Adsorption studies of a krypton film adsorbed on catalytically synthesized multiwalled carbon nanotubes: Dependence on the nanotube morphology

Krypton adsorption isotherms on multiwalled carbon nanotubes have been measured at 77 K and compared to those obtained under the same conditions on exfoliated graphite. The results are discussed in the light of the nanotube morphology, as determined by transmission electron microscopy and electron energy loss spectroscopy. The isotherms exhibit two steps representative of successive monomolecular layer condensations on the external walls of nanotubes, instead of five steps on graphite. The monolayer condensation pressures are higher than those observed with graphite, which probably limits their number at krypton bulk condensation pressure. Near the completion of the first condensed layer, a second transition towards a phase of higher density occurs, the nature of which is discussed.