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

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 [CzCnMIm]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 (Copt) of [CzCnMIm]Br. Compared with [CnMIm]Br, [CzCnMIm]Br was more effective with the smaller Copt and more individual CNTs, reflecting the effect of the carbazole moiety. The adsorption of [CzCnMIm]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.

Graphical abstractCNTs were dispersed in water using a surface-active ionic liquid with a polycyclic aromatic moiety and a long hydrophobic chain.Figure optionsDownload full-size imageDownload high-quality image (118 K)Download as PowerPoint slideResearch highlights► Surfactants enhanced the solubilization of CNTs in water. ► Polycyclic compounds enhanced the solubilization of CNTs in water. ► [CzCnMIm]Br contains a polycyclic aromatic moiety and a long hydrophobic chain. ► [CzCnMIm]Br shows a strong ability to disperse CNTs in water.