NMR Studies on the Solution Property and Function of Ion Exchangers

Abstract

In order to understand adsorption mechanisms of ion-exchangers and selective adsorbents, properties of the gel internal solution, and the structure and the reactivity of adsorbed species should be clarified. This review article describes author's studies using multinuclear NMR method on the hydrolysis reactions, acid dissociation and complexation of oxoanions adsorbed onto ion-exchangers and selective adsorbents. The hydrolysis of cyclo-triphosphate in anion-exchange resins was significantly retarded compared to that in a basic solution. This retardation was shown to be entirely due to a much more unfavorable ΔH^‡ for the reaction in the resin phase. Boron and vanadium (V) species adsorbed onto polysaccharide gels were characterized: 1: 1 (α, β) and/or (α, γ), and 1: 2 (α, β) (α, β), (α, γ) (α, γ) and/ or (α, β) (α, γ) complexes for boron in sephadex and cellulose, and a 1: 1 (N, O, O) complex for vanadium (V) in ECTEOLA-cellulose. The adsorption behavior of boron onto N-methylglucamine resin was well interpreted in terms of pH in the resin phase (not in the external solution) estimated by NMR measurements of a probe species. The maximum adsorption around pH 9 of the equilibrated solution is due to the fact that the pH in the resin phase remains higher than that in the external solution.