International Journal of Polymer Science
Volume 2018 (2018), Article ID 3417060, 6 pages
https://doi.org/10.1155/2018/3417060

Research Article

Preparation and Microwave Absorption Properties of Polyaniline and Magnetite Core-Shell-Structured Hybrid

Xuan Zhang

Department of Chemical Engineering, Northwest University, China

Correspondence should be addressed to Xuan Zhang; zhangxuan0904@stumail.nwu.edu.cn

Received 29 June 2018; Revised 7 August 2018; Accepted 9 August 2018; Published 24 October 2018

Academic Editor: Zhiyuan Xiong

Copyright © 2018 Xuan Zhang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

In this study, polyaniline and Fe₃O₄ (PAN@Fe₃O₄) hybrids are fabricated and their microwave absorption property is studied. PAN@Fe₃O₄ hybrids are fabricated by the in situ aniline polymerization at spherical of Fe₃O₄ which is prepared by the solvothermal process. Fourier-transform infrared spectrophotometer (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are applied to confirm the composition of the fabricated PAN@Fe₃O₄ hybrids. The morphologies of PAN@Fe₃O₄ hybrids are studied by scanning electron microscope (SEM) and transmission electron microscopy (TEM). The content of polyaniline in the PAN@Fe₃O₄ hybrids is calculated by thermogravimetric analysis (TGA). The magnetic properties of PAN@Fe₃O₄ hybrids are characterized by vibrating sample magnetometer (VSM). The microwave absorption property of PAN@Fe₃O₄ hybrids are measured on a vector network analyzer. The research show that the microwave absorptions property of the obtained PAN@Fe₃O₄ hybrids can be adjusted by controlling the in situ aniline polymerization at spherical of Fe₃O₄.

1. Introduction

With the expansion use of electric device, including personal computers, mobile phones, microwave oven, and other military equipment and/or space equipment, microwave has become a new pollution to our health [1–6]. The effective way to solve this problem is the development of new microwave absorption materials [7, 8]. The basic requirement of the microwave absorption materials is to show strong microwave absorption, represented by reflection loss [9]. Usually, the microwave absorption materials are to dissipate the incident microwave which includes the dielectric dissipation and magnetic dissipation [10, 11]. Excellent microwave absorption materials also exhibit compatibility between the dielectric dissipation and magnetic dissipation. The magnetic dissipation can be easily achieved by using magnetic materials such as magnetic iron oxide. As a result, magnetite is mostly utilized as microwave absorption materials [12, 13]. The dielectric dissipation can be achieved by introducing the dielectric materials and/or conducting materials [14, 15]. These include phthalocyanine copper and its derivatives [16], the carbon materials including CNT [17], carbon black, and graphene [18], and the conducting polymers such as polyaniline and polythiophene [19]. The conducting polymers that usually combine the low density and excellent conductivity have attracted considerable attention both from the research and the practical application. In the conducting polymers, polyaniline (PAN) can be easily obtained and shows excellent conductivity after doping. Up to now, PAN has been used to prepare composites with polyethylene, poly(vinylidene fluoride), graphene, CNT, and others [20, 21].

With the magnetite as the magnetic dissipation part and PAN as the dielectric dissipation part, PAN and magnetite hybrid materials can be obtained to be used as microwave absorption materials. However, another problem is the compatibility between them due to the inorganic part of magnetite and organic part of PAN. To solve this problem, core-shell-structured hybrid containing magnetite core and PAN shell can be imagined.

In this study, we fabricated hybrid PAN@Fe₃O₄ by the in situ aniline polymerization at the spherical of Fe₃O₄ which is prepared by the solvothermal process. The PAN@Fe₃O₄ hybrids are characterized by XPS, XRD, TGA, SEM, TEM, FTIR, and VSM. After that, microwave absorption property of the prepared PAN@Fe₃O₄ hybrids is studied in detail.

2. Experimental Section

2.1. Materials

Ethylene glycol (99%), FeCl₃·6H₂O (99%), and polyethylene glycol 2000 (99%) were purchased from Kelong Reagents, Chengdu, China. Sodium dodecyl benzene sulfonate (SDBS, 99%), hydrochloric acid (37%), ammonium sulfate (98%), and aniline (99%) were purchased from Changzheng Reagents, Chengdu, China. Other chemicals and reagents were commercial available products, and all of them were used as received.

