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Sonochemical synthesis of CoFe2O4 nanoparticles and their application in magnetic polystyrene nanocomposites
G Model
JIEC-1851; No. of Pages 5 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Sonochemical synthesis of CoFe2O4 nanoparticles and their application in magnetic polystyrene nanocomposites Jilla Saffari a,*, Davood Ghanbari b, Noshin Mir c, Khatereh Khandan-Barani a a
Department of Chemistry, Islamic Azad University, Zahedan Branch, P.O. Box 98135-978, Zahedan, Iran Young Researchers and Elite Club, Arak Branch, Islamic Azad University, Arak, Iran c Department of Chemistry, University of Zabol, P.O. Box 98615-538, Zabol, Iran b
A R T I C L E I N F O
Article history: Received 22 December 2013 Accepted 6 January 2014 Available online xxx Keywords: PS CoFe2O4 Sonochemical method Nanocomposite
A B S T R A C T
CoFe2O4 (CoFe) nanoparticles were synthesized via a facile surfactant-free sonochemical reaction. For preparation of magnetic polymeric films, CoFe2O4 nanoparticles were added to polystyrene (PS). Nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Magnetic properties of the samples were investigated using an alternating gradient force magnetometer (AGFM). CoFe2O4 nanoparticles exhibit a ferromagnetic behaviour with a saturation magnetization of 62 emu/g and a coercivity of 640 Oe at room temperature. By preparing magnetic films the coercivity is increased. The coercivity of PS/CoFe2O4 (10%) nanocomposites is higher than that obtained for PS/CoFe2O4 (30%). ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Besides the growth of novel nanomaterials throughout the early modern period, magnetic nanostructures have been attracting increasing attention among the various scientific communities. Due to their wide range of application, magnetic nanostructures have been extensively studied in all scientific areas [1–4]. One of the most engrossing magnetic products has been organic– inorganic magnetic nanocomposites which has captivated many interests due to their easy processability, low-cost manufacturing and excellent thermal and mechanical properties. Polymer matrix nanocomposites have also been extensively investigated, since just a small amount of nanoparticles as an additive leads to production of novel high-performance materials with excellent physicochemical properties [5–9]. Polystyrene is widely used because of its process ability properties and relatively low cost [10,11]. There are many different methods for fabrication of various nanostructures [12–14] as well as magnetic nanoparticles. Among these techniques, ultrasonic technique competes with the others due its low cost and suitable properties and this technique is a process well suited to large-scale production. Because of the cavitation process in aqueous medium, a temperature of approximately 5000 8C and a pressure of more than 1800 kPa is created in the solution which is capable of many unusual chemical reactions occurrence [15,9]. Recently, ultrasonic assisted methods have been extensively used in preparation of magnetic nanoparticles [16,17]. * Corresponding author. Tel.: +98 5412441600. E-mail address: [email protected] (J. Saffari).
One of the most significant classes of magnetic materials is the ferrites. The ferrite materials may be classified into three different classes; spinel ferrites, garnet ferrites and hexagonal ferrites. The ferrites used for magnetic recording, data storage materials, radar absorbing materials due to their strong magnetic losses at the range of GHz frequency, magnetoelectric/multiferroic applications [18–22]. We report the synthesis of CoFe2O4 using sonochemical reaction. In order to make magnetic polymeric films, the CoFe2O4 nanoparticles were then incorporated in the PS polymer. Magnetic properties of CoFe2O4 nanoparticles and PS/CoFe2O4 nanocomposites were characterized and their magnetic behaviour was studied. 2. Experimental 2.1. Materials and methods All the chemicals were used as received without further purifications. XRD patterns were recorded by a Philips, X-ray diffractometer using Ni-filtered Cu Ka radiation. SEM images were obtained using a KYKY instrument model EM-3200. Prior to taking images, the samples were coated by a very thin layer of Au (using a BAL-TEC SCD 005 sputter coater) to make the sample surface conductor, prevent charge accumulation, and obtain a better contrast. A multiwave ultrasonic generator (Bandeline MS 73), equipped with a converter/transducer and titanium oscillator, operating at 20 kHz with a maximum power output of 100 W was used for the ultrasonic irradiation. Room temperature magnetic
1226-086X/$ – see front matter ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2014.01.010
Please cite this article in press as: J. Saffari, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.010
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JIEC-1851; No. of Pages 5 2
J. Saffari et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Fig. 1. Schematic diagram of (a) sonochemical synthesis and (b) preparation of nanocomposite. Fig. 3. SEM images of CoFe (a) without using ultrasonic and (b) nanoparticles synthesized at 60 W.
