Gaseous Diffusion of Active Oxygen Species Generated at Photocatalyst and its Applications

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TiO_2 photocatalysts have been known to exhibit strong oxidizing abilities under UV light, which could oxidize most organic species. It has been believed that the oxidative decomposition of organic species takes place only at the TiO_2 surface. However, we have recently found that active oxygen species not only exist on the TiO_2 surface, but also diffuse through the gas phase and oxidize organic species placed apart from the TiO_2. Silicon, diamond, silver, and copper could also be oxidized by this phenomenon, remote oxidation. Remote oxidation of various targets using photomask was compared to Fenton and photo-Fenton reactions. The results suggested that the active species directly oxidizeing substrates was most likely hydroxyl radical. Varying the distance between the TiO_2-coated photomask and substrates from 10 to 100 μm showed similar patterns on the substrate. Based on these results, the mechanism of the reaction was proposed that hydrogen peroxide generated at the TiO_2 surface diffuses to targets through air, where the hydrogen peroxide is photoactivated and then decomposed to hydroxyl radical, which, in turn, oxidizes the targets. Photocatalytic lithography was developed based on the remote oxidation effect with resolution of 〜5 μm.