- Email: [email protected]
polythiophene composites
Synthetic Metals 162 (2012) 1643–1647
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Preparation and electromagnetic properties of La-doped barium-ferrite/polythiophene composites Yu Xie a,b,∗ , Xiaowei Hong a , Xiaoying Wang c , Jie Zhao a , Yunhua Gao b,∗ , Yun Ling a , Sifeng Yan a , Lei Shi a , Kai Zhang a a
Key Laboratory of Jiangxi Province for Ecological Diagnosis-Remediation and Pollution Control, Nanchang Hangkong University, Nanchang 330063, China Key Laboratory of Photochemical Conversion and Optoelectronic Materials, TIPC, CAS, Beijing 100190, China c State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, China b
a r t i c l e
i n f o
Article history: Received 14 May 2012 Received in revised form 22 June 2012 Accepted 24 June 2012 Available online 20 August 2012 Keywords: Magnetic material Conductive polymer Composite materials Electrical properties Magnetic properties
a b s t r a c t La-doped barium-ferrite/polythiophene (LB/PTh) composites have been successfully synthesized by in situ chemical polymerization with ferric chloride (FeCl3 ) as an initiator. Crystal structure was investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Morphology was investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Electromagnetic of composites was tested by four-probe conductivity tester and vibrating sample magnetometer (VSM). The results of XRD indicated that La3+ had entered into the lattice of barium ferrite. FTIR spectra demonstrated that there were interactions between ferrite particles and PTh. TEM and SEM studies showed that the composites presented the core–shell structure. The electrical conductivity of the composites decreases with the ferrite particles content increase. Under applied magnetic field, nanocomposite exhibited the hysteretic loops of the ferromagnetic behavior. The saturation magnetization and coercivity of nanocomposites varied with the content of ferrite particles. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
1. Introduction The combination of semiconducting and mechanical properties of conjugated polymers with the properties of metals or semiconducting inorganic particles has brought new prospects for applications [1–4]. Conducting polymers have attracted much attention because of their potential applications including chemical and biological sensors, electronic devices and microwave absorption materials, due to their remarkable easy process ability and excellent electrical properties and so on [5–9]. Among the conducting polymers, PTh has received more importance due to its high charge carrier mobility, environmental stability and longer wavelength absorption compared with other polymers [10,11]. M-type barium ferrite is a promising material in many fields because it possesses fairly large magnetocrystalline anisotropy, high Curie temperature, relatively large magnetization, excellent chemical stability, and corrosion resistivity [12]. Magnetic-conductive composites with an organized structure usually provide a new functional hybrid, which has synergetic or complementary behavior between magnetic and conductive
materials. Polyaniline/BaFe12 O19 composites were prepared by Ting et al. and the results showed that a wider absorption frequency range could be obtained by adding different polyaniline contents [13]. Polyaniline/MnFe2 O4 nanocomposites were synthesized through in situ polymerization by Hosseinia et al. [14]. (BaFe12 O19 + BaTiO3 )/polyaniline composites were obtained and a significant absorption frequency range shifting and thermal extinction could be obtained by adding polyaniline to the BaFe12 O19 + BaTiO3 blend [15]. Z-type Ba-ferrite/polymer composites were synthesized and the results showed that the particle size of Ba-ferrite fillers has a significant influence on the effective properties of the two-phase composites [16]. Herein, we report an easy chemical synthesis of La-doped barium-ferrite/polythiophene (LB/PTh) nanocomposites by in situ chemical polymerization with ferric chloride (FeCl3 ) as an initiator. LB/PTh composites with different mass ratio of thiophene monomer to La-doped barium-ferrite were prepared. The final nanocomposites were characterized and the experimental results were discussed. 2. Experimental 2.1. Materials
∗ Corresponding authors at: No. 696 Fenghe Southern Avenue, Nanchang City, Jiangxi Province 330063, China. E-mail addresses: xieyu [email protected] (Y. Xie), [email protected] (Y. Gao).
