期刊
ENVIRONMENTAL SCIENCE & TECHNOLOGY
卷 -, 期 -, 页码 -出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.2c04772
关键词
ion separation; Arrhenius approach; energy barrier; ion dehydration; molecular simulations
资金
- National Key Research and Development Program of China [2019YFC0408200]
- National Natural Science Foundation of China [52100103]
This study elucidated the mechanisms governing the selective transport of polyamide NF membranes by using a series of monovalent cations. It was found that the selective transport of a single cation was not correlated with hydrated radius or hydration energy, but rather dominated by the transmembrane energy barrier of the pairing anion. Molecular dynamics simulations revealed that the distinct hydration structure of cations was the primary origin of the energy barrier difference. Furthermore, membrane grafting modification achieved a significant enhancement in ion separation efficiency by enlarging the energy barrier difference of dominant ions.
Nanofiltration (NF) membranes are playing in-creasingly crucial roles in addressing emerging environmental challenges by precise separation, yet understanding of the selective transport mechanism is still limited. In this work, the underlying mechanisms governing precise selectivity of the polyamide NF membrane were elucidated using a series of monovalent cations with minor hydrated radius difference. The observed selectivity of a single cation was neither correlated with the hydrated radius nor hydration energy, which could not be explained by the widely accepted NF model or ion dehydration theory. Herein, we employed an Arrhenius approach combined with Monte Carlo simulation to unravel that the transmembrane process of the cation would be dominated by its pairing anion, if the anion has a greater transmembrane energy barrier, due to the constraint of anion-cation coupling transport. Molecular dynamics simulations further revealed that the distinct hydration structure was the primary origin of the energy barrier difference of cations. The cation having a larger incompressible structure after partial dehydration through subnanopores would induce a more significant ion-membrane interaction and consequently a higher energy barrier. Moreover, to validate our proposed mechanisms, a membrane grafting modification toward enlarging the energy barrier difference of dominant ions achieved a 3-fold enhancement in ion separation efficiency. Our work provides insights into the precise separation of ionic species by NF membranes.
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