Molecular insights into charged nanofiltration membranes: Structure, water transport, and water diffusion
Molecular insights into charged nanofiltration membranes: Structure, water transport, and water diffusion
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DOI：
10.1016/j.memsci.2021.120057
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发表时间：
2021-11
影响因子：
9.5
通讯作者：
Suwei Liu;S. Ganti-Agrawal;S. Keten;Richard M. Lueptow
中科院分区：
文献类型：
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作者：
Suwei Liu;S. Ganti-Agrawal;S. Keten;Richard M. Lueptow
虽然基于聚酰胺的反渗透（RO）和纳滤（NF）膜广泛用于脱盐和水净化，但膜孔隙率和电荷对水传输的影响仍有待在分子水平上充分理解。在这里，我们使用分子动力学（MD）来建立56个不同的哌嗪基NF膜模型，其覆盖膜密度范围为0.78 g cm− 3至1.08 g cm− 3。这些膜模型具有各种电荷浓度，对应于4-11的pH范围。结果表明，膜电荷与膜密度或水的传输不是单调相关的。相反，水传输主要由膜的物理性质决定，具体地，膜密度，带电荷的膜端基和抗衡离子引起膜的溶胀，这往往会增加通量。此外，水分子在膜内的扩散系数与膜密度密切相关。即使在分子模拟中采用的大压力下，水的扩散率也与跨膜压力无关。因此，跨膜压力使水分子通过膜的无规行走的方向偏置，导致水通量，但不改变它们在膜内的总体流动性。这些发现揭示了膜性质和水传输之间的关系，为荷电膜，以及提供新的见解NF膜的结构在分子尺度上。
While polyamide-based reverse osmosis (RO) and nanofiltration (NF) membranes are widely used for desalination and water purification, the influence of membrane porosity and charge on water transport remains to be fully understood at a molecular level. Here we use molecular dynamics (MD) to build 56 distinct piperazine-based NF membranes models, which cover a membrane density range of 0.78 g cm− 3 to 1.08 g cm− 3. These membrane models have various charge concentrations, corresponding to a pH range of 4–11. Results indicate that membrane charge is not monotonically correlated with the membrane density or the water transport. Instead, the water transport is mostly determined by the membrane’s physical properties, specifically, the membrane density, with charged membrane end groups and counterions causing swelling of the membrane, which tends to increase flux. Additionally, the diffusion coefficient of water molecules within the membrane is strongly correlated with the membrane density. The diffusivity of water is independent of the transmembrane pressure, even under the large pressures employed in molecular simulations. Thus, the transmembrane pressure biases the direction of the random walk of water molecules through the membrane resulting in a water flux but does not alter their overall mobility within the membrane. These findings shed light on the relationship between membrane properties and water transport for charged membranes, as well as providing new insights into the structure of NF membranes at a molecular scale.