sample was carbonized under nitrogen atmosphere at 700 °C for 1 h, the heating rate was 5 °C/min−1. Furthermore, the obtained products were soaked in 1 M HCl solution for 5 h. Finally, the obtained porous biomass carbon material was washed by 1 M HCl solution and deionized water several times subsequently, and drying the product at 60 °C for 24 h.
3. Results and discussion In order to realize the integrated design of structure and multi-loss mechanism of high performances microwave absorbing composites. The magnetic functionalized porous biomass carbon materials coupling with aligned polyaniline were carried out in this work and the procedure for the preparation is depicted in Scheme 1. Firstly, the porous biomass carbon (PBC) was prepared by KOH activation and carbonization. And then, the as prepared biomass carbon was magnetic functionalized by the formation of aggregated Fe3O4 nano-crystallines on its surface via hydrothermal reaction under alkaline conditions. Finally, the aligned PANI growth on the magnetic functionalized biomass carbon direct through a typical dilute solution of in situ polymerization. The formation mechanism of aligned PANI can be depicted as follows: At the beginning, PANI oligomer was synthesized through in situ polymerization on the surface of Fe3O4/PBC composites due to the presence of functional group and π-π stacking acts as an initiator. Then the heterogeneous nucleation of PANI occurs in the course of polymerization for the formation of many tiny PANI protuberances, which act as the new active nucleation sites for the further growth of aligned polyaniline on the Fe3O4/PBC surface. Fig. 1 shows the morphology and microstructure of the PBC, Fe3O4/ PBC and A-PANI/Fe3O4/PBC. It is clear that PBC shows the well-developed and open porous structure with the average pore diameter in the range of 0.2–2 μm (Fig. 1a). As shown in Fig. 1b, it can be observed that the Fe3O4 nanoparticles covered on the surface and inter-pore of
2.3. Preparation of magnetic functionalized porous biomass carbon 150 mg of porous biomass carbon (PBC) was added in 20 ml ethylene glycol solution and stirred at room temperature for 30 min, and then 0.2 mmol ferric chloride, 1.2 g sodium acetate and 0.2 g sodium citrate were added to the above mixed solution under stirring. After 1 h, the mixture was transferred into a 50 ml Teflon-lined stainless-steel autoclave and kept at 200 °C for 10 h. After reaction, the mixture was cooled to room temperature, and the product was obtained by centrifugation, washed with ethanol and deionized water for several times, and finally dried at 50 °C for 24 h. The obtained products of Fe3O4 functionalized porous biomass carbon composite was denoted as Fe3O4/PBC. 2.4. Preparation of aligned PANI/Fe3O4/porous biomass carbon composite For the synthesis of the aligned PANI/Fe3O4 functionalized porous biomass carbon composites, 150 mg Fe3O4/PBC was dispersed in 50 ml
Scheme 1. Schematic illustration on the fabrication of A-PANI/Fe3O4/PBC composite. 177
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Fig. 1. The SEM images of PBC (a), Fe3O4/PBC (b), A-PANI/Fe3O4/PBC (c), the magnified image of A-PANI/Fe3O4/PBC (d), the TEM (e) and HRTEM (f) images of APANI/Fe3O4/PBC.
exhibits diffraction peaks appeared at 30.2°, 35.6°, 43.2°, 57.2°, 62.7°, which can be corresponding to the (220), (311), (400), (511) and (440) planes of cubic Fe3O4 (JCPDS no. 75-0033) [18], respectively. In addition, the broad diffraction peaks of the amorphous carbon and PANI peaks disappears in the XRD pattern of the A-PANI/Fe3O4/PBC composite, which may because the characteristic peaks of graphite and PANI are covered by the strong characteristic diffraction peaks of Fe3O4. Fig. 2c shows the hysteresis loop of the Fe3O4/PBC and A-PANI/ Fe3O4/PBC composites. The measured saturation magnetization intensity of the Fe3O4/PBC and A-PANI/Fe3O4/PBC composites is 59 emu/g and 28 emu/g, respectively. The results showed that the magnetic saturation value of A-PANI/Fe3O4/PBC is smaller than the Fe3O4/ PBC, which is attributed to the incorporation of nonmagnetic component of PANI. At the same time, the coercivity (Hc) and residual magnetization of composites can be neglected, which indicates that composites have superparamagnetic properties [26]. The surface electronic state and composition of A-PANI/Fe3O4/PBC composite is further confirmed by XPS and results as are shown in Fig. 3. In Fig. 3a, compared to PBC, Fe3O4/PBC composite displays an obvious Fe2p peak, illustrating the presence of the Fe3O4 nanoparticles. Moreover, A-PANI/Fe3O4/PBC composite has the same Fe2p peak as the Fe3O4/PBC, and increased intensities of N1s peaks appears at 399.2 eV originating from the PANI. Fig. 3b–d displays high-resolution C1s, N1s and Fe2p of A-PANI/Fe3O4/PBC fitted by using a Gaussian method. The C1s peak can be split into three peaks at 283.9 eV, 286.0 eV and 286.5 eV, corresponding to the CeC/C]C, CeO and CeN bonds [27], respectively (Fig. 3b). The N1s peak can be deconvoluted into three subpeaks at 398.8 eV, 399.6 eV and 401.2 eV, which is assigned to the quinoid amine (=N-), benzenoid amine (eNHe) and nitrogen cationic amine (-N+-) structure [28], respectively (Fig. 3c), indicating the emeraldine salt form of PANI decorated on the Fe3O4/PBC composite, which may benefit to improve the electrical transmission performance of composite. The Fe2p peak can be decomposed into two peaks at 724.0 eV and 710.6 eV (Fig. 3d), which was fitted two spin–orbit peaks of the Fe 2p3/2 and Fe2p1/2, respectively [29].
