title: Diameter and metallicity dependent redox influences on the separation of single-wall carbon nanotubes.
abstract: 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)H2O <==> SWNT + nH(+) + (n/4)O2, amine-induced pH changes as well as variations in H2O and O2 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 (I(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.
authors.affiliation: Nanomaterials Optoelectronics Laboratory, Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA.
authors.forename: Sang N
authors.initials: SN
authors.lastname: Kim
authors.forename: Zhengtang
authors.initials: Z
authors.lastname: Luo
authors.forename: Fotios
authors.initials: F
authors.lastname: Papadimitrakopoulos
mesh_terms: D005591:Chemical Fractionation / Q000379:methods*; D008422:Materials Testing; D008670:Metals / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D037742:Nanotubes, Carbon / Q000737:chemistry*; D010084:Oxidation-Reduction; D010316:Particle Size; D012996:Solutions; D055672:Static Electricity
chemical_list: D008670:Metals; D037742:Nanotubes, Carbon; D012996:Solutions