Individual single-walled nanotubes and hydrogels made by oxidative exfoliation of carbon nanotube ropes

Single-walled carbon nanotubes were oxidized by a technique previously developed for the oxidation of graphite to graphite oxide (GO). This process involves treatment with concentrated H₂SO₄ containing (NH₄)₂S₂O₈ and P₂O ₅, followed by H₂SO₄ and KMnO₄. Oxidation results in complete exfoliation of nanotube ropes to yield individual oxidized tubes that are 40-500 nm long. The C:O:H atomic ratio of vacuum-dried oxidized nanotubes is approximately 2.7:1.0:1.2. XPS and IR spectra show evidence for surface O - H, C = O, and COOH groups. The oxidized nanotubes slowly form viscous hydrogels at unusually low concentration (≥0.3 wt %), and this behavior is attributed to the formation of a hydrogen-bonded nanotube network, The oxidized tubes bind readily to amine-coated surfaces, on which they adsorb as smooth and dense monolayer films. Thin films of the oxidized nanotubes show ohmic current-voltage behavior, with resistivities in the range of 0.2-0.5 Ω-cm.