PBC, and the average particle size is about 200 nm. After in situ polymerization, aligned PANI nanorods well decorated on the surface and inter-pore of the Fe3O4/PBC composites, and a certain amount of Fe3O4 nanoparticles are covered by PANI (Fig. 1c–d). In addition, the porous structure of the A-PANI/Fe3O4/PBC is maintained after polymerization of aniline, which will increase the propagation path of electromagnetic wave in the composites. The structure of A-PANI/Fe3O4/PBC composite was further demonstrated by TEM and HRTEM, and the results are shown in Fig. 1e and f. It is obvious found that Fe3O4 nanoparticles in A-PANI/Fe3O4/ PBC are formed by the accumulation of small grains (Fig. 1e). From the HRTEM image of composites (Fig. 1f), it is clearly observed that the APANI/Fe3O4/PBC composite displays obvious lattice fringes (0.148 nm) fit well to the (440) plane of Fe3O4 nanoparticle [18]. The molecular characteristics of PBC, Fe3O4/PBC, A-PANI/Fe3O4/ PBC was further characterized by FTIR and the results are shown in Fig. 2a. It is clearly observed that PBC exhibits three characteristic peaks at 3433 cm−1, 1637 cm−1 and 1075 cm−1 corresponding to the eOH, C]O and CeN stretching vibration, respectively [19]. For Fe3O4/PBC composites, the observed new band at 587 cm−1 can be assigned to FeeO bond stretching [20], which indicated the existence of Fe3O4 nanoparticle. As for the A-PANI/Fe3O4/PBC, the several new characteristic peaks corresponding to the fundamental vibrations of PANI can be observed as follows: the peaks at 1568 cm−1 and 1484 cm−1 were contributed to the C]C of stretching vibration of the quinoid (N) and benzenoid (B) rings [21], indicating the oxidation state of emeraldine base polyaniline [22]; the peak at 1296 cm−1 is corresponding to the CeN+ stretching vibration, which can be identified the formation of the emeraldine salt form of PANI [23]; the peaks at 794 cm−1 and 1126 cm−1 can be assigned to the in-plane and out-ofplane CeH bending [24]. The results demonstrate that the successful incorporation of PANI with PBC. In addition, the A-PANI/Fe3O4/PBC also displays the peak of FeeO, confirming that Fe3O4 nanoparticles remain stable during the process of aniline polymerization under acidic conditions. The crystal structure of the PBC, Fe3O4/PBC and A-PANI/Fe3O4/ PBC was investigated by XRD patterns are shown in Fig. 2b. For the PBC, the broad peak located at 2θ = 23° and low intensity peak located at 2θ = 43° is assigned to the (002) and (110) crystal plants of graphitic carbon [25]. The Fe3O4/PBC and A-PANI/Fe3O4/PBC composites
3.1. Microwave absorption properties To investigated the microwave absorbing performance of PBC, 178
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Fig. 2. The FTIR spectra (a) and XRD patterns (b) of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC, the magnetic hysteresis loops of the Fe3O4/PBC and A-PANI/Fe3O4/ PBC.
structure can improve the EM wave absorption of material. In addition, it can be also observed that the RL peaks of each composites in different frequency move toward lower frequency with the increase of thickness. Such phenomenon can be explained by the quarter-wavelength cancellation model [31,32]. These results certainly prove that the thickness of absorbers is one of the key factors of microwave absorbing properties. In order to analyze the microwave absorbing mechanism, the electromagnetic parameters of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC in the frequency range of 2.0–18.0 GHz are investigated, and the results are shown in Fig. 5. The ε′ of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC exhibit a decline behavior with the increase of frequency (Fig. 5a), which is mainly due to the various polarizabilities and electric displacement cannot be maintained with the variational microwave band [33]. For example, the values ε′ of PBC, Fe3O4/PBC and A-PANI/Fe3O4/ PBC decrease gradually from 8.99 to 6.30, 17.06 to 10.14 and 9.88 to 4.21, respectively (Fig. 5b). It is clear that the values ε´´ of PBC, Fe3O4/ PBC and A-PANI/Fe3O4/PBC display fluctuations in the range of 1.17–2.70, 3.94 to 6.32 and 1.58 to 5.46, respectively. Furthermore, Fe3O4/PBC and A-PANI/Fe3O4/PBC composite exhibit a large resonance peak in the frequency range of 4.72–12.4 GHz and 6.14–16.2 GHz respectively, which is a typical nonlinear resonance phenomenon aroused by the dipole polarization and interface polarization [34]. Fig. 5c and d displays the real (μ′) and imaginary (μ´´) of complex permeability of the PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC in the frequency range of 2–18 GHz. The μ′ of the PBC is basically maintained about 1 in the whole frequency range, whereas the μ′ of the Fe3O4/PBC and A-PANI/Fe3O4/PBC have slightly fluctuant in the whole
Fe3O4/PBC and A-PANI/Fe3O4/PBC composites, the reflection loss (RL) can be calculated based on the transmission line theory by the following two equations [30]:
RL = 20 log
Zin − 1 Zin + 1
(1)
The normalized input impedance (Zin) is given by the formula.
