Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06520-8286, United States.
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
ACS Nano. 2022 Sep 27;16(9):15249-15260. doi: 10.1021/acsnano.2c06633. Epub 2022 Sep 8.
Ion-surface interactions can alter the properties of nanopores and dictate nanofluidic transport in engineered and biological systems central to the water-energy nexus. The ion adsorption process, known as "charge regulation", is ion-specific and is dependent on the extent of confinement when the electric double layers (EDLs) between two charged surfaces overlap. A fundamental understanding of the mechanisms behind charge regulation remains lacking. Herein, we study the thermodynamics of charge regulation reactions in 20 nm SiO channels via conductance measurements at various concentrations and temperatures. The effective activation energies () for ion conductance at low concentrations (strong EDL overlap) are ∼2-fold higher than at high concentrations (no EDL overlap) for the electrolytes studied here: LiCl, NaCl, KCl, and CsCl. We find that values measured at high concentrations result from the temperature dependence of viscosity and its influence on ion mobility, whereas values measured at low concentrations result from the combined effects of ion mobility and the enthalpy of cation adsorption to the charged surface. Notably, the for surface reactions increases from 7.03 kJ mol for NaCl to 16.72 ± 0.48 kJ mol for KCl, corresponding to a difference in surface charge of -8.2 to -0.8 mC m, respectively. We construct a charge regulation model to rationalize the cation-specific charge regulation behavior based on an adsorption equilibrium. Our findings show that temperature- and concentration-dependent conductance measurements can help indirectly probe the ion-surface interactions that govern transport and colloidal interactions at the nanoscale─representing a critical step forward in our understanding of charge regulation and adsorption phenomena under nanoconfinement.
离子-表面相互作用可以改变纳米孔的性质，并决定工程和生物系统中的纳滤传输，这些系统是水-能源纽带的核心。离子吸附过程，称为“电荷调节”，是离子特异性的，并且取决于两个带电表面之间的双电层（EDL）重叠时的限制程度。对电荷调节背后的机制的基本理解仍然缺乏。在这里，我们通过在不同浓度和温度下进行电导测量来研究 20nmSiO 通道中电荷调节反应的热力学。对于这里研究的电解质：LiCl、NaCl、KCl 和 CsCl，在低浓度（强 EDL 重叠）下，离子电导的有效活化能（）比在高浓度（无 EDL 重叠）下高约 2 倍。我们发现，在高浓度下测量的值来自于粘度的温度依赖性及其对离子迁移率的影响，而在低浓度下测量的值来自于离子迁移率和阳离子吸附到带电表面的焓的综合影响。值得注意的是，表面反应的值从 NaCl 的 7.03kJmol增加到 KCl 的 16.72±0.48kJmol，分别对应于表面电荷的-8.2 到-0.8mC m的差异。我们构建了一个电荷调节模型，根据吸附平衡来合理推断阳离子特异性的电荷调节行为。我们的研究结果表明，温度和浓度依赖性电导测量可以帮助间接探测控制纳米尺度传输和胶体相互作用的离子-表面相互作用，这代表了我们对纳米限制下的电荷调节和吸附现象的理解向前迈出了关键一步。
