Liu Suwei, Foo Zihao, Lienhard John H, Keten Sinan, Lueptow Richard M
Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208, USA.
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Membranes (Basel). 2025 Jun 18;15(6):184. doi: 10.3390/membranes15060184.
Polyamide membranes, such as nanofiltration (NF) membranes, are widely used for water purification. However, the mechanisms of solute transport and solute rejection due to solute charge interactions with the membrane remain unclear at the molecular level. Here, we use molecular dynamics simulations to examine the transport of single-solute feeds through charged nanofiltration membranes with different membrane charge concentrations of COO- and NH+2 resulting from the deprotonation or protonation of polymeric end groups according to the pH level that the membrane experiences. The results show that Na+ and Cl- solute ions are better rejected when the membrane has a higher concentration of negatively charged groups, corresponding to a higher pH, whereas CaCl2 is well rejected at all pH levels studied. These results are consistent with those of experiments performed at the same pH conditions as the simulation setup. Moreover, solute transport behavior depends on the membrane functional group distribution. When COO- functional groups are concentrated at membrane feed surface, ion permeation into the membrane is reduced. Counter-ions tend to associate with charged functional groups while co-ions seem to pass by the charged groups more easily. In addition, steric effects play a role when ions of opposite charge cluster in pores of the membrane. This study reveals solute transport and rejection mechanisms related to membrane charge and provides insights into how membranes might be designed to achieve specific desired solute rejection.
聚酰胺膜，如纳滤（NF）膜，广泛用于水净化。然而，在分子水平上，溶质与膜之间因电荷相互作用导致的溶质传输和溶质截留机制仍不清楚。在此，我们使用分子动力学模拟来研究单溶质进料在带电荷的纳滤膜中的传输情况，这些膜具有不同浓度的COO-和NH+2电荷，这是由于聚合物端基根据膜所处的pH值去质子化或质子化而产生的。结果表明，当膜带有更高浓度的带负电基团（对应更高的pH值）时，Na+和Cl-溶质离子的截留效果更好，而CaCl2在所有研究的pH水平下都能被很好地截留。这些结果与在与模拟设置相同的pH条件下进行的实验结果一致。此外，溶质的传输行为取决于膜官能团的分布。当COO-官能团集中在膜进料表面时，离子向膜内的渗透会减少。反离子倾向于与带电荷的官能团结合，而共离子似乎更容易通过带电荷的基团。此外，当相反电荷的离子在膜孔中聚集时，空间位阻效应会起作用。本研究揭示了与膜电荷相关的溶质传输和截留机制，并为如何设计膜以实现特定的所需溶质截留提供了见解。
