Preparation and electrochemical characterizations of cation-exchange membranes with different functional groups

Phosphonic acid, carboxylic acid and sulphonic acid cation-exchange membranes were prepared from interpolymer of polyvinyl chloride and styrene-divinylbenzene copolymers. Introduction of the different functional groups was confirmed by FTIR, CHNS analysis and ion-exchange capacity measurements. Membrane potential measurements were performed in mono- and bi-valent electrolyte solutions in order to observe the selectivity of these membranes for different types of counter-ions. Membrane potential data in conjunction with membrane conductance data were analyzed in terms of phenomenological coefficients using non-equilibrium thermodynamic principles. All these membranes exhibited good selectivity for Na+ counter-ion. Low selectivity of phosphonic acid membrane observed for bi-valent counter-ions in comparison to sulphonic acid or carboxylic acid membrane may be because of binding of bi-valent cations with the phosphonic acid group. It was concluded that phosphonic acid membrane is most suitable for the electro-driven separations of same type of charged ions. (C) 2004 Elsevier B.V. All rights reserved.