Zin =
μr 2π tanh ⎡j ⎛ ⎞ fd μrεr ⎤ εr ⎝ ⎣ c ⎠ ⎦
(2)
Where εr and μr stand for the complex permittivity and permeability of absorbers; f, d and c is the frequency, the thickness of absorbers and the speed of light in a vacuum, respectively. The frequency dependence RL of the PBC, Fe3O4/PBC and A-PANI/ Fe3O4/PBC composites are shown in Fig. 4. As demonstrated in Fig. 4a, compared to PBC and Fe3O4/PBC composite, it can be clearly found that the A-PANI/Fe3O4/PBC composite exhibits excellent microwave absorbing performance. The minimum RL of the A-PANI/Fe3O4/PBC is up to −44.8 dB at 10.67 GHz with the thickness of 2.7 mm, and the effective absorbing bandwidth (EAB, RL < −10 dB) reaches 4.69 GHz. The curves of RL relating to frequency and thickness to contribute compare the EAB of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC are shown in Fig. 4b–d. It is can be clearly found that the EBA of A-PANI/ Fe3O4/PBC reached 13.4 GHz with corresponding thickness of 1.7–5 mm, which is broader than that of the PBC (EAB = 6.43 GHz) and Fe3O4/PBC (EAB = 12.2 GHz). Besides, The EM wave absorption property of A-PANI/Fe3O4/PBC composite is greatly superior to the Fe3O4 related composites (Table S1), demonstrating that the aligned 179
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Fig. 3. XPS spectra of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC composites: (a) survey scan of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC composites, (b) C1s, (c) N1s and (d) Fe2p of A-PANI/Fe3O4/PBC composite.
frequency range, which was aroused from the natural ferromagnetic resonance [35]. Meanwhile, it is clear observed that the μ´´ of the Fe3O4/PBC and A-PANI/Fe3O4/PBC appear peaks in the frequency range of 5.49–13.1 GHz and 8.93–16.3 GHz respectively, indicating that the composite materials have certain magnetic loss characteristics. Surprisingly, the μ´´ of Fe3O4/PBC and A-PANI/Fe3O4/PBC are negative values in high frequency range of 5.85–13.11 GHz, 8.90–15.93 GHz, respectively, which is mainly due to the movement of electrons resulting in magnetic energy radiation of the sample [36,37]. As shown in Fig. 5e–f, the tanδE of A-PANI/Fe3O4/PBC appears stronger resonance peaks compared to PBC and Fe3O4/PBC, suggesting that the A-PANI/ Fe3O4/PBC composite has obvious dielectric relaxation processes under alternating EM filed. The tanδM values of Fe3O4/PBC and A-PANI/ Fe3O4/PBC appear resonance peaks in the high frequency range, which further demonstrating that magnetic loss of Fe3O4/PBC and A-PANI/ Fe3O4/PBC composites. In order to further explore the possible loss mechanism under the enhanced microwave absorbing performance of composites, the ColeCole semicircle curves of samples are discussed in detail. According to Debye theory, the relative complex permittivity can be expressed by the following equation [38]:
εr = ε∞ +
εs − ε∞ = ε′ − jε′′ 1 + j2πfτ
ε′′ =
εs − ε∞ 1 + (2πf )2τ 2
(5)
From equations (4) and (5), it can be further deduced that:
⎛ε′ − ⎝
εs + ε∞ 2 ε − ε∞ 2 ⎞ + (ε′′)2 = ⎛ s ⎞ 2 ⎠ ⎝ 2 ⎠
(6)
Here, the Cole-Cole semicircle curves of ε′ versus ε´´ plots for the samples of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC are shown in Fig. 6. It can be clear that the number Cole-Cole semicircles of A-PANI/ Fe3O4/PBC is more than PBC and pure Fe3O4/PBC, which is due to that the existence of more interfaces in the A-PANI/Fe3O4/PBC gives rise to the relaxation process. Moreover, these semicircles demonstrate the contribution of the Debye relaxation process in the enhanced dielectric properties. Therefore, Cole-Cole plots observations also confirm the results of excellent EM wave absorbing performance of the A-PANI/ Fe3O4/PBC. The main loss mechanism of A-PANI/Fe3O4/PBC composite is shown in Fig. 7. Firstly, the introduction of Fe3O4 nanoparticles make the absorber not only have dielectric loss but also increases the magnetic loss, which is conductive to improve the impedance matching of the absorber, further facilitating the effective entry of the incident electromagnetic wave into the absorber and absorbing the electromagnetic wave. Secondly, there are large number of interfaces and defects among PBC, Fe3O4 and PANI, which cause the interface polarization and dipole polarization, and it may beneficial to improve the electromagnetic loss of the absorber. In addition, the unique structure of aligned PANI is similar to an antenna, when incident microwave is propagated on to the conducting PANI nanorods, the microwave energy can be converted into the form of microcurrent by polarization, then the electromagnetic energy is transformed to heat energy or other forms
(3)
where the definitions are the relative dielectric permittivity ε∞, complex permittivity εr, static permittivity εs at the high-frequency limit, frequency f and polarization relaxation time τ. The ε′ and ε´´ can be deduced as given below:
ε′ = ε∞ +
2πfτ (εs − ε∞) 1 + (2πf )2τ 2
(4) 180
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Fig. 4. The RL (a) of the PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC composites at the thickness of 2.7 mm, The RL of the (b) PBC, (c) Fe3O4/PBC and (d) A-PANI/ Fe3O4/PBC at different thicknesses from 1.7 to 5 mm.
