- Email: [email protected]
Shape-controlled synthesis of Fe3O4 rhombic dodecahedrons and nanodiscs
Materials Letters 117 (2014) 10–13
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Shape-controlled synthesis of Fe3O4 rhombic dodecahedrons and nanodiscs Zhiming Chen a,b,n, Zhirong Geng b, Tingxian Tao a, Zhilin Wang b a b
College of Biochemical Engineering, Anhui Polytechnic University, Wuhu 241000, PR China State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 28 August 2013 Accepted 20 November 2013 Available online 28 November 2013
Fe3O4 rhombic dodecahedrons with only {110} facets exposed and nanodiscs bounded entirely by {111} facets were fabricated via a one-pot hydrothermal approach. The morphologies, structures and magnetic properties of the rhombic dodecahedrons and nanodiscs were investigated through different analytical tools. Batch experiments indicated that the reaction temperature and amount of N2H4 H2O play important roles in determining the sizes and morphologies of the products. Magnetic analysis revealed that the magnetic properties are closely related to the morphologies of the magnetites. The synthesized Fe3O4 nanocrystals are hoped to have important applications in advanced magnetic materials and catalytic fields. & 2013 Elsevier B.V. All rights reserved.
Keywords: Fe3O4 nanoparticles Rhombic dodecahedrons Nanodiscs Crystal growth Magnetic materials
1. Introduction Over the past decade, the precise architectural manipulation of Fe3O4 nanoparticles with well-defined morphologies and accurate tunable sizes have been a research hotspot not only for fundamental scientific interest but also for their various applications in fields such as magnetic storage, catalyst, electrode materials, drug delivery, medical diagnostics and therapeutics. So, many efforts have been devoted to explore excellent synthetic approaches for the fabrication of Fe3O4 crystals with controlled shape to enhance their performance in currently existing applications. Thus far, a wide variety of Fe3O4 morphologies, including nanoparticles, nanocubes, nanowires, nanotubes, nanorods, nanoplates, nanorings, octahedrons and polyhedrons have been successfully synthesized [1–13]. However, most of the reported morphologies are bound by {111}, {100} or both {111} and {100} facets. From the perspective of crystallography, magnetite (Fe3O4) is a ferromagnetic iron oxide having a cubic inverse spinel structure with oxygen anions forming a face-center-cubic (FCC) closed packing [12]. As a FCC crystal, a general sequence of surface energies may hold, γ{111}o γ{100} o γ{110} [14], which means that Fe3O4 crystals exclusively enclosed by {110} surfaces have been rarely exploited because the {110} lattice planes have the highest surface energy among the low-index facets, thus exhibiting faster growth kinetics than the others, resulting in their disappearance during
n Corresponding author at: College of Biochemical Engineering, Anhui Polytechnic University, Wuhu 241000, PR China. Tel.: þ86 553 2871254. E-mail address: [email protected] (Z. Chen).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.11.076
the crystal growth. Moreover, it is widely accepted that Fe3O4 nanocrystals with exposed {110} facets exhibited high catalytic activity and have special applications in optical, electrical and magnetic devices [12]. Therefore, the development of alternative methodologies for the facile and well-controlled synthesis of Fe3O4 nanocrystals possessing active basal surfaces {110} remains an important challenge. Herein, we present a facile protocol for the shape-controlled synthesis of Fe3O4 rhombic dodecahedrons with only {110} facets exposed and nanodiscs bounded entirely by {111} facets. It is found that the reaction temperature and amount of N2H4 H2O have important effects on the sizes and morphologies of the magnetic nanocrystals. Besides, the magnetic properties of the two kinds of nanocrystals are investigated. 2. Experimental Materials and method: FeCl2 4H2O, H2C2O4 2H2O, N2H4 H2O, NH3 H2O and acetone were of analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China), and used without further purification. Deionized water was used throughout. In a typical procedure, the starting solution was prepared by mixing 0.5 mmol FeCl2 4H2O, 0.5 mmol H2C2O4 2H2O and 5 mmol N2H4 H2O in 45 mL water. The resulting solution was transferred into stainless-steel autoclaves lined with poly(tetrafluoroethylene) and maintained at 140 1C for 3 h and then cooled to room temperature. The as-obtained precipitate was collected, washed with distilled water and acetone several times, and dried in air. Using the same procedures, the reaction temperature and
Z. Chen et al. / Materials Letters 117 (2014) 10–13
quantity of N2H4 H2O were varied in the experiments to obtain products with a desired morphology. Characterizations: Phase identification via X-ray diffraction (XRD) was collected on a Shimadzu XRD-6000 X-ray diffractometer. The morphologies of the samples were observed by field-emission scanning electron microscopy (SEM, S-4800) and high resolution transmission electron microscopy (HRTEM, JOEL-2010). The magnetic properties of the products were studied with a superconducting quantum interference device (SQUID, Quantum Design MPMS XL-7).
