Probing ion transfer at the liquid/liquid interface by scanning electrochemical microscopy (SECM)
Probing ion transfer at the liquid/liquid interface by scanning electrochemical microscopy (SECM)
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DOI：
10.1021/jp9828282
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发表时间：
1998-12-03
影响因子：
3.3
通讯作者：
Mirkin, MV
中科院分区：
文献类型：
--
作者：
Shao, YH;Mirkin, MV
描述了一种使用扫描电化学显微镜（SECM）来探测液体/液体和液体/膜界面的反应性的新方法。一个充满溶剂（例如，水）与外溶液（例如有机）不混溶的微孔作为SECM尖端。尖端电流是由于移液器和外部溶液之间的离子传递所致。当这样的尖端接近宏观液体/液体或液体/膜界面时，IT过程会耗尽相位边界附近转移离子的浓度。如果第二阶段（例如，另一个水溶液）包含相同的离子，则耗尽在整个界面上会导致IT。尖端电流取决于界面-IT反应的速率，可以从尖端电流与距离曲线中提取。通过在相边界上扫描移液尖端，可以获得界面的地形图像和IT反应性的地图，例如，在聚碳酸酯膜中微米大小的孔的高分辨率反馈模式图像。先前针对被相对较厚的绝缘玻璃护套包围的金属尖端开发的反馈模式SECM理论并不完全适用于移液尖端。具有不同绝缘体厚度的移液尖端的理论尖端电流与距离曲线的家族是通过使用偏微分方程的数值解，使用商业自适应网格程序PDESE2获得的。开发的理论以两个分析近似的形式介绍，适用于扩散控制的异质反应和阻断界面。还讨论了快速测量IT动力学的可能性。
A new way of using the scanning electrochemical microscope (SECM) to probe ion transfer (IT) reactivity of the liquid/liquid and liquid/membrane interfaces is described. A micropipet filled with solvent (e.g., water) immiscible with the outer solution (e.g., organic) serves as an SECM tip. The tip current is due to transfer of an ion between the pipet and the outer solution. When such a tip approaches a macroscopic liquid/liquid or liquid/membrane interface, the IT process depletes the concentration of the transferred ion near the phase boundary. If the second phase (e.g., another aqueous solution) contains the same ion, the depletion results in the IT across the interface. The tip current depends on the rate of the interfacial-IT reaction, which can be extracted from the tip current vs distance curves. By scanning the pipet tip over the phase boundary the topographic images and maps of IT reactivity of the interface can be obtained, e.g., high-resolution feedback mode images of micrometer-sized pores in polycarbonate membranes. The feedback-mode SECM theory previously developed for metal tips surrounded by a relatively thick insulating glass sheath is not fully applicable to the pipet tips. A family of theoretical tip current vs distance curves for pipet tips with different insulator thicknesses is obtained by numerical solution of partial differential equations using,a commercial adaptive grid program, PDEase2. The developed theory is presented in the form of two analytical approximations suitable for diffusion-controlled heterogeneous reaction and for a blocking interface. The possibilities of measuring fast IT kinetics are also discussed.