2.2. Synthesis of CoFe2O4 nanoparticles properties were investigated using an alternating gradient force magnetometer (AGFM) device, made by Meghnatis Daghigh Kavir Company in an applied magnetic field sweeping between 10,000 Oe.
0.001 mol Co(NO3)2 6H2O and 0.002 mol of Fe(NO3)3 9H2O are dissolved in 100 mL of distilled water. Then 20 mL of NaOH solution 1 M is slowly added to the solution, under ultrasonic
Fig. 2. XRD pattern of the CoFe2O4 nanoparticles.
Please cite this article in press as: J. Saffari, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.010
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JIEC-1851; No. of Pages 5 J. Saffari et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
3
Fig. 4. SEM images of CoFe nanoparticles obtained at 40 W.
Fig. 5. SEM images of CoFe nanoparticles achieved at 75 W.
waves (60 W) for 30 min. The solution is heated at 80 8C for 2 h. The black precipitate is then centrifuged and rinsed with distilled water, followed by being left in an atmosphere environment to dry. Fig. 1 shows the schematic diagram for experimental setup used in this sonochemical reaction.
Without using ultrasonic waves bigger particles (bulk product) were obtained. SEM image of the product without using ultrasound is shown in Fig. 3a. Ultrasonic irradiation creates bubbles which produces high temperature and energy after decomposition. This process provides appropriates amounts of energy for formation of CoFe nanoparticles.
2.3. Preparation of PS-CoFe nanocomposites First, 0.9 g (0.7 g) of polystyrene is dissolved in 10 mL dichloromethane solution. Then 0.1 g (or 0.3 g) of CoFe2O4 nanoparticles is dispersed in 10 mL of dichloromethane solution with ultrasonic waves (15 min, 60 W). The nanoparticles dispersion is then slowly added to the polymer solution. The new solution is then mixed and stirred for 6 h. The product is casted on a glass plate and is left for 2 h in order to evaporate the solvent.
3. Results and discussion XRD pattern of CoFe2O4 nanoparticles is shown in Fig. 2. The XRD pattern of as-prepared CoFe2O4 nanoparticles is indexed as a pure cubic phase (space group: Fd3m) which is very close to the literature values (JCPDS No. 01-1121). The crystallite size measurements were also carried out using the Scherrer equation [5], Dc = Kl/b cosu, where K usually takes a value of about 0.9, b is the width of the observed diffraction peak at its half maximum intensity (FWHM) and l is the X-ray wavelength (CuKa radiation, equals to 0.154 nm). The estimated crystallite size is about 21 nm.
Fig. 6. TEM image of PS-CoFe nanocomposite.
Please cite this article in press as: J. Saffari, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.010
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JIEC-1851; No. of Pages 5 J. Saffari et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
4
80 20
Magnetization(emu/g)
Magnetization (emu/g)
60 40 20 0 -20 -40
0
-10
-20
-60 -80
10
-10000
-5000
0
5000
-10000
10000
-5000
0
5000
10000
Applied Field(Oe)
Applied field (Oe)
Fig. 9. Magnetization loop of PS-CoFe (30%) nanocomposite.
Fig. 7. Magnetization loop of CoFe nanoparticles.
