Removal of internal caps during hydrothermal treatment of bamboo-like carbon nanotubes and application of tubes in phenol adsorption.

Experimental data on the influence of the hydrothermal opening procedure conditions on the polarity, surface chemical composition and adsorption properties of multiwalled carbon nanotubes toward phenol are reported. The enthalpy of immersion measurements is reported, and it is shown that with the rise in burn-off, a progressive rise in nanotube surface polarity was observed. Using XPS data, the surface groups are identified. Moreover, by the analysis of HRTEM images and the values of enthalpy of immersion in benzene, it is shown that the removal of internal caps takes place mainly at higher burn-offs (larger than ca. 15%). Obtained series of nanotubes is tested in phenol adsorption, and calculated differential enthalpies of adsorption values are in the range of those determined for adsorption on graphite. Basing on obtained data, it is shown that the state of phenol in first layer is close to solid for adsorption on closed tubes and progressively approaches the state of supercooled liquid after tube opening and with the rise in burn-off.