Dispersion of carbon nanotubes by carbazole-tailed amphiphilic imidazolium ionic liquids in aqueous solutions

Abstract

Surfactants with a polycyclic aromatic moiety and a long hydrocarbon chain, carbazole-tailed amphiphilic imidazolium ionic liquids 1-[ n-( N-carbazole)alkyl]-3-methylimidazolium bromide [CzC n MIm]Br ( n = 10 and 12), were designed to disperse carbon nanotubes (CNTs) in aqueous solutions. UV–vis–NIR spectra were performed to determine the dispersion of CNTs and the optimal concentration ( C opt) of [CzC n MIm]Br. Compared with [C n MIm]Br, [CzC n MIm]Br was more effective with the smaller C opt and more individual CNTs, reflecting the effect of the carbazole moiety. The adsorption of [CzC n MIm]Br molecules on CNTs was investigated by zeta-potential, surface tension, fluorescence, and 1H NMR. Having zeta-potentials higher than 15 mV contributed to the long-term stability of aqueous CNT dispersions. The significant fluorescence quenching and the upfield shift of carbazole protons support the π– π stacking interaction between carbazole moieties and the π-networks of CNTs. Meanwhile, the upfield shift of imidazolium protons indicates the cation– π interaction between the imidazolium ions and the π-networks of CNTs.