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Synthesis and properties of magnetite Fe3O4 via a simple hydrothermal route
Solid State Sciences 12 (2010) 1422e1425
Contents lists available at ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Synthesis and properties of magnetite Fe3O4 via a simple hydrothermal route Jun Liang*, Li Li, Min Luo, Junzhuo Fang, Yanrui Hu College of Chemistry and Chemical Engineering, Key Laboratory of Energy Resources and Chemical Engineering, Ningxia University, Yinchuan 750021, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 January 2010 Received in revised form 22 May 2010 Accepted 25 May 2010 Available online 1 June 2010
Magnetic Fe3O4 crystals were synthesized by a simple hydrothermal method using K4Fe(CN)6 as single precursor. The chemical compositions and morphologies of the as-prepared samples were characterized in detail by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and scanning electron microscopy (SEM). The experimental results show that the magnetic Fe3O4 particles are facilely prepared by the hydrothermal reaction of K4Fe(CN)6 and NaOH at 200 C. Regular octahedral Fe3O4 crystals are obtained when Na2S2O3 is added to the reaction system. The possible mechanism was discussed to elucidate the formation of the magnetic Fe3O4 crystals. Besides, the magnetic investigations show that the values of saturation magnetization and coercivity of octahedral Fe3O4 are about 87 emu/g and 184 Oe, respectively. Octahedral Fe3O4 also exhibits relatively good catalytic performance in the oxidation of styrene. Ó 2010 Elsevier Masson SAS. All rights reserved.
Keywords: Magnetic material Chemical synthesis Microstructure Magnetic property
1. Introduction
2. Experimental
Magnetic materials have been extensively studied because of their potential applications in areas such as magnetic storage [1], electro-photo graphic developer [2], pigment [3],protein separation [4], drug targeting delivery [5], cancer therapy and medical imaging [6], dynamic sealing [7], and catalyst [8], etc. Among magnetic materials, magnetite (Fe3O4), a ferromagnetic ore compound, has elicited increasing interests. During the past decades, various methods have been used for the preparation of magnetic Fe3O4, such as reduction of hematite [9,10], co-precipitation route [11], microwave plasma synthesis [12], microemulsion methods [13], ultrasound irradiation [14], and hydrothermal process [15],etc. Among all these methods, some hydrothermal routes assisted by surfactant or template and some hydrothermal reduction routes have been reported to prepare magnetic Fe3O4 octahedra [16e19]. Herein, we report a simple and rapid hydrothermal method to prepare magnetic Fe3O4 particles by hydrothermal reaction of K4Fe(CN)6 and NaOH under mild conditions. When the appropriate amount of Na2S2O3 was added into the reaction system, regular octahedral Fe3O4 crystals were the final products.
All reagents used in the experiment were of analytical grade and used without further purification. In a typical synthesis of magnetic Fe3O4 particles, 0.422 g of K4Fe(CN)6 was dissolved in 30 mL of deionized water under stirring. Then 0.4 g of NaOH was added. The mixture was stirred to form a homogeneous solution at room temperature and transferred into a 40 mL Teflon-lined stainless steel autoclave, and maintained at 200 C for 90 min. After the reaction completed, the black solid product was collected by centrifugation and washed several times with anhydrous ethanol. The solid was dried under vacuum for 5 h. When 0.372 g Na2S2O3 was added to the reaction system, whereas other reaction conditions were kept the same, octahedral Fe3O4 crystals were obtained. The samples were characterized by X-ray power diffraction (XRD) on a D/Max 2200 V/PC X-ray diffractometer using Cu (35 kV, 200 mA) radiation. The compositions of the samples were identified by X-ray photoelectron spectra (XPS, PHI5300). Morphologies of the samples were examined by scanning electron microscopy (SEM, KYKY-2800B). The magnetic property of the sample was measured by a BHV-55 vibrating sample magnetometer at room temperature. Moreover, catalytic activity testing was performed using a batch type reactor operated under atmospheric pressure in the oxidation of styrene [8].Typically, N,N-dimethylformamide was used as a solvent, and O2 was bubbling into the liquid mixture containing styrene and the solvent, and the liquid organic products
* Corresponding author. Tel.: þ86 951 3820380. E-mail address: [email protected] (J. Liang). 1293-2558/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2010.05.022
J. Liang et al. / Solid State Sciences 12 (2010) 1422e1425
Fig. 1. XRD patterns of the magnetic Fe3O4 particles (a) and octahedral Fe3O4 crystals (b) obtained at 200 C for 90 min, respectively.
