Department of Chemistry, The University of Western Ontario, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada.
Phys Chem Chem Phys. 2012 Oct 28;14(40):13949-54. doi: 10.1039/c2cp42107k. Epub 2012 Sep 11.
The formal transfer potentials of hydrophilic alkali metal ions Li(+), Na(+), K(+), Rb(+), and Cs(+) were determined at water|room temperature ionic liquid (w|RTIL) interfaces. A working curve for an interface held at the tip of a micropipette (25 μm in diameter) was developed through simulated cyclic voltammograms (CVs) via finite element analysis with Comsol Multiphysics software. This methodology takes advantage of the symmetric diffusion regime experienced at the w|RTIL micropipette interface between two immiscible electrolytic solutions (micro-ITIES) which generates peak-shaped waves in the forward and reverse scans similar to those in CVs obtained at large (centimeter scale) ITIES. Through the simulation a profile of IT was generated in order to construct the working curve from which, in conjunction with experimentally obtained CVs, the formal transfer potentials were extrapolated. The unique characteristics of diffusion at an interface utilizing a pulled capillary make this approach possible. Additionally, within the simulation the geometry can be tailored to approximate closely the actual physical and experimental conditions. In this way the formal transfer potentials of Li(+), Na(+), K(+), Rb(+), and Cs(+) were found to be 0.565, 0.548, 0.521, 0.531, and 518 V, respectively, at the interface between water and our extremely hydrophobic ionic liquid, trihexyltetradecylphosphonium tetrakis(pentafluorophenyl)borate. The implications of these constants towards the evaluation of metal ion extractions will also be discussed.
亲水性碱金属离子 Li(+)、Na(+)、K(+)、Rb(+) 和 Cs(+) 在水|室温离子液体 (w|RTIL) 界面的正式转移电位已被确定。通过 Comsol Multiphysics 软件的有限元分析模拟循环伏安法 (CV)，开发了一种在微管尖端（直径 25 μm）保持的界面工作曲线。这种方法利用了在两种不混溶电解质溶液（微ITIES）之间的 w|RTIL 微管界面经历的对称扩散状态，在正向和反向扫描中产生类似在大（厘米尺度）ITIES 中获得的 CV 的峰形波。通过模拟生成了 IT 轮廓，以便从构建工作曲线中推断出正式的转移电位，该工作曲线与实验获得的 CV 一起使用。利用拉制的毛细管在界面处扩散的独特特性使得这种方法成为可能。此外，在模拟中，几何形状可以进行调整以近似实际的物理和实验条件。通过这种方式，Li(+)、Na(+)、K(+)、Rb(+) 和 Cs(+) 的正式转移电位分别在水和我们极疏水的离子液体三己基十四烷基膦四（五氟苯基）硼酸盐之间的界面处被发现为 0.565、0.548、0.521、0.531 和 518 V。这些常数对金属离子萃取评估的影响也将被讨论。
