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Synthesis of single-crystalline alpha-FeOOH nanorods with semi-hard magnetic property
Materials Letters 61 (2007) 4318 – 4320 www.elsevier.com/locate/matlet
Synthesis of single-crystalline alpha-FeOOH nanorods with semi-hard magnetic property Ming-Wang Shao ⁎, Hui-Zhao Ban, Yan-Hua Tong, Hui Hu, Li-Ling Niu, Hua-Zhong Gao, Yin Ye Anhui Key Laboratory of Functional Molecular Solids, and College of Chemistry and Materials Science, Anhui Normal University, Wuhu 241000, PR China Received 18 October 2006; accepted 27 January 2007 Available online 6 February 2007
Abstract Goethite (α-FeOOH) nanorods were synthesized via hydrothermal method. The experimental results indicate that the uniform α-FeOOH nanorods, with length up to nearly 1 μm and diameter of ca. 50 nm, demonstrate perfect crystallinity and the growth direction of [001]. Owing to the characteristics of single-crystalline structure and high purity, the hysteresis loop of the resulting products shows semi-hard magnetic behavior compared to antiferromagnetic bulk with high-coercivity in nature. © 2007 Elsevier B.V. All rights reserved. Keywords: Magnetic materials; Nanomaterials; FeOOH; Hydrothermal method
1. Introduction Goethite (α-FeOOH), a kind of abundant mineral with interesting magnetic properties [1,2], mainly exists in soil, sediment and iron ore. Known as antiferromagnetic materials [3], it may be widely applied in modern industry, for example, rocket propeller [4,5]. Compared to bulk material, one-dimensional (1D) α-FeOOH has different outstanding magnetic properties, possibly explained by the fact that it bears a small longitudinal remanent magnetic moment and also has a negative anisotropy of magnetic susceptibility. Such a combination of dipolar and quadrupolar orders induces original symmetries somewhat hybrid between those of nematics and ferrofluids [6,7]. It is the excellent structure and properties that enable α-FeOOH nanomaterials to be applied in many fields, such as precursor for heterogeneous catalysts, absorptions of metal ion [8–11], and magnetic media [12].
⁎ Corresponding author. Tel./fax: +86 553 3869302. E-mail addresses: [email protected] (M.-W. Shao), [email protected] (H.-Z. Ban), [email protected] (Y.-H. Tong), [email protected] (H. Hu), [email protected] (L.-L. Niu), [email protected] (H.-Z. Gao), [email protected] (Y. Ye). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.01.094
Therefore, the preparation of nanostructural α-FeOOH has been widely studied and various methods have been proposed [6,13–15]. To the best of our knowledge yet, there are few reports on the synthesis of uniform α-FeOOH nanorods, especially with semi-hard magnetic properties. Here, singlecrystalline α-FeOOH nanorods on a large scale were reported. The as-obtained products yield semi-hard magnetic properties, which have promising technological application, such as highfrequency field-amplifying component (e.g., in read–write heads for computer disk memories). 2. Experimental The experimental procedure is as follows: 0.042 g sodium dodecyl benzene sulfonate (SDBS) was added into 12 mL 2.88 × 10− 2 mol L− 1 of FeSO4 solution accompanying with magnetic stirring. Then, 0.045 g Na2C2O4 and 0.768 g NaOH were added successively. After stirring for 30 min, the wellproportioned mixture was loaded into a Teflon-lined stainless steel autoclave, which was maintained at 130 °C for 36 h. After being cooled to room temperature, the products were washed with distilled water and absolute ethanol for several times, and then dried in vacuum at 60 °C for 6 h. The phase purity of the as-prepared products was determined by X-ray diffraction (XRD) using a Shimadzu XRD-6000 X-ray
