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Green synthesis of soya bean sprouts-mediated superparamagnetic Fe3O4 nanoparticles
ARTICLE IN PRESS Journal of Magnetism and Magnetic Materials 322 (2010) 2938–2943
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Green synthesis of soya bean sprouts-mediated superparamagnetic Fe3O4 nanoparticles Yan Cai a, Yuhua Shen a,b,n, Anjian Xie a,b,n, Shikuo Li a, Xiufang Wang a a b
School of Chemistry and Chemical Engineering, Anhui University, Hefei 230039, PR China State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China
a r t i c l e in f o
a b s t r a c t
Article history: Received 27 January 2010 Received in revised form 18 April 2010 Available online 6 May 2010
Superparamagnetic Fe3O4 nanoparticles were first synthesized via soya bean sprouts (SBS) templates under ambient temperature and normal atmosphere. The reaction process was simple, eco-friendly, and convenient to handle. The morphology and crystalline phase of the nanoparticles were determined from scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD) spectra. The effect of SBS template on the formation of Fe3O4 nanoparticles was investigated using X-ray photoemission spectroscopy (XPS) and Fouriertransform infrared spectroscopy (FT-IR). The results indicate that spherical Fe3O4 nanoparticles with an average diameter of 8 nm simultaneously formed on the epidermal surface and the interior stem wall of SBS. The SBS are responsible for size and morphology control during the whole formation of Fe3O4 nanoparticles. In addition, the superconducting quantum interference device (SQUID) results indicate the products are superparamagnetic at room temperature, with blocking temperature (TB) of 150 K and saturation magnetization of 37.1 emu/g. & 2010 Elsevier B.V. All rights reserved.
Keywords: Fe3O4 Magnetic nanoparticle Green synthesis
1. Introduction Magnetite (Fe3O4), as a significant member of magnetic nanomaterials, has recently been subject to extensive research for many practical applications such as catalysis, magnetic storage media, magnetic field assisted separations and analyses, targeted drug delivery, and contrast agents in magnetic resonance imaging (MRI) [1–6]. Conventional chemical synthesis by precipitation, high-temperature reactions, sol–gel reactions, decomposition of organometallic precursors, polyol methods, etc. has already been described to produce magnetic nanoparticles [7–10]. With the concern for environmental contaminations, ‘‘green’’ methods for the synthesis of nanoparticles are also heightened as the chemical procedures generate a large amount of hazardous byproducts. As an alternative to conventional methods, biosynthesis involving organisms ranging from bacteria to fungi and plants are considered safe and ecologically sound for the nanomaterial fabrication [11–13]. Soya bean sprouts (SBS), the sprout form of soya bean, are an ideal biotemplate for the preparation and self-organization of inorganic materials. Wu et al. [14,15] have used mung bean
n Corresponding authors at: School of Chemistry and Chemical Engineering, Anhui University, Hefei 230039, PR China. Tel.: +86 551 5108090; fax: + 86 551 5108702. E-mail addresses: [email protected] (Y. Shen), [email protected] (A. Xie).
0304-8853/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2010.05.009
sprout (MBS) as template to fabricate novel fractal BaCrO4 crystals and PbSe nanorods. Biologically, the physiological characteristics and basic nutritional components in SBS and MBS have little differences. Both of them have a uniaxial pore structure with a biological surface pattern and contain a lot of biomolecules, such as proteins, celluloses, vitamins, amino acids, etc. Statistically, there are 4.5 g of proteins contained in every 100 g of wet SBS and the content is almost twice as much as that of MBS. In principle, Fe3 + and Fe2 + ions in solution should be trapped on the wall of SBS by electrostatic attraction and/or chelation. Then, Fe3O4 nanoparticles would form on the wall of SBS via in situ coprecipitation process under alkalinity condition. As we know, SBS also contains many reductive materials such as vitamin C, which may play an antioxidative role in the reaction. Hence SBS are an appropriate and available living biotemplate to synthesize Fe3O4 nanoparticles via in situ coprecipitation process without the protection of inert atmosphere. In our work, Fe3O4 nanoparticles were simultaneously formed on the epidermal surface and the interior stem wall of SBS; the particles are superparamagnetic. To the best of our knowledge, the use of plants templates at room temperature for the synthesis of Fe3O4 nanoparticles has not been reported. This attractive method is facile and convenient, requires neither harsh conditions nor extra modifiers, provides an economical route to fabricate other functional inorganic nanomaterial.