were quantified by a gas chromatograph using toluene as an internal standard. 3. Results and discussion The crystal structure was determined by X-ray diffraction (XRD) measurement. XRD patterns of the as-obtained magnetic Fe3O4 particles and octahedral Fe3O4 crystals are shown in Fig. 1. All the diffraction peaks of the samples can be indexed to a pure facecentered cubic phase (fcc, space group Fd-3 m) of magnetite structure according to JCPDS card no.85-1436. No peaks of hematite, metal hydroxides, or other impurities were detected, indicating high purity and crystallinity of Fe3O4. Thus, we can conclude that whether Na2S2O3 was added into the reaction system or not, the products are pure face-centered cubic phase of Fe3O4. More details about the composition of the sample were further identified by X-ray photoelectron spectroscopy (XPS). The spectra of the sample corresponding to the binding energies of Fe 2 p and O 1s are shown in Fig. 2. It shows that the photoelectron peaks of 710.8, 724.2, and 531.5 eV correspond to Fe 2p2/3, Fe 2p1/2, and O 1s, respectively. The data are consistent with the values in the literature [20], which further proves the composition of the magnetic Fe3O4.
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Fig. 3. SEM image of the magnetic Fe3O4 particles obtained in the absence of Na2S2O3.
The morphology and size of the as-prepared Fe3O4 were investigated by SEM. Fig. 3 presents a SEM image of the magnetic Fe3O4 particles obtained in the absence of Na2S2O3. We observe that, in addition to the octahedral Fe3O4 particles, some Fe3O4 crystals with irregular shapes are also obtained. However, it is worthy mentioning that uniform octahedral Fe3O4 crystals are facilely achieved when the appropriate amount of Na2S2O3 is introduced into the hydrothermal system. A typical large-area SEM image of the as-prepared product is shown in Fig. 4a, the image indicates that the product mainly consists of a large quantity of octahedra. Fig. 4b shows a partially enlarged SEM image of the asprepared product, and the well-shaped octahedral Fe3O4 crystals have typical edges with the lengths of less than 3 mm. In view of the above results, we think that the simple hydrothermal routes for the synthesized Fe3O4 may be carried out by eqs. (1) and (2). When no Na2S2O3 was introduced, the magnetic Fe3O4 particles are facilely obtained by eq. (1), the product is major in the octahedral crystals and irregular aggregates (Fig. 3). When Na2S2O3 is introduced into the reaction system, and the molar ratio of Na2S2O3 and K4Fe(CN)6 is gradually increased to 1.5:1, the product is major in octahedral crystals (Fig. 4). The possible hydrothermal route is shown by eq. (2). These results indicate that the Fe(CN)64 ion and the quantity of Na2S2O3 play important roles
Fig. 2. XPS spectra of the as-prepared Fe3O4.
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J. Liang et al. / Solid State Sciences 12 (2010) 1422e1425
Fig. 4. (a) Typical large-area image and (b) partially enlarged image of the as-obtained Fe3O4 octahedra.
in determining the morphology of the final Fe3O4 particles. On the one hand, Fe(CN)64 is a very stable
FeðCNÞ6
4
þOH þ O2 ðaqÞ/Fe3 O4 ðsÞ þ CN þ H2 O
(1)
4 2 þS2 O2 FeðCNÞ6 3 þ OH þ O2 ðaqÞ/Fe3 O4 ðsÞ þ S4 O6 þ CN þ H2 O
(2) 35
complex ion (Kf ¼ 10 ) with a regular octahedral structure, so the complex ion can not only kinetically control the reaction rates but also provide the octahedral coordination environments for Fe2þ ion. The theoretical growth habit of the Fe3O4 crystals is the octahedron. On the other hand, it is noteworthy that adding of a weak reducing agent Na2S2O3 may provide a weak reducing atmosphere [19] in the formation process of magnetite. So it can also kinetically control and limit the chemical oxidation rates of Fe(CN)64 to a great extent [eq (2)]. On the basis of the above two factors, the renascent Fe3O4 nuclei are probably restricted to an epitaxial environment and naturally incline to grow into the octahedron. Besides, it is known that the shape of crystals is mostly determined by the relative growth rates along different directions. Wang [21] pointed out that the shape of an fcc crystal is mainly determined by the ratio of the growth rate along <100> to that along <111>, and octahedrons bounded by eight <111> planes will be formed when the ratio is relatively high, and some studies [16,21] suggested that the slow reaction rate is favorable for the faster growth rate along
Fig. 5. Magnetization-hysteresis loop of the as-prepared sample measured at room temperature.
