Studies On The Hydrophilic Anion Transfer Reactions At The Liquid/Liquid Interface Modified By Anion Exchange Membrane

Anion transfer (AT) across biomembrane is one of the significant biological transmembrane processes. therefore, extensive research efforts have been devoted to study the anion transfer reaction at the liquid/liquid (L/L) interface because L/L interface is considered as a simple model to mimic semi-biomembrane. However, it is still a challenging task to investigate the AT processes of highly hydrophilic anions at the L/L interface. Several methods focusing on the micro-L/L interface electrochemistry have been developed to study the AT processes which are impossible to be observed at the conventional L/L interface (mm-sized). Such as, membrane-modified L/L interface electrochemistry and nanopipette voltammetry method.Commercial ion exchange membranes (IEMs) including anion exchange membrane (AEMs) have been extensively used in numerous industrial fields due to the excellently charge/size-relative permselectivity. However, the study of AEM by far only focus on the permselectivity between ions having same or different charged sign at the aqueous phase. Since the carrying electrical charges and pore size of the ion-exchange membrane can affect on the anions transfer at the aqueous phase which inspired us to. design a modified L/L interface by using AEMs to study the anion transfer reactions. Herein, first, we explored the feasibility of electrochemical study toward AT processes at the L/L interface modified by commercial heterogeneous or homogeneous AEM (hetero-AEM or homo-AEM, respectively) containing quaternary ammonium group. Significantly, fascinating IT phenomena were observed using a homo-AEM, including the remarkable extension of polarization window, well-defined transfer waves of highly hydrophilic anions (SO42- and NO2-), and the amazing positive-shift of their transfer potentials. According to the simplest capillary model and the two-phase structural model of IEMs, a new mechanism based on the sieving effect and pre-dehydration in combination with electrostatic effects dominantly induced by the gel phase of AEMs was proposed to attribute the change in energy barrier of IT reactions which led to the corresponding inconceivable IT phenomena occurring at the AEM-modified L/L interface. As far as we have known, this IT mechanism firstly reveal that the dehydration process prior to IT at the L/L interface induced by extremely narrow pores can lower the energy barriers of some AT reactions at the L/L interface. Moreover, The technique of liquid/liquid electrochemistry should allow the measurement of diffusion coefficients for anions within microporous hosts. Based on the diffusion coefficients, kinetic parameters of the transfer of several anions across water/DCE interface were extracted using chronocoulometry.Combination of AEMs and L/L interface electrochemistry developed in this work is expected to bring new insight into some fields focused on the transport processes of hydrated ions through IEMs in desalination or across biomembrane in bioscience. On the one hand, this work not only enrich the studies of L/L interface electrochemistry but also extend the usages of IEMs from the ion permeation in aqueous solution to the ion transfer at the L/L interface. On the other hand, the modification of AEMs can provide extremely narrow pores with size close to those hydrated ions at the L/L interface and then reveal the potentially significant role of dehydration induced by narrow pores in the change of energy barrier of IT reactions at the L/L interface.