ARTICLE IN PRESS Y. Cai et al. / Journal of Magnetism and Magnetic Materials 322 (2010) 2938–2943
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2. Materials and methods 2.1. Materials The soya bean sprouts (SBS) used in this experiment were fresh and purchased from the supermarket of Anhui University. Ammonium ferrous sulfate hexahydrate (Fe(NH4)2(SO4)2 6H2O), ferric chloride hexahydrate (FeCl3 6H2O), sodium hydroxide (NaOH), and absolute alcohol (CH3CH2OH) were all A.R. grade and obtained from Shanghai Reagent Co. Ltd. (China) and were used without further purification. Double distilled water was used in this experiment. 2.2. Synthesis of Fe3O4 nanoparticles using SBS templates
2.3. Characterization The epidermal surface and the interior stem of SBS and SBS/Fe3O4 were investigated by S-4800 scanning electron microscopy (SEM). Transmission electron microanopy (TEM), selected area electron diffraction (SAED) and high-resolution TEM (HRTEM) were taken on JEM model 100SX and 2010 electron microscopes (Japan Electron Co.) and operated at accelerating voltages of 80 and 200 kV, respectively. The X-ray diffraction (XRD) pattern was obtained on a MAP18XAHF instrument, with the X-ray diffractometer using Cu Ka radiation at a scan rate of 0.03 2y s 1 to determine the crystalline phase. FT-IR spectra were recorded with a Fourier-transform infrared spectrophotometer Niolet 870 between 4000 and 400 cm 1 with a resolution of 4 cm 1. XPS measurement was carried out on a VG ESCALAB MKII instrument at a pressure greater than 10 6 Pa. The general scan C1s, N1s, O1s, and Fe2p core level spectra were recorded with un-monochromatized Mg Ka radiation. The core level binding energies (BEs) were aligned with respect to the C1s BE of 285.0 eV. The magnetic properties of Fe3O4 nanoparticles were investigated using a quantum design superconducting quantum interference device (SQUID) magnetometer (MPMS-XL). The temperature dependence of magnetization was measured at an applied field of 100 Oe between 0 and 300 K using the zero field-cooling (ZFC) and field-cooling (FC) procedures. The hysteresis loops were measured at 1.7 and 300 K, respectively.
3. Results and discussion Superparamagnetic Fe3O4 nanoparticles can be obtained by coprecipitation of Fe2 + and Fe3 + inside SBS. SBS used in the synthesis were shown in Fig. 1a, the stem was milky white. The formation of Fe3O4 particles was first detected by the color changes in SBS over the reaction time and later confirmed via preliminary magnetic test under external magnetic field. The
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Fig. 1. Photographs of SBS (a), SBS/Fe2 + /Fe3 + (b), SBS/Fe3O4 (c) and the SBS/Fe3O4 fragments in a vial under external magnetic field (d). The solutions are all pure water.
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Prior to the experiment, SBS were washed with distilled water several times. The SBS (except laminae) were immersed into a suitable proportion of Fe2 + and Fe3 + solution for 4 h at room temperature, then taken out and washed with distilled water to ensure that no ions were left on the epidermal surface of SBS; the sample was referred to as SBS/Fe2 + /Fe3 + . The epidermal surface turned black 5 min later followed by immersing SBS/Fe2 + /Fe3 + into NaOH solution. The SBS were kept immersed in the solution for 30 min, then taken out and washed repeatedly with distilled water and absolute ethanol, the sample was denoted as SBS/Fe3O4. The different products formed on the epidermal surface and interior stem of SBS/Fe3O4 were successively collected via processes of milling, magnetic separation, washing and drying.
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Fig. 2. XRD patterns of Fe3O4 samples obtained from interior stem wall (a) and epidermal surface (b) of SBS.
stem of SBS/Fe2 + /Fe3 + was also milky white (Fig. 1b) before the reaction with OH ions and changed to black (Fig. 1c) after the reaction time of 5 min and the color did not change any more with reaction time. The characteristic black color of Fe3O4 particles provided a convenient signature to indicate their formation on SBS. Then the SBS/Fe3O4 (except laminae) sample was cut into small pieces, which showed fast movement to the applied magnetic field (Fig. 1d). The phenomenon further demonstrated that the Fe3O4 particles existed on the SBS possessed strong magnetic properties. XRD patterns of the as-prepared Fe3O4 nanoparticles from interior stem wall (a) and epidermal surface (b) of SBS are shown in Fig. 2. The Bragg reflections show that the two samples are in the same space group. The peaks are assigned to diffraction from the (2 2 0), (3 1 1), (4 0 0), (5 1 1), (4 4 0) and (5 3 3) planes of cubic inverse spinel Fe3O4, which are in good agreement with the reported data (JCPDS: 75-1610). This indicates that Fe3O4 magnetite nanoparticles can be attained by such a facile and green method. Typical SEM images of epidermal surface and the interior stem of SBS and SBS/Fe3O4 are shown in Fig. 3a–d. The epidermis (Fig. 3a) of SBS is not smooth and has well-distributed grooves
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Y. Cai et al. / Journal of Magnetism and Magnetic Materials 322 (2010) 2938–2943
Fig. 3. SEM images of the epidermal surface (a) and the cross section of the interior stem (b) of SBS; and Fe3O4 nanoparticles presented on the epidermal surface (c) and on interior stem wall (d) of SBS; TEM image (e) and HRTEM images (f) of the Fe3O4 nanoparticles obtained from SBS.