2.2. Preparation of Fe₃O₄

Magnetite was fabricated by the solvothermal process throughout previous literature [8]. FeCl₃·6H₂O (10.0 g) and polyethylene glycol 2000 (3.7 g) were mixed with 160 ml ethylene glycol at RT, followed by adding sodium acetate trihydrate (27.0 g). The system was mixed by mechanical agitation as well as ultrasonication for 40 min to form an orange solution. After that, the above-prepared mixture was poured into an autoclave; the whole system was heated at 180°C for 12 h, after that it was cooled down to RT. The product was segregated by a magnet and was purified 3–5 times with purified water and ethanol, respectively. Finally, the product was dried under vacuum at 70°C for 8 h.

2.3. Preparation of Polyaniline and Fe₃O₄ (PAN@Fe₃O₄) Hybrids

The polyaniline and Fe₃O₄ (PAN@Fe₃O₄) hybrids were fabricated by the in situ aniline polymerization at the spherical of Fe₃O₄ with the existence of ammonium sulfate. With the change of the amount of the aniline and ammonium sulfate, polyaniline and Fe₃O₄ hybrids with different contents of polyaniline were obtained. The typical procedure is as follows: 0.25 g Fe₃O₄ was dispersed in 100 ml deionized water with the help of SDBS (25 mg) and mechanical agitation. After that, the system was cooled at 0–5°C through the ice. At the time, aniline (0.25 ml), dissolved in 0.1 mol/l HCl (50 ml), was also cooled at 0–5°C through another ice system. The cooled aniline solution was mixed with the Fe₃O₄ dispersion with vigorous mechanical agitation in the ice bath. The ammonium sulfate (2.5 g) was dissolved in 25 ml purified water at 0–5°C in the third ice bath. After being cooled down, the ammonium sulfate was put dropwise in Fe₃O₄ and aniline mixture. The polymerization was kept on for at least 12 h. In this study, three polyaniline and Fe₃O₄ hybrids named as PAN@Fe₃O₄-1, PAN@Fe₃O₄-2, and PAN@Fe₃O₄-3 were prepared.

2.4. Characterization

The structure of PAN@Fe₃O₄ hybrid materials was characterized by XRD (Rigaku RINT 2400) and XPS (PHI-5300 ESCA). FTIR (8000S) was also utilized to characterize the PAN@Fe₃O₄ hybrids. The content of polyaniline in the PAN@Fe₃O₄ hybrid was calculated by TGA (Q50). The morphologies of PAN@Fe₃O₄ hybrids were studied by SEM (JSM-6490LV) and TEM (H600). The magnetic property of PAN@Fe₃O₄ hybrids was studied by VSM (BHV-525). The electromagnetic property of PAN@Fe₃O₄ hybrids was tested on a vector network analyzer (8720ET) at 0.5–18 GHz. The sample was fabricated through blending PAN@Fe₃O₄ hybrids with wax in a mass ratio of 3 : 1.

3. Results and Discussion

In the study, polyaniline and Fe₃O₄ (PAN@Fe₃O₄) hybrids are fabricated and their microwave absorption property is studied. The PAN@Fe₃O₄ hybrid is fabricated by the in situ aniline polymerization at the spherical of Fe₃O₄ which is prepared by the solvothermal process [8]. Figure 1 shows FTIR spectra of PAN, Fe₃O₄, as well as PAN@Fe₃O₄-1; compared with that of Fe₃O₄, the FTIR curves of PAN@Fe₃O₄-1 show additional absorption peaks at 3430 cm⁻¹ (N-H), 1585 and 1496 cm⁻¹ (benzene ring), and 1189 cm⁻¹ (AR-N) which indicate the existence of polyaniline in the system [19]. In addition, the peak at 588 cm⁻¹ (Fe-O) is observed on the spectra curves of Fe₃O₄ and PAN@Fe₃O₄-1.

Figure 1: FTIR spectrum of PAN, Fe₃O₄, and PAN@Fe₃O₄-1.

