Facilitated transport of halides through Nafion ionomer membrane modified with lanthanide complexes

Permeation of chloride and bromide through Nafion(TM) 117 modified with hydrophobic metal complexes of EU3+ and Pr3+ with thenoyl trifluoro acetone (TTA), beta-isopropyl tropolone (IPT) and 8-hydroxyquinoline (oxine) has been studied. The complexes were precipitated within the polymer bed with an aqueous-alcoholic solution of the reagents at a pH between 5 and 6. The permeation fluxes of the halides have been calculated by measuring the concentrations of the anions in the receiving solutions using ion chromatography. The high flux values have been attributed to the direct coordination of the inorganic anions to the central metal ions in their complexes. The chloride ion having a smaller radius and higher free energy of hydration as compared to bromide, showed higher permeation. The cations associated with the corresponding anion is also transported along with the anion. The size of the accompanying cation has a strong influence on anion permeation. (C) 1998 Published by Elsevier Science B.V.