Thiophene monomer was purchased from Sigma. Lanthanum nitrate (La(NO3 )3 ·9H2 O), barium nitrate (Ba(NO3 )2 ), ferric
0379-6779/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.synthmet.2012.06.025
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Y. Xie et al. / Synthetic Metals 162 (2012) 1643–1647
Table 1 The stoichiometric amounts of every material used to prepare BaLax Fe12−x O19 (LB) particles.
x = 0.00 x = 0.04 x = 0.08 x = 0.12
La(NO3 )3 ·9H2 O(g)
Ba(NO3 )2 (g)
Fe(NO3 )3 ·9H2 O (g)
Citric acid (g)
0.00000 0.13029 0.25993 0.38864
1.96146 1.96063 1.96026 1.96012
36.36170 36.23719 36.11923 25.99710
20.48710 20.49000 20.49010 20.48866
nitrate (Fe(NO3 )3 ·9H2 O), ferric chloride (FeCl3 ) and citric acid (C6 H8 O7 ·H2 O) were all analytical reagent grade and used as received. 2.2. Preparation of La-doped barium-ferrite Stoichiometric amounts (Table 1) of La(NO3 )3 ·9H2 O, Ba(NO3 )2 , citric acid and Fe(NO3 )3 ·9H2 O were dissolved in aqueous solution. The system stopped being stirred at 80 ◦ C until the wet gel was formed. The wet gel quickly inflated and formed loose black powders with lots of gas releasing in self-propagating solution combustion reaction. The black powders were sintered at 950 ◦ C for 2 h and the target product was obtained. 2.3. Preparation of LB/PTh composites Composites were prepared by in situ chemical polymerization in aqueous solution in Scheme 1. Ferrite particles were suspended in 0.5 M HCl solution with ultrasonic dispersion for 40 min. 1 mL thiophene monomer was added into the suspension and suspension was stirred for 30 min. FeCl3 solution was slowly added dropwise into the suspension within 30 min, and the suspension kept being stirred at 0 ◦ C for 10 h. Suspension was filtered and the black powders were obtained. The black powders were washed with 0.1 M HCl solution and deionized water, and then were dried under vacuum at 50 ◦ C for 24 h. The target composites were obtained. 2.4. Characterization The morphology and properties of samples were characterized by X-ray diffraction (Analytical, Holland), SEM (SU1510, HITACHI, Japan), FT-IR (Nicolet 5700), VSM (Lakeshore 7404) and four-probe conductivity tester (RTS-9).
Fig. 1. XRD patterns of BaFe12 O19 (a), PTh (d), and PTh/BaLax Fe12−x O19 composites containing 15 wt.% BaLax Fe12−x O19 : x = 0.04 (b) and x = 0.08 (c).
the peak at 1640 cm−1 is assigned to C C characteristic peak. The peak at 784 cm−1 is assigned to the C H out-of-plane vibration of the 2,5-substituted thiophene ring created by the polymerization of thiophene monomers. The peak at approximately 692 cm−1 denotes the C S stretch in the thiophene ring [20–22]. The peaks at 596 cm−1 and 440 cm−1 are attributed to the characteristic Fe O stretching vibration band [23]. The IR spectra of LB/PTh composites (Fig. 2b and c) are almost identical to that of PTh (Fig. 2a). But to some extent, the PTh in the
3. Results and discussion 3.1. X-ray diffraction
3.2. FT-IR spectra Fig. 2 shows the FT-IR spectra of LB particles and LB/PTh composites. In Fig. 2b, two peaks in the range of 2800–3000 cm−1 are attributed to the characteristic C H stretching vibrations, and
(a) Transmittance(%)
Phase investigation of the crystallized products is performed by XRD and the diffraction pattern is presented in Fig. 1. Fig. 1a shows the single-phase hexaferrite structure with no extra reflections and is well indexed to the crystal plane of hexaferrite (0 0 6), (1 1 0), (1 0 7), (1 1 4), (2 0 3), (2 0 5), (2 0 6), (2 0 7), (2 0 1 1) and (2 2 0) [17]. Fig. 1d shows one broad diffraction peak centered at 2 = 24.6◦ , which is the characteristic peak of PTh which can be ascribed to the intermolecular – stacking emerges [18]. Fig. 1b shows the characteristic peaks of ferrite and PMT including the peaks at 2 = 24.7◦ , 30.3◦ , 32.2◦ , 34.1◦ , 37.0◦ , 40.3◦ , 42.4◦ , 55.0◦ , 56.6◦ and 63.0◦ [19]. In addition, the intensity of characteristic diffraction peaks of PTh in the nanocomposites is weakened by ferrite particles, which reveals that ferrite particles can influence the crystallinity of PTh.
