Separation of Single-Walled Carbon Nanotubes Using the Amino Acid Surfactant N-Cocoyl Sarcosinate

Understanding the interaction nature between dispersants and single-walled nanotubes (SWNTs) is crucial for separating SWNTs. In this work, it was found that amide groups of the amino acid surfactant N-cocoyl sarcosinate (N-CS) molecules could be anchored on SWNTs by a π–π-stacking interaction, offering the opportunity for alkyl chains to closely adsorb on SWNTs under an hydrophobic effect, with the winding directions found to be adjusted to match the chiral angles of SWNTs, which made N-CS molecules not only uniformly wrap around SWNTs but also recognize the chiral angle of SWNTs, guaranteeing the effective individualization and the multiple separation of SWNTs. Resorting to the scalable technique of density gradient ultracentrifugation, the mixture of SWNTs was first separated by diameter because the amount of N-CS adsorbed on SWNTs is proportional to the surface area of SWNTs. Afterward, when sodium dodecylsulfate (SDS) was added as the cosurfactant, a different number of SDS molecules were inserted into the SWNT/N-CS assemblies to enhance the density difference among SWNTs with different chiral angles, ensuring the separation of SWNTs by chiral angles. On the basis of the recognition of SWNTs by dispersants, the difference among SWNTs could be effectively established, providing a precondition for the accurate separation of SWNTs.