SEM image of CoFe nanoparticles prepared at 60 W is shown in Fig. 3b which illustrates nanoparticles with average diameter of 60 nm. The effect of ultrasonic power on the morphology of the products is shown in Figs. 4 and 5. Fig. 4 shows SEM images of product obtained at lower power (40 W) that confirm nanoparticles with mediocre diameter of 70 nm are synthesized. The influence of higher power on the particle size has been investigated. All the SEM results approve that in all three different conditions nanoparticles are prepared with average particle size lower than 100 nm. TEM image of PS/CoFe (30%) nanocomposite is illustrated in Fig. 6 which confirms the appropriate dispersion of CoFe nanoparticles in the polymeric matrixes. Room temperature magnetic properties of samples were studied using an AGFM device. The hysteresis loop for CoFe nanoparticles is shown in Fig. 7. Based on our search in the literature very few work has been done on hard magnetic polymeric nanocomposites. We studied the magnetic interaction between the nanoparticles surrender by the polymeric chains. This interaction leads to a remarkable increase (from 640 to 975 Oe) of nanoparticle coersivities compared with the pure cobalt ferrite nanoparticles (Table 1). Hysteresis loops for PS/CoFe (10%) and PS/CoFe (30%) are illustrated in Figs. 8 and 9, respectively. It can be concluded that cobalt ferrite particles in the nanocomposites are sufficiently far away from each other so that their magnetic behaviour is not
Table 1 Coercivity, remanence and saturation magnetization of the CoFe nanoparticles and nanocomposites. Sample
Saturation magnetization (emu/g)
Coercivity (Oe)
Remanence (emu/g)
CoFe PS/CoFe (10%) PS/CoFe (30%)
62 5.3 16.9
640 975 881
21.9 2.2 6.4
influenced by the stray fields of their neighbour particles and this results in the dependent uncoupled (non-interacting) domains. The results indicate that, forming the nanocomposite and distributing of the magnetic nanoparticles into the polymer matrix leads in increasing the coercivity. A possible explanation for this result could be as follow: The magnetic moments of magnetic
Magnetization(emu/g)
6 4 2 0 -2 -4 -6 -10000
-5000
0
5000
10000
Applied Field(Oe) Fig. 8. Magnetization curve of PS-CoFe (10%) nanocomposite.
Fig. 10. Schematic illustration of (a) CoFe nanoparticles distributed in polymer matrix in absence of magnetic field and (b) presence of a magnetic field.
Please cite this article in press as: J. Saffari, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.010
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Fig. 11. Attraction of the products by magnet (a) CoFe nanoparticles; (b) PS-CoFe (10%) nanocomposite and (c) PS-CoFe (30%) nanocomposite.
nanoparticles are pined by the poly styrene matrix chains, so that a higher magnetic field is required to align the single domain nanoparticles in the field direction. This effect is illustrated in Fig. 10 schematically. Generally, coercivity of magnetic nanocomposites highly depends on the magnetic nanoparticle distribution into the polymeric matrixes. In order to make 1 g of magnetic nanocomposite, 0.1 g (or 0.3 g) of cobalt ferrite nanoparticles is added to 0.9 g (or 0.7 g) of polystyrene. Thus, the nanocomposite magnetization (defined as the magnetic moment per unit volume) is about one tenth (or one fourth) of that obtained for cobalt ferrite nanoparticles. The saturation magnetization of nanoparticles is much higher than those of obtained for PS-CoFe nanocomposites. Attraction of CoFe nanoparticles, PS-CoFe (10%) nanocomposite and PS-CoFe (30%) nanocomposite films by magnet are shown in Fig. 11a–c, respectively. 4. Conclusions CoFe2O4 nanoparticles are synthesized via a simple sonochemical reaction. It was found that the as-obtained CoFe2O4 nanoparticles exhibit a ferromagnetic behaviour with a saturation magnetization of 62 emu/g and a coercivity of 640 Oe at room temperature. In order to make magnetic films, CoFe2O4 nanoparticles were then added to PS matrixes. Nanocomposites were then characterized using XRD, SEM and AGFM spectroscopy. It was shown that distribution of the CoFe2O4 nanoparticles into the polymeric matrixes increases the coercivity.
