Separation of Small-Diameter Single-Walled Carbon Nanotubes in One to Three Steps with Aqueous Two-Phase Extraction

An aqueous two-phase extraction (ATPE) technique capable of separating small-diameter single-walled carbon nanotubes in one, two, or at the most three steps is presented. Separation is performed in the well-studied two-phase system containing polyethylene glycol and dextran, but it is achieved without changing the global concentration or ratio of cosurfactants. Instead, the technique is reliant upon the different surfactant shell around each nanotube diameter at a fixed surfactant concentration. The methodology to obtain a single set of surfactant conditions is provided, and strategies to optimize these for other diameter regimes are discussed. In total, 11 different chiralities in the diameter range 0.69-0.91 nm are separated. These include semiconducting and both armchair and nonarmchair metallic nanotube species. Titration of cosurfactant suspensions reveal separation to be driven by the pH of the suspension with each (n,m) species partitioning at a fixed pH. This allows for an (n,m) separation approach to be presented that is as simple as pipetting known volumes of acid into the ATPE system.