Studies On The Selective Ion Transfer Reactions At The Liquid/Liquid Interface Modified By Ion Exchange Membrane

Ion-exchange membrane （IEM） is a membranous ion exchange resin with ion selectivity, and the property of ion selectivity makes it have some advantages to the application of the desalination of saltwater, preparation of pure water, chemical separation and so on. The liquid/liquid interface modified by IEM and the simple ion transfer reactions studied at such a modified interface expand the applications of IEM to the liquid/liquid interface electrochemistry. This study focused on the thermodynamic and kinetic studies of ion transfer of SO₄^2- at the water/1,2-dichloroethane （W/DCE） interface modified by the anion exchange membrane （AEM） and investigated the ion transfer reactions and phase transfer crystallization at the W/DCE interface modified by the cation exchange membrane （CEM）.This study firstly applied the AEM of homogeneous quaternary ammonium type to modify the W/DCE interface, and employed cyclic voltammetry （CV）, differential pulse voltammetry （DPV） and chronocoulometry to investigate the transfer process of SO₄^2- with strong hydrophilic at the interface. It was found that the electrochemical window could be extended by the modification of W/DCE interface with such an AEM. In addition, the well-defined CV and DPV curves corresponding to the ion transfer of highly hydrophilic SO₄^2- could be obtained at the modified W/DCE interface. According to the linear relationship between the peak current of CV and the square root of scan rate, as well as the equation of Randles Sevcik, the diffusion coefficient of SO₄^2- in the membrane containing water was calculated to be about 7.6×10-8 cm/s. In addition, the peak current of DPV increased linearly with the concentration of SO₄^2- within the range of 5-25 mmol/L. Moreover, the standard reaction rate constant of the ion transfer of SO₄^2- at such an AEM-modified W/DCE interface was estimated to be about 1.49×10-3 cm/s via chronocoulometry.Furthermore, this study made use of CEM to modify the W/DCE interface and investigated the ion transfer phenomena at the W/DCE interface modified by the CEM. The research found that the homogeneous CEM could not exhibit the similar properties with the homogeneous AEM, and the interface modified by the CEM was not stable and the electrochemical window was relatively narrow. However, W/DCE interface modified by a heterogeneous CEM got a relatively wide electrochemical window, and the transfer of K+on this interface can be directly observed, in addition, complete CV and DPV curves of the transfer of K+can be obtained. Then, crystals on the membrane were received by using the methods of amperometric i-t curve and phase transfer crystallization. Finally, the crystal was characterized by fourier transform infrared spectroscopy （FTIR）, scanning electron microscope （SEM）, energy dispersive spectrometer （EDS） and X-ray diffractometry （XRD）, and it turned out to be the ionic crystal—potassium tetraphenylborate （KTPB）.This work not only enrichs the research of liquid/liquid interface electrochemistry, but also applies a method of phase transfer crystallization to prepare ionic crystals at the membrane-modified liquid/liquid interface. This work is helpful to further expand the applications of the liquid/liquid interface electrochemistry and the ion-exchange membranes.