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diffractometer equipped with CuKα radiation (λ = 0.1546 nm). A scanning rate of 0.05° s− 1 was applied to record the pattern in the 2θ range of 10–80°. Scanning electron microscopy (SEM) image was taken on X-600 scanning electron microscope. The nanostructures of the products were further observed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), which were taken on a JEOL-2010 transmission electron microscopy, with an accelerating voltage of 200 kV. Hysteresis loop was recorded on a BHV-55 vibrating magnetometer. 3. Results and discussion Fig. 1 shows the XRD pattern of typical products and all diffraction peaks can be indexed as the orthorhombic phase of FeOOH (JCPDS file No. 81-0462). The absence of impure phase suggests that the products have high purity. The cell parameters of FeOOH are calculated to be a = 0.4625 ± 0.0007 nm, b = 0.9981 ± 0.0015 and c = 0.3022 ± 0.0003 nm, which are in accordance with the JCPDS data (a = 0.4618 nm, b = 0.9952 nm and, c = 0.3023 nm). The SEM image shown in Fig. 2a gives a general view of morphology of the as-prepared products, which have rod-like shape. Their TEM image (Fig. 2b) presents the nanorods with the length up to ca. 1 μm and average diameter of 50 nm. The SAED pattern (Fig. 2c, inset) indicates that the as-prepared products are single crystalline. The bright diffraction spots can be indexed as (020) and (001) crystal planes with the axis zone of [100]. HRTEM (Fig. 2c) is employed to give a close observation of the microstructure of the product. The image demonstrates high crystallinity with clear and highly ordered crystal lattice, which can be indexed as (020) and (001) plane, the growth direction of the α-FeOOH nanorods is determined as [001]. The above characterization results coincide with each other, which adequately confirm the sample of uniform α-FeOOH nanorods with single-crystalline structure. To investigate the growth mechanism of the as-prepared products, a number of controlled experiments were performed. Keeping the other synthesis condition constant without adding of Na2C2O4, many nanoparticles and only few short nanorods formed as shown in Fig. 3a, which indicates that Na2C2O4 may play an important role during the formation of rod-like shape. And if SDBS was not used, uneven nanorods were utilized (Fig. 3b), which indicates that SDBS should be indispensable in the fabrication of uniform products. As to the quantity
Fig. 1. XRD pattern of products showing orthorhombic phase of α-FeOOH.
Fig. 2. (a) SEM and (b) TEM images of large-scale α-FeOOH nanorods with high aspect ratio; (c) HRTEM image indicating [001] growth direction and SAED pattern (inset) revealing the single crystal nature.
of Na2C2O4 and SDBS, we also have done a lot of comparative experiments, and find the relatively narrow range of Na2C2O4 (0.04–0.05 g) and SDBS (0.70–0.80 g) to obtain optimal products. The effect of reaction time on products' size was also investigated at different times. When the reaction time was only 2 h, the products took the morphology of nanorod with average diameter of 20 nm and length
Fig. 3. TEM images of the products prepared (a) without using Na2C2O4, showing little and small nanorods; (b) without using SDBS presenting nonuniform nanorods; (c) at reaction time of 2 h; and (d) at reaction time of 12 h.
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transformer, with low wastage energy and find potential application in magnetic field.
4. Conclusions In summary, α-FeOOH nanorods have been synthesized on a large scale via hydrothermal method. A series of characterization indicate that the as-prepared products have high quality in crystal and little defects and high purity. The semi-hard magnetic property resulting from 1D nanomaterial may extend their application range. Acknowledgments Fig. 4. Hysteresis loops of α-FeOOH nanorods measured at room temperature.
