Cholic acid covalently bound to multi-walled carbon nanotubes: Improvements on dispersion stability

Despite the vast volume of literature regarding the interaction between carbon nanotubes and surfactants, the effect of the covalent attachment of an amphiphilic surfactant based on a biomimetic approach to multiwalled carbon nanotubes (MWCNT) has not been explored. In this report, the functionalization of the MWCNT surface with cholic acid by a chemical route is described. A three-step MWCNT chemical modification route was carried out and the properties of the intermediate and final materials were evaluated employing X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM),atomic force microscopy (AFM) and zeta potential measurements. After functionalization, the MWCNT showed a facial bio-amphiphilic behavior; improving the dispersion stability as compared to commercial and oxidized MWCNT. The resulting material preserved the pristine multi-walled structure and originated surprisingly stable dispersions in aqueous and organic polar and low-polarity solvents.