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 AgNO3 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.
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