Biopolymer-Assisted Green Synthesis of Iron Oxide Nanoparticles and

Jun 24, 2008 - Combinatorial Discovery of Novel Amphiphilic Polymers for the Phase Transfer of Magnetic Nanoparticles. Benjamin W. Muir , Bradford A. ...
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10398

J. Phys. Chem. C 2008, 112, 10398–10401

Biopolymer-Assisted Green Synthesis of Iron Oxide Nanoparticles and Their Magnetic Properties Shuyan Gao,*,† Youguo Shi,‡ Shuxia Zhang,† Kai Jiang,† Shuxia Yang,† Zhengdao Li,† and Eiji Takayama-Muromachi‡ College of Chemistry and EnVironmental Science, Henan Normal UniVersity, Xinxiang 453007, People’s Republic of China, and AdVanced Nano Materials Laboratory (ANML), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan ReceiVed: March 17, 2008; ReVised Manuscript ReceiVed: April 15, 2008

Magnetite nanoparticles were fabricated using a biopolymer (sodium alginate)-assisted route via redox-based hydrothermal method using FeCl3 · 6H2O and urea as the starting materials. The morphology, composition, and phase structure of as-prepared powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that biopolymer plays dual roles, reduction, and stabilization, in the formation of the products. This method can be easily controlled and is expected to be applicable for the preparation of other metal oxides. The sample demonstrated a typical ferromagnetic behavior from a direct current SQUID magnetometer (Quantum Design MPMS). Introduction During recent years, the development of nanotechnology enabled us to synthesize functional materials in low dimensions, including metals,1 semiconductors,2 hybrid materials,3 and so forth.4 As previously described in multiple publications, the controlled synthesis of magnetic nanoparticles is of high scientific and technological interest.5 Magnetite (Fe3O4) is a common ferrite having a cubic inverse spinel structure. The compound exhibits unique electric and magnetic properties based on the transfer of electrons between Fe2+ and Fe3+ in the octahedral sites. Interest in the magnetite has centered on applications such as multiterabit magnetic storage devices,6 ferrofluids,7 sensors,8 spintronics,9 separation processes,10 MRI contrast enhancement agents,11 and especially biomedical fields.12 Magnetite nanoparticles are usually synthesized by the coprecipitation of ferrous (Fe2+) and ferric (Fe3+) ions by a base.13 Other synthetic methods include the thermal decomposition of an alkaline solution of an Fe3+ chelate in the presence of hydrazine and the sonochemical decomposition of an Fe2+ salt followed by thermal treatment.14 Uniformly sized magnetite nanoparticles were synthesized by the high-temperature reaction of Fe(acac)3 in octyl ether and oleic acid or lauric acid or a mixture of four solvents and ligands, namely, phenyl ether, 1,2hexadecanediol, oleic acid, and oleylamine.15 Even though they produce highly crystalline and uniformly sized magnetic nanoparticles, these synthetic procedures are not exempt of drawbacks, because they require expensive and often toxic reagents, complicated synthetic steps, and high reaction temperatures. To understand the environmental implications of these nanoparticles and to facilitate their potential applications, it is important to develop a simple, green, and generic method for the preparation of Fe3O4 nanoparticles. * To whom correspondence should be addressed. Telephone: +86-3733326544. Fax: +86-373-3326544. E-mail: [email protected]. † Henan Normal University. ‡ NIMS.

In this work, we show that such drawbacks can be overcome by using biopolymer, sodium alginate, as reducing and stabilizing agent at the same time, instead of toxic organic acids and amines commonly used. As we know, sodium alginate is a popular additive and naturally derived linear anionic copolymer of 1,4-linked β-D-mannuronic acid (M-block) and R-L-guluronic acid (G-block) residues arranged in a nonregular blockwise pattern by varying proportions of GG, MG, and MM blocks. The extensive number of carboxyl groups present in sodium alginate can make hydrogels form in the presence of cations via an ionic interaction between the acid groups on the G blocks and the chelating ions. So, sodium alginate sol, to some extent, can act as nanoreactor to template and stabilize nanoparticles. Additionally, the majority of methods reported to date use reducing agents, such as hydrazine, sodium borohydride (NaBH4), and dimethylformamide (DMF). All of these are highly reactive chemicals and pose potential environmental and biological risks. The reduction properties of sodium alginate comes from the abundant hydroxyl groups and has been verified in the synthesis of single crystalline gold nanodisks.16 With heating in the present method, the sodium alginate becomes a mild, inexpensive, and nontoxic reducing agent. Finally, its benign water-solubility makes fabrication of nanocrystals processing in water medium. This is very crucial for “green chemistry”. Herein we report a one-pot green chemistry reaction method for the formation of high-purity magnetite nanocrystals from sodium alginate and FeCl3 in alkaline solution. The as-prepared magnetite nanoparticles have an average diameter of around 24.5 nm. The procedure that we report here, in comparison with common previous protocols reported in the literature, is a green, environment-friendly, and direct one-step process for the preparation of Fe3O4 nanoparticles. Also, the magnetic properties of the samples were obtained from a direct current (dc) SQUID magnetometer (Quantum Design MPMS). According to the magnetic hysteresis curve, the sample exhibits a ferromagnetic behavior, which are expected to be applicable in high-density recording media in future nanodevices.

