Synthetic polymer membranes are enabling components in key technologies at the water–energy nexus, including desalination and energy conversion, because of their high water/salt selectivity or ionic conductivity. However, many applications at the water–energy nexus require ion selectivity, or separation of specific ionic species from other similar species. Here, the ion selectivity of conventional polymeric membrane materials is assessed and recent progress in enhancing selective transport via tailored free volume elements and ion–membrane interactions is described. In view of the limitations of polymeric membranes, three material classes—porous crystalline materials, 2D materials, and discrete biomimetic channels—are highlighted as possible candidates for ion-selective membranes owing to their molecular-level control over physical and chemical properties. Lastly, research directions and critical challenges for developing bioinspired membranes with molecular recognition are provided.

中文翻译：

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用于在水-能量关系中进行选择性离子分离的膜材料

合成聚合物膜因其高水/盐选择性或离子电导率而成为水-能源关系关键技术的组成部分，包括海水淡化和能量转换。然而，水-能量关系的许多应用需要离子选择性，或将特定离子物质与其他类似物质分离。在这里，评估了传统聚合物膜材料的离子选择性，并描述了通过定制的自由体积元素和离子膜相互作用增强选择性传输的最新进展。鉴于高分子膜的局限性，可分为三类材料——多孔结晶材料、二维材料、和离散的仿生通道——由于它们对物理和化学特性的分子水平控制，被强调为离子选择性膜的可能候选者。最后，提供了开发具有分子识别功能的仿生膜的研究方向和关键挑战。