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whose widths are about 15–35 mm, while the interior stem (Fig. 3b) is composed of many canaliculi whose apertures are about 60–85 mm. After the reaction, quite a number of spherical nanoparticles with uniform size are packed closely both on the epidermis (Fig. 3c) and interior stem (Fig. 3d) of SBS/Fe3O4. Thus it can be concluded from SEM and XRD measurements that the morphology and crystalline phase of the Fe3O4 nanoparticles are unaffected by the different spatial structures between the external and internal portions of SBS template. TEM image (Fig. 3e) indicates that the average size of the as-prepared Fe3O4 nanoparticles is about 8 nm. Electron diffraction pattern (Fig. 3e inset) reveals that the sample is polycrystalline. HRTEM image (Fig. 3f) shows that the nanoparticles are structurally uniform with a lattice fringe spacing about 0.25 nm, which corresponds well with the values of 0.253 nm of the (3 1 1) lattice plane of the cubic Fe3O4 obtained from the JCPDS database (JCPDS card no. 75-1610). FT-IR measurements of SBS in different experimental stage were carried out to reveal the possible formation process of Fe3O4 nanoparticles. Fig. 4a represents the FT-IR spectrum of pure SBS and there are several characteristic protein bands. The peaks centered at 1645, 1520, and 1235 cm 1 are assigned to the amide I, amide II, and amide III bands of protein owing to C ¼O, N–H stretching vibrations, and C–N bending vibrations in the proteins, respectively. The band at 1460 cm 1 probably originates from the
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symmetric stretching vibrations of COO groups of amino acid residues with free carboxylate groups in the protein. The peaks at 1402 and 1082 cm 1 are possibly the bending vibrations of C–OH
ARTICLE IN PRESS Y. Cai et al. / Journal of Magnetism and Magnetic Materials 322 (2010) 2938–2943
groups and the antisymmetric stretching band of C–O–C groups of protein or polysaccharide. The band at 675 cm 1 is due to the plane bending vibration of N–H groups in the proteins [16]. Compared with the pure SBS, several significant changes are observed in the FT-IR spectrum of SBS/Fe2 + /Fe3 + (Fig. 4b). The peak of amide I band blue-shifts from 1645 to below 1630 cm 1, which indicates that the SBS attracted with the Fe2 + and Fe3 + ions via O from the carbonyl group in the proteins. The FT-IR spectrum of SBS/Fe3O4 is shown in Fig. 4c. In contrast to Fig. 4b, the variation of peaks located at 1200–1800 cm 1 is small, and the appearance of the new peak at 576 cm 1 is the typical characteristic absorption peak of Fe3O4 [17]. The FT-IR results indicate the presence of proteins and other biomolecules in the SBS and these biomolecules may participate in the formation of Fe3O4 nanoparticles. X-ray photoelectron spectra of the Fe3O4 nanoparticles obtained from SBS are shown in Fig. 5a–d. The general scan spectrum (Fig. 5a) shows the presence of strong C1s, O2p, N1s, and Fe2p peaks. The binding energies at 723.8 and 710.5 eV (Fig. 5a inset), corresponding to Fe2p3/2 and Fe2p1/2, respectively, are in good agreement with the values reported for Fe3O4 in the literature [18]. The C1s core level spectrum from the nanoparticles is shown in Fig. 5b and it can be decomposed into three chemically distinct components at 284.6, 286.0, and 287.9 eV. The main C1s peak at 284.6 eV can be assigned to the carbon atoms within a phenyl rings of tyrosine, tryptophan,
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and/or phenylalanine residues of the protein; the peak at 286.0 eV is attributed to the electron emissions from carbons in carbonyl groups (carbonyl carbons of the proteins or polysaccharides), and the 287.9 eV peak is most likely from carbons a to the carbonyl carbons. The N1s core level (Fig. 5c) can also be resolved into two components, centered at 399.5 and 401.4 eV, assigned to neutral amine and protonated amine groups present in the protein moiety. The O1s core level (Fig. 5d) can be decomposed into three chemically distinct components at 529.8, 531.6, and 533.2 eV. The peak at 531.6 eV is typical for O1s of iron oxide [19]; the high BE component observed at 529.8 and 533.2 eV can be assigned to carboxylate groups [16]. Thus it can be concluded from XPS measurements that some SBS biomolecules or residues were left on the surface of Fe3O4 nanoparticles. Based on the results presented above, we suppose the following model for the formation of Fe3O4 nanoparticles via SBS templates. Firstly, when SBS were immersed in a mixture of Fe2 + and Fe3 + solution, Fe3 + and Fe2 + ions first entered SBS and then preferentially combined with oxygen in the carbonyl or carboxylate groups by electrostatic attraction and/or chelation. Secondly, after immersed in NaOH solution, the OH ions entered SBS/Fe2 + /Fe3 + , Fe3O4 nanoparticles simultaneously came into being both on the epidermal surface and on the interior stem wall of SBS. During nucleation, proteins and other biomolecules could control nucleation position through special confinement.
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Fig. 5. The general XPS spectra (a) of Fe3O4 sample obtained from SBS; the spectra of C1s, N1s, and O1s core levels are (b), (c), and (d), respectively.
