Long-Term Stable Dispersion of Multiwalled Carbon Nanotubes by Peroxydisulfate upon Ultrasonication Activation.

Poor dispersibility of carbon nanotubes greatly hinders their practical applications. Herein, a long-term stable dispersion of multiwalled carbon nanotubes (MWCNTs) in peroxydisulfate (PDS) is achieved. MWCNTs at 40 mg L are completely dispersed by PDS upon ultrasonication (US/PDS) within 64 min and a stable dispersion is maintained at least 20 days. Mechanistically, US created defects on the nanomaterial and PDS-origin free radicals attacked these defects to introduce O-containing moieties (─OH and ─COOH). Interestingly, dispersion efficiency of MWCNTs by US/PDS initially at pH 7 and 3.8 is comparable, but lower than that initially at pH 12. Both •OH and SO are produced under alkaline condition, while SO is the dominant free radicals initially at pH 7 and 3.8 during the whole dispersion period. Stronger dispersion of MWCNTs initially at pH 12 resulted from greater amounts of O-containing moieties mainly in ─OH (46.32%) rather than ─COOH (24.19%) form. This differential more strongly promotes MWCNTs-water interaction via hydrogen bonding, thereby enhancing the dispersion. Notably, no significant mass loss of MWCNTs occurred during dispersion. Overall, the developed method achieves long-term stable dispersion of MWCNTs in a manner that can significantly extend their applications.