Selectivity and polarization in water channel membranes: lessons learned from polymeric membranes and CNTs
Selectivity and polarization in water channel membranes: lessons learned from polymeric membranes and CNTs
复制标题
水通道膜的选择性和极化：从聚合物膜和碳纳米管中汲取的经验教训
DOI：
10.1039/c8fd00054a
复制
发表时间：
2018
影响因子：
3.4
通讯作者：
Freger, Viatcheslav
中科院分区：
文献类型：
--
作者：
Freger, Viatcheslav
水通道被自然界用来移动纯水穿过细胞膜，同时选择性地排斥盐。目前，合成通道成功地模拟了水的渗透，但即使是最好的通道，例如碳纳米管（CNT）和氧化石墨烯堆，仍然达不到选择性目标。本文分析了可能有助于提高和控制盐截留率的因素，从传统膜和碳纳米管的经验教训的基础上。首先，它强调了提高离子自能（介电机制）的重要性，这表明使通道既狭窄又被低介电环境包围是高选择性的关键。相比之下，单独的孔电荷是不够的，但它可能有助于提高和调整离子排斥，只要在低介电孔中增强的非平均场效应，例如离子缔合和吸附，特别是H+和OH−离子，在通道设计中得到正确理解和解决。其次，分析了浓差极化（CP）的作用，发现在孤立的通道或微小的膜中，CP水平明显较低。然而，扩散场的几何形状应该改变，并且CP应该在包含密集间隔的通道阵列的宏观膜中急剧增加。如果在膜设计中没有适当解决，则在按比例放大的基于通道的膜中增加的CP水平可能显著损害观察到的选择性，并且需要将选择性目标重新设定为甚至更具挑战性的值。这些观点可能有助于指导未来高性能人工水道的发展及其在下一代水净化膜中的应用。
Water channels are employed by nature to move pure water across cell membranes while selectively rejecting salts. At present, synthetic channels successfully mimic water permeation, yet even the best channels, such as carbon nanotubes (CNTs) and graphene oxide stacks, still fall short of the selectivity target. The present paper analyzes factors that may help to enhance and control salt rejection based on the lessons learned from conventional membranes and CNTs. First, it highlights the importance of raising the ion self-energy (dielectric mechanism), which suggests that having the channels both narrow and surrounded by a low-dielectric environment is key to high selectivity. In contrast, pore charge alone is insufficient, yet it may help to enhance and tune ion rejection, provided that non-mean-field effects enhanced in low-dielectric pores, such as ion association and sorption, especially of H+ and OH− ions, are properly understood and addressed in the channel design. Second, the role of concentration polarization (CP) is analyzed, which shows that the CP level is apparently low in isolated channels or microscopically small membranes. However, the geometry of the diffusion field should change and CP should increase drastically in macroscopic membranes incorporating densely spaced channel arrays. If not properly addressed in membrane design, the increased CP level in scaled-up channel-based membranes may significantly compromise the observed selectivity and require that target of selectivity be re-set to an even more challenging value. These points may help guide the future development of high-performance artificial water channels and their scale-up towards utilization in next-generation water purification membranes.