11
3. Results and discussion Fig. 1a shows a typical low-magnification SEM image of the products obtained in the solution contained 5 mmol N2H4 H2O at 140 1C for 3 h and reveals that the sample is in the form of rhombic dodecahedral morphology with a diameter of 150–300 nm. The enlarged SEM image reveals that the as-prepared Fe3O4 nanocrystals are enclosed by 12 well-defined {110} planes with cubic crystal symmetry (Fig. 1b and c). Fig. 1d and e show typical TEM
Fig. 1. (a and b) SEM images of Fe3O4 rhombic dodecahedrons, (c) schematic diagram of Fe3O4 rhombic dodecahedron, (d and e) TEM images of Fe3O4 rhombic dodecahedrons, (f) SAED and (g) HRTEM images of an individual rhombic dodecahedron oriented along [1̄ 12].
12
Z. Chen et al. / Materials Letters 117 (2014) 10–13
images of the Fe3O4 rhombic dodecahedrons. It is clear that the projection views of the particles are hexagonal, square and polygon shapes. Fig. 1f shows the selected area electron diffraction (SAED) pattern obtained from a single rhombic dodecahedron with the electron beam perpendicular to the hexagon in Fig. 1e. The SAED pattern can be indexed to the [1̄ 12] zone axis of a single crystal of fcc Fe3O4, indicating that the synthesized Fe3O4 nanocrystals are single-crystalline and bound by {110} basal planes. The lattice spacings of 0.297 and 0.242 nm measured from the highresolution TEM image correspond to the (220) and (22̄ 2) crystalline planes of fcc Fe3O4 (Fig. 1g), which also demonstrates the exposed surface of the {110} facets. Interestingly, as shown in Fig. 2, when the reaction was performed in the solution containing 7 mmol N2H4 H2O at 120 1C for 3 h, uniform Fe3O4 nanodiscs with a diameter of 80–250 nm were fabricated in large quantities. Moreover, it can be clearly observed that Fe3O4 nanodiscs were bounded completely by two {111} facets and all the exposed surfaces are round and smooth with no obvious defects. The X-ray diffraction (XRD) patterns (Fig. 3) clearly show that all of the diffraction peaks of the rhombic dodecahedrons and nanodiscs could be indexed to the FCC structure of Fe3O4 (JCPDS no. 74-1910). It is worth noting that obvious changes in the intensity ratios for various peaks were observed, giving further support to the above morphology observations. More specifically, in the case of rhombic dodecahedrons, the intensity ratio of 1.5 for the (220) and (111) diffractions was remarkably higher than the powder intensity ratio (0.15), confirming that these crystals were primarily composed of {110}
crystalline planes. In contrast, the intensity ratio for the (220) and (111) peaks for Fe3O4 nanodiscs was only 0.14, suggesting that their surfaces are dominated by {111} planes. In order to understand the shape control of Fe3O4 nanocrystals in the reaction system, control experiments were conducted to elucidate the growth mechanism of Fe3O4 rhombic dodecahedrons and nanodiscs. It is found that the reaction temperature plays an important role in the size of Fe3O4 rhombic dodecahedrons. SEM images of the samples obtained at 160 and 120 1C are shown in Fig. S1a and b. When the synthesis was performed at 160 1C, the as-obtained products were rhombic dodecahedrons with a
Fig. 3. XRD patterens of (a) Fe3O4 rhombic dodecahedrons and (b) Fe3O4 nanodiscs.
