Oxidation of single-walled carbon nanotubes in dilute aqueous solutions by ozone as affected by ultrasound

A clean and simple wet chemical process using dilute aqueous ozone (03) solution with or without ultrasound (US) was used to functionalize single-walled carbon nanotubes (SWCNTs). Both 03 and O-3/US treatments greatly increased the stability of SWCNTs in water. Results of X-ray photoelectron spectroscopy (XPS) showed that the surface oxygen to carbon atomic ratio increased by more than 600% after 72 h Of 03 treatment. Moreover, the effective particle size of SWCNTs was reduced from the initial 4400 to similar to 300 and similar to 150 nm, after 24 h Of 03 and O-3/US treatment, respectively. The zeta potential of treated SWCNTs decreased from 3.0 to -35.0 mV (at pH 4) after 2 h of treatment with both 03 and O-3/US. Based on the XPS results, the oxidation pathway was proposed: at the onset of the oxidation reaction, the C=C double bond was first converted to -C-OH which was then oxidized to -C=O and O=C-OH concurrently. Oxidation reactions could be described well with first order expressions. Treatment time controlled the extent of surface oxidation and subsequently the stability and dispersion of SWCNTs in water. (c) 2008 Elsevier Ltd. All rights reserved.