<100> compared to that along <111> due to the lowest energy of the <111> surfaces. So the obtained octahedral crystals may be formed. Magnetic hysteresis curve of the sample measured at room temperature is shown in Fig. 5. The hysteresis loop of the octahedral Fe3O4 shows ferromagnetic behavior with saturation magnetization (Ms) and coercivity (Hc) values of about 87 emu/g and 184 Oe, respectively, and the data are near the values reported for Fe3O4 micro-crystals in the literature [22]. Zheng [16] and Qian [17] suggested that magnetic properties of magnetic materials are influenced by many factors, such as size, structure, and morphologies etc. They also believed that different types of anisotropy have a significant effect on the saturation values of magnetic materials. So the magnetic behavior in this work may ascribe to the crystalline structure, crystal anisotropy and shape anisotropy. Catalytic properties of octahedral Fe3O4 were tested by the oxidation reaction of styrene. Fig. 6 shows the dependence of rates of styrene oxidation with respect to styrene concentration which was varied from 0 to 1.6 mol$L1, while the catalyst is fixed at 3.0 mg at 373 K. The initial rates of styrene oxidation and turnover number (TON) were found to exhibit first-order dependence with
Fig. 6. Influence of the styrene concentration on catalytic performances for the oxidation of styrene over Fe3O4: (-) styrene conversion rate, (C) TON, (B) epoxide selectivity. Conditions: T ¼ 373 K; DMF, 20 mL; flow rate of O2, 3.0 mL min1; Fe3O4, 3.0 mg.
J. Liang et al. / Solid State Sciences 12 (2010) 1422e1425
respect to styrene concentration, and styrene oxide selectivity was almost 59%. The data indicate that octahedral Fe3O4 can catalyze the oxidation of styrene and exhibits higher activity than the previously reported Fe3O4 in the oxidation of styrene [8]. Therefore, octahedral Fe3O4 is found to show better catalytic performance in the oxidation of styrene. 4. Conclusions In summary, we have developed a simple and rapid hydrothermal method to synthesize magnetic Fe3O4 crystals using K4Fe (CN)6 as single precursor. The experimental results demonstrate that the magnetic Fe3O4 particles are easily prepared by the reaction of Fe(CN)64, OH and dissolved oxygen. Molar ratio of Fe(CN)64 and S2O2 3 plays crucial factor in controlling the morphology of the final Fe3O4 crystals. The reaction mechanism via the chemical oxidation of Fe(CN)64 and the growth mechanism of octahedron are suggested. Besides, the as-prepared Fe3O4 octahedra not only show relatively high ferromagnetic property at room temperature but also exhibit good catalytic performance in the oxidation of styrene. Acknowledgements This work has been supported by Program Foundation of Institutions of Higher Education of Ningxia Province (2008), the Science Foundation of Ningxia University (ndzr09-2) and the
1425
Natural Science Foundation of Ningxia Province (Grant no. NZ0916).
