Electrodialytic transport properties of cation exchange membranes in the presence of cyclodextrins

After commercial cation exchange membranes (NEOSEPTA) had been immersed in an aqueous cyclodextrin solutions, electrodialysis of a 1:1 mixed solutions of alkaline earth metal ions and sodium chloride was carried out in the pr esence of cyclodextrins in the desalting side solution. Adsorption of the c yclodextrins in the membrane matrix was confirmed by IR spectrum, X-ray pho toelectron spectroscopy (XPS) and the weight increase of each corresponding component of the membranes. As a result of adsorption of the cyclodextrins in the membranes, transport numbers of alkaline earth metal ions relative to sodium ions decreased compared with those of the membranes without cyclo dextrins. Water content in the membrane increased and a ratio of calcium io ns (alkaline earth metal ions) to sodium ions in the membrane phase decreas ed after adsorption of the cyclodextrins. This is due to existence of the c ompounds having hydrophilic outer surface, cyclodextrins, in the membrane m atrix. The decrease in the transport number of calcium ions relative to sod ium ions was due to both decrease in a ratio of mobility of calcium ions to that of sodium ions and decrease in an ionic ratio of calcium ions to sodi um ions in the membrane phase. (C) 2001 Elsevier Science B.V. All rights re served.