Remote Bleaching of Methylene Blue by UV-Irradiated TiO₂ in the Gas Phase

The remote bleaching of a dye, methylene blue, by UV-irradiated TiO 2 was studied in the gas phase. A TiO 2 -coated glass plate was faced to a glass plate coated with methylene blue, separated by a small gap (12.5 to 500 μm), and the TiO 2 coating was irradiated with UV light from the back. As a result, methylene blue was bleached in the gas phase containing oxygen, although it was inhibited by ethanol vapor. The remote bleaching is not a simple reduction of methylene blue to its leuco form; methylene blue is probably oxygenated or decomposed. The bleaching process may be caused by active oxygen species that are generated at the TiO 2 surface and transported to the methylene blue layer.