Oxygen transport in zeolite Y measured by quenching of encapsulated tris(bipyridyl)ruthenium

This study deals with emission quenching of zeolite encapsulated trisbipyridyl ruthenium (II) (Ru(bpy)(3)(2+)) by oxygen. Oxygen saturated solutions of Ru(bpy)(3)(2+) typically show about 70% quenching (I-0/I = 3.3), where I-0 and I are the peak intensities of the emission in N-2 and O-2, respectively. However, an aqueous suspension of Ru(bpy)(3)(2+)-zeolite Na-Y (Si/Al = 2.5) (abbreviated as Ru-Na-Y) showed no quenching at all. This observation motivated us to analyze how the transport of O-2 is occurring in the zeolite. Upon exposure of solid Ru-Na-Y (99% of intrazeolitic water) to N-2/O-2 dry gases, quenching in oxygen was found to be 5% (I-0/I = 1.07). Partial dehydration at room temperature with loss of 33% of the water molecules from the zeolite led to 66% (I-0/I = 2.96) quenching. Dehydration of Ru-Na-Y at 250 degreesC under vacuum overnight led to complete loss of intrazeolitic water and increased quenching to 90% (I-0/I = 10.7). Nanocrystalline Ru(bpy)(3)(2+)-zeolite Y upon vacuum dehydration lost 55% of the intrazeolitic water and showed 96% (I-0/I = 25.3) quenching. The extent of quenching of Ru(bpy)(3)(2+) in zeolites by O-2 is by far the largest as compared to previously studied matrices, and is being attributed to confinement Of O-2 in the supercages, which leads to increase in number of collisions with Ru(bpy)(3)(2+) and enhanced quenching. However, these samples showed complete lack of sensitivity (I-0/I = 1) to oxygen upon exposure to water saturated gas or dissolved gas. Dealumination of zeolite framework by treatment with (NH4)(2)SiF6 produced a framework of Si/Al = 9.5, and with SiCl4 a framework of Si/Al > 100. With increasing dealumination, the extent of quenching by dissolved 02 increased. (C) 2003 Elsevier Science Inc. All rights reserved.