Control of Ionic Interactions in Silver Salt−Polymer Complexes with Ionic Liquids: Implications for Facilitated Olefin Transport

Abstract

The ionic liquids 1-butyl-3-methyl imidazolium BMIM+NO3- and BMIM+BF4- have been successfully utilized to increase the activity in reversible π-complexation with olefins of silver cations in silver polymer electrolytes consisting of AgNO3 dissolved in poly(2-ethyl-2-oxazoline) (POZ). In the absence of the ionic liquids, AgNO3 is not readily dissolved in POZ and is instead because of its high lattice energy present mostly as chemically less active ion pairs or higher order aggregates. The activation of Ag+ in silver polymer electrolytes in the presence of these ionic liquids is principally due to the reduction of the interactions between Ag+ and NO3- produced by the interaction between BMIM+ and NO3-, and this effect does not occur in the presence of common salts such as NaNO3. We investigated these systems with FT-IR, FT-Raman, and XPS and calculated the theoretical electronic structures of the relevant species. The increased activity in these membranes of Ag+ in reversible π-complexation with olefins was further confirmed by evaluating the sorption and desorption behavior of propylene and the performances of the membranes in the separation of olefin/paraffin mixtures.