Morphological control of ferromagnetic nanotubes: wall thickness, diameter, and length

Although magnetic nanotubes exhibit many potential applications ranging from drug or gene delivery to bioseparation, catalysis, electromagnetic or magneto-optic devices, and many others, their developments are at relatively infant stages. Recently, we utilized biologically active phospholipids (PLs) as templates to produce ferromagnetic magnetite/carbon/magnetite concentric nanotubes (FMNTs) in which simple synthetic efforts resulted in the formation of an electrically conductive carbon layer sandwiched between ferromagnetic magnetite phases, thus offering magnetic and electric attributes combined in one nanotube. Since the geometry and size of each of the FMNT components are critical factors in controlling desirable magnetic and electrical properties, control of the wall thickness as well as the diameter and length is of particular interest. This study reports the development of a simple synthetic approach to control the geometry of FMNTs by changing the concentration levels of the reactants and solvent conditions. Using this approach we synthesized concentric carbon-magnetite nanotubes with a variable thickness of 6, 10, and 60 nm conductive carbon layers and 12 to 45 nm magnetic magnetite layers. As a result, saturation magnetization values could be incrementally tuned from 40 to 79 emu g−1.