(448j) Synthesis of Fe3O4 and Au-Fe3O4 Dumbbell Nanoparticles By Thermal Decomposition Using Different Reducing Agents

Over the last decade, magnetic nanomaterials have gained a lot of interest in the fields of data storage, hyperthermia therapy, magnetic resonance imaging (MRI) as contrast agent, etc. Au nanoparticles are available for various applications due to their optical and catalytic properties. Synthesis of multifunctional nanomaterials such as core/shell, patchy, janus or flower-like nanoparticles have attracted much more attention in recent years. Especially dumbbell-shaped nanoparticles facilitate the attachment of different functionalization of each particle due to its asymmetric surface. These structures usually have significant properties such as optical, magnetic, plasmonic, catalytic, etc. and these outstanding properties provide usage in many diverse platforms [1]. Also, biocompatible Au-Fe₃O₄ dumbbell nanoparticles are advantageous to be used in biomedical applications. Furthermore, easy modification of iron oxide and gold sides of Au-Fe₃O₄dumbbell nanoparticles allows them to obtain bifunctional nanostructures.

In the literature, stabilization and synthesis of iron oxide nanoparticles with narrow size distribution have been studied in detail [2-4]. Preparation of Fe₃O₄ and Au-Fe₃O₄ nanoparticles was achieved at high-temperatures and reduction of Fe(acac)₃ (acac= acetylcetonate) was performed by using 1, 2-hexadecanediol or 1, 2-tetradecanediol [3, 4]. In this study, Fe₃O₄ nanoparticles have been synthesized via thermal decomposition of iron precursor and Au-Fe₃O₄ dumbbell nanoparticles were obtained with nucleation and growth of iron oxide nanoparticles over different sized AuNPs. In order to synthesize monodisperse Fe₃O₄ andAu-Fe₃O₄dumbbell nanoparticles via thermal decomposition method, we used an alternative reducing agent which has not been used before. In order to analyze the morphology, size and size distribution of the particles, High Resolution Transmission Electron Microscopy (HR-TEM) analysis was performed. Also, Dynamic Light Scattering (DLS), Vibrating Sample Magnetometer (VSM), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR) were used to implement a detailed characterization of nanoparticles.

To obtain monodisperse Fe₃O₄ NPs, Fe(acac)₃ was used as precursor, oleylamine and oleic acid as stabilizing agents and a reducing agent, which contains one hydroxyl and a carboxyl group. According to TEM images, 6 nm sized magnetite nanoparticles have narrow size distribution and high crystallinity. Monodisperse Au nanoparticles were synthesized according to previous reports [5]. Synthesis of 5 and 9 nm sized gold nanoparticles was achieved by the reduction reaction of HAuCl₄ solution. Afterwards, these oleylamine capped gold nanoparticles were used to obtain different sized Au-Fe₃O₄ dumbbell nanoparticles. To perform the synthesis of dumbbell nanoparticles, reaction solution in 1-octadecene was heated at 200°C under a flow of N₂. Then under a blanket of N₂, AuNPs was added to the solution and the solution was heated to reflux. After cooled down to room temperature, the particles were washed with iso-propanol, centrifuged and redispersed into 1-octadecene or hexane.

TEM images of Fe₃O₄ NPs showed that the particle size was 6 nm and Au-Fe₃O₄ dumbbell nanoparticles were 5-15 nm and 9-15 nm. From DLS measurements, it was seen that hydrodynamic radii of Fe₃O₄ NPs and dumbbell nanoparticles were 7.4 nm and 11 nm respectively in 1-octadecene solvent. It can conclude that the results of TEM and DLS analyses were consistent with each other due to attraction of solvent and ligands on the surface of particles. Five XRD peaks at 30.1°, 35.5°, 42.5°, 52.5°, and 62.1° were observed which can be assigned as the fcc Fe₃O₄. Moreover, characteristic peaks for Au at 38.12°, 44.4°, 64.6° and 77.5° were obtained for dumbbell NPs.

We have investigated the influence of reducing agents in the synthesis of iron oxide nanoparticles. Results showed that high-temperature synthesis of Fe₃O₄ and Au-Fe₃O₄nanoparticles can be performed successfully.

REFERENCES

[1] H. Yu, M. Chen, P. M. Rice, S. X. Wang, R. L. White, S. Sun, "Dumbbell-like Bifunctional Auâ??Fe₃O₄Nanoparticles" Nano Letters, 5, 379-382, 2005.

[2] Z. Xu, C. Shen, Y. Hou, H. Gao, S. Sun, "Oleylamine as Both Reducing Agent and Stabilizer in a Facile Synthesis of Magnetite Nanoparticles", Chem. Mater., 21, 1778â??1780, 2009.

[3] S. Sun, H. Zeng, "Size-Controlled Synthesis of Magnetite Nanoparticles" J. Am. Chem. Soc., 124, 8204-8205, 2002.

[4] M. Lattuada, T. A. Hatton, "Functionalization of Monodisperse Magnetic Nanoparticles", Langmuir, 23, 2158-2168, 2007.

[5] B. Wu, H. Zhang, C. Chen, S. Lin, and N. Zheng, "Interfacial Activation of Catalytically Inert Au (6.7 nm)-Fe₃O₄ Dumbbell Nanoparticles for CO Oxidation", Nano Res, 2, 975-983, 2009.