ARTICLE IN PRESS Y. Cai et al. / Journal of Magnetism and Magnetic Materials 322 (2010) 2938–2943
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Fig. 6. Temperature-dependent of the ZFC/FC magnetization measured with a magnetic field of 100 Oe (a); the magnetic hysteresis loops obtained at 300 K (b) and 1.7 K (c) for Fe3O4 nanoparticles in powder state.
During the further growth period, SBS biotemplate could induce the growth of the nuclei. Therefore, small and stable spherical Fe3O4 nanoparticles were formed. The SBS are responsible for size and morphology control during the whole formation of Fe3O4 nanoparticles. The magnetic measurement of Fe3O4 nanoparticles reveals the superparamagnetic behaviors at room temperature. Standard zerofield-cooling (ZFC) and field-cooling (FC) measurements of Fe3O4 nanoparticles give a blocking temperature (TB) of about 150 K with a broad peak (Fig. 6a), which suggests that there are strong magnetic dipole–dipole and/or exchange interactions among the particles. One can see that the slopes of the sample in both FC and ZFC measurement are equal to each other at high temperature above the TB, which indicates the particles are free to align with the field during the measuring time at high temperature, and this state is considered to be superparamagnetic [20]. The field-dependent magnetization measurement at 300 K (Fig. 6b) suggests that the Fe3O4 nanoparticles have magnetization saturation (Ms) values of 37.1 emu/g and no remanence is detected. The hysteresis loops further confirmed the superparamagnetism of the particles, which is good for their applications. The nanoparticles show ferrimagneticlike properties at 1.7 K (Fig. 6c) and the saturation magnetization (Ms) is about 44.7 emu/g, the coercive field (Hc) is about 454.6 Oe, and the remanent magnetization (Mr) is about 11.3 emu/g. From the hysteresis, it can be seen that the Ms at 300 K is smaller than that at 1.7 K. Lower Ms is expected at higher temperature because of the superparamagnetism.
4. Conclusions In conclusion, we have demonstrated the green synthesis of superparamagnetic Fe3O4 nanoparticles via SBS templates. The SBS play a controlling role during the whole formation of Fe3O4 nanoparticles and a probable mechanism is also given. This method is clean, nontoxic, environment-friendly and also represents an important advance in the use of plants over microorganisms in the biosynthesis of Fe3O4 nanoparticles.
Acknowledgments This work was supported by the National Science Foundation of China (grants 20871001, 20671001, 20731001), the Major Program of Anhui Provincial Education Department (grant ZD2007004-1), the Research Fund for the Doctoral Program of Higher Education of China (grant 20070357002), and the Functional Material of Inorganic Chemistry of Anhui Province. References [1] [2] [3] [4] [5]
J.P. Ge, T. Huynh, Y.X. Hu, Y.D. Yin, Nano Lett. 8 (2008) 931. S.H. Sun, C.B. Murray, D. Weller, L. Folks, A. Moser, Science 287 (2000) 1989. A.H. Latham, A.P. Tarpara, M.E. Williams, Anal. Chem. 79 (2007) 5746. N. Pamme, A. Manz, Anal. Chem. 76 (2004) 7250. W. Zhao, J. Gu, L. Zhang, H. Chen, J. Shi, J. Am. Chem. Soc. 127 (2005) 8916.
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[6] M. Brahler, R. Georgieva, N. Buske, A. Muller, S. Muller, J. Pinkernelle, U. Teichgraber, A. Voigt, H. Baumler, Nano Lett. 6 (2006) 2505. [7] T. Hyeon, S.S. Lee, J. Park, Y. Chung, H.B. Na, J. Am. Chem. Soc. 123 (2001) 12798. [8] X.Q. Xu, C.H. Deng, M.X. Gao, W.J. Yu, X.Q. Xu, P.Y. Yang, X.M. Zhang, Adv. Mater. 18 (2006) 3289. [9] C. Albornoz, S.E. Jacobo, J. Magn. Magn. Mater. 305 (2006) 12. [10] S. Sun, H. Zeng, J. Am. Chem. Soc. 124 (2002) 8204. [11] D. Philip, Spectrochim. Acta Pt. A 73 (2009) 374. [12] A. Bharde, D. Rautaray, V. Bansal, A. Ahmad, I. Sarkar, S.M. Yusuf, M. Sanyal, M. Sastry, Small 2 (2006) 135. [13] A. Bharde, A. Yogesh, M. Sastry, J. Am. Chem. Soc. 127 (2005) 9326.
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[14] Y. Yan, Q.S. Wu, L. Li, Y.P. Ding, Cryst. Growth Des. 6 (2006) 769. [15] L. Li, Q.S. Wu, Y.P. Ding, Nanotechnology 15 (2004) 1877. [16] S.K. Li, Y.H. Shen, A.J. Xie, X.R. Yu, L.G. Qiu, L. Zhang, Q.F. Zhang, Green Chem. 9 (2007) 852. [17] K. Tao, H.J. Dou, K. Sun, Chem. Mater. 18 (2006) 5273. [18] S.Y. Lian, Z.H. Kang, E.B. Wang, M. Jiang, C.W. Hu, L. Xu, Solid State Commun. 127 (2003) 605. [19] G.F. Zou, K. Xiong, C.L. Jiang, H. Li, T.W. Li, J. Du, Y.T. Qian, J. Phys. Chem. B 109 (2005) 18356. [20] T.Z. Yang, C.M. Shen, Z. Li, H.R. Zhang, C.W. Xiao, S.T. Chen, Z.C. Xu, D.X. Shi, J.Q. Li, H.J. Gao, J. Phys. Chem. B 109 (2005) 23233.
