Aqueous dispersion of carbon nanotubes by chlorine dioxide oxidation

The poor solubility and dispersibility of single-walled carbon nanotubes (SWCNTs) in aqueous media remain critical limitations for their practical application because conventional oxidative treatments typically require harsh conditions that degrade the nanotube structure. Here, we report a simple and scalable method for dispersing SWCNTs in water via chlorine dioxide (ClO₂˙)-mediated oxidation under ambient conditions. The treatment selectively introduced oxygenated functionalities-including hydroxy, carbonyl, and carboxy groups-onto the CNT surface while preserving the tubular framework, as confirmed by transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy analyses. The resulting dispersions exhibited long-term colloidal stability without the need for surfactants, supported by a strongly negative ζ potential (-41.6 mV). Importantly, electronic conductivity was largely maintained: the resistivity of oxidized CNT films was only threefold higher than that of sodium cholate-dispersed CNTs (0.045 vs. 0.016 Ω cm at 25 °C), with <10% variation between 25 and 50 °C. This unique balance between enhanced aqueous dispersibility and preserved charge transport underscores ClO₂˙ oxidation as a green and effective strategy for producing water-processable CNTs, showing promise for applications in pharmaceutical drugs, printable electronics, functional composites, energy storage, and sensing.