Li Shuang, Zhang Xinke, Liu Yuzhen, Su Jiaye
Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, Jiangsu, 210094, China.
MIIT Key Laboratory of Semiconductor Microstructure and Quantum Sensing, Nanjing University of Science and Technology, Nanjing, Jiangsu, 210094, China.
Phys Chem Chem Phys. 2022 Jun 1;24(21):13245-13255. doi: 10.1039/d2cp00025c.
Inspired by the high water permeability and excellent salt rejection of hourglass-shape aquaporin channels, asymmetric channels have attracted increasing attention in recent years. In this work, we use molecular dynamics simulations to explore the transport of an ionic solution through asymmetric graphene channels under a pressure difference. We observe an interesting asymmetric desalination phenomenon when changing the channel geometry. Specifically, the fluxes of water and ions in the convergent direction are larger than those in the divergent direction; however, the salt rejection rates exhibit an opposite behavior. This is because the strong steric effect of the channel tip results in a direct ion rejection. Moreover, in the convergent transport direction, the ions can deposit inside the channel near the tip, resulting in an ion blockage effect that ultimately leads to an abnormal descending order of fluxes of water and ions with the channel size. The ion density peaks near the tip and the asymmetric occupancy distribution provide a direct validation for the ion blockage phenomenon. We also observed flux rectification for both water and ions, depending on the pressure and channel size. These results provide a fundamental understanding of the unique ionic transport in asymmetric graphene channels, which should have great implications for designing desalination devices.
受沙漏形水通道蛋白通道的高水渗透性和优异的拒盐性能启发，近年来非对称通道引起了越来越多的关注。在这项工作中，我们使用分子动力学模拟来研究离子溶液在压力差作用下通过非对称石墨烯通道的传输。当改变通道几何形状时，我们观察到一种有趣的非对称脱盐现象。具体而言，水和离子在收敛方向上的通量大于发散方向上的通量；然而，拒盐率表现出相反的行为。这是因为通道尖端的强空间效应导致直接的离子排斥。此外，在收敛传输方向上，离子可以沉积在通道尖端附近内部，导致离子阻塞效应，最终导致水和离子通量随通道尺寸出现异常的降序排列。尖端附近的离子密度峰值和不对称占据分布为离子阻塞现象提供了直接验证。我们还观察到水和离子的通量整流，这取决于压力和通道尺寸。这些结果为非对称石墨烯通道中独特的离子传输提供了基本理解，这对设计脱盐装置应该具有重要意义。