10.1021/jp802500a CCC: $40.75  2008 American Chemical Society Published on Web 06/24/2008

Magnetic Iron Oxide Nanoparticle Green Synthesis

J. Phys. Chem. C, Vol. 112, No. 28, 2008 10399

Experimental Section All chemicals were used as received. Sodium alginate was purchased from Acros, while all other chemicals were supplied by Beijing Chemicals Co. Ltd. To prepare Fe3O4 nanparticles, 0.5 g of urea was added to 10 mL of aqueous solution containing 1.5 mmol of FeCl3, which was followed by the dropwise addition of 25 mL of a 25.4 mM sodium alginate aqueous solution (calculated by the repeating unit). Subsequently, the resulting solution was transferred into a 50 mL Teflon-lined autoclave and heated at 453 K for 24 h. A black solid product aggregated at the bottom of the vessel, indicating the formation of magnetic Fe3O4. The products were collected, then washed with distilled water several times (to remove remnant starting materials remaining in final products), and finally dried in air. The phase and purity of the product was determined by powder X-ray diffraction (XRD), using a Rigaku D/Max 2500 V/PC X-ray diffractometer equipped with high-intensity Cu KR1 radiation (λ ) 1.54056 Å). The morphology and size of the sample were examined by field emission scanning electron microscopy (FESEM, an XL30 ESEM FEG scanning electron microscopy operated at 20 kV). X-ray photoelectron spectroscopy (XPS) was collected on an ESCALab MKII X-ray photoelectron spectrometer, using nonmonochromatized Mg KR X-ray as excitation source. The magnetic susceptibility was measured by using a superconducting quantum interference device (SQUID) (MPMS-7 T; Quantum Design). For measurement, a plastic straw held a plastic capsule containing a 16.2 mg Fe3O4 sample. Results and Discussions Biosynthesis is well-established for the production of small metallic particles.17 The characteristic materials obtained by using the biomass are metals. In the case of Fe ions, the reduction did not reach into metal clusters. In this way, the first parameters to evaluate are the size and the elements present in the nanoparticles. FESEM observations show that the panoramic morphology of the as-obtained product is mainly uniform and spheric architectures (Figure 1). To confirm the structure and size distribution of the product, we obtained TEM image (Figure 2A), which further verified the spheric structure of the products. By statistically analyzing the particles in Figure 2A, the average diameter is about 27.2 nm (Figure 2B). It shows that these nanoparticles display a narrow size distribution. Hence, the reduction of metallic ions by sodium alginate to generate particles is verified. The phase structure and composition of these clusters were identified by XRD and XPS. An XRD pattern (Figure 3a) of the prepared product can be clearly seen and indexed to the face-centered cubic spinel structure of pure Fe3O4 with a lattice parameter of a ) 8.393 Å, which is very close to the reported value (JCPDS 65-3107) and expected for this green synthesis route; i.e., the reduction of Fe3+ by biopolymer leads to magnetite as the final product. The broadening of these diffraction peaks indicated that the sample was composed of nanosized particles. The XPS spectra of the products corresponding to the binding energies of Fe2p and O1s are depicted by curve a in Figure 4A and Figure 4B, which shows that the binding energies relating to Fe2p3/2, Fe2p1/2, and O1s are about 711, 725, and 531 eV, respectively. The data are consistent with the values reported for Fe3O4 in the literature.18 Therefore, XPS data together with XRD result prove the composition and structure of the product. In this biopolymer-assisted route, the addition of sodium alginate and its amount are the key factors to the green synthesis

Figure 1. A typical FESEM image (A) and high-magnification image (B) of the product.

