Amphoteric blend ion-exchange membranes for separating monovalent and bivalent anions in electrodialysis

It is of significant importance to develop highly monovalent anion-selective membranes (MASM) having stable structure for a wide range of applications. To realize the efficient monovalent/bivalent anion separation, in this work, three amphoteric ion-exchange membranes (AIEMs) through blending were fabricated for use in electrodialysis (ED). The three membranes were prepared by blending amino-containing poly(arylene ether sulfone) (PAES-NH 2 ) with 10, 15, and 20 wt% of sulfonated polysulfone (SPSf), respectively, followed by grafting imidazolium salt-terminated side alkyl chains on PAES backbone. Our investigations demonstrate that each transparent AIEM shows good miscibility between the two components, which has been verified by a homogeneous structure via SEM observation and by an even distribution of N element via EDX mapping. In the ED process at a current density of 2.5 mA cm −2 , AIEM with 15 wt% of SPSf shows the superior perm-selectivity (Cl – /SO 4 2– ) of 21.8, relative to many reported MASMs having modified surfaces (<6.0), which is synergistically contributed by (i) electrostatic repulsion difference from the negatively-charged sulfonate groups against monovalent Cl – ions and bivalent SO 4 2– ions and (ii) hydrated energy difference of hydrated Cl – /SO 4 2– ions. This work thus presents a strategy to guide the architectural design of advanced MASMs.