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Green synthesis of soya bean sprouts-mediated superparamagnetic Fe3O4 nanoparticles Yan Cai a, Yuhua Shen a,b,n, Anjian Xie a,b,n, Shikuo Li a, Xiufang Wang a a b
School of Chemistry and Chemical Engineering, Anhui University, Hefei 230039, PR China State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China
a r t i c l e in f o
a b s t r a c t
Article history: Received 27 January 2010 Received in revised form 18 April 2010 Available online 6 May 2010
Superparamagnetic Fe3O4 nanoparticles were first synthesized via soya bean sprouts (SBS) templates under ambient temperature and normal atmosphere. The reaction process was simple, eco-friendly, and convenient to handle. The morphology and crystalline phase of the nanoparticles were determined from scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD) spectra. The effect of SBS template on the formation of Fe3O4 nanoparticles was investigated using X-ray photoemission spectroscopy (XPS) and Fouriertransform infrared spectroscopy (FT-IR). The results indicate that spherical Fe3O4 nanoparticles with an average diameter of 8 nm simultaneously formed on the epidermal surface and the interior stem wall of SBS. The SBS are responsible for size and morphology control during the whole formation of Fe3O4 nanoparticles. In addition, the superconducting quantum interference device (SQUID) results indicate the products are superparamagnetic at room temperature, with blocking temperature (TB) of 150 K and saturation magnetization of 37.1 emu/g. & 2010 Elsevier B.V. All rights reserved.
Keywords: Fe3O4 Magnetic nanoparticle Green synthesis
1. Introduction Magnetite (Fe3O4), as a significant member of magnetic nanomaterials, has recently been subject to extensive research for many practical applications such as catalysis, magnetic storage media, magnetic field assisted separations and analyses, targeted drug delivery, and contrast agents in magnetic resonance imaging (MRI) [1–6]. Conventional chemical synthesis by precipitation, high-temperature reactions, sol–gel reactions, decomposition of organometallic precursors, polyol methods, etc. has already been described to produce magnetic nanoparticles [7–10]. With the concern for environmental contaminations, ‘‘green’’ methods for the synthesis of nanoparticles are also heightened as the chemical procedures generate a large amount of hazardous byproducts. As an alternative to conventional methods, biosynthesis involving organisms ranging from bacteria to fungi and plants are considered safe and ecologically sound for the nanomaterial fabrication [11–13]. Soya bean sprouts (SBS), the sprout form of soya bean, are an ideal biotemplate for the preparation and self-organization of inorganic materials. Wu et al. [14,15] have used mung bean
n Corresponding authors at: School of Chemistry and Chemical Engineering, Anhui University, Hefei 230039, PR China. Tel.: +86 551 5108090; fax: + 86 551 5108702. E-mail addresses: [email protected] (Y. Shen), [email protected] (A. Xie).
0304-8853/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2010.05.009
sprout (MBS) as template to fabricate novel fractal BaCrO4 crystals and PbSe nanorods. Biologically, the physiological characteristics and basic nutritional components in SBS and MBS have little differences. Both of them have a uniaxial pore structure with a biological surface pattern and contain a lot of biomolecules, such as proteins, celluloses, vitamins, amino acids, etc. Statistically, there are 4.5 g of proteins contained in every 100 g of wet SBS and the content is almost twice as much as that of MBS. In principle, Fe3 + and Fe2 + ions in solution should be trapped on the wall of SBS by electrostatic attraction and/or chelation. Then, Fe3O4 nanoparticles would form on the wall of SBS via in situ coprecipitation process under alkalinity condition. As we know, SBS also contains many reductive materials such as vitamin C, which may play an antioxidative role in the reaction. Hence SBS are an appropriate and available living biotemplate to synthesize Fe3O4 nanoparticles via in situ coprecipitation process without the protection of inert atmosphere. In our work, Fe3O4 nanoparticles were simultaneously formed on the epidermal surface and the interior stem wall of SBS; the particles are superparamagnetic. To the best of our knowledge, the use of plants templates at room temperature for the synthesis of Fe3O4 nanoparticles has not been reported. This attractive method is facile and convenient, requires neither harsh conditions nor extra modifiers, provides an economical route to fabricate other functional inorganic nanomaterial.