Fig. 5. Electromagnetic parameters of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC:(a) the real part (ε′) and (b) imaginary (ε″) of complex permittivity, (c) the real part (μ′) and (d) imaginary part (μ″) of complex permeability, (e) dielectric loss (tanδE) and (f) magnetic loss (tanδM). 181
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Fig. 6. Typical Cole-Cole semicircles for the PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC.
of energy, and finally dissipate. Moreover, the porous structure of the composite causes multiple scattering and reflection of electromagnetic waves, which expands the propagation path of electromagnetic waves.
demonstrated by morphology and structure characterization. Compared to PBC and Fe3O4/PBC, A-PANI/Fe3O4/PBC exhibits excellent microwave absorbing performance. The minimum RL of A-PANI/Fe3O4/PBC composite is up to 44.8 dB at 10.67 GHz with the thickness of 2.7 mm, and effective absorbing bandwidth (RL < −10 dB) reaches 4.69 GHz. The excellent absorbing performance of A-PANI/Fe3O4/PBC composite is mainly attributed to its multi-loss mechanisms, good impedance matching and geometrical effect. Therefore, A-PANI/Fe3O4/PBC
4. Conclusion In summary, the A-PANI/Fe3O4/PBC composite via hydrothermal and in situ polymerization. The porous and aligned structure can be
Fig. 7. Schematic representation of possible microwave absorption mechanisms of A-PANI/Fe3O4/PBC composite. 182
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composite with excellent electromagnetic wave absorbing performance may have a good application prospect.
[16]
Acknowledgements [17]
This work was supported by Zhejiang Provincial Natural Science Foundation of China (No. LY19E030009) and National Natural Science Foundation of China (No.51503183); Key Program for International Science and Technology Cooperation Projects of Ministry of Science and Technology of China (No. 2016YFE0125900).
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Appendix A. Supplementary data
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Supplementary data to this article can be found online at https:// doi.org/10.1016/j.compscitech.2019.02.031.
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Contents lists available at ScienceDirect
Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech
Construction of polyaniline aligned on magnetic functionalized biomass carbon giving excellent microwave absorption properties
T
Qixin Yanga, Yiyuan Shia, Yu Fanga, Yubing Donga, Qingqing Nia,b, Yaofeng Zhua,∗, Yaqin Fua a b
Key Laboratory of Advanced Textile Materials and Manufacturing Technology Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, Zhejiang, 310018, China Interdisciplinary Graduate School of Science and Technology, Shinshu University, Tokida, Ueda, 386-8576, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: A: Hybrid composites B: Magnetic properties B: Interface
A novel ternary nanocomposite of Fe3O4 functionalized porous biomass carbon decorated by aligned polyaniline (A-PANI/Fe3O4/PBC) was successfully fabricated by hydrothermal and in situ oxidative polymerization. The morphology and structure of the composite was characterized by X-ray diffraction, fourier transform infrared spectra, scanning electron microcopy, transmission electron microscopy, X-ray photoelectron spectra and vibrating sample magnetometer. The microwave absorbing properties of A-PANI/Fe3O4/PBC composite were investigated in the frequency of 2–18 GHz. The results indicated that the A-PANI/Fe3O4/PBC composite possess excellent microwave absorbing performance, and the minimum reflection loss can be up to −44.8 dB at 10.67 GHz, effective absorbing bandwidth (RL < −10 dB) reaches 4.69 GHz with a thickness of 2.7 mm. The excellent microwave absorbing performance of composite was mainly related to the multi-loss mechanisms, good impedance matching, synergistic and geometrical effect of porous biomass carbon, magnetic particles and aligned PANI.
1. Introduction Nowadays, electromagnetic wave pollution and interference caused by the explosive development of information technology have severe effect on human health and the normal operation of electronic devices [1,2]. To solve these problems, researchers have devoted much efforts to develop the high-performance microwave absorbing materials (MAMs) enjoying the advantage of the light weight, thin thickness, broad frequency and strong absorption [3,4]. In the past years, carbonaceous materials have been reported used as microwave absorbers for their features of good stability, low density and good electrical conductivity [5], such as graphene [6], carbon nanotubes (CNTs) [7], carbon fibers [8], biomass carbon [9]. Among these carbonaceous materials, biomass carbon materials have attracted more attention for microwave absorption applications because of its advantage properties also including simple fabrication process, low cost and wide variety of sources [10]. Additionally, the unique porous structures and high pore volume of biomass carbon makes it a promising candidate for electromagnetic microwave absorbers [11]. Unfortunately, similar to other carbon materials, the single dielectric loss of biomass carbon materials may result in impedance mismatching, which seriously hinders their practical application as high performance of MAMs. As we know, in the past decades, Fe3O4 nanoparticles have been ∗
used as one of effective components to obtain MAMs with excellent microwave absorption properties, which they exhibit advantages of surface activity, high saturation magnetization and good magnetic loss absorbing properties [12,13]. Therefore, coupling Fe3O4 nanoparticle with carbon materials may contribute the high complex permeability values to composites because of their large saturation magnetization, which give a chance to compensate the high conductivity of carbon materials and further improve its impedance matching effectively. Besides, a recent progress reveals that designing and construction of nanostructure with special geometrical morphologies may be beneficial for electromagnetic wave absorption [14,15]. The rational geometrical morphologies design of composites can induce multiple reflection and scattering under alternated electromagnetic field, which will extent transmission path of electromagnetic wave. Meanwhile, it can also provide large amounts of nano-interfaces to improve interfacial polarization which could balance the strong conductive loss. Polyaniline (PANI) has been promised to be an ideal candidate for constructing reasonable geometrical morphologies of composites due to its geometry can be controlled by rational synthetic routes [16,17]. Moreover, the tunable conductivity of PANI can balance MAM impedance matching and further enhance it attenuate capability. Therefore, combination of PANI with special geometrical morphologies and magnetically decorated porous biomass carbon to construct excellent microwave
Corresponding author. E-mail address: [email protected] (Y. Zhu).
https://doi.org/10.1016/j.compscitech.2019.02.031 Received 25 October 2018; Received in revised form 23 January 2019; Accepted 28 February 2019 Available online 02 March 2019 0266-3538/ © 2019 Elsevier Ltd. All rights reserved.
