Photochemical Charge Transfer and Hydrogen Evolution Mediated by Oxide Semiconductor Particles in Zeolite-Based Molecular Assemblies

Two integrated systems for light-induced vectorial electron transfer are described. Both utilize photosensitized semiconductor particles grown in linear channel zeolites as components of the electron transfer chain. One system consists of internally platinized zeolites L and mordenite containing TiO 2 particles and methylviologen ions, with a size-excluded photosensitizer, tris(2,2‘-bipyridyl-4,4‘-dicarboxylate)ruthenium (RuL 3 2+ ), adsorbed on the external surface of the zeolite/TiO 2 composite. In the other system, Nb 2 O 5 replaces TiO 2 . The kinetics of photochemical electron transfer reactions and charge separation were studied by diffuse reflectance flash photolysis. Despite very efficient initial charge separation, the TiO 2 system does not generate hydrogen photochemically in the presence of an electrochemically reversible, anionic electron donor, methoxyaniline N, N ‘-bis(ethyl sulfonate). Only the Nb 2 O 5 -containing composites evolved hydrogen photochemically under these conditions. These results are interpreted in terms of semiconductor band energetics and the irreversibility of electron transfer from Nb 2 O 5 to intrazeolitic platinum particles.