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. (c) 2013 Elsevier B.V. All rights reserved.