ARTICLE IN PRESS Y. Cai et al. / Journal of Magnetism and Magnetic Materials 322 (2010) 2938–2943
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2. Materials and methods 2.1. Materials The soya bean sprouts (SBS) used in this experiment were fresh and purchased from the supermarket of Anhui University. Ammonium ferrous sulfate hexahydrate (Fe(NH4)2(SO4)2 6H2O), ferric chloride hexahydrate (FeCl3 6H2O), sodium hydroxide (NaOH), and absolute alcohol (CH3CH2OH) were all A.R. grade and obtained from Shanghai Reagent Co. Ltd. (China) and were used without further purification. Double distilled water was used in this experiment. 2.2. Synthesis of Fe3O4 nanoparticles using SBS templates
2.3. Characterization The epidermal surface and the interior stem of SBS and SBS/Fe3O4 were investigated by S-4800 scanning electron microscopy (SEM). Transmission electron microanopy (TEM), selected area electron diffraction (SAED) and high-resolution TEM (HRTEM) were taken on JEM model 100SX and 2010 electron microscopes (Japan Electron Co.) and operated at accelerating voltages of 80 and 200 kV, respectively. The X-ray diffraction (XRD) pattern was obtained on a MAP18XAHF instrument, with the X-ray diffractometer using Cu Ka radiation at a scan rate of 0.03 2y s 1 to determine the crystalline phase. FT-IR spectra were recorded with a Fourier-transform infrared spectrophotometer Niolet 870 between 4000 and 400 cm 1 with a resolution of 4 cm 1. XPS measurement was carried out on a VG ESCALAB MKII instrument at a pressure greater than 10 6 Pa. The general scan C1s, N1s, O1s, and Fe2p core level spectra were recorded with un-monochromatized Mg Ka radiation. The core level binding energies (BEs) were aligned with respect to the C1s BE of 285.0 eV. The magnetic properties of Fe3O4 nanoparticles were investigated using a quantum design superconducting quantum interference device (SQUID) magnetometer (MPMS-XL). The temperature dependence of magnetization was measured at an applied field of 100 Oe between 0 and 300 K using the zero field-cooling (ZFC) and field-cooling (FC) procedures. The hysteresis loops were measured at 1.7 and 300 K, respectively.
3. Results and discussion Superparamagnetic Fe3O4 nanoparticles can be obtained by coprecipitation of Fe2 + and Fe3 + inside SBS. SBS used in the synthesis were shown in Fig. 1a, the stem was milky white. The formation of Fe3O4 particles was first detected by the color changes in SBS over the reaction time and later confirmed via preliminary magnetic test under external magnetic field. The
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Fig. 1. Photographs of SBS (a), SBS/Fe2 + /Fe3 + (b), SBS/Fe3O4 (c) and the SBS/Fe3O4 fragments in a vial under external magnetic field (d). The solutions are all pure water.
Intensity (a.u.)
Prior to the experiment, SBS were washed with distilled water several times. The SBS (except laminae) were immersed into a suitable proportion of Fe2 + and Fe3 + solution for 4 h at room temperature, then taken out and washed with distilled water to ensure that no ions were left on the epidermal surface of SBS; the sample was referred to as SBS/Fe2 + /Fe3 + . The epidermal surface turned black 5 min later followed by immersing SBS/Fe2 + /Fe3 + into NaOH solution. The SBS were kept immersed in the solution for 30 min, then taken out and washed repeatedly with distilled water and absolute ethanol, the sample was denoted as SBS/Fe3O4. The different products formed on the epidermal surface and interior stem of SBS/Fe3O4 were successively collected via processes of milling, magnetic separation, washing and drying.
b
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Fig. 2. XRD patterns of Fe3O4 samples obtained from interior stem wall (a) and epidermal surface (b) of SBS.
stem of SBS/Fe2 + /Fe3 + was also milky white (Fig. 1b) before the reaction with OH ions and changed to black (Fig. 1c) after the reaction time of 5 min and the color did not change any more with reaction time. The characteristic black color of Fe3O4 particles provided a convenient signature to indicate their formation on SBS. Then the SBS/Fe3O4 (except laminae) sample was cut into small pieces, which showed fast movement to the applied magnetic field (Fig. 1d). The phenomenon further demonstrated that the Fe3O4 particles existed on the SBS possessed strong magnetic properties. XRD patterns of the as-prepared Fe3O4 nanoparticles from interior stem wall (a) and epidermal surface (b) of SBS are shown in Fig. 2. The Bragg reflections show that the two samples are in the same space group. The peaks are assigned to diffraction from the (2 2 0), (3 1 1), (4 0 0), (5 1 1), (4 4 0) and (5 3 3) planes of cubic inverse spinel Fe3O4, which are in good agreement with the reported data (JCPDS: 75-1610). This indicates that Fe3O4 magnetite nanoparticles can be attained by such a facile and green method. Typical SEM images of epidermal surface and the interior stem of SBS and SBS/Fe3O4 are shown in Fig. 3a–d. The epidermis (Fig. 3a) of SBS is not smooth and has well-distributed grooves
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Fig. 3. SEM images of the epidermal surface (a) and the cross section of the interior stem (b) of SBS; and Fe3O4 nanoparticles presented on the epidermal surface (c) and on interior stem wall (d) of SBS; TEM image (e) and HRTEM images (f) of the Fe3O4 nanoparticles obtained from SBS.