References [1] G. Bate, Ferromagnetic material. in: E.D. Wohlfarth (Ed.), Recording Materials, vol. 2. North-Holland Publishing Co., Amsterdam, 1980, pp. 381e507 (Chapter 7). [2] P.E. Matijeric, in: L.L. Hench, D.B. Ulrich (Eds.), Colloid Science of Composite System, Science of Ceramic Chemical Processing, John Wiley&Sons, NewYork, 1986, pp. 463e481. [3] S. Zakaria, B.H. Ong, T.G.M. van de Ven, Colloids and surf., a-physicochem. Eng. Asp. 251 (2004) 1. [4] H.W. Gu, K. Xu, C.J. Xu, B. Xu, Chem. Commun. (2006) 941. [5] S. Yu, M. Yoshimur, Adv. Funct. Mater. 12 (2002) 9. [6] A.K. Gupta, M. Gupta, Biomater 26 (2005) 3995. [7] P.J. Ripka, Magn. Magn. Mater. 215 (2000) 735. [8] J. Liang, Q. Tang, Y. Wang, Chem. Lett. 33 (2004) 1140. [9] L.S. Darken, R.W. Gurry, J. Am. Chem. Soc. 68 (1946) 798. [10] V. Osterhout, in: D.S. Craik (Ed.), Magnetic Oxides, John Wiley & Sons, New York, 1975. [11] G. Visalakski, G. Venkateswaran, S.K. Kulshreshtha, P.H. Moorphy, Mater. Res. Bull. 28 (1993) 829. [12] D. Vollath, D.V. Szabó, R.D. Taylor, J.O. Willis, J. Mater. Res. 12 (1997) 2175. [13] Z.H. Zhou, J. Wang, X. Liu, J. Mater. Chem. 11 (2001) 1704. [14] R.V. Kumar, Y. Koltypin, X.N. Xu, Y. Yeshurun, A. Gedanken, I. Felner, J. Appl. Phys. 89 (2001) 6324. [15] Y.T. Qian, Y. Xie, C. He, J. Li, Z.Y. Chen, Mater. Res. Bull. 29 (1994) 953. [16] D. Zhang, X. Zhang, X. Ni, J. Song, H.G. Zheng, Cryst. Growth Des. 10 (2007) 2117. [17] J. Zhang, Q. Kong, J. Du, D. Ma, G. Xi, Y.T. Qian, J. Cryst. Growth 308 (2007) 159. [18] L.J. Zhao, H.J. Zhang, Y. Xing, S.Y. Song, Mater. Lett. 63 (2009) 307. [19] R. Fan, X.H. Chen, Z. Gui, L. Liu, Z.Y. Chen, Mater. Res. Bull. 36 (2001) 497. [20] W. Kim, K. Kawaguchi, N. Koshizaki, J. Appl. Phys. 93 (2003) 8032. [21] Z.L. Wang, J. Phys. Chem. B. 104 (2000) 1153. [22] L.J. Zhao, H.J. Zhang, Y. Xing, S.Y. Song, S.Y. Yu, Chem. Mater. 20 (2008) 198.
Contents lists available at ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Synthesis and properties of magnetite Fe3O4 via a simple hydrothermal route Jun Liang*, Li Li, Min Luo, Junzhuo Fang, Yanrui Hu College of Chemistry and Chemical Engineering, Key Laboratory of Energy Resources and Chemical Engineering, Ningxia University, Yinchuan 750021, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 January 2010 Received in revised form 22 May 2010 Accepted 25 May 2010 Available online 1 June 2010
Magnetic Fe3O4 crystals were synthesized by a simple hydrothermal method using K4Fe(CN)6 as single precursor. The chemical compositions and morphologies of the as-prepared samples were characterized in detail by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and scanning electron microscopy (SEM). The experimental results show that the magnetic Fe3O4 particles are facilely prepared by the hydrothermal reaction of K4Fe(CN)6 and NaOH at 200 C. Regular octahedral Fe3O4 crystals are obtained when Na2S2O3 is added to the reaction system. The possible mechanism was discussed to elucidate the formation of the magnetic Fe3O4 crystals. Besides, the magnetic investigations show that the values of saturation magnetization and coercivity of octahedral Fe3O4 are about 87 emu/g and 184 Oe, respectively. Octahedral Fe3O4 also exhibits relatively good catalytic performance in the oxidation of styrene. Ó 2010 Elsevier Masson SAS. All rights reserved.
Keywords: Magnetic material Chemical synthesis Microstructure Magnetic property
1. Introduction
2. Experimental
Magnetic materials have been extensively studied because of their potential applications in areas such as magnetic storage [1], electro-photo graphic developer [2], pigment [3],protein separation [4], drug targeting delivery [5], cancer therapy and medical imaging [6], dynamic sealing [7], and catalyst [8], etc. Among magnetic materials, magnetite (Fe3O4), a ferromagnetic ore compound, has elicited increasing interests. During the past decades, various methods have been used for the preparation of magnetic Fe3O4, such as reduction of hematite [9,10], co-precipitation route [11], microwave plasma synthesis [12], microemulsion methods [13], ultrasound irradiation [14], and hydrothermal process [15],etc. Among all these methods, some hydrothermal routes assisted by surfactant or template and some hydrothermal reduction routes have been reported to prepare magnetic Fe3O4 octahedra [16e19]. Herein, we report a simple and rapid hydrothermal method to prepare magnetic Fe3O4 particles by hydrothermal reaction of K4Fe(CN)6 and NaOH under mild conditions. When the appropriate amount of Na2S2O3 was added into the reaction system, regular octahedral Fe3O4 crystals were the final products.
