Photocatalytic bactericidal effect of TiO2 thin films: Dynamic view of the active oxygen species responsible for the effect

The role of active oxygen species in the photocatalytic bactericidal effect was investigated using a thin transparent titanium dioxide (TiO2) him. The viable number of Escherichia coli (E. coli) significantly decreased on the illuminated TiO2 him, and the bactericidal effect was observed even when E. coli was separated from the TiO2 surface with a 50 mu m porous membrane. Mannitol, a hydroxyl radical scavenger, inhibited the effect only in the absence of the membrane. In contrast, catalase inhibited the effect in all cases. On the basis of these results, the long-range bactericidal effect of hydrogen peroxide was proposed, together with a cooperative effect due to other oxygen species. (C) 1997 Elsevier Science S.A.