Elsevier

Applied Surface Science

Volume 253, Issue 5, 30 December 2006, Pages 2611-2617
Applied Surface Science

Oleic acid coating on the monodisperse magnetite nanoparticles

https://doi.org/10.1016/j.apsusc.2006.05.023Get rights and content

Abstract

Monodisperse magnetite nanoparticles provide a more factual model to study the interface interactions between the surfactants and magnetic nanoparticles. Monodisperse magnetite nanoparticles of 7 and 19 nm coated with oleic acid (OA) were prepared by the seed-mediated high temperature thermal decomposition of iron(III) acetylacetonate (Fe(acac)3) precursor method. Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) reveal that the OA molecules were adsorbed on the magnetic nanoparticles by chemisorption way. Analyses of transmission electron microscopy (TEM) shows the OA provided the particles with better isolation and dispersibility. Thermogravimetric analysis (TGA) measurement results suggest that there were two kinds of different binding energies between the OA molecules and the magnetic nanoparticles. The cover density of OA molecules on the particle surface was significantly various with the size of magnetite nanoparticles. Magnetic measurements of the magnetite nanoparticles show the surface coating reduced the interactions among the nanoparticles.

Introduction

Magnetic nanoparticles have been of great interests because of their extensive applications in high-density data storage, biochemistry, hyperthermia, in vivo drug delivery, MR contrast reagent [1], [2], [3], [4], [5], [6], [7]. To apply magnetic nanoparticles in various potential fields, it is very important to control the size and shape, and to keep the thermal and chemical stability by surface modification [8]. This modification generally will play a key role on the properties and applications of the magnetic nanoparticles in bio-solutions or tissue environments [9]. The magnetic structure of the surface layer usually is greatly different from that in the body of nanoparticle, and the magnetic interactions in the surface layer could have a notable effect on the magnetic properties of nanoparticles [10], [11]. Understanding the interaction between the surfactant and the nanoparticle is critical and essential to synthesis and application of nanoparticles.

Oleic acid (OA) is a commonly used surfactant to stabilize the magnetic nanoparticles synthesized by the traditional coprecipitation method, and some studies [12], [13] have proved that the strong chemical bond formed between the carboxylic acid and the amorphous iron and amorphous iron oxide nanoparticles. However, it is hardly to know the interaction between the single nanoparticle and surfactant from the “compositive” results given by these kinds of size and shape widely dispersed nanoparticles systems. For the nanoparticles with different sizes, the surface effects are significantly various due to the difference of volume fraction of surface atoms within the whole particle. Excitingly, the chemical routes of synthesis monodisperse magnetic nanoparticles by thermal decomposition method have obtained outstanding results [14], [15], [16], [17]. These monodisperse nanoparticles coated with OA may provide a factual system to get the exact information of the interaction and adsorption model at the interface. In the present work, monodisperse Fe3O4 nanoparticles with diameter of 7 and 19 nm were synthesized by the seed-mediated high temperature thermal decomposition of iron(III) acetylacetonate (Fe(acac)3) precursor method. The chemical structure of the surfactant adsorbed on the magnetite nanoparticles has been identified, and the model of OA molecules adsorbed on the nanoparticles surface was discussed.

Section snippets

Experimental

Magnetite nanoparticles were prepared according to the Sun's method [16]. Such nanoparticles then serve as seeds to grow larger nanoparticles in the seed-mediated growth process. It is worth to note that the OA as the surfactant added in the reaction mixture before the Fe3O4 nuclei produced, but not as usual way that the surfactant was modified after the Fe3O4 synthesised [18], [19], [20].

In a typical synthesis, Fe(acac)3 (2 mmol), 1,2-hexadecanediol (10 mmol), benzyl ether (20 ml), oleic acid (6 

Results and discussion

XRD patterns in Fig. 1 reveal the nanocrystal nature of the two samples. The position and relative intensity of all peaks match well with standard Fe3O4 powder diffraction data, indicating that each sample is Fe3O4 crystal.

To understand the adsorption mechanism of the OA on the surface of Fe3O4 nanoparticles, Fourier transform infrared measurements were carried out on the pure oleic acid and the composite Fe3O4 nanoparticles coated with OA. Fig. 2 shows the typical FTIR spectrum of the pure

Conclusions

Monodisperse magnetite nanoparticles coated with OA provided a factual system to get the exact information about the interaction and adsorption model at interface. Study shows the adsorption of OA molecules on the nanoparticles were by chemisorption in all cases, and the OA molecular coated on the particles surface with a single layer structure. Furthermore, the two distinct of surfactant desorbed on the particle surface implied that there were two kinds of different binding energies between

Acknowledgments

The authors are grateful to the 863 Hi-Tech Research and Development Program (2002AA302210) and Shanghai Nano Program (0249 nm071) for financial support.

References (29)

  • R. Hergt et al.

    J. Magn. Magn. Mater.

    (2004)
  • R.H. Kodama

    J. Magn. Magn. Mater.

    (1999)
  • L. Fu et al.

    Appl. Surf. Sci.

    (2001)
  • A.K. Gupta et al.

    J. Mater. Sci.-Mater. Med.

    (2004)
  • M. Johannsen et al.

    J. Endourol.

    (2004)
  • G.X. Li et al.

    J. Appl. Phys.

    (2003)
  • H.B. Shen et al.

    Chin. Sci. Bull.

    (2003)
  • H. Zeng et al.

    Nano Lett.

    (2004)
  • V.F. Puntes et al.

    Science

    (2001)
  • D.K. Kim et al.

    Chem. Mater.

    (2003)
  • A.T. Ngo et al.

    Eur. Phys. J. B

    (1999)
  • C.R. Vestal et al.

    J. Am. Chem. Soc.

    (2003)
  • N.Q. Wu et al.

    Nano Lett.

    (2004)
  • G. Kataby et al.

    Langmuir

    (1999)
  • Cited by (0)

    View full text