The photocatalytic activity of rutile and anatase TiO2 electrodes modified with plasmonic metal nanoparticles followed by photoelectrochemical measurements

In the present work, we investigated the behavior of titanium dioxide photocatalysts decorated with plasmonic metal - gold and silver - nanoparicles (NPs) for the photooxidation of small organic molecules. The TiO2 samples were large surface area thin film electrodes formed either by thermal oxidation of the Ti metal (for the rutile films) or deposited on the same substrate by a sol-gel method (for the anatase films). The TiO2 films were subsequently decorated with Au nanostructures using either photodeposition or vacuum sputtering. The Ag nanostructures were formed on TiO2 by electrodeposition. Although both the Au-TiO2 and the Ag-TiO2 films yielded photoanodic currents under illumination with visible wavelengths, consistent with the resonant frequencies of plasmonic metal NPs, prolonged polarization resulted in the drastic drop of photoactivity. Such deactivation, that did not affect the range of near-UV wavelengths absorbed by the pristine TiO2, has been assigned to the surface oxidation of the plasmonic NPs progressively blocking the charge regeneration within the metal nanoparticles. These results raise questions in regard to the use of Au-TiO2 and Ag-TiO2 photocatalysts for sunlight-driven photodegradation of organic contaminants in water.