HEOPTAHHHECKHE MATEPHAttbl, 2008, moM 44, № 3, c. 345-349
UDC 546.72
Preparation and Characterization of Fe304/Ag Composite Magnetic Nanoparticles
© 2008 r. C. H. Liu*, Z. D. Zhou*, X. Yu*, B. Q. Lv**, J. F. Mao*, D. Xiao*, **
*College of Chemistry, Sichuan University, Chengdu 610064, PR. China **College of Chemical Engineering, Sichuan University, Chengdu 610065, PR. China
e-mail: xiaodan@scu.edu.cn Received 02.02.2007
Fe3O4 magnetic nanoparticles being used as seeding materials, Ag+ ions on the Fe3O4 magnetic nanoparticles reduced to the metal form by tartaric acid using heated treatment. Thus, Fe3O4/Ag composite core-shell magnetic nanoparticles were synthesized. The products were characterized by transmission electron microscope (TEM) and X-ray diffraction (XRD). Both TEM and XRD results showed that the Ag nanoparticles were well distributed on the surface of Fe3O4 magnetic nanoparticles. The size for Fe3O4/Ag composite magnetic nano-particles which were spherical shape was =40 nm. Furthermore, the magnetic properties of samples were characterized on a vibrating sample magnetometer. Under optimal conditions, Fe3O4/Ag composite nanoparticles showed higher magnetism than pure Fe3O4 nanoparticles.
INTRODUCTION
In recent years, preparation of Fe3O4 magnetic nanoparticles [1-7] has been extensively studied because of their unique magnetic properties and good bio-compatibility. However, the application of Fe3O4 has been limited due to its inherent properties. Therefore, many researchers have focused on preparation of composite magnetic nanoparticles [8-25] to obtain novel properties. Compared with organic composite analogs [8, 9], inorganic composite magnetic nanoparticles [14, 16] are considered to be easier to prepare and more safe to be put into use. In general, it is well known that Ag has good antibiotic property and biocompatible. Silver nanoparticles have attracted a great deal of interest in recent years because they can be applied for electronics [26], optics [27-30] and catalysis [31]. Various Ag composite materials has been successfully synthesized, such as Co/Ag core/shell structure nanoparticles [32], Au/Ag core/shell nanoparticles [33], silver-halide composite structures [34], silver/silica composite structures [35], and Ag-coated polystyrene colloids [36]. However, the preparation and properties of Fe3O4/Ag composite magnetic nanoparticles [37-42] have been reported yet a few. In this paper, a novel and simple route was used to prepare Fe3O4/Ag composite magnetic nano-particles. Fe3O^/Ag composite magnetic nanoparticles have great advantages in obtaining an evenly disperse silver coating and may modify more functional groups on the surface of silver nanoparticles. The Fe3O^/Ag composite magnetic nanoparticles possess the surface character of Ag and the magnetic property of Fe3O4, and hence might have great potential applications in biological targeting, biological separation, high-density
magnetic recording, catalysis and targeting therapy fields in the near future.
EXPERIMENTAL
Iron (II) Sulfate hexahydrate, silver nitrate, ammonia and tartaric acid were purchased from Chengdu Chemical Reagent Corporation. All chemicals were of analytical grade. Double-distilled water was used throughout the experiment.
The structure analysis and morphology observation of the samples were performed on a JEOL H-800 transmission electron microscope (TEM). The phase analysis for the samples was conducted on an DX-1000 X-ray dif-fractometer with CuA"a radiation (X = 0.15406 nm). The magnetic properties of samples were measured with a vibrating sample magnetometer (VSM) (Lake Shore 7410).
Preparation of Fe3O4. The Fe3O4 magnetic nanoparticles as seeds were synthesized using a little modified procedure [3]. In a 1000 ml beaker, 4.0 g FeSO4 ■ 7H2O was dissolved in 600 ml water. And 20 ml NH3 ■ H2O (25-28%) was added dropped into the solution with stirring. The mixed solution was heated at 70-80°C for 6 min by microwave. Then the system was cooled to room temperature and separated by external magnetic field to obtain Fe3O4 particles. And products were washed three times with water and dried in vacuum desiccators.
Preparation of Fe3O4/Ag. The Fe3O4 nanoparticles seeds (= 1.0 g) were added into a 1.0 x 10-2 mol/l solution of silver nitrate (100 ml). When the mixture was heated to boiling, 1% tartaric acid (=1 ml) was added to it. The reaction was kept at boiling temperature for 5 min. Then the nanoparticles was separated out by external magnetic
346
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Fig. 1. TEM images of Fe3O4 particles (a) and Fe3O4/Ag composite particles (b).
Intensity, counts 600
500
400
300
200
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0
311
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111
4! r " T"" ™ p Wlr"
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440
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Intensity, counts
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10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90
26, deg 26, deg
Fig. 2. XRD patterns of Fe3O4 particles (a) and Fe3O4/Ag composite particles (b).
field and washed with water. Finally, Fe3O4/Ag composite magnetic nanoparticles were obtained.
