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, we show 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) were 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 4-fold higher than the flux of the state-of-the-art boron nitrate nanotubes. Further, the high performance of (9,8) s/c was also reproducible when embedded in lipid bilayers as synthetic high-water flux porins. Given the increasing availability of high-purity CNTs, our findings provide valuable guides for realizing novel CNT-enhanced nanofluidic systems.

From Behavior of Water on Hydrophobic Graphene Surfaces to Ultra-Confinement of Water in Carbon Nanotubes

“…Pascal et al reported that for armchair CNTs with increased diameters, water molecules present a bulk-like behavior when the CNT diameter is above 1.4 nm, while an ice-like water framework is characterized for CNT diameters ranging from 1.1 to 1.2 nm [ 41 ]. In a recent theoretical study, molecular dynamic simulations revealed that network formation in the form of a water chain occurred when molecules were successively arranged in CNT with diameters around 1.1 nm [ 39 ], which is in accordance with several previous studies [ 34 , 42 , 43 , 44 ]. Shayeganfar et al reported, thanks to ab initio computations, that a water tube shape is observed when confined in CNTs and BNNTs.…”

“…Simulations and experiments with water confined inside carbon nanotubes can reveal unusual physical properties, especially for diffusion behavior and viscosity. These properties strongly depend on the geometrical characteristics of the CNT (tube diameter and chirality) and can directly affect water distribution inside the cage leading to unusual water performance in a confined space [ 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. Several studies have shown for CNTs and BNNTs an ordered structure of water molecules essentially related to the metallicity and diameter of the tube.…”

Fast transport of water in carbon nanotubes: a review of current accomplishments and challenges

“…Moreover measuring the tube diameter, controlling the pressure difference to drive the fluid, and finally performing the nanolitre volume experiments are cumbersome procedures that may also lead to scattered data in experiments. Even subtle differences in the electronic properties of nanochannels can bring about a significant alteration in the slippage of fluid within these confinements [76,[127][128][129][130]. The atomic structure of a CNT determined by its chirality largely influences its electronic properties [131][132][133][134][135].…”

Thermodynamic Barrier for Nanoparticle Penetration into Nanotubes

“…Along this path, the force on the NP on each xoz plane remains balanced. This treatment has been used to study fluid penetration behaviors. − We set the axis direction of the CNT as the z direction, and thus the graphene sheet is placed on the x – y plane. The calculations of PMFs are performed on 3D grids, and the nanotube is placed at the center of a rectangular box.…”