of Fe3O4 nanoparticles. There are two functional groups (COOand OH) on the sodium alginate molecules, which are hydrophilic groups and can provide coordination sites. When Fe3+ ions enter into aqueous solution, the sites provide the necessary heterogeneous nucleation sites, and Fe3+ forms complexes with the hydrophilic functional groups. Herein, when the temperature is increased, these OH groups on the sodium alginate molecules will reduce Fe3+ ions to be Fe2+ ions; urea will decompose and release OH-, which with Fe3+ and Fe2+ ions forms the Fe3O4 crystalline nucleus and grow up on the coordination sites. Without the addition of sodium alginate, the final products are pure Fe2O3, even when other experimental conditions are kept the same (Figure 3d). With increasing the amount of sodium alginate from 0 to 5 mL and 15 mL, the products are mixtures of Fe2O3 and Fe3O4 (Figure 3c and Figure 3b, respectively). Until the volume of sodium alginate is increased to 25 mL or more, the product is pure Fe3O4 (Figure 3a). No external reductant was needed for Fe3+ reduction in the present method, further suggesting that sodium alginate itself is responsible for this reduction reaction. The hydroxyl groups in the repeating units of sodium alginate are hypothesized to be oxidized into carboxyl groups when FeIII is reduced to FeII, which can be referred to in the literature.16b To further confirm the transition process with the change of the amount of sodium alginate, the corresponding XPS data were shown in Figure 4A. In the absence of sodium alginate, we can see clearly the shakeup satellites in the 716-720 eV region (curve d in Figure 4A), which is characteristic for Fe3+ ions in Fe2O3.19 With the increase of the amount of sodium alginate (curves d and b), the peak of such shakeup satellites became weakened. This gave another piece of proof for the transition process.

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Figure 4. XPS Fe2p core-level spectra (A) of the samples a, b, and d (defined as in the caption of Figure 3 and denoted as curves a, b, and d, respectively), and O1s core-level spectra (B) of sample a.

Figure 2. Typical TEM image (A) and size distribution histogram (B) of the product.

Figure 5. Magnetization-hysteresis (M-H) loops of Fe3O4 nanoparticles measured at room temperature.

Figure 3. XRD patterns of (a) the as-prepared product, (b) sample obtained by decreasing the amount of 25.4 mM sodium alginate aqueous solution from 25 to 15 mL, (c) sample obtained by decreasing the amount of sodium alginate from 25 to 5 mL, and (d) sample obtained by decreasing the amount of sodium alginate from 25 to 0 mL under other identical conditions.

Magnetite differs from most other iron oxides in that it contains both divalent and trivalent iron. Its formula is written as Y[XY]O4 where X ) FeII, Y ) FeIII, and the brackets denote octahedral sites.20 To confirm the existence of both ions, a wellknown spot test is used.21 This method is based on the fact that FeII salts in acidic solutions react with R,R-phenanthroline to give a soluble, dark red complex. FeIII salts do not react under these conditions. This spot test was performed for the asprepared dried black powder, commercial Fe3O4, and commercial Fe2O3. The tests revealed a dark red color for the dried black powder, as well as for commercial Fe3O4. A colorless

solution was observed for commercial Fe2O3. This spot test provides more support for the identification of the black powder as Fe3O4.22 Figure 5 presents a hysteresis loop for Fe3O4 nanomaterials measured at room temperature. The hysteresis loop demonstrates a ferromagnetic behavior with the saturation magnetization (Ms) value about 62.1 emu/g, which is different from those reported for Fe3O4 nanomaterials.23 The remanent magnetic induction (Mr) and coercivity (Hc) values for our sample are about 8.9 emu/g and 93.6 Oe, both of which are lower than those of bulk Fe3O4.24 As we know, the effects of size, structure, and morphologies are concerned with the magnetic properties of the nanomaterials.23 Typical reasons for this include the reaction or complexation of the surface atoms of magnetic nanoparticles with surfactant, which may create a magnetically dead layer.25 With a significant fraction of surface atoms, any crystalline disorder within the surface layer may also lead to a significant decrease in the nanoparticle saturation magnetization. The underlying factor affecting the magnetic properties in our case needs further investigation.

