ELECTRON-TRANSFER IN AQUEOUS COLLOIDAL SNO2 SOLUTIONS

Electron-transfer reactions on transparent colloidal Sn02 have been examined by use of radiolytically generated reducing radicals, direct band-gap excitation, and photosensitization using Ru(bpy)32+. Colloidal Sn02 was found to be cathodically stable under the reducing conditions examined. Quantitative amounts of H2 formed in solution following electron transfer from radiolytically generated isopropyl alcohol radicals. No hydrogen, however, was produced if the sol was illuminated at 300 nm, even in the presence of a hole scavenger. Yet, if the electron acceptor methylviologen was present, the characteristic blue color of the viologen radical formed readily with time of illumination. Charge transfer from excited, adsorbed Ru(bpy)32+ was found to be strongly dependent on pH and electrolyte concentration. This has been scribed to the effect that pH and added electrolyte both control the electrostatic potential on the colloidal Sn02, which in turn influences the adsorption of the ruthenium complex and therefore the extent of quenching. © 1990, American Chemical Society. All rights reserved.