(b) (c)
(d)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm-1) Fig. 2. IR spectra of (a) PTh, (d) BaFe12 O19 , LB/PTh composites containing 15 wt.% LB particles: (b) x = 0.04 and (c) x = 0.08.
Y. Xie et al. / Synthetic Metals 162 (2012) 1643–1647
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Fig. 4. TEM images of PTh (a), LB/PTh nanocomposites containing 15 wt.% BaLax Fe12−x O19 particles: (b) x = 0.04 and (c) x = 0.08.
3.3. Morphology Fig. 3. SEM images of PTh (a) and LB/PTh nanocomposites containing 15 wt.% BaLax Fe12−x O19 particles: (b) x = 0.04 and (c) x = 0.08.
spectra of composites appears slight blue shift. It indicates that the ferrite particles are well encapsulated by PTh chains and there are some interactions between ferrite and polymer in the composites, which decreases the electron density and reduces the atomic force constant [24,25]. These results confirm that nanocomposites were composed of the PTh and LB particles [26,27].
The morphology of LB/PTh nanocomposites is shown in Figs. 3 and 4. SEM images revealed that PTh is deposited on the surface of LB particles which have a nucleus effect on the polymerization of PTh. TEM images indicate that the ferrite particles are embedded in PTh matrix forming the core–shell structure. The black core is magnetic ferrite particle and the light colored shell is PTh in the nanocomposites, due to the different electron penetrability. It indicates that the nanocomposites are composed of polycrystalline LB ferrite particles and PTh, which is in accordance with the results obtained by FT-IR analysis.
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Y. Xie et al. / Synthetic Metals 162 (2012) 1643–1647
Scheme 1. Illustration of the polymerization procedure for BaLax Fe12−x O19 /PTh composites. Table 2 The electrical conductivity of PTh and nanocomposites. Sample
Conductivity (S/cm)
PTh PTh/LB (5 wt.%) nanocomposite PTh/LB (10 wt.%) nanocomposite PTh/LB (15 wt.%) nanocomposite PTh/LB (20 wt.%) nanocomposite
12.50 × 10−4 8.52 × 10−4 6.99 × 10−4 4.20 × 10−4 1.42 × 10−4
3.4. Electrical conductivity The electrical conductivity values of PTh and nanocomposites are listed in Table 2. It indicates that the electrical conductivity of the composites decreases with the ferrite particles content increase. Conducting polymers are inherently conducting in nature due to the presence of a conjugated electron system in their structure. The main two reasons for the decrease in electrical conductivity are as follows. The first reason is that the insulating behavior of ferrite particles in the core of composites hinders the charge transfer in PTh. The second reason is that the generation of stable – bond between PTh and ferrite particles decreases the conjugated electron density in PTh [28]. 3.5. Magnetic properties Figs. 5 and 6 show the hysteresis loops of BaLax Fe12−x O19 and LB/PTh composites at room temperature. The magnetization of
Fig. 6. Magnetization hysteresis loops for: (A) LB/PTh composite (x = 0.00) and (B) LB/PTh composite (x = 0.04).
LB/PTh composites exhibits a clear hysteretic behavior. The magnetic parameters of composites determined by the hysteresis loops are given in Table 3. It can be observed that Ms and Hc of LB particles increase with the La3+ content, because a portion of divalent ions is substituted by La3+ at tetrahedral or octahedral sites, resulting in modifying the intrinsic magnetic properties of ferrites [29]. In addition, the MS of LB/PTh composites decreases compared to that of LB ferrite particles. According to the equation MS = ϕmS , MS is related to the volume fraction of the particles (ϕ) and the saturation moment of a single particle (mS ) [30]. As we know that the MS of LB/PTh nanocomposites mainly depends on the volume fraction of the magnetic ferrite particles. Moreover, the ferrite particles are encapsulated by the non-magnetic PTh coating layer. So there is a decrease in the saturation magnetization of composites.