Fig. 2. (a and b) SEM images of Fe3O4 nanodiscs, (c) schematic diagram of Fe3O4 nanodisc, (d and e) TEM images of Fe3O4 nanodiscs.
Z. Chen et al. / Materials Letters 117 (2014) 10–13
diameter of 80–250 nm. Careful observation shows that some of the rhombic dodecahedrons have smooth corners, exhibiting spheroidal shape. When the reaction temperature reduced to 120 1C, the resultant products were mixture of strip crystals and rhombic dodecahedrons with a size of 150–350 nm. Additionally, the morphologies of the as-synthesized Fe3O4 nanocrystals are dependent on the amount of N2H4 H2O. When the starting solution contained 6 mmol N2H4 H2O, Fe3O4 rhombic dodecahedrons (ca. 40%) and nanoplates coexisted (Fig. S1c). When 3.5 mmol N2H4 H2O was used, Fe3O4 rhombic dodecahedrons (ca. 80%) coexisted with nanorods (Fig. S1d). When 2.5 mmol N2H4 H2O was employed, the products were nanorods with a diameter of 10–30 nm and length of 120–160 nm (Fig. S1e). The corresponding XRD pattern indicated that all of the diffraction peaks of the nanorods could be readily assigned to FCC phase of Fe3O4 by comparison with the JCPDS card file no. 77-1545 (Fig. S2). Moreover, if N2H4 H2O was substituted by NH3 H2O, Fe3O4 nanoparticles were obtained (Fig. S1f). In general, the as-grown crystal morphology is dominated by the slow-growing faces because the fast-growing faces may grow out and not be represented in the final crystal habit. It is widely accepted that the growth rate could be tuned by bounding to the surfactants on the faces of nanocrystals. At a large amount of N2H4 H2O (7 mmol), the surface energy of the {111} planes is the highest among the low-index facets. N2H4 H2O molecules or NH4þ ions are selectively adsorbed on the {111} facets, and consequently the growth rate along the [111] direction is reduced, resulting in the formation of Fe3O4 nanodiscs. At a moderate quantity of N2H4 H2O (5 mmol), the surface energy of the {110} planes is the highest. N2H4 H2O molecules or NH4 þ ions are preferentially adsorbed on the {110} planes of Fe3O4 nuclei, and the growth rate along the [110] direction is reduced, leading to the formation of rhombic dodecahedral crystals. Whereas, at the small amount of N2H4 H2O (2.5 mmol), the surface energy of the {111} is the lowest. N2H4 H2O molecules or NH4þ ions are adsorbed on other low-index planes of Fe3O4 nuclei, and consequently minimize surface energy and growth kinetic of those facets, conducing to the growth along [110] direction to form Fe3O4 nanorods. Room temperature magnetic properties of Fe3O4 rhombic dodecahedrons and nanodiscs were investigated by a SQUID magnetometer. A typical ferromagnetic curve is shown in Fig. S3, which gives values of saturation magnetization (Ms) 77.1 and 58.8 emug 1 for Fe3O4 rhombic dodecahedrons and nanodiscs, respectively. The coercivity values (Hc) amount to 46.9 Oe for Fe3O4 rhombic dodecahedrons and 32.9 Oe for Fe3O4 nanodiscs. The Hc for Fe3O4 rhombic dodecahedrons is larger than that of Fe3O4 nanodiscs, which might be attributed to the shape anisotropy of Fe3O4 samples.
13
4. Conclusions In summary, we have proposed a facile and efficient process for the shape-controlled synthesis of Fe3O4 rhombic dodecahedrons and nanodiscs. The size, shape, and magnetic properties of the final products could be readily tuned by adjusting the experimental parameters, such as the reaction temperature and amount of N2H4 H2O. Our approach offers tremendous opportunities for the design of Fe3O4 nanocrystals with varying shapes, structures and properties. Furthermore, the Fe3O4 rhombic dodecahedrons bound with twelve high-energy {110} facets probably lead to future prospects toward their potential applications such as conspicuous catalytic activity.