RESULTS AND DISCUSSIONS
TEM Analysis. Figure 1 shows the representative images comparing Fe3O4 (a) with Fe3O4/Ag (b) nanoparticles, which were obtained from the procedure. We found three major differences by comparison. Firstly, although both Fe3O4 and Fe3O4/Ag nanoparticles are spherical shape as shown in Fig. 1, Fe3O4/Ag nanoparticles seem more compact and better separated, indicating that the Fe3O4/Ag composite magnetic nanoparti-cles should have a higher density than that of Fe3O4 nanoparticles. Secondly, the particles after coating with Ag appear rather darker than pure Fe3O4 seeds. Finally, the average particle size changed from ^30 nm (a) to ^40 nm (b). Clearly, the TEM data serve as an important piece of evidence for the formation of Fe3O4/Ag core-shell nanoparticles.
XRD Analysis. Figure 2 is typical powder XRD pattern prepared of Fe3O4 particles and Fe3O4/Ag composite particles, which were measured from 10° to 90° (26). The experimentally obtained patterns were identi-
fied through comparison with standard Fe3O4 and Ag patterns (PDF standard cards). The data (Fig. 2a) shows characteristic peaks at 26 = 18.3°, 30.1°, 35.5°, 37.1°, 43.0°, 53.4°, 56.9°, 62.7°, 74.3°, 78.7° and 89.0°, which can be indexed to 111, 220, 311, 222, 400, 422, 511, 440, 533, 622 and 731 planes of Fe3O4 with PDF standard cards № 65-3107. This revealed that the resultant particles were pure Fe3O4. In Fig. 2b, all the 26 and indices corresponding to both the Fe3O4 and Ag pattern prove the formation of Ag-coated Fe3O4 nanoparticles. The XRD peaks for the Fe3O4/Ag nanoparticles are similar to these reported by Mandal et al. [38]. Clearly, the XRD peaks for Fe3O4/Ag nanoparticles (Fig. 2b) are similar to that for the Fe3O4 nanoparticles (Fig. 2a). The only difference lies in the diffraction peaks for Ag nanoparticles. In Fig. 2b we obtained 26 and indices corresponding to Ag (peaks at 26 = 38.1°, 44.6°, 64.7°, 77.5° and 81.8° indicating indices corresponding to 111, 200, 220, 311 and 222). All the reflection peaks can be well indexed with PDF standard cards № 65-2871. The average size of Fe3O4 particles calculated by using Scherer's equation was about 29.2 nm, whereas the average size increases to 40.7 nm after the Fe3O4 particles coated with silver. The results were in
HEOPrAHHHECKHE MATEPHA^bl tom 44 № 3 2008
10 ml-
5 mb
Fe3O4 Fe3O4/Ag
\
Magnetic field
Magnetic field
Fig. 3. Magnetization behavior of Fe3O4 and Fe3O4/Ag in experiments.
good agreement with the data obtained from the TEM images (shown in Fig. 1). Thus both XRD and TEM provide strong evidence that the Fe3O4/Ag composite magnetic nanoparticles are core-shell structure.
Magnetic Analysis. Here, we have described a simple way according to the literature [13] with a little modification to determine of magnetism of samples. As Fig. 3 shown, the Fe3O4 magnetic nanoparticles and the Fe3O4/Ag composite magnetic nanoparticles were separated by external magnetic field. By contrast, we found that Fe3O4/Ag composite magnetic nanoparticles subsided more quickly, indicating that they have higher magnetism.
The magnetic properties were measured using VSM magnetometer (Fig. 4). From Fig. 4, it can be seen that saturated magnetization for Fe3O4 and Fe3O4/Ag takes values 75.75 and 84.72 emu/g, respectively. Obviously, the saturated magnetization of Fe3O^/Ag is higher. The anisotropic energy is changed when Ag coated on the surface of Fe3O4 because of the dipolar interactions be-
Moment, emu 1.8 -
0 5000 10000 15000 20000
Field, G
Fig. 4. Magnetization curves of Fe3O4 (1) and Fe3O4/Ag (2). НЕОРГАНИЧЕСКИЕ МАТЕРИАЛЫ том 44 < 3
tween particles, which lead to a raise of the saturated magnetization value [43].
CONCLUSIONS
A novel and simple method for preparation of Fe3O4/Ag composite magnetic nanoparticles has been developed. The Fe3O^Ag composite magnetic nanoparticles characterization was spherical shape and average size was =40 nm. The magnetism of the Fe3O4/Ag composite nanoparticles is higher than pure Fe3O4 nano-particles. The Fe3O4/Ag composite magnetic nanoparti-cles have the some advantages, such as low cost, convenient preparation, short reaction time, easy separation and easy modification functional groups on of surfaces silver nanoparticles. It is expected to apply to biological and clinical analysis by further research development.
ACKNOWLEDGEMENTS
This work was supported by the National Natural Science Foundation of China (20575042).
REFERENCES
1. Arturo M, Lopez Q, Jose R. Magnetic Iron Oxide Nanoparticles Synthesized Via Microemulsions // J. Colloid Interface Sci. 1993. V. 158. № 2. P. 446-451.
2. Chiang C.L, Sung C.S. Purification of Transfection-Grade Plasmid DNA from Bacterial Cells with Super-paramagnetic Nanoparticles // J. Magn. Magn. Mater. 2006. V. 302. № 1. P. 7-13.
3. Hai Y B, Yuan H.Y., Xiao D. Preparation of Fe3O4 Nanoparticles by Microwave Method // Chem. Res. Ap-pl. 2006. V. 18. № 6. P. 744-7
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