Selective removal of metallic single-walled carbon nanotubes by microwave-assisted treatment of SWCNTs with nitronium ions

Abstract

A facile and rapid technique for the selective removal of metallic single-walled carbon nanotubes (M-SWCNTs) was developed by microwave-assisted treatment of SWCNTs with nitronium ions. Upon exposure to microwaves, M-SWCNTs homogeneously dispersed in organic solution were prone to react with an electron acceptor reagent, i.e., positively charged nitronium ions as compared to their counterpart, namely, semiconducting (S)-SWCNTs. The well-functionalized M-SWCNTs were separated and removed from residual S-SWCNTs by ultracentrifugation and filtration. The resulting material contained highly enriched S-SWCNTs, the proportion of which increased from approximately 62 mol% in as-received SWCNTs to nearly 90 mol%. The effectiveness in removing M-SWCNTs was confirmed by the resonant Raman spectra and UV-vis-NIR absorption spectra. The microwave-enhanced separation mechanism was discussed as well.