Effect of surface cleaning and functionalization of nanotubes on gas adsorption

Abstract

We present adsorption isotherm results for methane at $77\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ on multiwalled carbon nanotubes exposed to oxygen plasma for varying periods of time. We found a sharpening of the adsorption steps in the high pressure region of isotherms measured on nanotubes exposed to oxygen plasma for $24\phantom{\rule{0.3em}{0ex}}\mathrm{h}$. Transmission electron microscopy characterization and Raman spectroscopic measurements performed on the nanotube samples provide evidence that the appearance of the step is a consequence of surface modification of the nanotubes resulting from the removal of amorphous carbon, generation of defects, and surface functionalization of the nanotubes due to prolonged plasma exposure. Our results suggest that application of this procedure could lead to tunable nanotube surfaces with controllable adsorption properties.