Primary passages for various TiO2 photocatalysts studied by means of luminol chemiluminescent probe

Photocatalytic properties of TiO2 aqueous suspension were analyzed by means of the chemiluminescent probe method, which enables us to monitor superoxide ions (O-.(2)-) and hydrogen peroxide (H2O2) in the reaction system. The amount of produced O-.(2)- is independent of the surface properties of TiO2, while H2O2 is formed significantly for smaller particles with large amount of surface hydroxyl groups. The amount of produced (OH)-O-. radicals was estimated from the effect of Cl- ions on the O-.(2)- formation and found to be large for the TiO2 having a large amount of surface hydroxyl groups. This difference is explained to originate from the different structure of hole intermediates, based on the ESR measurements for these powders at 77 K.