of 180 nm (Fig. 3c); if the time increases to 12 h, the products are uniform (Fig. 3d) and average diameter and length enlarge to 25 nm and 400 nm, respectively. The length and diameter of nanorods increase as the extension of reaction time increases. On the basis of the above analysis, a possible mechanism is proposed. At first, SDBS forms micelle and serves as minitype reactor during the process. C2O2− 4 enters the micelle by ion exchange and reacts with Fe2+ to form FeC2O4. As NaOH is added, OH− enters the micelle in place of C2O2− 4 so that FeC2O4 begins to be gradually transferred into Fe(OH)2. That's because the concentration of Fe2+ to precipitate Fe(OH)2 is much lower than that of FeC2O4. Fe(OH)2 of layered compound nature is apt to form 1D nanomaterial, which is finally oxidized into α-FeOOH nanorods. All the reactions may be formularized as follows: Fe2þ þ C2 O2− 4 →FeC2 O4 FeC2 O4 þ 2OH− →FeðOHÞ2 þ C2 O2− 4 FeðOHÞ2 þ 1=2O2 →α FeOOH þ H2 O: The magnetic properties of nanomaterials have been known to be strongly dependent on the nanoparticle size, shape, structure, crystallinity, and composition [16]. The hysteresis loop of α-FeOOH nanorods measured at room temperature is displayed in Fig. 4. In general, α-FeOOH nanorods presents semi-hard magnetic behavior. The coercivity (199.2 Oe) of nanorods significantly decreases compared to bulk in nature (5950.0 Oe) [3]. This phenomenon is caused by the localization of the nucleation mode. For zero disorder, the localization length goes to infinity and the reversal degenerates into coherent rotation [17]. Thus, the single-crystalline structure of α-FeOOH nanorods as discussed above should be responsible for the sharp reduction of coercivity, although it is less well understood from the size effects. The coercivity reduction is indeed observed in other real wires [18]. This semi-hard magnetic properties of the rod-like α-FeOOH nanomaterials may have an advantage at electrical machinery,
The project was supported by the National Natural Science Foundation of China (20571001) and Excellent Scholar Foundation of Anhui Province Education. References [1] M.M. Ibrahim, G. Edwards, M.S. Seehra, B. Ganguly, G.P. Huffman, J. Appl. Phys. 75 (1994) 5873. [2] B.J. Lemaire, P. Davidson, J. Ferre, J.P. Jamet, P. Panine, I. Dozov, J.P. Jolivet, Phys. Rev. Lett. 88 (2002) 25507. [3] C. Miguel, A. Zhukov, J.J. del Val, J. Gonzalez, J. Magn. Magn. Mater. 294 (2005) 245. [4] V.R. Pradhan, J.W. Tierney, I. Wender, G.P. Huffman, Energy Fuels 5 (1991) 497. [5] G.P. Huffman, B. Ganguly, J. Zhao, K.R.P.M. Rao, N. Shah, Z. Feng, F.E. Huggins, M.M. Taghiei, F. Lu, I. Wender, V.R. Pradhan, F.W. Tierney, M.S. Seehra, M.M. Ibrahim, J. Shabtai, E.M. Eyring, Energy Fuels 7 (1993) 285. [6] B.J. Lemaire, P. Davidson, J. Ferre, J.P. Jamet, P. Panine, I. Dozov, J.P. Jolivet, Phys. Rev. Lett. 88 (2002) 125507. [7] B.J. Lemaire, P. Davidson, P. Panine, J.P. Jolivet, Phys. Rev. Lett. 93 (2004) 267801. [8] K.J. Gallagher, Nature 226 (1970) 1225. [9] J. Cai, J. Liu, Z. Gao, A. Navrotsky, S.L. Suib, Chem. Mater. 13 (2001) 4595. [10] R. Patterson, H. Rahman, J. Colloid Interface Sci. 94 (1983) 60. [11] R. Patterson, H. Rahman, J. Colloid Interface Sci. 97 (1984) 423. [12] G. Wirnsberger, K. Gatterer, H. Fritzer, W. Grogger, B. Pillep, P. Behrens, M. Hansen, C. Bender Koch, Chem. Mater. 13 (2001) 1453. [13] D.J. Burleson, R.L. Penn, Langmuir 22 (2006) 402. [14] S. Krehula, S. Popovic, S. Music, Mater. Lett. 54 (2002) 108. [15] R. Frost, H.Y. Zhu, P. Wu, T. Bostrom, Mater. Lett. 59 (2005) 2238. [16] S.A. Koch, G. Palasantzas, T. Vystavel, J.Th.M.De. Hosson, Phys. Rev., B 71 (2005) 085410. [17] D.J. Sellmyer, M. Zheng, R. Skomski, J. Phys., Condens. Matter 13 (2001) R433. [18] H. Zeng, M. Zheng, R. Skomski, D.J. Sellmyer, Y. Liu, L. Menon, S. Bandyopadhyay, J. Appl. Phys. 87 (2000) 4718.
