Spectroscopic Studies of Colloidal Solutions of Nanocrystalline Ru(bpy)32+−Zeolite Y

Abstract

Preparation of suspensions of Ru(bpy)32+−zeolite Y has made it possible to use conventional optical transmission spectroscopic methods to examine the entrapped Ru(bpy)32+ species within the zeolite. To prepare the suspensions, the surface hydroxyl groups of nanocrystalline zeolite Y were silylated using n-octadecyltrichlorosilane. The hydrocarbon sheath on the surface of the zeolites prevented agglomeration of the particles and made the surface hydrophobic enough for dispersion in toluene. The spectroscopic properties of the entrapped Ru(bpy)32+ were measured via transmission techniques. For low levels of zeolite in the suspension (1 mg/10 mL), the scattering was low, and the absorption and fluorescence spectra of Ru(bpy)32+-entrapped zeolite Y were quantitatively identical to the solution spectra with comparable Ru(bpy)32+ concentrations. This suggests that all of the Ru(bpy)32+ inside the zeolite is being sampled and the extinction coefficient of the complex is not altered upon incorporation inside the zeolite. The nature of the quenching mechanism in the Ru(bpy)32+−viologen−zeolite Y system was studied by steady-state fluorescence and lifetime measurements, and it was determined to be mostly due to static quenching. Intrazeolitic electron transfer from the photogenerated viologen radical to Ru(bpy)33+ was followed by flash photolysis, and information about the dynamics of the electron-transfer process was obtained. Comparison of the electron-transfer and quenching data with previous studies on zeolite samples examined by diffuse reflectance methods led to the conclusion that, in reflectance measurements, mostly the surface of the zeolite is sampled. The suspensions, on the other hand, provide a method to examine molecules inside the crystal. Overall, this study demonstrates that zeolite-entrapped complexes can be examined using transmission spectroscopic techniques by using nanocrystalline zeolites with modified surfaces.