Acknowledgment This work has been supported financially by Islamic Azad University Zahedan Branch Research.
References [1] J.H. Lee, Y.M. Huh, Y.w. Jun, J.w. Seo, J.T. Jang, H.T. Song, S. Kim, E.J. Cho, H.G. Yoon, J.S. Suh, J. Cheon, Nat. Med. 13 (2006) 95. [2] Q.A. Pankhurst, J. Connolly, S.K. Jones, J. Dobson, J. Phys. D: Appl. Phys. 36 (2003) R167. [3] C. Sun, J.S.H. Lee, M. Zhang, Adv. Drug Deliv. Rev. 60 (2008) 1252. [4] Y.H. Kim, S.J. Park, Curr. Appl. Phys. 11 (2011) 462. [5] B.Y. Geng, J.Z. Ma, J.H. You, Cryst. Growth Des. 8 (2008) 1443. [6] B. Jia, L. Gao, J. Phys. Chem. C 112 (2008) 666. [7] X. Sun, C. Zheng, F. Zhang, Y. Yang, G. Wu, A. Yu, N. Guan, J. Phys. Chem. C 113 (2009) 16002. [8] R. Jalajerdi, F. Gholamian, H. Shafie, A. Moraveji, D. Ghanbari, J. Nanostructures 2 (2012) 105. [9] G. Nabiyouni, D. Ghanbari, J. Appl. Polym. Sci. 125 (2012) 3268. [10] V.K. Sankaranarayanan, Q.A. Pankhurst, D.P.E. Dickson, C.E. Johnson, J. Magn. Magn. Mater. 120 (1993) 73. [11] K.V.P.M. Shafi, I. Felner, Y. Mastai, A. Gedanken, J. Phys. Chem. B 103 (1999) 3358. [12] M. Sabet, M. Salavati-Niasari, M. Ashjari, D. Ghanbari, M. Dadkhah, J. Inorg. Organomet. Polym. Mater. 22 (2012) 1139. [13] M. Sabet, M. Salavati-Niasari, D. Ghanbari, O. Amiri, M. Yousefi, Mater. Sci. Semiconduc. Process 16 (2013) 696. [14] M. Salavati-Niasari, E. Esmaeili, M. Sabet, J. Cluster Sci. 24 (2013) 799. [15] E. Matuevic, J. Colloid Interf. Sci. 117 (1987) 593. [16] G. Nabiyouni, D. Ghanbari, A. Yousofnejad, M. Seraj, J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.030. ¨ zkan, M. Volkan, Mater. Lett. 98 (2013) 90. [17] B. Ku¨c¸u¨k, N. O [18] G. Nabiyouni, A. Yousofnejad, M. Seraj, F. Akhtarian, D. Ghanbari, J. Nanostructures 2 (2013) 525. [19] Z. Yang, C.S. Wang, X.H. Li, H.X. Zeng, Mater. Sci. Eng. B Adv. 90 (2002) 142. [20] D. Ghanbari, M.Salavati-Niasari, M. Sabet, J. Cluster Sci. 23 (2012) 1081. [21] D. Lisjak, M. Drofenik, J. Eur. Ceram. Soc. 26 (2006) 3681. [22] U. Topal, H. Ozkan, H. Sozeri, J. Magn. Magn. Mater. 284 (2004) 416.