Table 3 The magnetic parameters of BaLax Fe12−x O19 and LB/PTh composites.
Fig. 5. Magnetization hysteresis loops for: (a) BaLax Fe12−x O19 (x = 0.00) and (b) BaLax Fe12−x O19 (x = 0.04).
Sample
Ms (emu/g)
Hc (Oe)
BaLax Fe12−x O19 (x = 0.00) BaLax Fe12−x O19 (x = 0.04) LB/PTh composite (x = 0.00) LB/PTh composite (x = 0.04)
8.2813 80.1179 2.0084 1.5783
5007.8369 5023.5109 5914.0382 5736.3394
Y. Xie et al. / Synthetic Metals 162 (2012) 1643–1647
4. Conclusion LB/PTh composites with the magnetic and electronic properties are successfully synthesized in the form of core–shell structure by in situ polymerization of thiophene in the presence of LB particles. TEM images indicate that nanocomposites present the core–shell structure with a magnetic core of ferrite and a conducting shell of PTh. Under applied magnetic field the nanocomposites exhibit the hysteresis loops of the ferromagnetic nature. The magnetic parameters such as saturation magnetization and coercivity of nanocomposites depend on the ferrite particles content. In addition, La3+ doping can lead to the lattice distortion of BaFe12 O19 particles, resulting in the saturation magnetization increase of BaFe12 O19 particles. Acknowledgments The authors thank the financial support for this work of National Natural Science Foundation of China (20904019 and 20807021), State Key Laboratory of Pulp and Paper Engineering, South China University of Technology (200928), the Aviation Science Fund (2011ZF56015), Key Laboratory of Photochemical Conversion and Optoelectronic Material, TIPC, CAS (PCOM201028 and PCOM201130), Jiangxi Province Youth Scientists Cultivating Object Program (20112BCB23017), Jiangxi Province Science and Technology Project (20112BBG70001) and Jiangxi Province Education Department of Science and Technology Project (GJJ11501). References [1] G.R. Pedro, Advanced Materials 13 (2001) 163. [2] P.T. Nguyen, U. Rammelt, W. Plieth, Macromolecular Symposium 187 (2002) 929.
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[3] B. Garcia, A. Lamzoudi, F. Pillier, H. Nguyen Thi Le, C. Deslouis, Journal of The Electrochemical Society 149 (2002) 560. [4] S. Tagmouti, A. Outzourhit, A. Oueriagli, M. Khaidar, M. Elyacoubi, R. Evrard, E.L. Ameziane, Thin Solid Films 379 (2000) 272. [5] B. Adhikari, S. Majumdar, Progress in Polymer Science 29 (2004) 699. [6] T.H. Ting, R.P. Yu, Y.N. Jau, Materials Chemistry and Physics 126 (2011) 364. [7] M. Woodson, J. Liu, Journal of the American Chemical Society 128 (2006) 3760. [8] B. Li, D.N. Lambeth, Nano Letters 8 (2008) 3563. [9] D.S. Sutar, N. Padma, D.K. Aswal, S.K. Deshpande, S.K. Gupta, J.V. Yakhmi, Sensors and Actuators B 128 (2007) 286. [10] G.A. Snook, P. Kao, A.S. Best, Journal of Power Sources 196 (2011) 1. [11] T.A. Skotheim, R.L. Elsenbaumer, J.R. Reynolds (Eds.), Handbook of Conducting Polymers, Marcel Decker, New York, 1998, p. 225. [12] K.B.M. Paul, Physica B 388 (2007) 337. [13] T.H. Ting, K.H. Wu, Journal of Magnetism and Magnetic Materials 322 (2010) 2160. [14] S.H. Hosseinia, S.H. Mohsenib, A. Asadniac, H. Kerdarid, Journal of Alloys and Compound 509 (2011) 4682. [15] C.C. Yang, Y.J. Gung, C.C. Shih, W.C. Hung, K.H. Wu, Journal of Magnetism and Magnetic Materials 323 (2011) 933. [16] B.W. Li, Y. Shen, Z.X. Yue, C.W. Nan, Journal of Magnetism and Magnetic Materials 313 (2007) 322. [17] Z. Durmus, B. Unal, M.S. Toprak, H. Sozeri, A. Baykal, Polyhedron 30 (2011) 1349. [18] Y.N. Li, G. Vamvounis, S. Holdcroft, Macromolecules 35 (2002) 6900. [19] D. Mishra, S. Anand, R.K. Panda, R.P. Das, Materials Chemistry and Physics 86 (2004) 132. [20] M.R. Karim, C.J. Lee, M.S. Lee, Journal of Polymer Science Part A: Polymer Chemistry 44 (2006) 5283. [21] M.R. Karim, K.T. Lim, C.J. Lee, M.S. Lee, Synthetic