All reagents used in the experiment were of analytical grade and used without further purification. In a typical synthesis of magnetic Fe3O4 particles, 0.422 g of K4Fe(CN)6 was dissolved in 30 mL of deionized water under stirring. Then 0.4 g of NaOH was added. The mixture was stirred to form a homogeneous solution at room temperature and transferred into a 40 mL Teflon-lined stainless steel autoclave, and maintained at 200 C for 90 min. After the reaction completed, the black solid product was collected by centrifugation and washed several times with anhydrous ethanol. The solid was dried under vacuum for 5 h. When 0.372 g Na2S2O3 was added to the reaction system, whereas other reaction conditions were kept the same, octahedral Fe3O4 crystals were obtained. The samples were characterized by X-ray power diffraction (XRD) on a D/Max 2200 V/PC X-ray diffractometer using Cu (35 kV, 200 mA) radiation. The compositions of the samples were identified by X-ray photoelectron spectra (XPS, PHI5300). Morphologies of the samples were examined by scanning electron microscopy (SEM, KYKY-2800B). The magnetic property of the sample was measured by a BHV-55 vibrating sample magnetometer at room temperature. Moreover, catalytic activity testing was performed using a batch type reactor operated under atmospheric pressure in the oxidation of styrene [8].Typically, N,N-dimethylformamide was used as a solvent, and O2 was bubbling into the liquid mixture containing styrene and the solvent, and the liquid organic products
* Corresponding author. Tel.: þ86 951 3820380. E-mail address: [email protected] (J. Liang). 1293-2558/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2010.05.022
J. Liang et al. / Solid State Sciences 12 (2010) 1422e1425
Fig. 1. XRD patterns of the magnetic Fe3O4 particles (a) and octahedral Fe3O4 crystals (b) obtained at 200 C for 90 min, respectively.
were quantified by a gas chromatograph using toluene as an internal standard. 3. Results and discussion The crystal structure was determined by X-ray diffraction (XRD) measurement. XRD patterns of the as-obtained magnetic Fe3O4 particles and octahedral Fe3O4 crystals are shown in Fig. 1. All the diffraction peaks of the samples can be indexed to a pure facecentered cubic phase (fcc, space group Fd-3 m) of magnetite structure according to JCPDS card no.85-1436. No peaks of hematite, metal hydroxides, or other impurities were detected, indicating high purity and crystallinity of Fe3O4. Thus, we can conclude that whether Na2S2O3 was added into the reaction system or not, the products are pure face-centered cubic phase of Fe3O4. More details about the composition of the sample were further identified by X-ray photoelectron spectroscopy (XPS). The spectra of the sample corresponding to the binding energies of Fe 2 p and O 1s are shown in Fig. 2. It shows that the photoelectron peaks of 710.8, 724.2, and 531.5 eV correspond to Fe 2p2/3, Fe 2p1/2, and O 1s, respectively. The data are consistent with the values in the literature [20], which further proves the composition of the magnetic Fe3O4.
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Fig. 3. SEM image of the magnetic Fe3O4 particles obtained in the absence of Na2S2O3.