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of 1 M HClO4 solution with stiring for 10 min. Then, 0.6 mmol of aniline and ammonium persulfate (the molar ratio of aniline/APS was 1:1.25) was added into above suspension solution sequentially, and followed by stirring for 10 h at room temperature. The synthesized products were washed alternately with ethanol and deionized water for 3 times and then dried at 45 °C for 24 h. Finally, the aligned PANI/Fe3O4 functionalized porous biomass carbon composites was denoted as A-PANI/ Fe3O4/PBC.
absorbers are expected and meaningful. In this regard, aligned PANI grown vertically on magnetic Fe3O4 functionalized porous biomass carbon materials (A-PANI/Fe3O4/PBC) have been fabricated by a synthetic method based on simple hydrothermal and in situ polymerization. The morphology, microstructural, and microwave absorption properties of the composite were investigated in detail. The results indicated that the A-PANI/Fe3O4/PBCparaffin wax composite (A-PANI/Fe3O4/PBC absorbers weight fraction = 30 wt%) exhibited superior microwave absorption properties due to the combined action of electric loss, magnetic loss, impedance matching and geometrical effect. Therefore, it is expected that this work will provide a new direction for the preparation of novel microwave absorbing materials.
2.5. Characterizations Scanning electron microscope (SEM, Hitachi S-4800) and transmission electron microscope (TEM, JEOL JEM-2100F) were used to observe the microstructure and morphology of the materials. Fourier Transform Infrared Spectroscopy (FT-IR) was observed by Nicolet 5700 with KBr pellets. The crystal phase structure of the material was analyzed by XRD (Bruker AXS, D8-Discover Cu Kα radiation) and Raman spectrophotometer (LabRAM HR Evolution, Horiba, 785 nm laser). The magnetic properties of the samples were tested by Lake Shore 7047 vibratory magnetometer (VSM) of Lake Shore Company of USA at room temperature. X-ray photoelectron spectroscopy (XPS, K-Alpha) was used to study the chemical composition and chemical binding state of the sample surface. Complex permittivity and permeability of the samples were studied by the vector network analyzer (VNA, Agilent N5224A) in the 2–18 GHz frequency range. The as prepared A-PANI/ Fe3O4/PBC was mixed with wax in a mass ratio of 30 wt%, and then the mixture was pressed into a toroid shape with an outer diameter of 7.0 nm and inner diameter of 3.0 mm.
2. Experimental section 2.1. Materials Ferric trichloride (FeCl3), Ethylene glycol (C2H6O2), Sodium Citrate (Na3C6H5O7), sodium acetate (C2H3NaO2) and Ammonium persulfate (APS) were supplied from Shanghai Macklin Biochemical Co. Ltd. Aniline (AN) was obtained by Aladdin chemistry Co. Ltd. Perchloric acid (HClO4) was purchase by Hangzhou Gaojing Fine chemical industry Co. Ltd. All the reagents were of analytical grade and used as received. 2.2. Preparation of porous biomass carbon The natural loofah used as raw material, the sample was soaked in 1 M KOH solution at 70 °C for 12 h and dried in vacuum oven at 60 °C for 12 h subsequently. Then the sample was carbonized under nitrogen atmosphere at 700 °C for 1 h, the heating rate was 5 °C/min−1. Furthermore, the obtained products were soaked in 1 M HCl solution for 5 h. Finally, the obtained porous biomass carbon material was washed by 1 M HCl solution and deionized water several times subsequently, and drying the product at 60 °C for 24 h.
3. Results and discussion In order to realize the integrated design of structure and multi-loss mechanism of high performances microwave absorbing composites. The magnetic functionalized porous biomass carbon materials coupling with aligned polyaniline were carried out in this work and the procedure for the preparation is depicted in Scheme 1. Firstly, the porous biomass carbon (PBC) was prepared by KOH activation and carbonization. And then, the as prepared biomass carbon was magnetic functionalized by the formation of aggregated Fe3O4 nano-crystallines on its surface via hydrothermal reaction under alkaline conditions. Finally, the aligned PANI growth on the magnetic functionalized biomass carbon direct through a typical dilute solution of in situ polymerization. The formation mechanism of aligned PANI can be depicted as follows: At the beginning, PANI oligomer was synthesized through in situ polymerization on the surface of Fe3O4/PBC composites due to the presence of functional group and π-π stacking acts as an initiator. Then the heterogeneous nucleation of PANI occurs in the course of polymerization for the formation of many tiny PANI protuberances, which act as the new active nucleation sites for the further growth of aligned polyaniline on the Fe3O4/PBC surface. Fig. 1 shows the morphology and microstructure of the PBC, Fe3O4/ PBC and A-PANI/Fe3O4/PBC. It is clear that PBC shows the well-developed and open porous structure with the average pore diameter in the range of 0.2–2 μm (Fig. 1a). As shown in Fig. 1b, it can be observed that the Fe3O4 nanoparticles covered on the surface and inter-pore of
2.3. Preparation of magnetic functionalized porous biomass carbon 150 mg of porous biomass carbon (PBC) was added in 20 ml ethylene glycol solution and stirred at room temperature for 30 min, and then 0.2 mmol ferric chloride, 1.2 g sodium acetate and 0.2 g sodium citrate were added to the above mixed solution under stirring. After 1 h, the mixture was transferred into a 50 ml Teflon-lined stainless-steel autoclave and kept at 200 °C for 10 h. After reaction, the mixture was cooled to room temperature, and the product was obtained by centrifugation, washed with ethanol and deionized water for several times, and finally dried at 50 °C for 24 h. The obtained products of Fe3O4 functionalized porous biomass carbon composite was denoted as Fe3O4/PBC. 2.4. Preparation of aligned PANI/Fe3O4/porous biomass carbon composite For the synthesis of the aligned PANI/Fe3O4 functionalized porous biomass carbon composites, 150 mg Fe3O4/PBC was dispersed in 50 ml
Scheme 1. Schematic illustration on the fabrication of A-PANI/Fe3O4/PBC composite. 177
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Fig. 1. The SEM images of PBC (a), Fe3O4/PBC (b), A-PANI/Fe3O4/PBC (c), the magnified image of A-PANI/Fe3O4/PBC (d), the TEM (e) and HRTEM (f) images of APANI/Fe3O4/PBC.