Acknowledgment This work is supported by the National Natural Science Foundation of PR China (21101002, 21275072, 21201101 and 21171003), and the opening research foundations of State Key Laboratory of Coordination Chemistry of Nanjing University.
Appendix A. Supplementary materials Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.11. 076. References [1] Guardia P, Labarta A, Batlle XJ. Phys Chem C 2011;115:390–6. [2] Kim D, Lee N, Park M, Kim BH, An K, Hyeon TJ. Am Chem Soc 2009;131:454–5. [3] Bodnarchuk MI, Lechner RT, Hesser G, Schaffler F, Heiss WJ. Am Chem Soc 2007;129:6352–3. [4] Zhang LH, Wu JJ, Liao HB, Hou YL, Gao S. Chem Commun 2009:4378–80. [5] Suber L, Imperatori P, Ausanio G, Fabbri F, Hofmeister HJ. Phys Chem B 2005;109:7103–9. [6] Geng BY, Zhan FM, Jiang H, Guo YJ, Xing ZJ. Chem Commun 2008:5773–5. [7] Jia CJ, Sun LD, Luo F, Han XD, Heyderman LJ, Yan ZG, et al. J Am Chem Soc 2008;130:16968–77. [8] Milosevic I, Jouni H, David C, Warmont F, Bonnin D, Motte LJ. Phys Chem C 2011;115:18999–9004. [9] Liu XM, Kim JK. Mater Lett 2009;63:428–30. [10] Lu J, Jiao XL, Chen DR, Li WJ. Phys Chem C 2009;113:4012–7. [11] Li XY, Liu DP, Song SY, Wang X, Ge X, Zhang HJ. CrystEngComm 2011;13:6017–20. [12] Geng BY, Ma JZ, You JH. Cryst Growth Des 2008;8:1443–7. [13] Zeng Y, Hao R, Xing BG, Hou YL, Xu ZC. Chem Commun 2010;46:3920–2. [14] Wang ZLJ. Phys Chem B 2000;104:1153–75.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Shape-controlled synthesis of Fe3O4 rhombic dodecahedrons and nanodiscs Zhiming Chen a,b,n, Zhirong Geng b, Tingxian Tao a, Zhilin Wang b a b
College of Biochemical Engineering, Anhui Polytechnic University, Wuhu 241000, PR China State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 28 August 2013 Accepted 20 November 2013 Available online 28 November 2013
Fe3O4 rhombic dodecahedrons with only {110} facets exposed and nanodiscs bounded entirely by {111} facets were fabricated via a one-pot hydrothermal approach. The morphologies, structures and magnetic properties of the rhombic dodecahedrons and nanodiscs were investigated through different analytical tools. Batch experiments indicated that the reaction temperature and amount of N2H4 H2O play important roles in determining the sizes and morphologies of the products. Magnetic analysis revealed that the magnetic properties are closely related to the morphologies of the magnetites. The synthesized Fe3O4 nanocrystals are hoped to have important applications in advanced magnetic materials and catalytic fields. & 2013 Elsevier B.V. All rights reserved.