Metals 157 (2007) 1008. [22] M.G. Han, S.H. Foulger, Advanced Materials 16 (2004) 231. [23] S.R. Hafner, Zeitschrift für Kristallographie 115 (1961) 331. [24] R. Kostic, D. Rakovic, S.A. Stepanyan, I.E. Davidova, L.A. Gribov, Journal of Chemical Physics 102 (1995) 3104. [25] W. Chen, X. Li, G. Xue, Z. Wang, W. Zou, Applied Surface Science 218 (2003) 216. [26] P. Gomez-Romero, Advanced Materials 13 (2001) 163. [27] P.R. Somani, R. Marimuthu, A.B. Mandale, Polymer 42 (2001) 2991. [28] S.A. Saafan, T.M. Meaz, E.H. El-Ghazzawy, Journal of Magnetism and Magnetic Material 323 (2011) 1517–1524. [29] Y.Q. Li, Y. Huang, S.H. Qi, F.F. Niu, L. Niu, Journal of Magnetism and Magnetic Material 323 (2011) 2224. [30] F. Sauzedde, A. Elaissari, C. Pichot, Colloid & Polymer Science 277 (1999) 846.
Contents lists available at SciVerse ScienceDirect
Synthetic Metals journal homepage: www.elsevier.com/locate/synmet
Preparation and electromagnetic properties of La-doped barium-ferrite/polythiophene composites Yu Xie a,b,∗ , Xiaowei Hong a , Xiaoying Wang c , Jie Zhao a , Yunhua Gao b,∗ , Yun Ling a , Sifeng Yan a , Lei Shi a , Kai Zhang a a
Key Laboratory of Jiangxi Province for Ecological Diagnosis-Remediation and Pollution Control, Nanchang Hangkong University, Nanchang 330063, China Key Laboratory of Photochemical Conversion and Optoelectronic Materials, TIPC, CAS, Beijing 100190, China c State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, China b
a r t i c l e
i n f o
Article history: Received 14 May 2012 Received in revised form 22 June 2012 Accepted 24 June 2012 Available online 20 August 2012 Keywords: Magnetic material Conductive polymer Composite materials Electrical properties Magnetic properties
a b s t r a c t La-doped barium-ferrite/polythiophene (LB/PTh) composites have been successfully synthesized by in situ chemical polymerization with ferric chloride (FeCl3 ) as an initiator. Crystal structure was investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Morphology was investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Electromagnetic of composites was tested by four-probe conductivity tester and vibrating sample magnetometer (VSM). The results of XRD indicated that La3+ had entered into the lattice of barium ferrite. FTIR spectra demonstrated that there were interactions between ferrite particles and PTh. TEM and SEM studies showed that the composites presented the core–shell structure. The electrical conductivity of the composites decreases with the ferrite particles content increase. Under applied magnetic field, nanocomposite exhibited the hysteretic loops of the ferromagnetic behavior. The saturation magnetization and coercivity of nanocomposites varied with the content of ferrite particles. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
1. Introduction The combination of semiconducting and mechanical properties of conjugated polymers with the properties of metals or semiconducting inorganic particles has brought new prospects for applications [1–4]. Conducting polymers have attracted much attention because of their potential applications including chemical and biological sensors, electronic devices and microwave absorption materials, due to their remarkable easy process ability and excellent electrical properties and so on [5–9]. Among the conducting polymers, PTh has received more importance due to its high charge carrier mobility, environmental stability and longer wavelength absorption compared with other polymers [10,11]. M-type barium ferrite is a promising material in many fields because it possesses fairly large magnetocrystalline anisotropy, high Curie temperature, relatively large magnetization, excellent chemical stability, and corrosion resistivity [12]. Magnetic-conductive composites with an organized structure usually provide a new functional hybrid, which has synergetic or complementary behavior between magnetic and conductive
