Polster Jake W, Acar Elif Turker, Aydin Fikret, Zhan Cheng, Pham Tuan Anh, Siwy Zuzanna S
Department of Chemistry, University of California, Irvine, California 92697, United States.
Department of Chemistry, Faculty of Engineering, Istanbul University - Cerrahpasa, Avcılar, 34320 Istanbul, Turkey.
ACS Nano. 2020 Apr 28;14(4):4306-4315. doi: 10.1021/acsnano.9b09777. Epub 2020 Mar 19.
Understanding ion transport in nanoporous materials is critical to a wide variety of energy and environmental technologies, ranging from ion-selective membranes, drug delivery, and biosensing, to ion batteries and supercapacitors. While nanoscale transport is often described by continuum models that rely on a point charge description for ions and a homogeneous dielectric medium for the solvent, here, we show that transport of aqueous solutions at a hydrophobic interface can be highly dependent on the size and hydration strength of the solvated ions. Specifically, measurements of ion current through single silicon nitride nanopores that contain a hydrophobic-hydrophilic junction show that transport properties are dependent not only on applied voltage but also on the type of anion. We find that in Cl-containing solutions the nanopores only conducted ionic current above a negative voltage threshold. On the other hand, introduction of large polarizable anions, such as Br and I, facilitated the pore wetting, making the pore conductive at all examined voltages. Molecular dynamics simulations revealed that the large anions, Br and I, have a weaker solvation shell compared to that of Cl and consequently were prone to migrate from the aqueous solution to the hydrophobic surface, leading to the anion accumulation responsible for pore wetting. The results are essential for designing nanoporous systems that are selective to ions of the same charge, for realization of ion-induced wetting in hydrophobic pores, as well as for a fundamental understanding on the role of ion hydration shell on the properties of solid/liquid interfaces.
了解纳米多孔材料中的离子传输对于从离子选择性膜、药物递送、生物传感，到离子电池和超级电容器等广泛的能源和环境技术至关重要。虽然纳米级传输通常由连续介质模型描述，该模型依赖于对离子的点电荷描述和对溶剂的均匀介电介质，但在此我们表明，疏水性界面处水溶液的传输高度依赖于溶剂化离子的大小和水合强度。具体而言，通过含有疏水 - 亲水结的单个氮化硅纳米孔的离子电流测量表明，传输特性不仅取决于施加的电压，还取决于阴离子的类型。我们发现，在含氯溶液中，纳米孔仅在负电压阈值以上传导离子电流。另一方面，引入大的可极化阴离子，如溴离子和碘离子，促进了孔的润湿，使孔在所有测试电压下都具有导电性。分子动力学模拟表明，与氯离子相比，大阴离子溴离子和碘离子具有较弱的溶剂化壳，因此易于从水溶液迁移到疏水表面，导致负责孔润湿的阴离子积累。这些结果对于设计对相同电荷离子具有选择性的纳米多孔系统、实现疏水孔中的离子诱导润湿以及从根本上理解离子水合壳对固/液界面性质的作用至关重要。
