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. (C) 2003 Elsevier B.V. All rights reserved.