Ru(bpy)32+/TiO2-Codoped Zeolites: Synthesis, Characterization, and the Role of TiO2 in Electron Transfer Photocatalysis

Novel heterogeneous photocatalysts were developed which are able to transfer electrons from excited Ru(II) donors within the zeolite framework to Co(III) acceptor complexes in the exterior. The materials were prepared and characterized by elemental analysis, electrochemical methods, diffuse reflectance, and raster and transmission electron microscopy. The catalysts consist of zeolite Y-encapsulated Ru(bpy)32+ (bpy = 2,2'-bipyridine) sensitizers in close proximity to TiO2 nanoparticles on the same support. The photophysical properties of Ru(bpy)32+ within the zeolite supercages were investigated at different loadings of Ru(bpy)32+ and TiO2. The photoexcited MLCT state of the zeolite-entrapped Ru(bpy)32+ reacts via electron transfer with Co(dpphen)33+ (dpphen = 4,7-diphenyl-1,10-phenanthroline) in the exterior of the zeolite particles. The relative quenching of Ru(bpy)32+ by external Co(dpphen)33+ increases as the TiO2 content within the zeolite is increased, where electron transfer from Ru(bpy)32+ complexes within the interior of the zeolite are able to transfer electrons to Co(dpphen)33+. This observation indicates that electrons can be transported from the interior of the zeolite to the surface in the presence of an appropriate electron relay, such as TiO2 nanoparticles.