Specific-ion selectivity is a highly desirable feature for the next generation of membranes. However, existing membranes rely on differences in charge, size and hydration energy, which limits their ability to target individual ion species. Here we demonstrate a nanocomposite ion-exchange membrane material that enables a reverse-selective transport mechanism that can selectively pass a single ion species. We demonstrate this transport mechanism with phosphate ions selectively transporting across negatively charged cation exchange membranes. Selective transport is enabled by the in situ growth of hydrous manganese oxide nanoparticles throughout a cation exchange membrane that provide a diffusion pathway via phosphate-specific, reversible outer-sphere interactions. On incorporating the hydrous manganese oxide nanoparticles, the membrane’s phosphate flux increased by a factor of 27 over an unmodified cation exchange membrane, and the selectivity of phosphorous over sulfate, nitrate and chloride reaches 47, 100 and 20, respectively. By pairing ion-specific outer-sphere interactions between the target ions and appropriate nanoparticles, these nanocomposite ion-exchange materials can, in principle, achieve selective transport for a range of ions.

特定离子选择性是下一代膜非常理想的特性。然而，现有的膜依赖于电荷、大小和水合能的差异，这限制了它们针对单个离子种类的能力。在这里，我们展示了一种纳米复合离子交换膜材料，它可以实现一种反向选择性传输机制，可以选择性地通过单一离子种类。我们证明了这种传输机制，磷酸根离子选择性地传输穿过带负电荷的阳离子交换膜。选择性运输是通过在整个阳离子交换膜中原位生长水合锰氧化物纳米颗粒来实现的，该阳离子交换膜通过磷酸盐特异性、可逆的外球相互作用提供扩散途径。在掺入水合氧化锰纳米粒子时，该膜的磷酸盐通量比未改性的阳离子交换膜提高了27倍，磷对硫酸盐、硝酸盐和氯化物的选择性分别达到47、100和20。通过配对目标离子和适当纳米颗粒之间的离子特异性外球相互作用，这些纳米复合离子交换材料原则上可以实现一系列离子的选择性传输。