Synthesis of single-crystalline alpha-FeOOH nanorods with semi-hard magnetic property Ming-Wang Shao ⁎, Hui-Zhao Ban, Yan-Hua Tong, Hui Hu, Li-Ling Niu, Hua-Zhong Gao, Yin Ye Anhui Key Laboratory of Functional Molecular Solids, and College of Chemistry and Materials Science, Anhui Normal University, Wuhu 241000, PR China Received 18 October 2006; accepted 27 January 2007 Available online 6 February 2007
Abstract Goethite (α-FeOOH) nanorods were synthesized via hydrothermal method. The experimental results indicate that the uniform α-FeOOH nanorods, with length up to nearly 1 μm and diameter of ca. 50 nm, demonstrate perfect crystallinity and the growth direction of [001]. Owing to the characteristics of single-crystalline structure and high purity, the hysteresis loop of the resulting products shows semi-hard magnetic behavior compared to antiferromagnetic bulk with high-coercivity in nature. © 2007 Elsevier B.V. All rights reserved. Keywords: Magnetic materials; Nanomaterials; FeOOH; Hydrothermal method
1. Introduction Goethite (α-FeOOH), a kind of abundant mineral with interesting magnetic properties [1,2], mainly exists in soil, sediment and iron ore. Known as antiferromagnetic materials [3], it may be widely applied in modern industry, for example, rocket propeller [4,5]. Compared to bulk material, one-dimensional (1D) α-FeOOH has different outstanding magnetic properties, possibly explained by the fact that it bears a small longitudinal remanent magnetic moment and also has a negative anisotropy of magnetic susceptibility. Such a combination of dipolar and quadrupolar orders induces original symmetries somewhat hybrid between those of nematics and ferrofluids [6,7]. It is the excellent structure and properties that enable α-FeOOH nanomaterials to be applied in many fields, such as precursor for heterogeneous catalysts, absorptions of metal ion [8–11], and magnetic media [12].
⁎ Corresponding author. Tel./fax: +86 553 3869302. E-mail addresses: [email protected] (M.-W. Shao), [email protected] (H.-Z. Ban), [email protected] (Y.-H. Tong), [email protected] (H. Hu), [email protected] (L.-L. Niu), [email protected] (H.-Z. Gao), [email protected] (Y. Ye). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.01.094
Therefore, the preparation of nanostructural α-FeOOH has been widely studied and various methods have been proposed [6,13–15]. To the best of our knowledge yet, there are few reports on the synthesis of uniform α-FeOOH nanorods, especially with semi-hard magnetic properties. Here, singlecrystalline α-FeOOH nanorods on a large scale were reported. The as-obtained products yield semi-hard magnetic properties, which have promising technological application, such as highfrequency field-amplifying component (e.g., in read–write heads for computer disk memories). 2. Experimental The experimental procedure is as follows: 0.042 g sodium dodecyl benzene sulfonate (SDBS) was added into 12 mL 2.88 × 10− 2 mol L− 1 of FeSO4 solution accompanying with magnetic stirring. Then, 0.045 g Na2C2O4 and 0.768 g NaOH were added successively. After stirring for 30 min, the wellproportioned mixture was loaded into a Teflon-lined stainless steel autoclave, which was maintained at 130 °C for 36 h. After being cooled to room temperature, the products were washed with distilled water and absolute ethanol for several times, and then dried in vacuum at 60 °C for 6 h. The phase purity of the as-prepared products was determined by X-ray diffraction (XRD) using a Shimadzu XRD-6000 X-ray