materials. Polyaniline/BaFe12 O19 composites were prepared by Ting et al. and the results showed that a wider absorption frequency range could be obtained by adding different polyaniline contents [13]. Polyaniline/MnFe2 O4 nanocomposites were synthesized through in situ polymerization by Hosseinia et al. [14]. (BaFe12 O19 + BaTiO3 )/polyaniline composites were obtained and a significant absorption frequency range shifting and thermal extinction could be obtained by adding polyaniline to the BaFe12 O19 + BaTiO3 blend [15]. Z-type Ba-ferrite/polymer composites were synthesized and the results showed that the particle size of Ba-ferrite fillers has a significant influence on the effective properties of the two-phase composites [16]. Herein, we report an easy chemical synthesis of La-doped barium-ferrite/polythiophene (LB/PTh) nanocomposites by in situ chemical polymerization with ferric chloride (FeCl3 ) as an initiator. LB/PTh composites with different mass ratio of thiophene monomer to La-doped barium-ferrite were prepared. The final nanocomposites were characterized and the experimental results were discussed. 2. Experimental 2.1. Materials
∗ Corresponding authors at: No. 696 Fenghe Southern Avenue, Nanchang City, Jiangxi Province 330063, China. E-mail addresses: xieyu [email protected] (Y. Xie), [email protected] (Y. Gao).
Thiophene monomer was purchased from Sigma. Lanthanum nitrate (La(NO3 )3 ·9H2 O), barium nitrate (Ba(NO3 )2 ), ferric
0379-6779/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.synthmet.2012.06.025
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Y. Xie et al. / Synthetic Metals 162 (2012) 1643–1647
Table 1 The stoichiometric amounts of every material used to prepare BaLax Fe12−x O19 (LB) particles.
x = 0.00 x = 0.04 x = 0.08 x = 0.12
La(NO3 )3 ·9H2 O(g)
Ba(NO3 )2 (g)
Fe(NO3 )3 ·9H2 O (g)
Citric acid (g)
0.00000 0.13029 0.25993 0.38864
1.96146 1.96063 1.96026 1.96012
36.36170 36.23719 36.11923 25.99710
20.48710 20.49000 20.49010 20.48866
nitrate (Fe(NO3 )3 ·9H2 O), ferric chloride (FeCl3 ) and citric acid (C6 H8 O7 ·H2 O) were all analytical reagent grade and used as received. 2.2. Preparation of La-doped barium-ferrite Stoichiometric amounts (Table 1) of La(NO3 )3 ·9H2 O, Ba(NO3 )2 , citric acid and Fe(NO3 )3 ·9H2 O were dissolved in aqueous solution. The system stopped being stirred at 80 ◦ C until the wet gel was formed. The wet gel quickly inflated and formed loose black powders with lots of gas releasing in self-propagating solution combustion reaction. The black powders were sintered at 950 ◦ C for 2 h and the target product was obtained. 2.3. Preparation of LB/PTh composites Composites were prepared by in situ chemical polymerization in aqueous solution in Scheme 1. Ferrite particles were suspended in 0.5 M HCl solution with ultrasonic dispersion for 40 min. 1 mL thiophene monomer was added into the suspension and suspension was stirred for 30 min. FeCl3 solution was slowly added dropwise into the suspension within 30 min, and the suspension kept being stirred at 0 ◦ C for 10 h. Suspension was filtered and the black powders were obtained. The black powders were washed with 0.1 M HCl solution and deionized water, and then were dried under vacuum at 50 ◦ C for 24 h. The target composites were obtained. 2.4. Characterization The morphology and properties of samples were characterized by X-ray diffraction (Analytical, Holland), SEM (SU1510, HITACHI, Japan), FT-IR (Nicolet 5700), VSM (Lakeshore 7404) and four-probe conductivity tester (RTS-9).