XPS is also used to characterize the composition of the obtained PAN@Fe₃O₄ hybrids. Figure 2(a) shows the XPS spectra of Fe₃O₄ and PAN@Fe₃O₄-1. On the spectrum of Fe₃O₄, the peaks at 534 eV and 716 eV correspond the O1s and Fe2p, while the peak at 287 eV is resulted from the C1s which might come from the ethylene glycol and polyethylene glycol 2000 used during the solvothermal process. The Fe2p peak can be divided into two peaks at 711 eV and 725 eV which come from Fe2p1/2 and Fe2p3/2 as shown in Figure 2(b); this confirms the existence of Fe₃O₄. In comparison, the XPS spectrum of PAN@Fe₃O₄-1 shows new peak at 405 eV which is attributed to the N1s from the polyaniline at the spherical of PAN@Fe₃O₄-1. Both of the FTIR and the XPS confirm the preparation of polyaniline and Fe₃O₄ hybrids [7].

(a)

(b)

Figure 2: XPS spectra of Fe₃O₄ and PAN@Fe₃O₄-1 (a) and Fe2p peak (b).

XRD is a technic to confirm component of prepared new nanocomposites by comparing XRD pattern peaks with the standard card. Figure 3 shows XRD curves of prepared samples. As shown in the picture, six peaks at 30°, 35°, 43°, 54°, 57°, and 63° which match well with (220), (311), (400), (422), (511), and (440) planes of the standard XRD of magnetite (JCPDS file no.19-0629) are observed on the curves of Fe₃O₄. While a wide peak at 20° is seen on the curves of PAN. PAN@Fe₃O₄-1 shows peaks combining from PAN and Fe₃O₄, indicating the composition of PAN and Fe₃O₄ in PAN@Fe₃O₄-1. The other samples also show similar XRD patterns which confirm the Fe₃O₄ in the PAN@Fe₃O₄ hybrids [22].

Figure 3: XRD pattern of Fe₃O₄, PAN@Fe₃O₄-1, PAN@Fe₃O₄-2, PAN@Fe₃O₄-3, and PAN.

After the characterization of the composition of PAN@Fe₃O₄ hybrids, the micro morphology of them is studied through SEM and TEM. Figure 4 shows SEM micro images of Fe₃O₄ and PAN@Fe₃O₄-1. As shown in the figure, the Fe₃O₄ exhibits smooth surface. In addition, anomalous nanoparticles including spheres, hemispheres, bowls, and open balls are observed for Fe₃O₄. While for PAN@Fe₃O₄-1, its surface becomes coarser indicating the existence of the polyaniline. More importantly, the shape of the PAN@Fe₃O₄-1 becomes regular spheres. The structure change of the PAN@Fe₃O₄-1 from Fe₃O₄ indicates the formation of the core-shell-structured particles.

(a)

(b)

Figure 4: SEM micro images of Fe₃O₄ and PAN@Fe₃O₄-1.

Figure 5 shows the TEM micro images of Fe₃O₄ and PAN@Fe₃O₄-1. Similar to that of the SEM micro image, the TEM micro image of Fe₃O₄ shows irregular shapes of nanoparticles. In addition, it is clearly that Fe₃O₄ shows hollow structure. As for that of PAN@Fe₃O₄-1, a shell can be observed at the spherical of the nanoparticles. What is more, it seems that the hollow structure of the Fe₃O₄ is filled with something after the polymerization of aniline. Both of the SEM and TEM results indicate the core-shell structure of PAN@Fe₃O₄-1.

(a)

(b)

Figure 5: TEM micro images of Fe₃O₄ and PAN@Fe₃O₄-1.

After the confirmation of the fabrication of PAN@Fe₃O₄ hybrids, the content of polyaniline in the PAN@Fe₃O₄ hybrids is calculated by the TGA measurement. Figure 6 shows the TGA curves of Fe₃O₄, PAN@Fe₃O₄-1, PAN@Fe₃O₄-2, and PAN@Fe₃O₄-3. Fe₃O₄ shows only 2% weight decrement when the temperature is up to 600°C, which is negligible. As for the PAN@Fe₃O₄ hybrids, obvious weight decrement resulting from the decomposing of polyaniline is observed. The residual mass of PAN@Fe₃O₄-1, PAN@Fe₃O₄-2, and PAN@Fe₃O₄-3 is 90%, 84%, and 77%, respectively. The TGA results mean that the content of polyaniline in PAN@Fe₃O₄-1, PAN@Fe₃O₄-2, and PAN@Fe₃O₄-3 is 10 wt%, 16 wt%, and 23 wt%, respectively.

