Carbon nanotubes present an important molecular-sized conduit because of their hydrophobic interiors and enahnced flow for water and other species. We have compared the the ionic transport of Li+ and the molecular transport of methanol through a 2.25-nm-diameter, 200-µm-long single-walled carbon nanotube. As the applied electric field was increased, the Li+ pore-blocking current was found to generally increase in the range of 1–6 pA. Likewise, above the observed threshold voltage of 700 mV, methanol exhibited pore blocking and the pore-blocking current also increased with applied field in the same range as for Li+, 1–6 pA. This similarity is explained by a simple model comparing the volumes of methanol and hydrated Li+. The dwell times for Li+ transport varied linearly with inverse electric field from 200 and 1200 ms for applied voltages between 200 and 1000 mV, indicating an electrophoretic mobility of 1.6 × 10–7 m2 V–1 s–1, in agreement with previous studies of alkali metal ions in SWNT nanopores. Conversely, the dwell times for methanol remained relatively constant at an average of 88 ms. The average velocity of the methanol molecules was found to be 2.3 × 10–3 m/s, which is too fast for diffusion and in agreement with predictions of a model developed for the electro-osmotic flow of neutral molecules through a small-diameter nanopore. This work is the first to measure the transport properties of neutral molecules through narrow-diameter nanopores and potentially useful information for systems such as fuel cells, in which motion through nanoconfined environments is very important.

Motion of Li+ and methanol through a 2.25-nm-diameter single-walled carbon nanotube

254th National Meeting (2017)

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