Evidence of thermal closing of atomic-vacancy holes in single-wall carbon nanohorns

Control of atomic-vacancy holes, which are the only pathways to internal hollow nanospaces, in walls of carbon nanostructures such as carbon nanotubes (CNTs) is crucial for material incorporation in and release from the nanospaces. We describe here a new approach to controlling the holes, that is, closing the holes using metal-free CNTs, single-wall carbon nanohorns. N₂ adsorption isotherm measurements explicitly showed that holes tended to close when the nanohorns were heated at 1200°C in Ar, as evidenced by a decrease of pore volume. Theoretical calculations indicated that the holes at the tips of the nanohorns closed but those in the sidewalls did not.