A diameter-selective chiral separation of single-wall carbon nanotubes using nitronium ions

We propose a method for a diameter-selective removal of metallic single-walled carbon nanotubes (m-SWCNTs) from semiconducting (s-) ones. Our separation technique is capable of 100% separation of semiconducting and metallic nanotubes for small diameter nanotubes. We dispersed SWCNT powder by sonication in a mixed solution of tetramethylene sulfone and chloroform, where nitronium ions were well dissolved. 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 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 m-SWCNTs were perfectly destroyed by nitronium ions and drained away as amorphous carbons. This preferable adsorption became obscured for nanotubes with diameters greater than 1.1 nm. The effectiveness of removing m-SWCNTs was confirmed by the transmission electron microscope observations, x-ray photo-emission spectra, resonant Raman spectra, and absorption spectra.