exhibits diffraction peaks appeared at 30.2°, 35.6°, 43.2°, 57.2°, 62.7°, which can be corresponding to the (220), (311), (400), (511) and (440) planes of cubic Fe3O4 (JCPDS no. 75-0033) [18], respectively. In addition, the broad diffraction peaks of the amorphous carbon and PANI peaks disappears in the XRD pattern of the A-PANI/Fe3O4/PBC composite, which may because the characteristic peaks of graphite and PANI are covered by the strong characteristic diffraction peaks of Fe3O4. Fig. 2c shows the hysteresis loop of the Fe3O4/PBC and A-PANI/ Fe3O4/PBC composites. The measured saturation magnetization intensity of the Fe3O4/PBC and A-PANI/Fe3O4/PBC composites is 59 emu/g and 28 emu/g, respectively. The results showed that the magnetic saturation value of A-PANI/Fe3O4/PBC is smaller than the Fe3O4/ PBC, which is attributed to the incorporation of nonmagnetic component of PANI. At the same time, the coercivity (Hc) and residual magnetization of composites can be neglected, which indicates that composites have superparamagnetic properties [26]. The surface electronic state and composition of A-PANI/Fe3O4/PBC composite is further confirmed by XPS and results as are shown in Fig. 3. In Fig. 3a, compared to PBC, Fe3O4/PBC composite displays an obvious Fe2p peak, illustrating the presence of the Fe3O4 nanoparticles. Moreover, A-PANI/Fe3O4/PBC composite has the same Fe2p peak as the Fe3O4/PBC, and increased intensities of N1s peaks appears at 399.2 eV originating from the PANI. Fig. 3b–d displays high-resolution C1s, N1s and Fe2p of A-PANI/Fe3O4/PBC fitted by using a Gaussian method. The C1s peak can be split into three peaks at 283.9 eV, 286.0 eV and 286.5 eV, corresponding to the CeC/C]C, CeO and CeN bonds [27], respectively (Fig. 3b). The N1s peak can be deconvoluted into three subpeaks at 398.8 eV, 399.6 eV and 401.2 eV, which is assigned to the quinoid amine (=N-), benzenoid amine (eNHe) and nitrogen cationic amine (-N+-) structure [28], respectively (Fig. 3c), indicating the emeraldine salt form of PANI decorated on the Fe3O4/PBC composite, which may benefit to improve the electrical transmission performance of composite. The Fe2p peak can be decomposed into two peaks at 724.0 eV and 710.6 eV (Fig. 3d), which was fitted two spin–orbit peaks of the Fe 2p3/2 and Fe2p1/2, respectively [29].
PBC, and the average particle size is about 200 nm. After in situ polymerization, aligned PANI nanorods well decorated on the surface and inter-pore of the Fe3O4/PBC composites, and a certain amount of Fe3O4 nanoparticles are covered by PANI (Fig. 1c–d). In addition, the porous structure of the A-PANI/Fe3O4/PBC is maintained after polymerization of aniline, which will increase the propagation path of electromagnetic wave in the composites. The structure of A-PANI/Fe3O4/PBC composite was further demonstrated by TEM and HRTEM, and the results are shown in Fig. 1e and f. It is obvious found that Fe3O4 nanoparticles in A-PANI/Fe3O4/ PBC are formed by the accumulation of small grains (Fig. 1e). From the HRTEM image of composites (Fig. 1f), it is clearly observed that the APANI/Fe3O4/PBC composite displays obvious lattice fringes (0.148 nm) fit well to the (440) plane of Fe3O4 nanoparticle [18]. The molecular characteristics of PBC, Fe3O4/PBC, A-PANI/Fe3O4/ PBC was further characterized by FTIR and the results are shown in Fig. 2a. It is clearly observed that PBC exhibits three characteristic peaks at 3433 cm−1, 1637 cm−1 and 1075 cm−1 corresponding to the eOH, C]O and CeN stretching vibration, respectively [19]. For Fe3O4/PBC composites, the observed new band at 587 cm−1 can be assigned to FeeO bond stretching [20], which indicated the existence of Fe3O4 nanoparticle. As for the A-PANI/Fe3O4/PBC, the several new characteristic peaks corresponding to the fundamental vibrations of PANI can be observed as follows: the peaks at 1568 cm−1 and 1484 cm−1 were contributed to the C]C of stretching vibration of the quinoid (N) and benzenoid (B) rings [21], indicating the oxidation state of emeraldine base polyaniline [22]; the peak at 1296 cm−1 is corresponding to the CeN+ stretching vibration, which can be identified the formation of the emeraldine salt form of PANI [23]; the peaks at 794 cm−1 and 1126 cm−1 can be assigned to the in-plane and out-ofplane CeH bending [24]. The results demonstrate that the successful incorporation of PANI with PBC. In addition, the A-PANI/Fe3O4/PBC also displays the peak of FeeO, confirming that Fe3O4 nanoparticles remain stable during the process of aniline polymerization under acidic conditions. The crystal structure of the PBC, Fe3O4/PBC and A-PANI/Fe3O4/ PBC was investigated by XRD patterns are shown in Fig. 2b. For the PBC, the broad peak located at 2θ = 23° and low intensity peak located at 2θ = 43° is assigned to the (002) and (110) crystal plants of graphitic carbon [25]. The Fe3O4/PBC and A-PANI/Fe3O4/PBC composites
3.1. Microwave absorption properties To investigated the microwave absorbing performance of PBC, 178
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Fig. 2. The FTIR spectra (a) and XRD patterns (b) of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC, the magnetic hysteresis loops of the Fe3O4/PBC and A-PANI/Fe3O4/ PBC.
