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 presence of cyclodextrins in the desalting side solution. Adsorption of the cyclodextrins in the membrane matrix was confirmed by IR spectrum, X-ray photoelectron 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 cyclodextrins. Water content in the membrane increased and a ratio of calcium ions (alkaline earth metal ions) to sodium ions in the membrane phase decreased after adsorption of the cyclodextrins. This is due to existence of the compounds having hydrophilic outer surface, cyclodextrins, in the membrane matrix. The decrease in the transport number of calcium ions relative to sodium 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 sodium ions in the membrane phase.