Abstract As a novel two-dimensional material, graphitic carbon nitride (g-C3N4) has proved to be promising for separation membrane. However, the assessment of nanoporous g-C3N4 membrane for efficient desalination process has not been systematically investigated yet. In this work, we designed three g-C3N4 nanopores with different shapes based on the membrane unit structure. The non-equilibrium molecular dynamics simulations were used to study the molecular mechanism of saline water permeation through the nanoporous g-C3N4 membranes. The relationship between water flow rate and external pressure was in good agreement with the classical hydrodynamics. Meanwhile, we observed that the local water diffusion coefficient increased as the enlargement of nanopore sizes, indicating that the nano-effect may also rule the water permeation. For desalination purposes, the designed g-C3N4 nanoporous membrane entirely rejected ions while maintaining a considerable water permeability of 14.9 L/cm2/day/MPa. By analyzing the trajectories of ions passing through the nanopores, we found that the configurational shape could divide one nanopore into several sub-regions, and specific ones may determine the desalination performance of the nanoporous membrane. This work unveils the molecular insights into the desalination process of nanoporous g-C3N4 membrane and further provides useful guidelines for the design of next generation desalination membranes with complex nanopore structures.

中文翻译：

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用于海水淡化的纳米多孔石墨氮化碳膜的分子动力学模拟导向合理设计

摘要 作为一种新型二维材料，石墨氮化碳（g-C3N4）已被证明在分离膜方面具有广阔的应用前景。然而，用于高效脱盐过程的纳米多孔 g-C3N4 膜的评估尚未得到系统研究。在这项工作中，我们基于膜单元结构设计了三个不同形状的 g-C3N4 纳米孔。非平衡分子动力学模拟用于研究盐水通过纳米多孔 g-C3N4 膜渗透的分子机制。水流量和外部压力之间的关系与经典流体动力学非常吻合。同时，我们观察到局部水扩散系数随着纳米孔径的增大而增加，表明纳米效应也可能支配水的渗透。出于脱盐目的，设计的 g-C3N4 纳米多孔膜完全排斥离子，同时保持了 14.9 L/cm2/day/MPa 的可观水渗透率。通过分析离子穿过纳米孔的轨迹，我们发现配置形状可以将一个纳米孔分成几个子区域，具体的子区域可以决定纳米孔膜的脱盐性能。这项工作揭示了对纳米多孔 g-C3N4 膜脱盐过程的分子见解，并进一步为具有复杂纳米孔结构的下一代脱盐膜的设计提供了有用的指导。我们发现配置形状可以将一个纳米孔分成几个子区域，具体的区域可能决定纳米孔膜的脱盐性能。这项工作揭示了对纳米多孔 g-C3N4 膜脱盐过程的分子见解，并进一步为具有复杂纳米孔结构的下一代脱盐膜的设计提供了有用的指导。我们发现配置形状可以将一个纳米孔分成几个子区域，具体的区域可能决定纳米孔膜的脱盐性能。这项工作揭示了对纳米多孔 g-C3N4 膜脱盐过程的分子见解，并进一步为具有复杂纳米孔结构的下一代脱盐膜的设计提供了有用的指导。