State Key Laboratory of Pollution Control and Resource Reuse, Shanghai Institute of Pollution Control and Ecological Security, Tongji Advanced Membrane Technology Center, School of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, Tennessee 37235-1831, United States.
Environ Sci Technol. 2024 Sep 3;58(35):15874-15884. doi: 10.1021/acs.est.4c07510. Epub 2024 Aug 22.
Nanofiltration (NF) membranes play a critical role in separation processes, necessitating an in-depth understanding of their selective mechanisms. Existing NF models predominantly include steric and Donnan mechanisms as primary mechanisms. However, these models often fail in elucidating the NF selectivity between ions of similar dimensions and the same valence. To address this gap, an innovative methodology was proposed to unravel new selective mechanisms by quantifying the nominal dielectric effect isolated from steric and Donnan exclusion through fitted pore dielectric constants by regression analysis. We demonstrated that the nominal dielectric effect encompassed unidentified selective mechanisms of significant relevance by establishing the correlation between the fitted pore dielectric constants and these hindrance factors. Our findings revealed that dehydration-induced ion-membrane interaction, rather than ion dehydration, played a pivotal role in ion partitioning within NF membranes. This interaction was closely linked to the nondeformable fraction of hydrated ions. Further delineation of the dielectric effect showed that favorable interactions between ions and membrane functional groups contributed to entropy-driven selectivity, which is a key factor in explaining ion selectivity differences between ions sharing the same size and valence. This study deepens our understanding of NF selectivity and sheds light on the design of highly selective membranes for water and wastewater treatment.
纳滤 (NF) 膜在分离过程中起着关键作用，因此需要深入了解其选择性机制。现有的 NF 模型主要包括空间和道南机制作为主要机制。然而，这些模型在解释具有相似尺寸和相同价态的离子之间的 NF 选择性时往往会失效。为了解决这一差距，提出了一种创新的方法，通过回归分析拟合孔径介电常数来量化从空间和道南排斥中分离出来的标称介电效应，从而揭示新的选择性机制。我们通过建立拟合孔径介电常数与这些阻碍因子之间的相关性，证明了标称介电效应包含了与离子尺寸和价态相同的离子之间具有重要相关性的未识别选择性机制。我们的研究结果表明，在 NF 膜中，离子与膜官能团之间的有利相互作用导致了熵驱动的选择性，这是解释具有相同尺寸和价态的离子之间离子选择性差异的关键因素，而不是离子脱水，在离子分配中起着关键作用。进一步分析介电效应表明，这种相互作用与水合离子的不可变形部分密切相关。这项研究加深了我们对 NF 选择性的理解，并为水和废水处理中高度选择性膜的设计提供了思路。