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diffractometer equipped with CuKα radiation (λ = 0.1546 nm). A scanning rate of 0.05° s− 1 was applied to record the pattern in the 2θ range of 10–80°. Scanning electron microscopy (SEM) image was taken on X-600 scanning electron microscope. The nanostructures of the products were further observed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), which were taken on a JEOL-2010 transmission electron microscopy, with an accelerating voltage of 200 kV. Hysteresis loop was recorded on a BHV-55 vibrating magnetometer. 3. Results and discussion Fig. 1 shows the XRD pattern of typical products and all diffraction peaks can be indexed as the orthorhombic phase of FeOOH (JCPDS file No. 81-0462). The absence of impure phase suggests that the products have high purity. The cell parameters of FeOOH are calculated to be a = 0.4625 ± 0.0007 nm, b = 0.9981 ± 0.0015 and c = 0.3022 ± 0.0003 nm, which are in accordance with the JCPDS data (a = 0.4618 nm, b = 0.9952 nm and, c = 0.3023 nm). The SEM image shown in Fig. 2a gives a general view of morphology of the as-prepared products, which have rod-like shape. Their TEM image (Fig. 2b) presents the nanorods with the length up to ca. 1 μm and average diameter of 50 nm. The SAED pattern (Fig. 2c, inset) indicates that the as-prepared products are single crystalline. The bright diffraction spots can be indexed as (020) and (001) crystal planes with the axis zone of [100]. HRTEM (Fig. 2c) is employed to give a close observation of the microstructure of the product. The image demonstrates high crystallinity with clear and highly ordered crystal lattice, which can be indexed as (020) and (001) plane, the growth direction of the α-FeOOH nanorods is determined as [001]. The above characterization results coincide with each other, which adequately confirm the sample of uniform α-FeOOH nanorods with single-crystalline structure. To investigate the growth mechanism of the as-prepared products, a number of controlled experiments were performed. Keeping the other synthesis condition constant without adding of Na2C2O4, many nanoparticles and only few short nanorods formed as shown in Fig. 3a, which indicates that Na2C2O4 may play an important role during the formation of rod-like shape. And if SDBS was not used, uneven nanorods were utilized (Fig. 3b), which indicates that SDBS should be indispensable in the fabrication of uniform products. As to the quantity
Fig. 1. XRD pattern of products showing orthorhombic phase of α-FeOOH.
Fig. 2. (a) SEM and (b) TEM images of large-scale α-FeOOH nanorods with high aspect ratio; (c) HRTEM image indicating [001] growth direction and SAED pattern (inset) revealing the single crystal nature.
of Na2C2O4 and SDBS, we also have done a lot of comparative experiments, and find the relatively narrow range of Na2C2O4 (0.04–0.05 g) and SDBS (0.70–0.80 g) to obtain optimal products. The effect of reaction time on products' size was also investigated at different times. When the reaction time was only 2 h, the products took the morphology of nanorod with average diameter of 20 nm and length
Fig. 3. TEM images of the products prepared (a) without using Na2C2O4, showing little and small nanorods; (b) without using SDBS presenting nonuniform nanorods; (c) at reaction time of 2 h; and (d) at reaction time of 12 h.
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M.-W. Shao et al. / Materials Letters 61 (2007) 4318–4320
transformer, with low wastage energy and find potential application in magnetic field.
4. Conclusions In summary, α-FeOOH nanorods have been synthesized on a large scale via hydrothermal method. A series of characterization indicate that the as-prepared products have high quality in crystal and little defects and high purity. The semi-hard magnetic property resulting from 1D nanomaterial may extend their application range. Acknowledgments Fig. 4. Hysteresis loops of α-FeOOH nanorods measured at room temperature.