structure can improve the EM wave absorption of material. In addition, it can be also observed that the RL peaks of each composites in different frequency move toward lower frequency with the increase of thickness. Such phenomenon can be explained by the quarter-wavelength cancellation model [31,32]. These results certainly prove that the thickness of absorbers is one of the key factors of microwave absorbing properties. In order to analyze the microwave absorbing mechanism, the electromagnetic parameters of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC in the frequency range of 2.0–18.0 GHz are investigated, and the results are shown in Fig. 5. The ε′ of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC exhibit a decline behavior with the increase of frequency (Fig. 5a), which is mainly due to the various polarizabilities and electric displacement cannot be maintained with the variational microwave band [33]. For example, the values ε′ of PBC, Fe3O4/PBC and A-PANI/Fe3O4/ PBC decrease gradually from 8.99 to 6.30, 17.06 to 10.14 and 9.88 to 4.21, respectively (Fig. 5b). It is clear that the values ε´´ of PBC, Fe3O4/ PBC and A-PANI/Fe3O4/PBC display fluctuations in the range of 1.17–2.70, 3.94 to 6.32 and 1.58 to 5.46, respectively. Furthermore, Fe3O4/PBC and A-PANI/Fe3O4/PBC composite exhibit a large resonance peak in the frequency range of 4.72–12.4 GHz and 6.14–16.2 GHz respectively, which is a typical nonlinear resonance phenomenon aroused by the dipole polarization and interface polarization [34]. Fig. 5c and d displays the real (μ′) and imaginary (μ´´) of complex permeability of the PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC in the frequency range of 2–18 GHz. The μ′ of the PBC is basically maintained about 1 in the whole frequency range, whereas the μ′ of the Fe3O4/PBC and A-PANI/Fe3O4/PBC have slightly fluctuant in the whole
Fe3O4/PBC and A-PANI/Fe3O4/PBC composites, the reflection loss (RL) can be calculated based on the transmission line theory by the following two equations [30]:
RL = 20 log
Zin − 1 Zin + 1
(1)
The normalized input impedance (Zin) is given by the formula.
Zin =
μr 2π tanh ⎡j ⎛ ⎞ fd μrεr ⎤ εr ⎝ ⎣ c ⎠ ⎦
(2)
Where εr and μr stand for the complex permittivity and permeability of absorbers; f, d and c is the frequency, the thickness of absorbers and the speed of light in a vacuum, respectively. The frequency dependence RL of the PBC, Fe3O4/PBC and A-PANI/ Fe3O4/PBC composites are shown in Fig. 4. As demonstrated in Fig. 4a, compared to PBC and Fe3O4/PBC composite, it can be clearly found that the A-PANI/Fe3O4/PBC composite exhibits excellent microwave absorbing performance. The minimum RL of the A-PANI/Fe3O4/PBC is up to −44.8 dB at 10.67 GHz with the thickness of 2.7 mm, and the effective absorbing bandwidth (EAB, RL < −10 dB) reaches 4.69 GHz. The curves of RL relating to frequency and thickness to contribute compare the EAB of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC are shown in Fig. 4b–d. It is can be clearly found that the EBA of A-PANI/ Fe3O4/PBC reached 13.4 GHz with corresponding thickness of 1.7–5 mm, which is broader than that of the PBC (EAB = 6.43 GHz) and Fe3O4/PBC (EAB = 12.2 GHz). Besides, The EM wave absorption property of A-PANI/Fe3O4/PBC composite is greatly superior to the Fe3O4 related composites (Table S1), demonstrating that the aligned 179
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Fig. 3. XPS spectra of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC composites: (a) survey scan of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC composites, (b) C1s, (c) N1s and (d) Fe2p of A-PANI/Fe3O4/PBC composite.