Fig. 1. XRD patterns of BaFe12 O19 (a), PTh (d), and PTh/BaLax Fe12−x O19 composites containing 15 wt.% BaLax Fe12−x O19 : x = 0.04 (b) and x = 0.08 (c).
the peak at 1640 cm−1 is assigned to C C characteristic peak. The peak at 784 cm−1 is assigned to the C H out-of-plane vibration of the 2,5-substituted thiophene ring created by the polymerization of thiophene monomers. The peak at approximately 692 cm−1 denotes the C S stretch in the thiophene ring [20–22]. The peaks at 596 cm−1 and 440 cm−1 are attributed to the characteristic Fe O stretching vibration band [23]. The IR spectra of LB/PTh composites (Fig. 2b and c) are almost identical to that of PTh (Fig. 2a). But to some extent, the PTh in the
3. Results and discussion 3.1. X-ray diffraction
3.2. FT-IR spectra Fig. 2 shows the FT-IR spectra of LB particles and LB/PTh composites. In Fig. 2b, two peaks in the range of 2800–3000 cm−1 are attributed to the characteristic C H stretching vibrations, and
(a) Transmittance(%)
Phase investigation of the crystallized products is performed by XRD and the diffraction pattern is presented in Fig. 1. Fig. 1a shows the single-phase hexaferrite structure with no extra reflections and is well indexed to the crystal plane of hexaferrite (0 0 6), (1 1 0), (1 0 7), (1 1 4), (2 0 3), (2 0 5), (2 0 6), (2 0 7), (2 0 1 1) and (2 2 0) [17]. Fig. 1d shows one broad diffraction peak centered at 2 = 24.6◦ , which is the characteristic peak of PTh which can be ascribed to the intermolecular – stacking emerges [18]. Fig. 1b shows the characteristic peaks of ferrite and PMT including the peaks at 2 = 24.7◦ , 30.3◦ , 32.2◦ , 34.1◦ , 37.0◦ , 40.3◦ , 42.4◦ , 55.0◦ , 56.6◦ and 63.0◦ [19]. In addition, the intensity of characteristic diffraction peaks of PTh in the nanocomposites is weakened by ferrite particles, which reveals that ferrite particles can influence the crystallinity of PTh.
(b) (c)
(d)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm-1) Fig. 2. IR spectra of (a) PTh, (d) BaFe12 O19 , LB/PTh composites containing 15 wt.% LB particles: (b) x = 0.04 and (c) x = 0.08.
Y. Xie et al. / Synthetic Metals 162 (2012) 1643–1647
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Fig. 4. TEM images of PTh (a), LB/PTh nanocomposites containing 15 wt.% BaLax Fe12−x O19 particles: (b) x = 0.04 and (c) x = 0.08.
3.3. Morphology Fig. 3. SEM images of PTh (a) and LB/PTh nanocomposites containing 15 wt.% BaLax Fe12−x O19 particles: (b) x = 0.04 and (c) x = 0.08.
spectra of composites appears slight blue shift. It indicates that the ferrite particles are well encapsulated by PTh chains and there are some interactions between ferrite and polymer in the composites, which decreases the electron density and reduces the atomic force constant [24,25]. These results confirm that nanocomposites were composed of the PTh and LB particles [26,27].
The morphology of LB/PTh nanocomposites is shown in Figs. 3 and 4. SEM images revealed that PTh is deposited on the surface of LB particles which have a nucleus effect on the polymerization of PTh. TEM images indicate that the ferrite particles are embedded in PTh matrix forming the core–shell structure. The black core is magnetic ferrite particle and the light colored shell is PTh in the nanocomposites, due to the different electron penetrability. It indicates that the nanocomposites are composed of polycrystalline LB ferrite particles and PTh, which is in accordance with the results obtained by FT-IR analysis.
