Acceleration of oxidations and retardation of reductions in photocatalysis of a TiO2/SnO2 bilayer-type catalyst

An anatase TiO2 film (75 +/- 5 nm thick) was formed on SnO2 film (580 +/- 80 nm thick) coated soda-lime glass by a sol-gel method (TiO2/SnO2/glass). Depth profiles of the compositions de;ermined by X-ray photoelectron spectroscopy confirmed that the amounts of Na+ and F- ions are negligibly small throughout the TiO2 film. The activities for four kinds of photocatalytic reactions (nu) were examined under no external applied potential in comparison with those of a TiO2/quartz standard sample (nu(0)) The TiO2/SnO2/glass bilayer-type photocatalyst showed remarkably higher activities for oxidations (nu/nu(0) = 3.0 +/- 0.2), whereas the activities for reductions are lower (nu/nu(0), = 0.62 +/- 0.03). These results could be explained by efficient charge separation via the interfacial electron transfer from TiO2 to SnO2. (C) 2000 The Electrochemical Society. S0013-4651 (00)03-020-2. All rights reserved.