Studies of Pyrene Fluorescence in Pressed Zeolite Discs

Zeolites are naturally found crystalline alumnosilicates which are used extensively in catalysis, ion-exchange, and molecular sieving applications. The structure of the zeolites of interest consists of tetraheda that are arranged to form sodalite and supercage structures. Pyrene is able to enter the supercages of the zeolite by adsorption from non-polar solvents, exhibits characteristic fluorescence emission when excited using uv light at 337 nm. In this study, the sodium ion exchanged forms of zeolites X and Y, synthetic analogues of naturally occurring faujacite mineral, were used. The purpose of this study was to determine what effects would be seen in discs prepared from zeolite powder loaded with pyrene prior to the pressing process. The pressing of the powders into discs at high pressures results in the entrapment of pyrene and a decrease in the efficiency of quenching by O2, as well as an inability to quench using peryelene and Ti02. This effect is greater in zeolite Y than in zeolite X. The ability to quench pyrene fluorescence is decreased further as the powders are loaded with higher concentrations of pyrene and when the powders are not heated subsequent to loading. Up to 65% of the pyrene fluorescence was unable to be quenched by oxygen in unheated NaY discs pressed at 5 metric tons. Using a reaction bomb and acetonitrile, all of the quenchable pyrene was able to be removed, leaving only unquenchable pyrene. This further supported the hypothesis that pyrene is in fact becoming trapped. P\u3erene phosphorescence was induced by exhaustive exchange of sodium ions with transition metal ions. We conclude from this study that most of the adsorbed pyrene remains near the particle exteriors. The change in quenching ability is due to the increased trapping of pyrene caused by sti\u27uctural damage near the exterior of the zeolite at particle-particle contact sites. This damage increased with increasing pressures used to form discs