Photochemical properties of Ag ion clusters included within ZSM-5 zeolites prepared by an ion-exchange method

Abstract

Photoluminescence investigations of the Ag ion-exchanged ZSM-5 (Ag+ /ZSM-5) zeolite revealed that a Ag ion cluster (Agnm+) exists in the pore structure of ZSM-5 exhibiting photoluminesm cence at 380 nm upon excitation at 332 nm. UV irradiation (λ = 285 nm) of Ag+ /ZSM-5 at 77 K leads to the transformation of Agnm+ into a different Ag ion cluster (Agm(n-1)+) which exhibits photoluminescence at 465 nm upon excitation at 315 nm. This photo-transformation of the Ag ion clusters was found to be thermally reversible under vacuum. It was demonstrated that an electron transfer from the photo-excited Al3+ -O2- to Agnm+ plays a significant role in this process. In the presence of oxygen, UV irradiation of Ag+ /ZSM-5 leads to the formation of O2- instead of an Ag ion cluster (Agm(n-1)+), suggesting that oxygen acts as an efficient electron scavenger, which interferes with the electron capture of Agnm+ under UV irradiation at 285 nm.