BNnanotubes coated with uniformly distributed Fe3O4nanoparticles: novel magneto-operable nanocomposites

Abstract

An ethanol-thermal process was developed for in situ formation of dense and uniformly distributed Fe₃O₄ nanoparticles on the surfaces of multi-walled boron nitride nanotubes (BNNTs). The morphology, structures and compositions of the synthesized nanocomposites were characterized by X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), high-angle annular dark-field (HAADF) STEM, selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS). Magnetic measurements using a superconducting-quantum-interference-device (SQUID) magnetometer showed that the nanocomposites exhibited normal ferromagnetism at low temperature (5 K), while they behaved as soft magnets with negligible coercivity, H_c, and remanance, M_r, at room temperature. Such magnetic behavior was attributed to the superparamagnetic nature of Fe₃O₄ nanoparticles attached to BNNTs. By virtue of the dense and uniform magnetic Fe₃O₄ coatings, the BNNTs could be physically manipulated in a relatively low magnetic field. The novel BNNT-based magnetic nanocomposites may find a wide range of potential applications in magnetorheological devices, microelectromechanical systems (MEMS), magnetic-targeted drug delivery and boron neutron capture therapy (BNCT).