Studies On The Ion Transfer Reactions At The Interface Between Two Immiscible Electrolyte Solutions Supported By Porous Membrane

Electrochemistry at the membrane-supported liquid/liquid (L/L) interface (or called as water/oil (W/O) interface or the Interface between Two Immiscible Electrolyte Solutions (ITIES)) has recently attracted much attention owing to its combining the advantages of micro-L/L interface electrochemistry with the diversity of membrane materials. Compared to the conventional L/L interface, the integration of micro-L/L interface arrays using porous membranes can enhance mass transfer, improve electroanalytical performances. The major contents in this paper include:the influence of membrane porosity on ion-transfer voltammetry at the L/L interface supported by disordered porous polyethylene terephthalate (PET) membranes with different porosity was systemically studied by cyclic voltammetry (CV) for the first time; the impact of ionic surfactant cetyltrimethylammonium bromide (CTAB) self-assembled within the silica nanochannels of HMSM on the IT voltammetric behavior and detection of folic acid (FA) at the meso-L/L interface arrays. The main results are as follows:1. The influence of membrane porosity on ion-transfer voltammetry at the L/L interface supported by disordered porous polyethylene terephthalate (PET) membranes with different porosity was systemically studied by cyclic voltammetry (CV) for the first time. Simple ion transfer (IT) of tetraethylammonium (TEA+) and perchlorate (ClO4-), as well as facilitated ion transfer (FIT) of K+by dibenzo-18-crown-6 (DB18C6) are adopted in this study. According to the normalized geometric parameter Kλ1/2 proposed by Amatore and Dryfe, the different value of Kλ1/2 for the ion transfer across the liquid/liquid interface supported by the bare PET membrane with different porosity are calculated. The results completely agree to the theory proposed by Amatore and Dryfe, namely, a symmetrically peak-shaped (a single liner diffusion field) CV curve is obtained if Kλ1/2> 10. A sigmoidal (non-interacting radial diffusion fields) voltammogram is observed when Kl1/2< 10. All above results demonstrate that ion transfer and facilitated ion transfer behaviors across the L/L interface supported by the bare PET are closely related with the porosity of the PET membrane.2. Voltammetric studies on the simple ion transfer (IT) behaviors of an important water-soluble B-vitamin, folic acid (FA), at the liquid/liquid (L/L) interface were firstly performed and applied as a novel detection method for FA under physiological conditions. Meso-water/1,6-dicholrohexane (W/DCH) and meso-water/organogel interface arrays were built by using a hybrid mesoporous silica membrane (HMSM) with unique structure of pores-in-pores and employed as the new platforms for the IT voltammetric study. In view of the unique structure of such a HMSM, the impact of ionic surfactant cetyltrimethylammonium bromide (CTAB) self-assembled within the silica nanochannels of HMSM on the IT voltammetric behavior and detection of FA at the meso-L/L interface arrays was systematically examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and differential pulse stripping voltammetry (DPSV). It is found that all the voltammetric responses of CV, DPV, and DPSV and the corresponding detection limit of FA at such meso-L/L interface arrays are closely related to the CTAB in HMSM. Significantly, the calculated detection limit of FA could be improved to 80 nM after the combination of DPSV technique with the additional preconcentration of FA in the silica-CTAB nanochannels through an anion-exchange process between FA-and the bromide of CTAB in HMSM.