Chemical method of filling carbon nanotubes with magnetic material

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Abstract

A versatile chemical method is used to fill multi-wall carbon nanotubes (MWCNTs) with magnetic material. The process appears to open up tips of 100% of MWCNTs that are observed but the filling yield is rather low. The filling yield improved greatly by introducing metal chelating polymer, chitosan, in the nanotubes. Mössbauer measurements of the filled MWCNTs suggest the presence of magnetic and non-magnetic phases of Fe nanoparticles. The hyperfine magnetic field of the magnetic phase increased from its room temperature value of 182–251 kOe at 20 K.

Introduction

After 31 years from their first synthesis by Endo and co-workers in 1976 [1], and 16 years from their comprehensive and detailed characterization by Iijima [2] in 1991, the saga to impregnate carbon nanotubes (CNTs) and multi-wall carbon nanotubes (MWCNTs) with different types of applications related materials has continued. Filling CNTs was pioneered by Ajayan and Iijima; they filled CNTs with molten lead [3] and later with molten vanadium oxide [4]. This method of nanocapillarity was also used to fill CNTs with molten silver nitrate [5] and with sulfur, selenium, and cesium [6]. A major difficulty in filling single-walled (SW) CNTs is the low dimensionality of the tube diameter, which is close to 1 nm. Another difficulty is the fact that the driving forces of nanocapillarity are not well understood. The low-dimensionality issue is generally overcome in the case of MWCNTs where the tube diameter could range from 10 to 30 nm even though the driving forces of capillary filling are similar to that of SWCNTs. This has led to the successful filling of MWCNTs by magnetic materials using various methods. For example, ferrite nanowires were synthesized by vigorous stirring of an aqueous solution, containing cobalt and iron nitrates together with MWCNTs [7] and MWCNTs were also filled with nickel and uranium oxides using a chemical method [8]. Here, we describe a chemical approach to fill MWCNTs by a magnetic material in order to develop synthesized nanosize magnets. Nanomagnets are important as vital component in nano-electromechanical systems (NEMS) and have potential applications ranging from medicine to defense [9], [10]. The objective of this work is to synthesize inside MWCNTs, an alternate permanent magnetic material, Sm2Fe17Nx. In the past, Sm2Fe17Nx has been prepared by various methods and characterized with several methods. Some of the methods employed to prepare this promising permanent magnet include arc-melting followed by nitrogenation [11], [12], induction heating of the metal ingots followed by nitrogenation [13], melt spinning of arc-melted ingots followed by nitogenation [14], magnetron sputtering [15], aerosol deposition method [16], [17], [18], spark plasma sintering [19], and mechanical alloying [20], [21]. In this work, a nano-sized Sm2Fe17Nx was encapsulated inside of a CNT using a versatile chemical method.

Section snippets

Experiment

Research grade commercial MWCNTs were obtained from Nano-Lab company (www.nano-lab.com). The reported specifications of the sample are: 95% purity, 20–50 nm outer diameter, and 5–20 μm average length. The following procedure was used to synthesize magnetic nanoparticles inside the MWCNTs: (1) MWCNTs were suspended in nitric acid containing hydrated iron nitrate (Fe(NO3)3·9H2O) which is ∼5% (w/w) and hydrated samarium nitrate (Sm(NO3)3·6H2O); (2) the suspension was refluxed for 4.5 h in silicon oil

Results and discussion

The TEM image of a network of MWCNTs filled with magnetic matter (Fig. 1) taken at 150 kV accelerating potential and at 100,000 magnification is shown. A limited number of fillings occurred as shown in the figure. The darker spots in the figure were analyzed with energy-dispersive X-ray (EDX) attached to the TEM and all were found to be iron-containing particles of length ranging from 5 to 30 nm. Although this result is tantalizing, the yield of partially filled nanotubes has been small, the

Conclusions

We have presented a unique and versatile chemical approach to fill MWCNTs with magnetic nanoparticles of Sm2Fe17Nx. The approach appears to have a great promise although the yield is low. The various attempts in the past to prepare the potentially important alternate permanent magnetic material, Sm2Fe17Nx, in the bulk form are discussed alongside the present effort to synthesize a nanoscale alternate permanent magnetic material, Sm2Fe17Nx, for the first time at this low dimension.

Acknowledgment

The first author would like to thank Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, for their support, Contract no. W1813LT-5006-7056.

References (22)

  • A. Oberlin et al.

    J. Crystal Growth

    (1976)
  • N. Keller et al.

    Carbon

    (2004)
  • N. Yoshida et al.

    Phys. B-Condens. Matter

    (2002)
  • M. Katter et al.

    J. Magn. Magn. Mat.

    (1992)
  • K. Kobayashi et al.

    J. Magn. Magn. Mat.

    (2002)
  • T. Maki et al.

    J. Alloys Compds.

    (2006)
  • Z. Dongtao et al.

    J. Rare Earths

    (2006)
  • X.C. Kou

    J. Alloys Compds.

    (1998)
  • D. Seifu et al.

    J. Magn. Magn. Mat.

    (1998)
  • S. Iijima

    Nature

    (1991)
  • P.M. Ajayan et al.

    Nature

    (1993)
  • Cited by (0)

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