Enhancement of microplasma-based water-solubilization of single-walled carbon nanotubesusing gas bubbling in water

Abstract

The authors have previously proposed a novel technique for the preparation ofwater-soluble carbon nanotubes (CNTs) using microplasma generated by a pulsed streamerdischarge in water. This paper describes an improvement in the method of themicroplasma-based CNT solubilization process by the use of gas bubbling in water.Oxygen, argon and nitrogen were used as bubbling gas in order to clarify the effectsof the gas species on the single-walled CNT (SWCNT) solubilization efficiency.Ultraviolet–visible absorption spectra of the SWCNT suspensions revealed that theSWCNT solubility was increased by more than two times by using gas bubbling togetherwith microplasma treatment. No significant difference was observed among thethree gas species tested. Fourier transform infrared (FTIR)spectroscopy and x-rayphotoelectron spectroscopy (XPS) analysis showed that the number of –OH groups,introduced on the SWCNT surface by the microplasma treatment, was increasedby gas bubbling. Optical emission measurements also showed that the numberof highly oxidative oxygen and hydrogen radicals, which were generated by themicroplasma, was also increased by gas bubbling. These results indicate that gasbubbling has positive effects on microplasma-based SWCNT solubilization as aresult of enhanced radical formation and functionalization of the SWCNT surface.