Metal-semiconductor sorting of large-diameter single-wall carbon nanotubes by pH-dependent binding to a hydrophobic-interaction adsorbent

Abstract

A batch adsorption method for sorting large-diameter single-walled carbon nanotubes (SWCNTs) is described that employs a hydrophobic-interaction chromatography (HIC) adsorbent and a single nonionic surfactant. The method is based on the creation of significant differences between metallic and semiconductor SWCNTs in their adsorption affinity to a HIC adsorbent. These differences are then used for the efficient separation of the electronic forms of large-diameter SWCNTs. To gain a better understanding of the mechanism involved, the effects of various HIC adsorbents under different pH conditions were studied. The results obtained demonstrate the importance of the type and density of the hydrophobic functional groups on the adsorbent in determining the relative strength of the adsorptive interactions for various electronic forms of SWCNTs. The results also show the effects of negatively charged adventitious functional groups on the nanotube on the relative hydrophobicity of the nanotubes. The method described here is implemented using widely-available HIC adsorbents, and only requires simple titration with HCl or NaOH to adjust the pH. Furthermore, the method is potentially suitable to be performed using liquid chromatography with a packed adsorbent column and with a liquid-phase pH gradient in order to achieve high-resolution separations.