Nanoscale Ionic Liquid/liquid Interface Transfer Reaction Of Electrochemical Research

Ion transfer reaction at Liquid/Liquid interface is relevant to many important chemical and biological systems such as chemical sensors、biomembranes and drug delivery systems. Nanopipet supported nanoscopic liquid/liquid interface have outstanding electrochemical properties including quick mass-transfer rate and overcoming resistive potential drop, thus it plays an essential role on inveistigation of ion transfer on liquid/liquid interfaces for theory and application. This paper mainly focuses on kinetics of ion transfer reaction and the diffusion of ions at nanoscopic liquid/liquid interface from nanopipets, research results are described as follows:(1) Micropipets were silanized and the silanization effect was characterized by cyclic voltammograms of TEA+transfer across the water/DCE interface supported on silanized micropipets, the measured diffusion coefficient of TEA+in DCE was10.2×10-6cm2/s. Nanopipets were silanized by an improved method, eg. silanized by the vapor of chlorotrimethylsilane. Characterization results of SEM and voltammetry of common ion showed nanopipets were correctly silanized. TEA+transfer across the water/DCE interface supported on silanized nanopipets was investigated by voltammetry of common ion, the kinetic parameters measured by fitting theoretical curves to experimental curves were k0=7.2±0.4cm/s、α=0.49±0.09, respectively. The a value is in agreement with the theoretical prediction. The independence of both k0and a from the pipet radius suggested TEA+transfer was not affected by the double layer effect. The values were also compared to values previously determined from voltammograms with TEA+present only in one phase and the differences were investigated. The accuracy of parameters measured from fitting mainly depends on the quality of volammograms, especially the magnitude of the capacitive current.(2) Nanopipets were silanized by the improved method. The characterization results from voltammetry of common ion TAB+and C8mim+suggested the nanopipets were silanized properly. The measured diffusion coefficient of TBA+in ionic liquid [THTDP+][C4C4N] by silanized nanopipet was (2.04±0.18)×10-8cm2/s, this value was the almost same with the diffusion coefficient of C8mim+which is2.08×10-8cm2/s. Perfectly retraceable voltammograms with similar positive and negative diffusion limiting currents were obtained when the concentration of the common ion in ionic liquid was about30times than its vaule in the filling aqueous solution and potential scan rates were very small.(3) TBA+and C8mim+transfer across the water/ionic liquid [THTDP+][C4C4N-] interface supported on silanized nanopipets was investigated by voltammetry of common ion, the determined kinetic parameters from fitting for TBA+and Cgmim+transfer reaction were k0=0.14±0.02cm/s、α=0.48±0.06and k0=0.17±0.01cm/s、α=0.49±0.06, respectivly。The a values agree with the theoretical prediction, but k0were much smaller than the standard ion transfer rate constant at water/organic solvent interface. The independence of both k0and a from the pipet radius suggested TEA+transfer was not affected by the double layer effect. The egress currents for ClO4-and TBA+across the water/ionic liquid interface supported on silanized nanopipets with different radius were also measured. The agreement for the ratio of these two currents with the theoretical prediction suggested that electrostatic effects from the glass wall didn’t significantly influenced the ion transfer from the inner nanopipet to the outer phase. The dynamics of interfacial response was investigated by changing the potential sweep rate. The cyclic voltammograms obtained at different potential sweep rates were not affected by slow relaxation of the electrical double layer structure at the water/ionic liquid interface.