Keywords: Fe3O4 nanoparticles Rhombic dodecahedrons Nanodiscs Crystal growth Magnetic materials
1. Introduction Over the past decade, the precise architectural manipulation of Fe3O4 nanoparticles with well-defined morphologies and accurate tunable sizes have been a research hotspot not only for fundamental scientific interest but also for their various applications in fields such as magnetic storage, catalyst, electrode materials, drug delivery, medical diagnostics and therapeutics. So, many efforts have been devoted to explore excellent synthetic approaches for the fabrication of Fe3O4 crystals with controlled shape to enhance their performance in currently existing applications. Thus far, a wide variety of Fe3O4 morphologies, including nanoparticles, nanocubes, nanowires, nanotubes, nanorods, nanoplates, nanorings, octahedrons and polyhedrons have been successfully synthesized [1–13]. However, most of the reported morphologies are bound by {111}, {100} or both {111} and {100} facets. From the perspective of crystallography, magnetite (Fe3O4) is a ferromagnetic iron oxide having a cubic inverse spinel structure with oxygen anions forming a face-center-cubic (FCC) closed packing [12]. As a FCC crystal, a general sequence of surface energies may hold, γ{111}o γ{100} o γ{110} [14], which means that Fe3O4 crystals exclusively enclosed by {110} surfaces have been rarely exploited because the {110} lattice planes have the highest surface energy among the low-index facets, thus exhibiting faster growth kinetics than the others, resulting in their disappearance during
n Corresponding author at: College of Biochemical Engineering, Anhui Polytechnic University, Wuhu 241000, PR China. Tel.: þ86 553 2871254. E-mail address: [email protected] (Z. Chen).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.11.076
the crystal growth. Moreover, it is widely accepted that Fe3O4 nanocrystals with exposed {110} facets exhibited high catalytic activity and have special applications in optical, electrical and magnetic devices [12]. Therefore, the development of alternative methodologies for the facile and well-controlled synthesis of Fe3O4 nanocrystals possessing active basal surfaces {110} remains an important challenge. Herein, we present a facile protocol for the shape-controlled synthesis of Fe3O4 rhombic dodecahedrons with only {110} facets exposed and nanodiscs bounded entirely by {111} facets. It is found that the reaction temperature and amount of N2H4 H2O have important effects on the sizes and morphologies of the magnetic nanocrystals. Besides, the magnetic properties of the two kinds of nanocrystals are investigated. 2. Experimental Materials and method: FeCl2 4H2O, H2C2O4 2H2O, N2H4 H2O, NH3 H2O and acetone were of analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China), and used without further purification. Deionized water was used throughout. In a typical procedure, the starting solution was prepared by mixing 0.5 mmol FeCl2 4H2O, 0.5 mmol H2C2O4 2H2O and 5 mmol N2H4 H2O in 45 mL water. The resulting solution was transferred into stainless-steel autoclaves lined with poly(tetrafluoroethylene) and maintained at 140 1C for 3 h and then cooled to room temperature. The as-obtained precipitate was collected, washed with distilled water and acetone several times, and dried in air. Using the same procedures, the reaction temperature and
Z. Chen et al. / Materials Letters 117 (2014) 10–13
quantity of N2H4 H2O were varied in the experiments to obtain products with a desired morphology. Characterizations: Phase identification via X-ray diffraction (XRD) was collected on a Shimadzu XRD-6000 X-ray diffractometer. The morphologies of the samples were observed by field-emission scanning electron microscopy (SEM, S-4800) and high resolution transmission electron microscopy (HRTEM, JOEL-2010). The magnetic properties of the products were studied with a superconducting quantum interference device (SQUID, Quantum Design MPMS XL-7).
11
3. Results and discussion Fig. 1a shows a typical low-magnification SEM image of the products obtained in the solution contained 5 mmol N2H4 H2O at 140 1C for 3 h and reveals that the sample is in the form of rhombic dodecahedral morphology with a diameter of 150–300 nm. The enlarged SEM image reveals that the as-prepared Fe3O4 nanocrystals are enclosed by 12 well-defined {110} planes with cubic crystal symmetry (Fig. 1b and c). Fig. 1d and e show typical TEM
Fig. 1. (a and b) SEM images of Fe3O4 rhombic dodecahedrons, (c) schematic diagram of Fe3O4 rhombic dodecahedron, (d and e) TEM images of Fe3O4 rhombic dodecahedrons, (f) SAED and (g) HRTEM images of an individual rhombic dodecahedron oriented along [1̄ 12].
