Binding of paramagnetic ions in ionomers. Cu2+ Ti3+ in Nafion membranes

Abstract

The ligation of Cu²⁺ and Ti³⁺ in Nafion ionomers swollen by water and methanol, respectively, has been studied as a function of cation concentration, temperature and solvent content. Both cations ligate to water oxygens and to the oxygens from the sulphonic groups of the polymer. Tetragonal and tetrahedral symmetries for Cu²⁺, and trigonally and tetragonally distorted octahedral symmetries for Ti³⁺ have been identified. The specific ligation is very sensitive to the amount of solvent in the membrane. In a wide range of cation concentrations we have detected both isolated and aggregated ions. The intercation distance is larger than ca. 10 Å for the aggregated ions. The results obtained suggest the existence of an interface in which the isolated ions are located, in addition to the polar phase where the ions are aggregated.