Abstract
X-ray absorption fine structure (XAFS) has proved very efficient for studying the local structure of counterions in ion-exchange resins. The principle of XAFS is briefly outlined, and its applications to ion-exchange systems are discussed in this review. When Br- and Cl--form anion-exchange resins are soaked in water, two different structures are detected; one comes from hydrated counterions, while the other is attributed to those bound by ion-exchange groups. A simple mathematical procedure has allowed us to separate the contributions from these two different origins, and finally indicates that ca 40% of counterions are dissociated from the ion-exchange sites when sufficient amount of water available for hydration. This structure is found for the anions attracted by the surface monolayers. Ion-exchange selectivity is also discussed based on these results.