Figure 6: TGA curves of Fe₃O₄ (curve 1), PAN@Fe₃O₄-1 (curve 2), PAN@Fe₃O₄-2 (curve 3), and PAN@Fe₃O₄-3 (curve 4).

The magnetic property of PAN@Fe₃O₄ hybrid composite was studied by a VSM. Figure 7 shows the saturation magnetization of the samples indicating the magnetic property of the PAN@Fe₃O₄ hybrids. According to the results, the saturation magnetization decreases with the increasing content of polyaniline due to the decrement of content of Fe₃O₄ which contributes the magnetic properties effectively. The saturation magnetization of PAN@Fe₃O₄-1, PAN@Fe₃O₄-2, and PAN@Fe₃O₄-3 is 75.3, 58.9, and 42.1 emu/g, respectively.

Figure 7: Magnetization curves of PAN@Fe₃O₄-1, PAN@Fe₃O₄-2, and PAN@Fe₃O₄-3.

With the fabrication and characterization of PAN@Fe₃O₄ hybrids, their microwave absorption property is studied. Permittivity ( =  + ) as well as permeability ( =  + ) were measured from 0.5–18 GHz for Fe₃O₄ and PAN@Fe₃O₄ hybrids. By using the obtained permittivity and permeability, PAN@Fe₃O₄ hybrids’ microwave absorption properties are calculated by using transmit line theory [23, 24]. Figure 8(a) exhibits reflection loss (RL) of Fe₃O₄; the minimum RL is −15.3, −12.7, −15.5, and −17.2 dB at 1.0, 1.5, 2.0, and 2.5 mm, respectively. Usually, the reflection loss below −10 dB indicates that 90% microwave energy is dissipated and the reflection loss below −20 dB means that 99% microwave energy is being dissipated. As the minimum reflection loss of Fe₃O₄ is higher than −20 dB, it is not good enough to be used directly.

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(b)

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(d)

Figure 8: Reflection loss of Fe₃O₄ (a), PAN@Fe₃O₄-1 (b), PAN@Fe₃O₄-2 (c), and PAN@Fe₃O₄-3 (d).

Figures 8(b) and 8(c) show the RL of PAN@Fe₃O₄-1 and PAN@Fe₃O₄-2. The outcome shows both RL of PAN@Fe₃O₄-1 and PAN@Fe₃O₄-2 are worse than that of Fe₃O₄, which might be contributed to the mismatching of impedance between Fe₃O₄ and polyaniline. While for PAN@Fe₃O₄-3, excellent microwave absorption property is obtained. As can be seen through Figure 8(d), the minimum RL of PAN@Fe₃O₄-3 is as low as −29.3 dB. The low reflection loss of PAN@Fe₃O₄-3 is due to the changeable content of polyaniline through the aniline polymerization at the spherical of Fe₃O₄. As a result, controlling the in situ aniline polymerization at the spherical of Fe₃O₄ can adjust the microwave absorption property of the obtained PAN@Fe₃O₄ hybrids.

4. Conclusions

In conclusion, a series of polyaniline and Fe₃O₄ (PAN@Fe₃O₄) hybrids was prepared to study their microwave absorption properties. PAN@Fe₃O₄ was fabricated by the in situ aniline polymerization at the spherical of Fe₃O₄. FTIR, XPS, and XRD measurements showed the composition of polyaniline and Fe₃O₄ in the prepared PAN@Fe₃O₄ hybrids. SEM and TEM micro images indicated the core-shell structure of the PAN@Fe₃O₄ hybrids. The TGA results suggested that the content of polyaniline in PAN@Fe₃O₄-1, PAN@Fe₃O₄-2, and PAN@Fe₃O₄-3 is 10 wt%, 16 wt%, and 23 wt%, respectively. The saturation magnetization of the PAN@Fe₃O₄ decreased with the increment of PAN content in the hybrids. The minimum reflection loss of PAN@Fe₃O₄-3 was as low as −29.3 dB which is much better than the other samples. Controlling the in situ aniline polymerization at the spherical of Fe₃O₄ can adjust the microwave absorption of the obtained PAN@Fe₃O₄ hybrids.

Data Availability

The data used to support the findings of this study are included within the article. The funding statement will be provided in the coming revised version.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.

Acknowledgments

The financial support from the National Natural Science Foundation of China (20176169) is gratefully acknowledged.

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