Please cite this article in press as: J. Saffari, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.010
JIEC-1851; No. of Pages 5 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Sonochemical synthesis of CoFe2O4 nanoparticles and their application in magnetic polystyrene nanocomposites Jilla Saffari a,*, Davood Ghanbari b, Noshin Mir c, Khatereh Khandan-Barani a a
Department of Chemistry, Islamic Azad University, Zahedan Branch, P.O. Box 98135-978, Zahedan, Iran Young Researchers and Elite Club, Arak Branch, Islamic Azad University, Arak, Iran c Department of Chemistry, University of Zabol, P.O. Box 98615-538, Zabol, Iran b
A R T I C L E I N F O
Article history: Received 22 December 2013 Accepted 6 January 2014 Available online xxx Keywords: PS CoFe2O4 Sonochemical method Nanocomposite
A B S T R A C T
CoFe2O4 (CoFe) nanoparticles were synthesized via a facile surfactant-free sonochemical reaction. For preparation of magnetic polymeric films, CoFe2O4 nanoparticles were added to polystyrene (PS). Nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Magnetic properties of the samples were investigated using an alternating gradient force magnetometer (AGFM). CoFe2O4 nanoparticles exhibit a ferromagnetic behaviour with a saturation magnetization of 62 emu/g and a coercivity of 640 Oe at room temperature. By preparing magnetic films the coercivity is increased. The coercivity of PS/CoFe2O4 (10%) nanocomposites is higher than that obtained for PS/CoFe2O4 (30%). ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Besides the growth of novel nanomaterials throughout the early modern period, magnetic nanostructures have been attracting increasing attention among the various scientific communities. Due to their wide range of application, magnetic nanostructures have been extensively studied in all scientific areas [1–4]. One of the most engrossing magnetic products has been organic– inorganic magnetic nanocomposites which has captivated many interests due to their easy processability, low-cost manufacturing and excellent thermal and mechanical properties. Polymer matrix nanocomposites have also been extensively investigated, since just a small amount of nanoparticles as an additive leads to production of novel high-performance materials with excellent physicochemical properties [5–9]. Polystyrene is widely used because of its process ability properties and relatively low cost [10,11]. There are many different methods for fabrication of various nanostructures [12–14] as well as magnetic nanoparticles. Among these techniques, ultrasonic technique competes with the others due its low cost and suitable properties and this technique is a process well suited to large-scale production. Because of the cavitation process in aqueous medium, a temperature of approximately 5000 8C and a pressure of more than 1800 kPa is created in the solution which is capable of many unusual chemical reactions occurrence [15,9]. Recently, ultrasonic assisted methods have been extensively used in preparation of magnetic nanoparticles [16,17]. * Corresponding author. Tel.: +98 5412441600. E-mail address: [email protected] (J. Saffari).
One of the most significant classes of magnetic materials is the ferrites. The ferrite materials may be classified into three different classes; spinel ferrites, garnet ferrites and hexagonal ferrites. The ferrites used for magnetic recording, data storage materials, radar absorbing materials due to their strong magnetic losses at the range of GHz frequency, magnetoelectric/multiferroic applications [18–22]. We report the synthesis of CoFe2O4 using sonochemical reaction. In order to make magnetic polymeric films, the CoFe2O4 nanoparticles were then incorporated in the PS polymer. Magnetic properties of CoFe2O4 nanoparticles and PS/CoFe2O4 nanocomposites were characterized and their magnetic behaviour was studied. 2. Experimental 2.1. Materials and methods All the chemicals were used as received without further purifications. XRD patterns were recorded by a Philips, X-ray diffractometer using Ni-filtered Cu Ka radiation. SEM images were obtained using a KYKY instrument model EM-3200. Prior to taking images, the samples were coated by a very thin layer of Au (using a BAL-TEC SCD 005 sputter coater) to make the sample surface conductor, prevent charge accumulation, and obtain a better contrast. A multiwave ultrasonic generator (Bandeline MS 73), equipped with a converter/transducer and titanium oscillator, operating at 20 kHz with a maximum power output of 100 W was used for the ultrasonic irradiation. Room temperature magnetic
1226-086X/$ – see front matter ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2014.01.010
Please cite this article in press as: J. Saffari, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.010
G Model
JIEC-1851; No. of Pages 5 2
J. Saffari et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Fig. 1. Schematic diagram of (a) sonochemical synthesis and (b) preparation of nanocomposite. Fig. 3. SEM images of CoFe (a) without using ultrasonic and (b) nanoparticles synthesized at 60 W.