12
Z. Chen et al. / Materials Letters 117 (2014) 10–13
images of the Fe3O4 rhombic dodecahedrons. It is clear that the projection views of the particles are hexagonal, square and polygon shapes. Fig. 1f shows the selected area electron diffraction (SAED) pattern obtained from a single rhombic dodecahedron with the electron beam perpendicular to the hexagon in Fig. 1e. The SAED pattern can be indexed to the [1̄ 12] zone axis of a single crystal of fcc Fe3O4, indicating that the synthesized Fe3O4 nanocrystals are single-crystalline and bound by {110} basal planes. The lattice spacings of 0.297 and 0.242 nm measured from the highresolution TEM image correspond to the (220) and (22̄ 2) crystalline planes of fcc Fe3O4 (Fig. 1g), which also demonstrates the exposed surface of the {110} facets. Interestingly, as shown in Fig. 2, when the reaction was performed in the solution containing 7 mmol N2H4 H2O at 120 1C for 3 h, uniform Fe3O4 nanodiscs with a diameter of 80–250 nm were fabricated in large quantities. Moreover, it can be clearly observed that Fe3O4 nanodiscs were bounded completely by two {111} facets and all the exposed surfaces are round and smooth with no obvious defects. The X-ray diffraction (XRD) patterns (Fig. 3) clearly show that all of the diffraction peaks of the rhombic dodecahedrons and nanodiscs could be indexed to the FCC structure of Fe3O4 (JCPDS no. 74-1910). It is worth noting that obvious changes in the intensity ratios for various peaks were observed, giving further support to the above morphology observations. More specifically, in the case of rhombic dodecahedrons, the intensity ratio of 1.5 for the (220) and (111) diffractions was remarkably higher than the powder intensity ratio (0.15), confirming that these crystals were primarily composed of {110}
crystalline planes. In contrast, the intensity ratio for the (220) and (111) peaks for Fe3O4 nanodiscs was only 0.14, suggesting that their surfaces are dominated by {111} planes. In order to understand the shape control of Fe3O4 nanocrystals in the reaction system, control experiments were conducted to elucidate the growth mechanism of Fe3O4 rhombic dodecahedrons and nanodiscs. It is found that the reaction temperature plays an important role in the size of Fe3O4 rhombic dodecahedrons. SEM images of the samples obtained at 160 and 120 1C are shown in Fig. S1a and b. When the synthesis was performed at 160 1C, the as-obtained products were rhombic dodecahedrons with a
Fig. 3. XRD patterens of (a) Fe3O4 rhombic dodecahedrons and (b) Fe3O4 nanodiscs.
Fig. 2. (a and b) SEM images of Fe3O4 nanodiscs, (c) schematic diagram of Fe3O4 nanodisc, (d and e) TEM images of Fe3O4 nanodiscs.
Z. Chen et al. / Materials Letters 117 (2014) 10–13
diameter of 80–250 nm. Careful observation shows that some of the rhombic dodecahedrons have smooth corners, exhibiting spheroidal shape. When the reaction temperature reduced to 120 1C, the resultant products were mixture of strip crystals and rhombic dodecahedrons with a size of 150–350 nm. Additionally, the morphologies of the as-synthesized Fe3O4 nanocrystals are dependent on the amount of N2H4 H2O. When the starting solution contained 6 mmol N2H4 H2O, Fe3O4 rhombic dodecahedrons (ca. 40%) and nanoplates coexisted (Fig. S1c). When 3.5 mmol N2H4 H2O was used, Fe3O4 rhombic dodecahedrons (ca. 80%) coexisted with nanorods (Fig. S1d). When 2.5 mmol N2H4 H2O was employed, the products were nanorods with a diameter of 10–30 nm and length of 120–160 nm (Fig. S1e). The corresponding XRD pattern indicated that all of the diffraction peaks of the nanorods could be readily assigned to FCC phase of Fe3O4 by comparison with the JCPDS card file no. 77-1545 (Fig. S2). Moreover, if N2H4 H2O was substituted by NH3 H2O, Fe3O4 nanoparticles were obtained (Fig. S1f). In general, the as-grown crystal morphology