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<p>To meet performance requirements, the next generation of gas separation membranes will need <i>both</i> high gas permeability and selectivity, attainable if we could coax adsorbates to minimize random Brownian motion and produce direction-specific diffusion along a desired axis. In this atomistic modeling study, we detail how direction-specific diffusion of CO<sub>2</sub> can be achieved in chiral hexagonal boron nitride nanotubes (hBNNTs) by means of a non-Knudsen diffusion mechanism. Our findings detail how this mechanism of diffusion is driven by interactions with the tube walls and enables the CO<sub>2</sub> molecules to diffuse along the nanotube’s z-axis with minimized collisions and directional changes. hBNNTs with chiral indices exhibit CO<sub>2</sub> diffusion rates faster than non-chiral tubes of comparable and larger diameters. Of the hBNNTs studied, a (7,3) tube appears to be ideally sized (3.7 Å radius) exhibiting CO<sub>2</sub> diffusion that is 3.4 times faster than diatomic N<sub>2</sub>. Applying this mechanism of diffusion to hypothetical sheet membranes prepared with aligned chiral (7,3) hBNNTs results in membranes with a calculated CO<sub>2</sub>/N<sub>2</sub> permselectivity of 170 and a CO<sub>2</sub> permeability limit of nearly 1.35 ×10<sup>7</sup> Barrer, readily surpassing the Robeson upper bound for CO<sub>2</sub>/N<sub>2</sub> separations.</p>

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Direction-specific enhanced diffusion of CO2 in chiral hexagonal boron nitride nanotubes

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月28日

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  • Manh-Thuong Nguyen,
  • David J. Heldebrant,
  • Jian Liu,
  • Abhoyjit S. Bhown,
  • Zhijie Xu

摘要

To meet performance requirements, the next generation of gas separation membranes will need both high gas permeability and selectivity, attainable if we could coax adsorbates to minimize random Brownian motion and produce direction-specific diffusion along a desired axis. In this atomistic modeling study, we detail how direction-specific diffusion of CO2 can be achieved in chiral hexagonal boron nitride nanotubes (hBNNTs) by means of a non-Knudsen diffusion mechanism. Our findings detail how this mechanism of diffusion is driven by interactions with the tube walls and enables the CO2 molecules to diffuse along the nanotube’s z-axis with minimized collisions and directional changes. hBNNTs with chiral indices exhibit CO2 diffusion rates faster than non-chiral tubes of comparable and larger diameters. Of the hBNNTs studied, a (7,3) tube appears to be ideally sized (3.7 Å radius) exhibiting CO2 diffusion that is 3.4 times faster than diatomic N2. Applying this mechanism of diffusion to hypothetical sheet membranes prepared with aligned chiral (7,3) hBNNTs results in membranes with a calculated CO2/N2 permselectivity of 170 and a CO2 permeability limit of nearly 1.35 ×107 Barrer, readily surpassing the Robeson upper bound for CO2/N2 separations.