Covalent organic frameworks (COFs) have received considerable attention in nanofiltration due to their tunable structures. While reducing the thickness to decrease the transport resistance at a nanometer scale, some factors would significantly reduce the desalination performance of COFs. Herein, the transport behavior as a function of layer number was investigated for TpPa-(OMe) COFs with nonequilibrium molecular dynamics simulations. With an increasing in the layer number, the ion rejection is enhanced from 50 % to nearly 80 % and then remains constant despite further increasing in the number of layers. From PMFs, it is discovered that the interfacial part makes a major contribution to the rejection. At this situation, while the thickness of the COF is smaller than the diameter of the ion hydration shell, the Mg only overcome a less energy to strip off the small part of water molecules in hydration shell to enter the pore, leading a smaller ion rejection.

中文翻译：

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通过超薄共价有机框架纳米片揭示界面和内部对流体传输行为的影响

共价有机骨架（COF）由于其可调节的结构而在纳滤领域受到广泛关注。虽然减小厚度以降低纳米尺度的传输阻力，但一些因素会显着降低COF的海水淡化性能。在此，通过非平衡分子动力学模拟研究了 TpPa-(OMe) COF 的传输行为随层数的变化。随着层数的增加，离子排斥率从 50% 增强到接近 80%，然后尽管层数进一步增加，离子排斥率仍保持恒定。从 PMF 中，我们发现界面部分对排斥反应做出了主要贡献。在这种情况下，当COF的厚度小于离子水化壳的直径时，Mg仅克服较少的能量来剥离水化壳中的小部分水分子进入孔隙，从而导致较小的离子排斥。