Electrochemical Investigation Across Liquid/Liquid Interface Supported With A Micro-cavity Electrode

Liquid/Liquid interface, or water/oil (W/O) interface, or the interface between two immiscible electrolyte solutions (ITIES), is the interface constructed by two immiscible electrolyte solutions. The charge transfer across ITIES is one of the most elementary physical chemistry processes. It is relevant to many fields such as chemistry sensors, pharmacology, phase transfer catalysis, physiological actions at biomembranes, solar cell, environmental protection etc, and has been made much process in the past fifty years. The microelectrode is one of the most important electrochemistry technique origined from the early 1980's. It can overcome the large IR drop caused' by the low conductivity of the organic phase. Compared with the conventional electrode, microelectrode has been confirmed to have more important theory and application value. In this thesis, a novel micro-cavity electrode was used to investigate the charge transfer across ITIES. The main research work concentrated on:(1) The electron transfer between potassium ferricyanide, potassium ferrocyanide (water phase) and ferrocene (oil phase) across two immiscible electrolyte solutions (ITIES) supported with micro-cavity electrode has been investigated with cyclic voltammetry, chronoamperometry and square wave voltammetry by a traditional three-electrodes system. The diffusion coefficient was derived from the data. The results showed that the ITIES supported by micro-cavity electrode would be a useful and efficient tool to investigate the charge transfer reactions at liquid/liquid interfaces.(2) A novel micro-cavity electrode has been developed to investigate the charge transfer at the water / 1,2-dichloroethane (DCE) micro ITIES (the interface between two immiscible electrolyte solutions) for solvent extraction of Ni(II). The influence of pH andextractant concentration was studied by using voltammetry, and electrochemical impedance spectroscopy (EIS), and the possible charge transfer mechanism was suggested. The kinetic parameters were also determined by numerical simulation for the experimental results of EIS. The results showed that the solvent extraction rate was accelerated by the imposed potential. It was also found that the micro-cavity electrode would be a useful and efficient tool for the study of ITIES systems for its simplicity and the very small IR even by using the conventional electrochemical setup with three-electrode configuration.(3) The facilitated ion transfer of the alkali metals across the water / 1,2-dicliloroethane (DCE) such interface supported with a micro-cavity electrode was investigated by using a novel neutral ionophore. The thermodynamic and kinetic parameters are evaluated and their relationship is discussed by using Butler-Volmer theory. The diffusion coefficient of L in DCE is measured as 4.5xlO cm s. The results show that the electrochemical behaviors the facilitated ion transfer is abided by a TIC/TID mechanism. When the alkali metal ion transfer across the interface, a 1:1 (metal: ionophore) complex was formed. The logarithm of the interfacial complexation constants between L and the ions are 10.5(NaL) and 9.1(KL/), respectively. The results show that this ionophore is suitable to be used to fabricate the electrochemical sensor of Na ion. Since the modification of aza-crown ethers is easy and flexible, this may provide a new choice of neutral ionphore for liquid-membrance ion selective electrode.