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)₃²⁺) by oxygen. Oxygen saturated solutions of Ru(bpy)₃²⁺ typically show about 70% quenching (I₀/I=3.3), where I₀ and I are the peak intensities of the emission in N₂ and O₂, respectively. However, an aqueous suspension of Ru(bpy)₃²⁺-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 O₂ is occurring in the zeolite. Upon exposure of solid Ru–Na–Y (99% of intrazeolitic water) to N₂/O₂ dry gases, quenching in oxygen was found to be 5% (I₀/I=1.07). Partial dehydration at room temperature with loss of 33% of the water molecules from the zeolite led to 66% (I₀/I=2.96) quenching. Dehydration of Ru–Na–Y at 250 °C under vacuum overnight led to complete loss of intrazeolitic water and increased quenching to 90% (I₀/I=10.7). Nanocrystalline Ru(bpy)₃²⁺-zeolite Y upon vacuum dehydration lost 55% of the intrazeolitic water and showed 96% (I₀/I=25.3) quenching. The extent of quenching of Ru(bpy)₃²⁺ in zeolites by O₂ is by far the largest as compared to previously studied matrices, and is being attributed to confinement of O₂ in the supercages, which leads to increase in number of collisions with Ru(bpy)₃²⁺ and enhanced quenching. However, these samples showed complete lack of sensitivity (I₀/I=1) to oxygen upon exposure to water saturated gas or dissolved gas. Dealumination of zeolite framework by treatment with (NH₄)₂SiF₆ 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 O₂ increased.