Coating and filling of carbon nanotubes with homogeneous magnetic nanoparticles

doi:10.1016/j.matlet.2006.07.163

Materials Letters

Volume 61, Issues 8–9, April 2007, Pages 1805-1808

https://doi.org/10.1016/j.matlet.2006.07.163 Get rights and content

Abstract

Magnetic multi-walled carbon nanotube (MWCNT) composites were obtained by decoration of metal oxide nanoparticles on or in carbon nanotubes. The method involved the dispersion of the carbon nanotubes in iron pentacarbonyl Fe(CO)₅ followed by vacuum thermolysis and subsequent oxidation. The magnetic iron oxide particle deposition was always homogeneous and could be controlled selectively on the outer, inner, or both surfaces of MWCNTs by using different MWCNTs. Since the hollow channels remained intact, these MWCNT based composites could find special applications in cellular delivery systems.

Introduction

Magnetic nanocomposites have potential applications in various areas such as magnetic recording, magnetic data storage devices, toners and inks for xerography, and magnetic resonance imaging. Therefore, studies on magnetic nanocomposites, especially on magnetic carbon nanotubes (CNTs), are rapidly expanding. Recently, Kozhuharova and co-workers synthesized aligned Fe–Co alloy-filled MWCNTs on silicon substrates via the pyrolysis of ferrocene/cobaltocene mixtures [1]. Stoffelbach and co-workers decorated MWCNTs with magnetic nanoparticles by adding a solution of positively charged Fe₃O₄ nanoparticles to the negatively charged MWCNTs [2]. Korneva proposed a new method to produce magnetic tubes by filling MWCNTs with ferrofluid [3]. Sun fabricated magnetic carbon nanotube composites by the decomposition of ferrocene on MWCNTs at different temperatures [4]. Various magnetic materials including iron [5], iron oxide [6], nickel [7], cobalt [8], CoFe₂O₄ [9] and FeCo [10] encapsulated in CNTs have been prepared. However, it is still difficult to uniformly modify CNTs with accessible cavities, which is essential for applying magnetic carbon nanotube composites in cellular delivery systems [11].

In this paper, Fe(CO)₅, a volatile organometallic compound, was used as the precursor to fabricate magnetic MWCNT composites with hollow tubular cavities. The MWCNTs with homogeneous γ-Fe₂O₃ magnetic particles on both the inner and outer surfaces were obtained by vacuum thermolysis and subsequent oxidation. The as-prepared γ-Fe₂O₃–MWCNT hybrids were polycrystalline with diameters of above 100 nm and lengths up to several micrometers. Magnetic measurements showed that the as-obtained MWCNT composites displayed ferrimagnetic properties at room temperature.

Section snippets

Experiment

Two types of MWCNTs were used in this study. Sample A was bought from Shenzhen Nanotech Port Co. Ltd (China), whereas sample B was provided by GSI Creos (Japan). The samples were purified via the following procedure: the commercial samples were sonicated with concentrated HNO₃ (68%) for 2 h, neutralized with NaOH, filtered, washed with distilled water, dried in a vacuum oven and then calcined at 450 °C for 15 min. The resultant sample A was sinuous and highly entangled, it was characterized by

Results and discussion

Fig. 1 showed the XRD patterns of the as-prepared MWCNT composites. According to the diffraction peaks in this figure, the one at 2θ = 26.3° could be indexed as the (002) reflection of graphite, while the other ones corresponded to both maghemite (γ-Fe₂O₃) and magnetite (Fe₃O₄). Although γ-Fe₂O₃ and Fe₃O₄ showed similar patterns in XRD, they could be efficiently distinguished by Raman spectroscopy. Fe₃O₄ had a main band centered at 667 cm^− 1 whereas γ-Fe₂O₃ showed three broad bands in the range of

Conclusion

In summary, we presented a simple and inexpensive approach for the modification of MWCNTs by maghemite nanoparticles. The MWCNTs with small inner diameters (5–10 nm) were densely coated with γ-Fe₂O₃ nanoparticles on the outer surface. And the MWCNTs with larger diameter (60–200 nm) were decorated with discrete nanoparticles on both the inner and outer surfaces and without hurting their hollow channels. These decorated materials will find applications in many fields as magnetic materials. And

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