frequency range, which was aroused from the natural ferromagnetic resonance [35]. Meanwhile, it is clear observed that the μ´´ of the Fe3O4/PBC and A-PANI/Fe3O4/PBC appear peaks in the frequency range of 5.49–13.1 GHz and 8.93–16.3 GHz respectively, indicating that the composite materials have certain magnetic loss characteristics. Surprisingly, the μ´´ of Fe3O4/PBC and A-PANI/Fe3O4/PBC are negative values in high frequency range of 5.85–13.11 GHz, 8.90–15.93 GHz, respectively, which is mainly due to the movement of electrons resulting in magnetic energy radiation of the sample [36,37]. As shown in Fig. 5e–f, the tanδE of A-PANI/Fe3O4/PBC appears stronger resonance peaks compared to PBC and Fe3O4/PBC, suggesting that the A-PANI/ Fe3O4/PBC composite has obvious dielectric relaxation processes under alternating EM filed. The tanδM values of Fe3O4/PBC and A-PANI/ Fe3O4/PBC appear resonance peaks in the high frequency range, which further demonstrating that magnetic loss of Fe3O4/PBC and A-PANI/ Fe3O4/PBC composites. In order to further explore the possible loss mechanism under the enhanced microwave absorbing performance of composites, the ColeCole semicircle curves of samples are discussed in detail. According to Debye theory, the relative complex permittivity can be expressed by the following equation [38]:
εr = ε∞ +
εs − ε∞ = ε′ − jε′′ 1 + j2πfτ
ε′′ =
εs − ε∞ 1 + (2πf )2τ 2
(5)
From equations (4) and (5), it can be further deduced that:
⎛ε′ − ⎝
εs + ε∞ 2 ε − ε∞ 2 ⎞ + (ε′′)2 = ⎛ s ⎞ 2 ⎠ ⎝ 2 ⎠
(6)
Here, the Cole-Cole semicircle curves of ε′ versus ε´´ plots for the samples of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC are shown in Fig. 6. It can be clear that the number Cole-Cole semicircles of A-PANI/ Fe3O4/PBC is more than PBC and pure Fe3O4/PBC, which is due to that the existence of more interfaces in the A-PANI/Fe3O4/PBC gives rise to the relaxation process. Moreover, these semicircles demonstrate the contribution of the Debye relaxation process in the enhanced dielectric properties. Therefore, Cole-Cole plots observations also confirm the results of excellent EM wave absorbing performance of the A-PANI/ Fe3O4/PBC. The main loss mechanism of A-PANI/Fe3O4/PBC composite is shown in Fig. 7. Firstly, the introduction of Fe3O4 nanoparticles make the absorber not only have dielectric loss but also increases the magnetic loss, which is conductive to improve the impedance matching of the absorber, further facilitating the effective entry of the incident electromagnetic wave into the absorber and absorbing the electromagnetic wave. Secondly, there are large number of interfaces and defects among PBC, Fe3O4 and PANI, which cause the interface polarization and dipole polarization, and it may beneficial to improve the electromagnetic loss of the absorber. In addition, the unique structure of aligned PANI is similar to an antenna, when incident microwave is propagated on to the conducting PANI nanorods, the microwave energy can be converted into the form of microcurrent by polarization, then the electromagnetic energy is transformed to heat energy or other forms
(3)
where the definitions are the relative dielectric permittivity ε∞, complex permittivity εr, static permittivity εs at the high-frequency limit, frequency f and polarization relaxation time τ. The ε′ and ε´´ can be deduced as given below:
ε′ = ε∞ +
2πfτ (εs − ε∞) 1 + (2πf )2τ 2
(4) 180
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Fig. 4. The RL (a) of the PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC composites at the thickness of 2.7 mm, The RL of the (b) PBC, (c) Fe3O4/PBC and (d) A-PANI/ Fe3O4/PBC at different thicknesses from 1.7 to 5 mm.
Fig. 5. Electromagnetic parameters of PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC:(a) the real part (ε′) and (b) imaginary (ε″) of complex permittivity, (c) the real part (μ′) and (d) imaginary part (μ″) of complex permeability, (e) dielectric loss (tanδE) and (f) magnetic loss (tanδM). 181
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Fig. 6. Typical Cole-Cole semicircles for the PBC, Fe3O4/PBC and A-PANI/Fe3O4/PBC.
of energy, and finally dissipate. Moreover, the porous structure of the composite causes multiple scattering and reflection of electromagnetic waves, which expands the propagation path of electromagnetic waves.
demonstrated by morphology and structure characterization. Compared to PBC and Fe3O4/PBC, A-PANI/Fe3O4/PBC exhibits excellent microwave absorbing performance. The minimum RL of A-PANI/Fe3O4/PBC composite is up to 44.8 dB at 10.67 GHz with the thickness of 2.7 mm, and effective absorbing bandwidth (RL < −10 dB) reaches 4.69 GHz. The excellent absorbing performance of A-PANI/Fe3O4/PBC composite is mainly attributed to its multi-loss mechanisms, good impedance matching and geometrical effect. Therefore, A-PANI/Fe3O4/PBC
4. Conclusion In summary, the A-PANI/Fe3O4/PBC composite via hydrothermal and in situ polymerization. The porous and aligned structure can be
Fig. 7. Schematic representation of possible microwave absorption mechanisms of A-PANI/Fe3O4/PBC composite. 182
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composite with excellent electromagnetic wave absorbing performance may have a good application prospect.
[16]
Acknowledgements [17]
This work was supported by Zhejiang Provincial Natural Science Foundation of China (No. LY19E030009) and National Natural Science Foundation of China (No.51503183); Key Program for International Science and Technology Cooperation Projects of Ministry of Science and Technology of China (No. 2016YFE0125900).
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Appendix A. Supplementary data
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Supplementary data to this article can be found online at https:// doi.org/10.1016/j.compscitech.2019.02.031.
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