Magnetic Iron Oxide Nanoparticle Green Synthesis Conclusion In summary, we have succeeded in synthesizing Fe3O4 nanoparticles using biopolymer-assisted green route. Here, biopolymer, sodium alginate, plays dual roles, reducing and stabilizing agent, in the formation of the product. Preliminary magnetic measurements exhibit evident ferromagnetic properties, which are expected to be applicable in high-density recording media in future nanodevices. The procedure that we report here, in comparison with common previous protocols reported in the literature, is a green, environment-friendly, and direct one-step process for the preparation of Fe3O4 nanoparticles. Acknowledgment. The authors are grateful to the National Natural Science Foundation of China (Grant No. 20571025) and Natural Science Foundation of Provincial Education Department of Henan (Grant 2008A150014) for financial support. References and Notes (1) (a) Zhou, Y.; Yu, S. H.; Wang, C. Y.; Zhu, Y. R.; Chen, Z. Y. AdV. Mater. 1999, 11, 850. (b) Li, L.; Zhang, Y.; Li, G. H.; Zhang, L. D. Chem. Phys. Lett. 2003, 378, 244. (c) Li, Y.; Li, C.; Cho, S. O.; Duan, G.; Cai, W. Langmuir 2007, 23, 9802. (d) Gao, S.; Zhang, H.; Liu, X.; Wang, X.; Sun, D.; Peng, C.; Zheng, G. Nanotechnology 2006, 17, 1599. (e) Gao, S.; Zhang, H.; Wang, X.; Mai, W.; Peng, C.; Ge, L. Nanotechnology 2005, 16, 1234. (f) Li, Y.; Lee, E. J.; Cho, S. O. J. Phys. Chem. C 2007, 111, 14813. (2) (a) Zhou, Y.; Antonietti, M. J. Am. Chem. Soc. 2003, 49, 14960. (b) Cao, B.; Cai, W.; Zeng, H. Appl. Phys. Lett. 2006, 88, 161101. (c) Li, L.; Wang, Y. W.; Huang, X. H.; Li, G. H.; Ang, R.; Zhang, L. D. Appl. Phys. Lett. 2006, 88, 103119. (d) Li, L.; Pan, S. S.; Dou, X. C.; Zhu, Y. G.; Huang, X. H.; Yang, Y. W.; Li, G. H.; Zhang, L. D. J. Phys. Chem. C 2007, 111, 7288. (e) Cao, B.; Cai, W.; Zeng, H.; Duan, G. J. Appl. Phys. 2006, 99, 073516. (f) Gao, S.; Zhang, H.; Wang, X.; Deng, R.; Sun, D.; Zheng, G. J. Phys. Chem. B 2006, 110, 15847. (g) Li, L.; Yang, Y. W.; Huang, X. H.; Li, G. H.; Zhang, L. D. J. Phys. Chem. B 2005, 109, 12394. (h) Li, Y.; Cai, W.; Duan, G.; Cao, B.; Sun, F.; Lu, F. J. Colloid Interface Sci. 2005, 287, 634. (3) (a) Li, L.; Yang, Y. W.; Li, G. H.; Zhang, L. D. Small 2006, 2, 548. (b) Gao, S.; Zhang, H.; Deng, R.; Wang, X.; Sun, D.; Zheng, G. Appl. Phys. Lett. 2006, 89, 123125. (c) Li, Y.; Huang, X. J.; Heo, S. H.; Li, C.; Choi, Y. K.; Cai, W. P.; Cho, S. O. Langmuir 2007, 23, 2169. (d) Zhou, Y.; Kogiso, M.; He, C.; Shimizu, Y.; Koshizaki, N.; Shimizu, T. AdV. Mater. 2007, 19, 1055. (e) Zhou, Y.; Ji, Q.; Masuda, M.; Kamiya, S.; Shimizu, T. Chem. Mater. 2006, 18, 403. (4) (a) Fang, X. S.; Ye, C. H.; Zhang, L. D.; Xie, T. AdV. Mater. 2005, 17, 1661. (b) Fang, X. S.; Ye, C. H.; Zhang, L. D.; Zhang, J. X.; Zhao, J. W.; Yan, P. Small 2005, 1, 422. (c) Li, Y.; Cai, W.; Duan, G. Chem. Mater. 2008, 20, 615. (5) (a) Leslie-Pelecky, D. L.; Rieke, R. D. Chem. Mater. 1996, 8, 1770. (b) Raj, K.; Moskowitz, R. J. Magn. Magn. Mater. 1990, 85, 233. (6) (a) Goya, G. F.; Berquo, T. S.; Fonseca, F. C. J. Appl. Phys. 2003, 94, 3520. (b) Matsunaga, T. Trends Biotechnol. 1991, 9, 91. (c) Black, C. T.; Murray, C. B.; Sandstrom, R. L.; Sun, S. Science 2000, 290, 1131. (d) BateG. In Ferromagnetic Materials, Recording Materials; Wohlfarth, E. D., Ed.; North-Holland: Amsterdam, The Netherlands1980; Vol. 2, p 381. (7) Raj, K.; Moskowitz, B.; Casciari, R. J. Magn. Magn. Mater. 1995, 149, 174. (8) Zeng, H.; Li, J.; Liu, J. P.; Wang, Z. L.; Sun, S. H. Nature 2002, 420, 395. (9) (a) Lu, Z. L.; Zou, W. Q.; Lv, L. Y.; Liu, X. C.; Li, S. D.; Zhu, J. M.; Zhang, F. M.; Du, Y. W. J. Phys. Chem. B 2006, 110, 23817. (b) Liao, Z. M.; Li, Y. D.; Xu, J.; Zhang, J. M.; Xia, K.; Yu, D. P. Nano Lett.

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