is dominated by the slow-growing faces because the fast-growing faces may grow out and not be represented in the final crystal habit. It is widely accepted that the growth rate could be tuned by bounding to the surfactants on the faces of nanocrystals. At a large amount of N2H4 H2O (7 mmol), the surface energy of the {111} planes is the highest among the low-index facets. N2H4 H2O molecules or NH4þ ions are selectively adsorbed on the {111} facets, and consequently the growth rate along the [111] direction is reduced, resulting in the formation of Fe3O4 nanodiscs. At a moderate quantity of N2H4 H2O (5 mmol), the surface energy of the {110} planes is the highest. N2H4 H2O molecules or NH4 þ ions are preferentially adsorbed on the {110} planes of Fe3O4 nuclei, and the growth rate along the [110] direction is reduced, leading to the formation of rhombic dodecahedral crystals. Whereas, at the small amount of N2H4 H2O (2.5 mmol), the surface energy of the {111} is the lowest. N2H4 H2O molecules or NH4þ ions are adsorbed on other low-index planes of Fe3O4 nuclei, and consequently minimize surface energy and growth kinetic of those facets, conducing to the growth along [110] direction to form Fe3O4 nanorods. Room temperature magnetic properties of Fe3O4 rhombic dodecahedrons and nanodiscs were investigated by a SQUID magnetometer. A typical ferromagnetic curve is shown in Fig. S3, which gives values of saturation magnetization (Ms) 77.1 and 58.8 emug 1 for Fe3O4 rhombic dodecahedrons and nanodiscs, respectively. The coercivity values (Hc) amount to 46.9 Oe for Fe3O4 rhombic dodecahedrons and 32.9 Oe for Fe3O4 nanodiscs. The Hc for Fe3O4 rhombic dodecahedrons is larger than that of Fe3O4 nanodiscs, which might be attributed to the shape anisotropy of Fe3O4 samples.
13
4. Conclusions In summary, we have proposed a facile and efficient process for the shape-controlled synthesis of Fe3O4 rhombic dodecahedrons and nanodiscs. The size, shape, and magnetic properties of the final products could be readily tuned by adjusting the experimental parameters, such as the reaction temperature and amount of N2H4 H2O. Our approach offers tremendous opportunities for the design of Fe3O4 nanocrystals with varying shapes, structures and properties. Furthermore, the Fe3O4 rhombic dodecahedrons bound with twelve high-energy {110} facets probably lead to future prospects toward their potential applications such as conspicuous catalytic activity.
Acknowledgment This work is supported by the National Natural Science Foundation of PR China (21101002, 21275072, 21201101 and 21171003), and the opening research foundations of State Key Laboratory of Coordination Chemistry of Nanjing University.
Appendix A. Supplementary materials Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.11. 076. References [1] Guardia P, Labarta A, Batlle XJ. Phys Chem C 2011;115:390–6. [2] Kim D, Lee N, Park M, Kim BH, An K, Hyeon TJ. Am Chem Soc 2009;131:454–5. [3] Bodnarchuk MI, Lechner RT, Hesser G, Schaffler F, Heiss WJ. Am Chem Soc 2007;129:6352–3. [4] Zhang LH, Wu JJ, Liao HB, Hou YL, Gao S. Chem Commun 2009:4378–80. [5] Suber L, Imperatori P, Ausanio G, Fabbri F, Hofmeister HJ. Phys Chem B 2005;109:7103–9. [6] Geng BY, Zhan FM, Jiang H, Guo YJ, Xing ZJ. Chem Commun 2008:5773–5. [7] Jia CJ, Sun LD, Luo F, Han XD, Heyderman LJ, Yan ZG, et al. J Am Chem Soc 2008;130:16968–77. [8] Milosevic I, Jouni H, David C, Warmont F, Bonnin D, Motte LJ. Phys Chem C 2011;115:18999–9004. [9] Liu XM, Kim JK. Mater Lett 2009;63:428–30. [10] Lu J, Jiao XL, Chen DR, Li WJ. Phys Chem C 2009;113:4012–7. [11] Li XY, Liu DP, Song SY, Wang X, Ge X, Zhang HJ. CrystEngComm 2011;13:6017–20. [12] Geng BY, Ma JZ, You JH. Cryst Growth Des 2008;8:1443–7. [13] Zeng Y, Hao R, Xing BG, Hou YL, Xu ZC. Chem Commun 2010;46:3920–2. [14] Wang ZLJ. Phys Chem B 2000;104:1153–75.