2.2. Synthesis of CoFe2O4 nanoparticles properties were investigated using an alternating gradient force magnetometer (AGFM) device, made by Meghnatis Daghigh Kavir Company in an applied magnetic field sweeping between 10,000 Oe.
0.001 mol Co(NO3)2 6H2O and 0.002 mol of Fe(NO3)3 9H2O are dissolved in 100 mL of distilled water. Then 20 mL of NaOH solution 1 M is slowly added to the solution, under ultrasonic
Fig. 2. XRD pattern of the CoFe2O4 nanoparticles.
Please cite this article in press as: J. Saffari, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.010
G Model
JIEC-1851; No. of Pages 5 J. Saffari et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
3
Fig. 4. SEM images of CoFe nanoparticles obtained at 40 W.
Fig. 5. SEM images of CoFe nanoparticles achieved at 75 W.
waves (60 W) for 30 min. The solution is heated at 80 8C for 2 h. The black precipitate is then centrifuged and rinsed with distilled water, followed by being left in an atmosphere environment to dry. Fig. 1 shows the schematic diagram for experimental setup used in this sonochemical reaction.
Without using ultrasonic waves bigger particles (bulk product) were obtained. SEM image of the product without using ultrasound is shown in Fig. 3a. Ultrasonic irradiation creates bubbles which produces high temperature and energy after decomposition. This process provides appropriates amounts of energy for formation of CoFe nanoparticles.
2.3. Preparation of PS-CoFe nanocomposites First, 0.9 g (0.7 g) of polystyrene is dissolved in 10 mL dichloromethane solution. Then 0.1 g (or 0.3 g) of CoFe2O4 nanoparticles is dispersed in 10 mL of dichloromethane solution with ultrasonic waves (15 min, 60 W). The nanoparticles dispersion is then slowly added to the polymer solution. The new solution is then mixed and stirred for 6 h. The product is casted on a glass plate and is left for 2 h in order to evaporate the solvent.
3. Results and discussion XRD pattern of CoFe2O4 nanoparticles is shown in Fig. 2. The XRD pattern of as-prepared CoFe2O4 nanoparticles is indexed as a pure cubic phase (space group: Fd3m) which is very close to the literature values (JCPDS No. 01-1121). The crystallite size measurements were also carried out using the Scherrer equation [5], Dc = Kl/b cosu, where K usually takes a value of about 0.9, b is the width of the observed diffraction peak at its half maximum intensity (FWHM) and l is the X-ray wavelength (CuKa radiation, equals to 0.154 nm). The estimated crystallite size is about 21 nm.
Fig. 6. TEM image of PS-CoFe nanocomposite.
Please cite this article in press as: J. Saffari, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.010
G Model
JIEC-1851; No. of Pages 5 J. Saffari et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
4
80 20
Magnetization(emu/g)
Magnetization (emu/g)
60 40 20 0 -20 -40
0
-10
-20
-60 -80
10
-10000
-5000
0
5000
-10000
10000
-5000
0
5000
10000
Applied Field(Oe)
Applied field (Oe)
Fig. 9. Magnetization loop of PS-CoFe (30%) nanocomposite.
Fig. 7. Magnetization loop of CoFe nanoparticles.
