Effects of Coadsorbed Water on the Mobility of Polyaromatic Hydrocarbons in Zeolite Y

Abstract

Triplet excited states of pyrene, phenanthrene, and naphthalene have been prepared in zeolite KY by pulsed laser excitation and the influence of coadsorbed water on quenching of these triplet states by ferrocene and the immobile ferrocene derivative ferrocenylmethytrimethylammonium cation (FcMN) has been studied by transient absorption spectroscopy. To make these measurements, probe loadings in KY have been kept deliberately low such that quenching involves migration of molecules from one supercage to another. In all cases, maxima in bimolecular triplet quenching rates versus the number of H 2 O per supercage (N sc ) were observed at N sc ≈ 4, a value which coincides with the number of H 2 O molecules that fill the sodalite cages. For pyrene quenching by FcMN, the effect of 4 H 2 O/sc was particularly dramatic, where the quenching rate increased by 3 orders of magnitude relative to dehydrated KY. Above N sc ) 4, further additions of H 2 O lowered the rate of quenching. The rate of triplet quenching by FcMN, where quenching results from motion of the aromatic probes in their triplet state to FcMN, generally followed the trend 3 Np* > 3 Ph* . 3 Py*. This trend, as well as the influence of coadsorbed H 2 O on quenching, have been explained by the effects of adsorption and molecular size on diffusion of these molecules in KY.

The photophysics of 1-hydroxypyrene, the acidity of its singlet excited state, and the nature of its photoionization process in polar media

“…The experimental details have been published in other studies. 10,11 It suffices here just to indicate some of the broad outlines of how the experiments were carried out. Steady state UV and fluorescence spectra were recorded using an SLM/ Aminco SPF 500 spectrofluorimeter and a Varian Carry 3 Spectrophotometer respectively.…”

Structure of adsorption complexes of water in zeolites of different types studied by infrared spectroscopy and inelastic neutron scattering

“…refs. [10][11][12][13][14]. However, in order to influence the adsorption properties of zeolites in a pre-determined manner by adsorbing small amounts of water detailed knowledge of the structure of adsorption complexes of the latter is extremely important.…”

Visual Observation of Contact‐Induced Intercrystalline Migration of Aromatic Species Adsorbed in Zeolites by Fluorescence Microscopy

“…Previous studies have demonstrated that the intracrystalline diffusivity of aromatic molecules such as Phe, anthracene, and naphthalene is affected by the degree of hydration of host zeolite Y. [29,30] For instance, small quantities (0.05-0.15 cm 3 g…”