A diameter-dependent separation of semiconducting from metallic single-wall carbon nanotubes by using nitronium ions

We have reported the density-functional calculations of NO2 adsorption on single-walled carbon nanotube (SWCNTs) walls. We find that NO2 adsorption is strongly electronic structure-and strain-dependent. The NO2 adsorption on metallic nanotubes (m-SWCNTs) was energetically more favorable than that on semiconducting nanotubes (s-SWCNTs) and furthermore the adsorption became less stable with increasing diameters of nanotubes. The adsorption barrier height shows similar dependence on the electronic structure and diameter to the adsorption energy. On the base of our theoretical model, we have found a method for a diameter-selective removal of metallic single-walled carbon nanotubes (m-SWCNTs) from semiconducting (s-) ones by stirring or sonication SWCNT powder in tetramethylene sulfone (TMS)/chloroform solution with nitronium hexafluoroantimonate (NO2SbF6: NHFA) and nitronium tetrafluoroborate (NO2BF4: NTFB). Positively charged nitronium ions were intercalated into nanotube bundles, where the intercalation was promoted also by the counter ions. Nitronium ions selectively attacked the sidewall of the m-SWCNTs due to the abundant presence of electron density at the Fermi level, thus yielding stronger binding energy compared to the counterpart s-SWCNTs. The s-SWCNTs were left on the filter after filtration, whereas the m-SWCNTs were disintegrated and drained away as amorphous carbons. The effectiveness of removing m-SWCNTs was confirmed by the resonant Raman spectra and absorption spectra. (C) 2006 Elsevier B.V. All rights reserved.