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whose widths are about 15–35 mm, while the interior stem (Fig. 3b) is composed of many canaliculi whose apertures are about 60–85 mm. After the reaction, quite a number of spherical nanoparticles with uniform size are packed closely both on the epidermis (Fig. 3c) and interior stem (Fig. 3d) of SBS/Fe3O4. Thus it can be concluded from SEM and XRD measurements that the morphology and crystalline phase of the Fe3O4 nanoparticles are unaffected by the different spatial structures between the external and internal portions of SBS template. TEM image (Fig. 3e) indicates that the average size of the as-prepared Fe3O4 nanoparticles is about 8 nm. Electron diffraction pattern (Fig. 3e inset) reveals that the sample is polycrystalline. HRTEM image (Fig. 3f) shows that the nanoparticles are structurally uniform with a lattice fringe spacing about 0.25 nm, which corresponds well with the values of 0.253 nm of the (3 1 1) lattice plane of the cubic Fe3O4 obtained from the JCPDS database (JCPDS card no. 75-1610). FT-IR measurements of SBS in different experimental stage were carried out to reveal the possible formation process of Fe3O4 nanoparticles. Fig. 4a represents the FT-IR spectrum of pure SBS and there are several characteristic protein bands. The peaks centered at 1645, 1520, and 1235 cm 1 are assigned to the amide I, amide II, and amide III bands of protein owing to C ¼O, N–H stretching vibrations, and C–N bending vibrations in the proteins, respectively. The band at 1460 cm 1 probably originates from the
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symmetric stretching vibrations of COO groups of amino acid residues with free carboxylate groups in the protein. The peaks at 1402 and 1082 cm 1 are possibly the bending vibrations of C–OH
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groups and the antisymmetric stretching band of C–O–C groups of protein or polysaccharide. The band at 675 cm 1 is due to the plane bending vibration of N–H groups in the proteins [16]. Compared with the pure SBS, several significant changes are observed in the FT-IR spectrum of SBS/Fe2 + /Fe3 + (Fig. 4b). The peak of amide I band blue-shifts from 1645 to below 1630 cm 1, which indicates that the SBS attracted with the Fe2 + and Fe3 + ions via O from the carbonyl group in the proteins. The FT-IR spectrum of SBS/Fe3O4 is shown in Fig. 4c. In contrast to Fig. 4b, the variation of peaks located at 1200–1800 cm 1 is small, and the appearance of the new peak at 576 cm 1 is the typical characteristic absorption peak of Fe3O4 [17]. The FT-IR results indicate the presence of proteins and other biomolecules in the SBS and these biomolecules may participate in the formation of Fe3O4 nanoparticles. X-ray photoelectron spectra of the Fe3O4 nanoparticles obtained from SBS are shown in Fig. 5a–d. The general scan spectrum (Fig. 5a) shows the presence of strong C1s, O2p, N1s, and Fe2p peaks. The binding energies at 723.8 and 710.5 eV (Fig. 5a inset), corresponding to Fe2p3/2 and Fe2p1/2, respectively, are in good agreement with the values reported for Fe3O4 in the literature [18]. The C1s core level spectrum from the nanoparticles is shown in Fig. 5b and it can be decomposed into three chemically distinct components at 284.6, 286.0, and 287.9 eV. The main C1s peak at 284.6 eV can be assigned to the carbon atoms within a phenyl rings of tyrosine, tryptophan,
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and/or phenylalanine residues of the protein; the peak at 286.0 eV is attributed to the electron emissions from carbons in carbonyl groups (carbonyl carbons of the proteins or polysaccharides), and the 287.9 eV peak is most likely from carbons a to the carbonyl carbons. The N1s core level (Fig. 5c) can also be resolved into two components, centered at 399.5 and 401.4 eV, assigned to neutral amine and protonated amine groups present in the protein moiety. The O1s core level (Fig. 5d) can be decomposed into three chemically distinct components at 529.8, 531.6, and 533.2 eV. The peak at 531.6 eV is typical for O1s of iron oxide [19]; the high BE component observed at 529.8 and 533.2 eV can be assigned to carboxylate groups [16]. Thus it can be concluded from XPS measurements that some SBS biomolecules or residues were left on the surface of Fe3O4 nanoparticles. Based on the results presented above, we suppose the following model for the formation of Fe3O4 nanoparticles via SBS templates. Firstly, when SBS were immersed in a mixture of Fe2 + and Fe3 + solution, Fe3 + and Fe2 + ions first entered SBS and then preferentially combined with oxygen in the carbonyl or carboxylate groups by electrostatic attraction and/or chelation. Secondly, after immersed in NaOH solution, the OH ions entered SBS/Fe2 + /Fe3 + , Fe3O4 nanoparticles simultaneously came into being both on the epidermal surface and on the interior stem wall of SBS. During nucleation, proteins and other biomolecules could control nucleation position through special confinement.
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Fig. 5. The general XPS spectra (a) of Fe3O4 sample obtained from SBS; the spectra of C1s, N1s, and O1s core levels are (b), (c), and (d), respectively.
