Behavior of inorganic nanoparticles in silver polymer electrolytes and their effects on silver ion activity for facilitated olefin transport

TiO₂ and Al₂O₃ nanoparticles having different chemical properties were introduced into a poly(2-ethyl-2- oxazoline) (POZ) membrane to make inactive AgNO₃ chemically more active in olefin complexation, resulting in facilitated olefin transport. The interaction schemes were particularly emphasized to understand the activation of AgNO ₃ for facilitated olefin transport. The separation performances were similar in both cases, consistent with similar changes in the binding energy of silver ions and the relative concentrations of the added ionic species. However, the bond strength of C=O in POZ increased with TiO₂ whereas it decreased with Al₂O₃, as confirmed by FT-IR spectroscopy. This difference was explained in terms of the difference in the zeta potential: TiO₂ and Al₂O₃ displayed zeta potentials of -18 and +6.5 mV at pH 4, respectively. On the basis of these, the following interaction scheme was proposed: the TiO₂ nanoparticles predominantly interact with silver cations, whereas the Al₂O₃ nanoparticles preferentially interact with NO₃^-. As a result, both nanoparticles help to loosen the bond strength between Ag+ and NO₃^-, resulting in the activation of the silver cations in olefin complexation; consequently, olefin transport is facilitated, which results in improved separation performance in the separation of propylene/propane mixtures.