NMR detection of single-walled carbon nanotubes in solution.

The detection of nanotube carbons in solution by (13)C NMR is reported. The highly soluble sample was from the functionalization of (13)C-enriched single-walled carbon nanotubes (SWNTs) with diamine-terminated oligomeric poly(ethylene glycol) (PEG(1500N)). The ferromagnetic impurities due to the residual metal catalysts were removed from the sample via repeated magnetic separation. The nanotube carbon signals are broad but partially resolved into two overlapping peaks, which are tentatively assigned to nanotube carbons on semiconducting (upfield) and metallic (downfield) SWNTs. The solid-state NMR signals of the same sample are similarly resolved. Mechanistic and practical implications of the results are discussed.