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During the further growth period, SBS biotemplate could induce the growth of the nuclei. Therefore, small and stable spherical Fe3O4 nanoparticles were formed. The SBS are responsible for size and morphology control during the whole formation of Fe3O4 nanoparticles. The magnetic measurement of Fe3O4 nanoparticles reveals the superparamagnetic behaviors at room temperature. Standard zerofield-cooling (ZFC) and field-cooling (FC) measurements of Fe3O4 nanoparticles give a blocking temperature (TB) of about 150 K with a broad peak (Fig. 6a), which suggests that there are strong magnetic dipole–dipole and/or exchange interactions among the particles. One can see that the slopes of the sample in both FC and ZFC measurement are equal to each other at high temperature above the TB, which indicates the particles are free to align with the field during the measuring time at high temperature, and this state is considered to be superparamagnetic [20]. The field-dependent magnetization measurement at 300 K (Fig. 6b) suggests that the Fe3O4 nanoparticles have magnetization saturation (Ms) values of 37.1 emu/g and no remanence is detected. The hysteresis loops further confirmed the superparamagnetism of the particles, which is good for their applications. The nanoparticles show ferrimagneticlike properties at 1.7 K (Fig. 6c) and the saturation magnetization (Ms) is about 44.7 emu/g, the coercive field (Hc) is about 454.6 Oe, and the remanent magnetization (Mr) is about 11.3 emu/g. From the hysteresis, it can be seen that the Ms at 300 K is smaller than that at 1.7 K. Lower Ms is expected at higher temperature because of the superparamagnetism.
4. Conclusions In conclusion, we have demonstrated the green synthesis of superparamagnetic Fe3O4 nanoparticles via SBS templates. The SBS play a controlling role during the whole formation of Fe3O4 nanoparticles and a probable mechanism is also given. This method is clean, nontoxic, environment-friendly and also represents an important advance in the use of plants over microorganisms in the biosynthesis of Fe3O4 nanoparticles.
Acknowledgments This work was supported by the National Science Foundation of China (grants 20871001, 20671001, 20731001), the Major Program of Anhui Provincial Education Department (grant ZD2007004-1), the Research Fund for the Doctoral Program of Higher Education of China (grant 20070357002), and the Functional Material of Inorganic Chemistry of Anhui Province. References [1] [2] [3] [4] [5]
J.P. Ge, T. Huynh, Y.X. Hu, Y.D. Yin, Nano Lett. 8 (2008) 931. S.H. Sun, C.B. Murray, D. Weller, L. Folks, A. Moser, Science 287 (2000) 1989. A.H. Latham, A.P. Tarpara, M.E. Williams, Anal. Chem. 79 (2007) 5746. N. Pamme, A. Manz, Anal. Chem. 76 (2004) 7250. W. Zhao, J. Gu, L. Zhang, H. Chen, J. Shi, J. Am. Chem. Soc. 127 (2005) 8916.
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[6] M. Brahler, R. Georgieva, N. Buske, A. Muller, S. Muller, J. Pinkernelle, U. Teichgraber, A. Voigt, H. Baumler, Nano Lett. 6 (2006) 2505. [7] T. Hyeon, S.S. Lee, J. Park, Y. Chung, H.B. Na, J. Am. Chem. Soc. 123 (2001) 12798. [8] X.Q. Xu, C.H. Deng, M.X. Gao, W.J. Yu, X.Q. Xu, P.Y. Yang, X.M. Zhang, Adv. Mater. 18 (2006) 3289. [9] C. Albornoz, S.E. Jacobo, J. Magn. Magn. Mater. 305 (2006) 12. [10] S. Sun, H. Zeng, J. Am. Chem. Soc. 124 (2002) 8204. [11] D. Philip, Spectrochim. Acta Pt. A 73 (2009) 374. [12] A. Bharde, D. Rautaray, V. Bansal, A. Ahmad, I. Sarkar, S.M. Yusuf, M. Sanyal, M. Sastry, Small 2 (2006) 135. [13] A. Bharde, A. Yogesh, M. Sastry, J. Am. Chem. Soc. 127 (2005) 9326.
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[14] Y. Yan, Q.S. Wu, L. Li, Y.P. Ding, Cryst. Growth Des. 6 (2006) 769. [15] L. Li, Q.S. Wu, Y.P. Ding, Nanotechnology 15 (2004) 1877. [16] S.K. Li, Y.H. Shen, A.J. Xie, X.R. Yu, L.G. Qiu, L. Zhang, Q.F. Zhang, Green Chem. 9 (2007) 852. [17] K. Tao, H.J. Dou, K. Sun, Chem. Mater. 18 (2006) 5273. [18] S.Y. Lian, Z.H. Kang, E.B. Wang, M. Jiang, C.W. Hu, L. Xu, Solid State Commun. 127 (2003) 605. [19] G.F. Zou, K. Xiong, C.L. Jiang, H. Li, T.W. Li, J. Du, Y.T. Qian, J. Phys. Chem. B 109 (2005) 18356. [20] T.Z. Yang, C.M. Shen, Z. Li, H.R. Zhang, C.W. Xiao, S.T. Chen, Z.C. Xu, D.X. Shi, J.Q. Li, H.J. Gao, J. Phys. Chem. B 109 (2005) 23233.