Scanning electrochemical microscopy (SECM) as a probe of transfer processes in two-phase systems: Theory and experimental applications of SECM-induced transfer with arbitrary partition coefficients, diffusion coefficients, and interfacial kinetics
Scanning electrochemical microscopy (SECM) as a probe of transfer processes in two-phase systems: Theory and experimental applications of SECM-induced transfer with arbitrary partition coefficients, diffusion coefficients, and interfacial kinetics
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DOI：
10.1021/jp973370r
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发表时间：
1998-02-26
影响因子：
3.3
通讯作者：
Unwin, PR
中科院分区：
文献类型：
--
作者：
Barker, AL;Macpherson, JV;Unwin, PR
介绍了扫描电化学显微镜诱导转移（SECMIT）作为一种探测电活性溶质在两个不混相之间分配动力学的新方法。分配过程最初处于平衡状态，但由于目标溶质在靠近与第二相界面的一相中的超微电极（UME）尖端处的电解而受到干扰。对于尖端和界面之间的特定分离，在UME处溶质的通量和电流流动主要由溶质的分配系数K-e、溶质在两相中的相对扩散系数γ和界面传递动力学决定。建立了在电位阶跃计时安培条件下的SECMIT数值模型，其中目标溶质在UME以扩散控制速率进行电解。当界面动力学是非极限时，稳态电流强烈依赖于产物K-e γ，特别是K-e γ > 1，而对于常数K-e γ，相应的时序电流响应取决于K-e和γ的单独值。原则上，这种方法提供了一种方法来确定扩散系数和/或目标溶质在介质中的浓度，而不需要与UME接触。在稳态条件下，说明了SECMIT的这一方面。通过研究(i)几种电活性离子在水凝胶和水溶液之间的转移和（ii）氧在水与1,2-二氯乙烷（DCE）或硝基苯（NB）之间形成的界面上的转移。通过研究铜离子在水相和含有肟配体Acorga P50 （LH）的DCE之间的萃取和剥离，说明了SECMIT在探测界面动力学中的应用。
Scanning electrochemical microscopy induced transfer (SECMIT) is introduced as a new approach for probing the dynamics of partitioning of electroactive solutes between two immiscible phases. The partitioning process, initially at equilibrium, is perturbed by electrolysis of the target solute at an ultramicroelectrode (UME) tip positioned in one phase, close to the interface with a second phase. For a particular separation between the tip and interface, the flux of solute-and hence current flowing-at the UME is governed primarily by the partition coefficient of the solute, K-e, the relative diffusion coefficients of the solute in the two phases, gamma, and the interfacial transfer kinetics. A numerical model is developed for SECMIT under potential step chronoamperometric conditions, where the target solute is electrolyzed at the UME at a diffusion-controlled rate. When the interfacial kinetics are nonlimiting, the steady-state current is strongly dependent on the product K-e gamma, particularly for K-e gamma > 1, while for constant K-e gamma the corresponding chronoamperometric response depends on the individual values of K-e and gamma. In principle, this methodology provides a route to determining the diffusion coefficient and/or concentration of a target solute in a medium, without contact from the UME. This aspect of SECMIT is illustrated, under steady-state conditions? through studies on the transfer of (i) several types of electroactive ions between hydrogels and aqueous solutions and (ii) oxygen transfer across the interface formed between water and either 1,2-dichloroethane (DCE) or nitrobenzene (NB). The application of SECMIT to probe interfacial kinetics is illustrated through studies of cupric ion extraction and stripping between an aqueous phase and DCE containing the oxime ligand, Acorga P50 (LH).