Photocatalytic activities enhanced for decompositions of organic compounds over metal-photodepositing titanium dioxide

Three kinds of metals (Pd, Cu, and Pt) have been photodeposited either individually or simultaneously on a transparent thin film of titanium dioxide (TiO₂) that covers the inside surface of a Pyrex glass tube and the photocatalytic activities of these preparations have been investigated based on the oxidative decompositions of 2,4-dinitrophenol (DNP), formaldehyde (HCHO), and trichloroethylene (TCE) dissolved in aqueous solutions. The initial rate of DNP decomposition by Pd/TiO₂ is 2.5 times higher than that by TiO₂. Similarly, the initial rate of HCHO decomposition by Pd/TiO₂ is increased by 5.1 times. Such remarkable enhancements in the photocatalytic decompositions are also obtained with Pd-Cu/TiO₂ and Pd-Cu-Pt/TiO₂. Furthermore, Pd/TiO₂ is effective to promote the photocatalytic decomposition of TCE. This is different from the experimental result that was recently reported by other researchers, who used Pd/TiO₂ particles in the form of aqueous slurries. Microscopic observations of the metals deposited on the TiO₂ films reveal that the morphologies of the metal-photodepositing TiO₂ preparations are remarkably different from that of the TiO₂ film; each metal possesses its own coating pattern. A series of the photocatalytic reaction experiments indicate that the photocatalytic activities of the metal-depositing TiO₂ preparations are superior to that of the TiO₂ film and are highly stable.