Diameter and Metallicity Dependent Redox Influences on the Separation of Single-Wall CNTs

Recently, it has become possible to separate and/or enrich fractions of single-wall carbon nanotubes (SWNTs) according to type (or otherwise termed "metallicity") and diameter (d t). Exposure of acid-treated SWNTs to amines has shown such separation. In this contribution, we describe the underlying mechanism for this separation and provide a better description of the physicochemical properties of charge-stabilized SWNT dispersions in polar aprotic media, such as N,N-dimethylformide (DMF). With the establishment of the reversible nature of the redox chemistry, SWNT n+ + (n/2)H 2O ⇌ SWNT + nH + + (n/4)O 2, amine-induced pH changes as well as variations in H 2O and O 2 concentration in DMF are shown to cause differential partial-reduction trends according to d t and metallicity. At a pH of 10, the (n,m)-SWNTs that resist complete reduction to their undoped state remain in suspension while the rest that lose their charges populate the precipitate. These d t- and metallicity-dependent redox and separation trends are modeled based on the Gibbs free energy and charge loss as it pertains to the (n,m)-dependent SWNT integrated density of states (l DOS) across the corresponding pH-induced redox jump. At a given redox potential, the relative placement of the van Hove singularities and continuum determines the amount of charge left on various (n,m)-SWNTs that governs their relative dispersion stability in DMF. © 2005 American Chemical Society