The morphology and size of the as-prepared Fe3O4 were investigated by SEM. Fig. 3 presents a SEM image of the magnetic Fe3O4 particles obtained in the absence of Na2S2O3. We observe that, in addition to the octahedral Fe3O4 particles, some Fe3O4 crystals with irregular shapes are also obtained. However, it is worthy mentioning that uniform octahedral Fe3O4 crystals are facilely achieved when the appropriate amount of Na2S2O3 is introduced into the hydrothermal system. A typical large-area SEM image of the as-prepared product is shown in Fig. 4a, the image indicates that the product mainly consists of a large quantity of octahedra. Fig. 4b shows a partially enlarged SEM image of the asprepared product, and the well-shaped octahedral Fe3O4 crystals have typical edges with the lengths of less than 3 mm. In view of the above results, we think that the simple hydrothermal routes for the synthesized Fe3O4 may be carried out by eqs. (1) and (2). When no Na2S2O3 was introduced, the magnetic Fe3O4 particles are facilely obtained by eq. (1), the product is major in the octahedral crystals and irregular aggregates (Fig. 3). When Na2S2O3 is introduced into the reaction system, and the molar ratio of Na2S2O3 and K4Fe(CN)6 is gradually increased to 1.5:1, the product is major in octahedral crystals (Fig. 4). The possible hydrothermal route is shown by eq. (2). These results indicate that the Fe(CN)64 ion and the quantity of Na2S2O3 play important roles
Fig. 2. XPS spectra of the as-prepared Fe3O4.
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J. Liang et al. / Solid State Sciences 12 (2010) 1422e1425
Fig. 4. (a) Typical large-area image and (b) partially enlarged image of the as-obtained Fe3O4 octahedra.
in determining the morphology of the final Fe3O4 particles. On the one hand, Fe(CN)64 is a very stable
FeðCNÞ6
4
þOH þ O2 ðaqÞ/Fe3 O4 ðsÞ þ CN þ H2 O
(1)
4 2 þS2 O2 FeðCNÞ6 3 þ OH þ O2 ðaqÞ/Fe3 O4 ðsÞ þ S4 O6 þ CN þ H2 O
(2) 35
complex ion (Kf ¼ 10 ) with a regular octahedral structure, so the complex ion can not only kinetically control the reaction rates but also provide the octahedral coordination environments for Fe2þ ion. The theoretical growth habit of the Fe3O4 crystals is the octahedron. On the other hand, it is noteworthy that adding of a weak reducing agent Na2S2O3 may provide a weak reducing atmosphere [19] in the formation process of magnetite. So it can also kinetically control and limit the chemical oxidation rates of Fe(CN)64 to a great extent [eq (2)]. On the basis of the above two factors, the renascent Fe3O4 nuclei are probably restricted to an epitaxial environment and naturally incline to grow into the octahedron. Besides, it is known that the shape of crystals is mostly determined by the relative growth rates along different directions. Wang [21] pointed out that the shape of an fcc crystal is mainly determined by the ratio of the growth rate along <100> to that along <111>, and octahedrons bounded by eight <111> planes will be formed when the ratio is relatively high, and some studies [16,21] suggested that the slow reaction rate is favorable for the faster growth rate along
Fig. 5. Magnetization-hysteresis loop of the as-prepared sample measured at room temperature.
<100> compared to that along <111> due to the lowest energy of the <111> surfaces. So the obtained octahedral crystals may be formed. Magnetic hysteresis curve of the sample measured at room temperature is shown in Fig. 5. The hysteresis loop of the octahedral Fe3O4 shows ferromagnetic behavior with saturation magnetization (Ms) and coercivity (Hc) values of about 87 emu/g and 184 Oe, respectively, and the data are near the values reported for Fe3O4 micro-crystals in the literature [22]. Zheng [16] and Qian [17] suggested that magnetic properties of magnetic materials are influenced by many factors, such as size, structure, and morphologies etc. They also believed that different types of anisotropy have a significant effect on the saturation values of magnetic materials. So the magnetic behavior in this work may ascribe to the crystalline structure, crystal anisotropy and shape anisotropy. Catalytic properties of octahedral Fe3O4 were tested by the oxidation reaction of styrene. Fig. 6 shows the dependence of rates of styrene oxidation with respect to styrene concentration which was varied from 0 to 1.6 mol$L1, while the catalyst is fixed at 3.0 mg at 373 K. The initial rates of styrene oxidation and turnover number (TON) were found to exhibit first-order dependence with
Fig. 6. Influence of the styrene concentration on catalytic performances for the oxidation of styrene over Fe3O4: (-) styrene conversion rate, (C) TON, (B) epoxide selectivity. Conditions: T ¼ 373 K; DMF, 20 mL; flow rate of O2, 3.0 mL min1; Fe3O4, 3.0 mg.
