Metallicity-Dependent Ultrafast Water Transport in Carbon Nanotubes

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 Å vs (9,7)_s/c , 10.88 Å; (9,8)_s/c , 11.53 Å vs (10,7)_met , 11.59 Å; and (9,9)_met , 12.20 Å vs (10,8)_s/c , 12.23 Å) 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.