The way to increase the monovalent ion selectivity of FujiFilm® anion-exchange membranes by cerium phosphate modification for electrodialysis desalination

Recently, the selectivity of ion-exchange membranes and its control have been the subject of numerous fundamental and applied studies. This paper reports an enhanced monovalent anion selectivity of hybrid membrane based on the FujiFilm® Type I anion-exchange membrane and in situ synthesized cerium phosphate (CeP) with a gradient distribution over the membrane thickness. The Cl/SO 4 -selectivity coefficient ( P(Cl/SO 4 ) ) of hybrid membranes reached 6.2. The effect of modification on the Cl/SO 4 selectivity passed through a minimum as the total concentration of the external solution increased from 0.04 M to 1 M. For low concentration electrolytes, Cl/SO 4 -selectivity improving was attributed to partial neutralization of positive fixed charges by negative fixed charges of cerium phosphate, which causes an effective decrease of ion-exchange capacity and reduction of electrostatic selectivity factor favouring sulfate transport; for high concentration electrolytes, to the formation of narrow transport channel between the surface of the inorganic nanoparticle and the pore wall, which causes a decrease of sulfate transport due to the size sieving effect. The hybrid membranes and cerium phosphate were characterized using ATR FTIR and 31 P MAS NMR spectroscopy, XRD analysis and scanning electron microscopy with EDX microanalysis. • Monovalent ion selectivity of AEMs was improved by cerium phosphate modification. • Up to a 55% increase in the Cl/SO4-selectivity coefficient was observed. • Selectivity improvement depends on the external electrolyte concentration. • It is assumed that a change in the separation mechanism causes this dependence.