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Y. Xie et al. / Synthetic Metals 162 (2012) 1643–1647
Scheme 1. Illustration of the polymerization procedure for BaLax Fe12−x O19 /PTh composites. Table 2 The electrical conductivity of PTh and nanocomposites. Sample
Conductivity (S/cm)
PTh PTh/LB (5 wt.%) nanocomposite PTh/LB (10 wt.%) nanocomposite PTh/LB (15 wt.%) nanocomposite PTh/LB (20 wt.%) nanocomposite
12.50 × 10−4 8.52 × 10−4 6.99 × 10−4 4.20 × 10−4 1.42 × 10−4
3.4. Electrical conductivity The electrical conductivity values of PTh and nanocomposites are listed in Table 2. It indicates that the electrical conductivity of the composites decreases with the ferrite particles content increase. Conducting polymers are inherently conducting in nature due to the presence of a conjugated electron system in their structure. The main two reasons for the decrease in electrical conductivity are as follows. The first reason is that the insulating behavior of ferrite particles in the core of composites hinders the charge transfer in PTh. The second reason is that the generation of stable – bond between PTh and ferrite particles decreases the conjugated electron density in PTh [28]. 3.5. Magnetic properties Figs. 5 and 6 show the hysteresis loops of BaLax Fe12−x O19 and LB/PTh composites at room temperature. The magnetization of
Fig. 6. Magnetization hysteresis loops for: (A) LB/PTh composite (x = 0.00) and (B) LB/PTh composite (x = 0.04).
LB/PTh composites exhibits a clear hysteretic behavior. The magnetic parameters of composites determined by the hysteresis loops are given in Table 3. It can be observed that Ms and Hc of LB particles increase with the La3+ content, because a portion of divalent ions is substituted by La3+ at tetrahedral or octahedral sites, resulting in modifying the intrinsic magnetic properties of ferrites [29]. In addition, the MS of LB/PTh composites decreases compared to that of LB ferrite particles. According to the equation MS = ϕmS , MS is related to the volume fraction of the particles (ϕ) and the saturation moment of a single particle (mS ) [30]. As we know that the MS of LB/PTh nanocomposites mainly depends on the volume fraction of the magnetic ferrite particles. Moreover, the ferrite particles are encapsulated by the non-magnetic PTh coating layer. So there is a decrease in the saturation magnetization of composites.
Table 3 The magnetic parameters of BaLax Fe12−x O19 and LB/PTh composites.
Fig. 5. Magnetization hysteresis loops for: (a) BaLax Fe12−x O19 (x = 0.00) and (b) BaLax Fe12−x O19 (x = 0.04).
Sample
Ms (emu/g)
Hc (Oe)
BaLax Fe12−x O19 (x = 0.00) BaLax Fe12−x O19 (x = 0.04) LB/PTh composite (x = 0.00) LB/PTh composite (x = 0.04)
8.2813 80.1179 2.0084 1.5783
5007.8369 5023.5109 5914.0382 5736.3394
Y. Xie et al. / Synthetic Metals 162 (2012) 1643–1647
4. Conclusion LB/PTh composites with the magnetic and electronic properties are successfully synthesized in the form of core–shell structure by in situ polymerization of thiophene in the presence of LB particles. TEM images indicate that nanocomposites present the core–shell structure with a magnetic core of ferrite and a conducting shell of PTh. Under applied magnetic field the nanocomposites exhibit the hysteresis loops of the ferromagnetic nature. The magnetic parameters such as saturation magnetization and coercivity of nanocomposites depend on the ferrite particles content. In addition, La3+ doping can lead to the lattice distortion of BaFe12 O19 particles, resulting in the saturation magnetization increase of BaFe12 O19 particles. Acknowledgments The authors thank the financial support for this work of National Natural Science Foundation of China (20904019 and 20807021), State Key Laboratory of Pulp and Paper Engineering, South China University of Technology (200928), the Aviation Science Fund (2011ZF56015), Key Laboratory of Photochemical Conversion and Optoelectronic Material, TIPC, CAS (PCOM201028 and PCOM201130), Jiangxi Province Youth Scientists Cultivating Object Program (20112BCB23017), Jiangxi Province Science and Technology Project (20112BBG70001) and Jiangxi Province Education Department of Science and Technology Project (GJJ11501). References [1] G.R. Pedro, Advanced Materials 13 (2001) 163. [2] P.T. Nguyen, U. Rammelt, W. Plieth, Macromolecular Symposium 187 (2002) 929.
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