(449ci) Electrokinetics and Electrochemical Characteristics of Ion-Exchange Particles

Ion-exchange particles (resin) find a number of applications in areas such as processing of radioactive waste, water purification or desalination. The last two mentioned examples are associated with electro-membrane separation processes in which finely ground ion-exchange particles embedded in polymeric binder (so called heterogeneous ion-exchange membranes) provide selectivity towards migration of ion caused by external electrical field. This selectivity comes from a so called fixed charge that is bound to polystyrene â?? divinylbenzene structure of ion-exchange particles and exerts electrostatic attraction and repulsion on mobile counter-ions (ion with opposite charge to that one of the fixed charge) and co-ion (ions with like charge to that one of the fixed charge), respectively.

Electrochemical properties of ion-exchange particles and their behavior in DC electrical field play a very important role in production of heterogeneous ion-exchange membranes with optimized properties for a given process. For instance, ion-exchange membranes for electrodialysis should have limited (ideally no) tendency to split water (they should only exchange ions) while membranes creating bipolar membranes (stack of a cation and anion exchange membrane) should have properties enhancing water splitting reaction. Functional properties of the membranes are mostly given by the properties of ion-exchange particles. Electrochemical characterization of single ion-exchange particles would thus open a new scenario for producing membranes with tailored properties for a given process. However, this characterization presents a difficult task due to technical challenges in the experimental set-up.

In this contribution, we will present our approach to electrochemical characterization of single ion-exchange particles and also to observation of fundamental phenomena (electrohydrodynamic vortices, water splitting) that occur on ion exchange particles provided by a company MemBrain a. s. (Czech Republic). These ion exchange particles are used for production of heterogeneous ion exchange membranes industrially used on a large-scale. We characterize the ion exchange particles by measuring current-voltage characteristics, and chronoamperometric curves. The electrokinetic behavior is studied by means of fluorescence microscopy when fluorescent markers are used for both imaging of vortices and tracking pH zones that develop on either side of the particles.