SEM image of CoFe nanoparticles prepared at 60 W is shown in Fig. 3b which illustrates nanoparticles with average diameter of 60 nm. The effect of ultrasonic power on the morphology of the products is shown in Figs. 4 and 5. Fig. 4 shows SEM images of product obtained at lower power (40 W) that confirm nanoparticles with mediocre diameter of 70 nm are synthesized. The influence of higher power on the particle size has been investigated. All the SEM results approve that in all three different conditions nanoparticles are prepared with average particle size lower than 100 nm. TEM image of PS/CoFe (30%) nanocomposite is illustrated in Fig. 6 which confirms the appropriate dispersion of CoFe nanoparticles in the polymeric matrixes. Room temperature magnetic properties of samples were studied using an AGFM device. The hysteresis loop for CoFe nanoparticles is shown in Fig. 7. Based on our search in the literature very few work has been done on hard magnetic polymeric nanocomposites. We studied the magnetic interaction between the nanoparticles surrender by the polymeric chains. This interaction leads to a remarkable increase (from 640 to 975 Oe) of nanoparticle coersivities compared with the pure cobalt ferrite nanoparticles (Table 1). Hysteresis loops for PS/CoFe (10%) and PS/CoFe (30%) are illustrated in Figs. 8 and 9, respectively. It can be concluded that cobalt ferrite particles in the nanocomposites are sufficiently far away from each other so that their magnetic behaviour is not
Table 1 Coercivity, remanence and saturation magnetization of the CoFe nanoparticles and nanocomposites. Sample
Saturation magnetization (emu/g)
Coercivity (Oe)
Remanence (emu/g)
CoFe PS/CoFe (10%) PS/CoFe (30%)
62 5.3 16.9
640 975 881
21.9 2.2 6.4
influenced by the stray fields of their neighbour particles and this results in the dependent uncoupled (non-interacting) domains. The results indicate that, forming the nanocomposite and distributing of the magnetic nanoparticles into the polymer matrix leads in increasing the coercivity. A possible explanation for this result could be as follow: The magnetic moments of magnetic
Magnetization(emu/g)
6 4 2 0 -2 -4 -6 -10000
-5000
0
5000
10000
Applied Field(Oe) Fig. 8. Magnetization curve of PS-CoFe (10%) nanocomposite.
Fig. 10. Schematic illustration of (a) CoFe nanoparticles distributed in polymer matrix in absence of magnetic field and (b) presence of a magnetic field.
Please cite this article in press as: J. Saffari, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.010
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5
Fig. 11. Attraction of the products by magnet (a) CoFe nanoparticles; (b) PS-CoFe (10%) nanocomposite and (c) PS-CoFe (30%) nanocomposite.
nanoparticles are pined by the poly styrene matrix chains, so that a higher magnetic field is required to align the single domain nanoparticles in the field direction. This effect is illustrated in Fig. 10 schematically. Generally, coercivity of magnetic nanocomposites highly depends on the magnetic nanoparticle distribution into the polymeric matrixes. In order to make 1 g of magnetic nanocomposite, 0.1 g (or 0.3 g) of cobalt ferrite nanoparticles is added to 0.9 g (or 0.7 g) of polystyrene. Thus, the nanocomposite magnetization (defined as the magnetic moment per unit volume) is about one tenth (or one fourth) of that obtained for cobalt ferrite nanoparticles. The saturation magnetization of nanoparticles is much higher than those of obtained for PS-CoFe nanocomposites. Attraction of CoFe nanoparticles, PS-CoFe (10%) nanocomposite and PS-CoFe (30%) nanocomposite films by magnet are shown in Fig. 11a–c, respectively. 4. Conclusions CoFe2O4 nanoparticles are synthesized via a simple sonochemical reaction. It was found that the as-obtained CoFe2O4 nanoparticles exhibit a ferromagnetic behaviour with a saturation magnetization of 62 emu/g and a coercivity of 640 Oe at room temperature. In order to make magnetic films, CoFe2O4 nanoparticles were then added to PS matrixes. Nanocomposites were then characterized using XRD, SEM and AGFM spectroscopy. It was shown that distribution of the CoFe2O4 nanoparticles into the polymeric matrixes increases the coercivity.
Acknowledgment This work has been supported financially by Islamic Azad University Zahedan Branch Research.
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