Metallicity-Dependent Ultrafast Water Transport in Carbon Nanotubes

Abstract

Carbon nanotubes (CNTs) with hydrophobic and atomically smooth inner channels are promising for building ultrahigh-flux nanofluidic platforms for energy harvesting, health monitoring, and water purification. Conventional wisdom is that nanoconfinement effects determine water transport in CNTs. Here, using full-atomistic molecular dynamics simulations, it is shown that water transport behavior in CNTs strongly correlates with the electronic properties of single-walled CNTs (metallic (met) vs semiconducting (s/c)), which is as dominant as the effect of nanoconfinement. Three pairs of CNTs (i.e., (8,8)(met), 10.85 angstrom vs (9,7)(s/c), 10.88 angstrom; (9,8)(s/c), 11.53 angstrom vs (10,7)(met), 11.59 angstrom; and (9,9)(met), 12.20 angstrom vs (10,8)(s/c), 12.23 angstrom) are used to investigate the roles of diameter and metallicity. Specifically, the (9,8)(s/c) can restrict the hydrogen-bonding-mediated structuring of water and give the highest reduction in carbon-water interaction energy, providing an extraordinarily high water flux, around 250 times that of the commercial reverse osmosis membranes and approximately fourfold higher than the flux of the state-of-the-art boron nitrate nanotubes. Further, the high performance of (9,8)(s/c) is also reproducible when embedded in lipid bilayers as synthetic high-water flux porins. Given the increasing availability of high-purity CNTs, these findings provide valuable guides for realizing novel CNT-enhanced nanofluidic systems.