J. Liang et al. / Solid State Sciences 12 (2010) 1422e1425
respect to styrene concentration, and styrene oxide selectivity was almost 59%. The data indicate that octahedral Fe3O4 can catalyze the oxidation of styrene and exhibits higher activity than the previously reported Fe3O4 in the oxidation of styrene [8]. Therefore, octahedral Fe3O4 is found to show better catalytic performance in the oxidation of styrene. 4. Conclusions In summary, we have developed a simple and rapid hydrothermal method to synthesize magnetic Fe3O4 crystals using K4Fe (CN)6 as single precursor. The experimental results demonstrate that the magnetic Fe3O4 particles are easily prepared by the reaction of Fe(CN)64, OH and dissolved oxygen. Molar ratio of Fe(CN)64 and S2O2 3 plays crucial factor in controlling the morphology of the final Fe3O4 crystals. The reaction mechanism via the chemical oxidation of Fe(CN)64 and the growth mechanism of octahedron are suggested. Besides, the as-prepared Fe3O4 octahedra not only show relatively high ferromagnetic property at room temperature but also exhibit good catalytic performance in the oxidation of styrene. Acknowledgements This work has been supported by Program Foundation of Institutions of Higher Education of Ningxia Province (2008), the Science Foundation of Ningxia University (ndzr09-2) and the
1425
Natural Science Foundation of Ningxia Province (Grant no. NZ0916).
References [1] G. Bate, Ferromagnetic material. in: E.D. Wohlfarth (Ed.), Recording Materials, vol. 2. North-Holland Publishing Co., Amsterdam, 1980, pp. 381e507 (Chapter 7). [2] P.E. Matijeric, in: L.L. Hench, D.B. Ulrich (Eds.), Colloid Science of Composite System, Science of Ceramic Chemical Processing, John Wiley&Sons, NewYork, 1986, pp. 463e481. [3] S. Zakaria, B.H. Ong, T.G.M. van de Ven, Colloids and surf., a-physicochem. Eng. Asp. 251 (2004) 1. [4] H.W. Gu, K. Xu, C.J. Xu, B. Xu, Chem. Commun. (2006) 941. [5] S. Yu, M. Yoshimur, Adv. Funct. Mater. 12 (2002) 9. [6] A.K. Gupta, M. Gupta, Biomater 26 (2005) 3995. [7] P.J. Ripka, Magn. Magn. Mater. 215 (2000) 735. [8] J. Liang, Q. Tang, Y. Wang, Chem. Lett. 33 (2004) 1140. [9] L.S. Darken, R.W. Gurry, J. Am. Chem. Soc. 68 (1946) 798. [10] V. Osterhout, in: D.S. Craik (Ed.), Magnetic Oxides, John Wiley & Sons, New York, 1975. [11] G. Visalakski, G. Venkateswaran, S.K. Kulshreshtha, P.H. Moorphy, Mater. Res. Bull. 28 (1993) 829. [12] D. Vollath, D.V. Szabó, R.D. Taylor, J.O. Willis, J. Mater. Res. 12 (1997) 2175. [13] Z.H. Zhou, J. Wang, X. Liu, J. Mater. Chem. 11 (2001) 1704. [14] R.V. Kumar, Y. Koltypin, X.N. Xu, Y. Yeshurun, A. Gedanken, I. Felner, J. Appl. Phys. 89 (2001) 6324. [15] Y.T. Qian, Y. Xie, C. He, J. Li, Z.Y. Chen, Mater. Res. Bull. 29 (1994) 953. [16] D. Zhang, X. Zhang, X. Ni, J. Song, H.G. Zheng, Cryst. Growth Des. 10 (2007) 2117. [17] J. Zhang, Q. Kong, J. Du, D. Ma, G. Xi, Y.T. Qian, J. Cryst. Growth 308 (2007) 159. [18] L.J. Zhao, H.J. Zhang, Y. Xing, S.Y. Song, Mater. Lett. 63 (2009) 307. [19] R. Fan, X.H. Chen, Z. Gui, L. Liu, Z.Y. Chen, Mater. Res. Bull. 36 (2001) 497. [20] W. Kim, K. Kawaguchi, N. Koshizaki, J. Appl. Phys. 93 (2003) 8032. [21] Z.L. Wang, J. Phys. Chem. B. 104 (2000) 1153. [22] L.J. Zhao, H.J. Zhang, Y. Xing, S.Y. Song, S.Y. Yu, Chem. Mater. 20 (2008) 198.