Synthesis of hermetically-sealed graphite-encapsulated metallic cobalt (alloy) core/shell nanostructures

Hermetically-sealed graphite encapsulated cobalt core/shell nanostructures have been prepared by the CO Boudouard reaction using in situ generated cobalt as the catalyst. Only core/shell nanostructures were obtained, rather than a mixture of cobalt nanoparticles with carbon nanotubes or nanofibers. The magnetic cobalt nanoparticles are highly crystallized with a hexagonal-close packed crystal phase (average diameter of ca. 25 nm) and coated with an 8–9 nm thick graphitic shell. The nanostructures have a high saturation magnetization of 85 emu/g and can be easily separated by an external magnet. The creation of the hermetically-sealed graphitic shell not only keeps the magnetic cobalt nanoparticles from reacting with strong mineral acids, but also has biocompatibility and makes further functionalization easy. A pseudo-planar aromatic molecule, xylenol orange, was used as the model molecule because it can be absorbed on the graphitic shell mainly by π–π stacking interaction. This was confirmed by Raman and ultraviolet–visible spectroscopy. Graphite encapsulated Fe2Co and Fe0.64Ni0.36 alloy core/shell nanostructures were also fabricated by this method.