Diverse Combinations of Multiple Surfactants for Chirality Recognition and Separation of Carbon Nanotubes

Compared with the single surfactants adopted in earlier studies, mixed surfactants exhibit superior capabilities in terms of chirality recognition and separation of single-wall carbon nanotubes (SWCNTs) because of their unique synergistic interactions in various liquid-phase separation methods. In this study, we designed diverse combinations of multiple surfactants and comprehensively investigated their chirality selectivity. The results of systematic separation experiments based on gel chromatography demonstrated a novel ternary-surfactant system, which has not been reported thus far but possesses significantly higher selectivity for both the diameter and chiral angle of SWCNTs than other combinations do. Through precise concentration modulation of ternary surfactants for controlling the chirality-selective adsorption and desorption of SWCNTs on a gel medium, we successfully separated near-zigzag single-chirality SWCNTs with ultrahigh and near-perfect optical chirality purity (∼100%), thereby reaching the highest level reported to date. Furthermore, the results of spectroscopic titration experiments and first-principle calculations revealed that the higher chirality selectivity originates from the much higher affinity of the present ternary-surfactant system for near-zigzag SWCNTs than for near-armchair SWCNTs, providing a greater understanding of the molecular interactions between surfactants and SWCNTs. Our findings address the issue of the greater difficulty in producing small-chiral angle SWCNTs and facilitate their applications in single-photon sources, optoelectronic devices, and bioimaging.