Suppression of silver ion reduction by Al(NO3)3 complex and its application to highly stabilized olefin transport membranes

It is well known that the reduction of AgBF4 to silver nanoparticles inevitably occurs over time even under dark conditions. In particular, the reduction rate of AgBF4 in a polymer/silver salt complex is much faster than for any other silver salt. However, when Al(NO3)3 was incorporated into a POZ/AgBF4 complex, the reduction of silver ion was suppressed for more than 14 days. Stable silver ions were confirmed by the separation performance of propylene/propane mixtures over time and by the color change of the POZ/AgBF4/Al(NO3)3 complex. FT-IR and FT-Raman spectroscopy showed that ionic aggregation between the silver ion of AgBF4 and NO3- of Al(NO3)3 occurred, which was much stronger in intensity than interactions in the POZ/Al(NO3)3 and POZ/AgNO3 complexes. This strong aggregation behavior was attributable to a favorable interaction between F− of AgBF4 and Al3+ of Al(NO3)3, resulting in a weakened interaction between Al3+ and its counteranions, which was confirmed by XPS.