The enantiomer-level isolation of single-walled carbon
nanotubes
(SWCNTs) in high concentration and with high purity for nanotubes
greater than 1.1 nm in diameter is demonstrated using a two-stage
aqueous two-phase extraction (ATPE) technique. In total, five different
nanotube species of ∼1.41 nm diameter are isolated, including
both metallics and semiconductors. We characterize these populations
by absorbance spectroscopy, circular dichroism spectroscopy, resonance
Raman spectroscopy, and photoluminescence mapping, revealing and substantiating
mod-dependent optical dependencies. Using knowledge of the competitive
adsorption of surfactants to the SWCNTs that controls partitioning
within the ATPE separation, we describe an advanced acid addition
methodology that enables the fine control of the separation of these
select nanotubes. Furthermore, we show that endohedral filling is
a previously unrecognized but important factor to ensure a homogeneous
starting material and further enhance the separation yield, with the
best results for alkane-filled SWCNTs, followed by empty SWCNTs, with
the intrinsic inhomogeneity of water-filled SWCNTs causing them to
be worse for separations. Lastly, we demonstrate the potential use
of these nanotubes in field-effect transistors.
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