of 180 nm (Fig. 3c); if the time increases to 12 h, the products are uniform (Fig. 3d) and average diameter and length enlarge to 25 nm and 400 nm, respectively. The length and diameter of nanorods increase as the extension of reaction time increases. On the basis of the above analysis, a possible mechanism is proposed. At first, SDBS forms micelle and serves as minitype reactor during the process. C2O2− 4 enters the micelle by ion exchange and reacts with Fe2+ to form FeC2O4. As NaOH is added, OH− enters the micelle in place of C2O2− 4 so that FeC2O4 begins to be gradually transferred into Fe(OH)2. That's because the concentration of Fe2+ to precipitate Fe(OH)2 is much lower than that of FeC2O4. Fe(OH)2 of layered compound nature is apt to form 1D nanomaterial, which is finally oxidized into α-FeOOH nanorods. All the reactions may be formularized as follows: Fe2þ þ C2 O2− 4 →FeC2 O4 FeC2 O4 þ 2OH− →FeðOHÞ2 þ C2 O2− 4 FeðOHÞ2 þ 1=2O2 →α FeOOH þ H2 O: The magnetic properties of nanomaterials have been known to be strongly dependent on the nanoparticle size, shape, structure, crystallinity, and composition [16]. The hysteresis loop of α-FeOOH nanorods measured at room temperature is displayed in Fig. 4. In general, α-FeOOH nanorods presents semi-hard magnetic behavior. The coercivity (199.2 Oe) of nanorods significantly decreases compared to bulk in nature (5950.0 Oe) [3]. This phenomenon is caused by the localization of the nucleation mode. For zero disorder, the localization length goes to infinity and the reversal degenerates into coherent rotation [17]. Thus, the single-crystalline structure of α-FeOOH nanorods as discussed above should be responsible for the sharp reduction of coercivity, although it is less well understood from the size effects. The coercivity reduction is indeed observed in other real wires [18]. This semi-hard magnetic properties of the rod-like α-FeOOH nanomaterials may have an advantage at electrical machinery,
The project was supported by the National Natural Science Foundation of China (20571001) and Excellent Scholar Foundation of Anhui Province Education. References [1] M.M. Ibrahim, G. Edwards, M.S. Seehra, B. Ganguly, G.P. Huffman, J. Appl. Phys. 75 (1994) 5873. [2] B.J. Lemaire, P. Davidson, J. Ferre, J.P. Jamet, P. Panine, I. Dozov, J.P. Jolivet, Phys. Rev. Lett. 88 (2002) 25507. [3] C. Miguel, A. Zhukov, J.J. del Val, J. Gonzalez, J. Magn. Magn. Mater. 294 (2005) 245. [4] V.R. Pradhan, J.W. Tierney, I. Wender, G.P. Huffman, Energy Fuels 5 (1991) 497. [5] G.P. Huffman, B. Ganguly, J. Zhao, K.R.P.M. Rao, N. Shah, Z. Feng, F.E. Huggins, M.M. Taghiei, F. Lu, I. Wender, V.R. Pradhan, F.W. Tierney, M.S. Seehra, M.M. Ibrahim, J. Shabtai, E.M. Eyring, Energy Fuels 7 (1993) 285. [6] B.J. Lemaire, P. Davidson, J. Ferre, J.P. Jamet, P. Panine, I. Dozov, J.P. Jolivet, Phys. Rev. Lett. 88 (2002) 125507. [7] B.J. Lemaire, P. Davidson, P. Panine, J.P. Jolivet, Phys. Rev. Lett. 93 (2004) 267801. [8] K.J. Gallagher, Nature 226 (1970) 1225. [9] J. Cai, J. Liu, Z. Gao, A. Navrotsky, S.L. Suib, Chem. Mater. 13 (2001) 4595. [10] R. Patterson, H. Rahman, J. Colloid Interface Sci. 94 (1983) 60. [11] R. Patterson, H. Rahman, J. Colloid Interface Sci. 97 (1984) 423. [12] G. Wirnsberger, K. Gatterer, H. Fritzer, W. Grogger, B. Pillep, P. Behrens, M. Hansen, C. Bender Koch, Chem. Mater. 13 (2001) 1453. [13] D.J. Burleson, R.L. Penn, Langmuir 22 (2006) 402. [14] S. Krehula, S. Popovic, S. Music, Mater. Lett. 54 (2002) 108. [15] R. Frost, H.Y. Zhu, P. Wu, T. Bostrom, Mater. Lett. 59 (2005) 2238. [16] S.A. Koch, G. Palasantzas, T. Vystavel, J.Th.M.De. Hosson, Phys. Rev., B 71 (2005) 085410. [17] D.J. Sellmyer, M. Zheng, R. Skomski, J. Phys., Condens. Matter 13 (2001) R433. [18] H. Zeng, M. Zheng, R. Skomski, D.J. Sellmyer, Y. Liu, L. Menon, S. Bandyopadhyay, J. Appl. Phys. 87 (2000) 4718.