Abstract
The production and decay of singlet molecular oxygen (¹O₂) in TiO₂ photocatalysis were investigated by monitoring its phosphorescence under various reaction conditions. First, the effects of additives such as KBr, KSCN, KI, H₂O₂, and ethanol on the amount of ¹O₂ produced by photo excitation of P25 TiO₂ were measured. The same additives were employed to investigate the effect on the amount of ・O₂^- produced. Comparison between the effects on ¹O₂ and ・O₂^- suggested that ¹O₂ is formed by the electron transfer mechanism, the reduction of molecular oxygens to ・O₂^- by photogenerated electrons and the subsequent oxidation of ・O₂^- to ¹O₂ by photogenerated holes. The formation of ¹O₂ decreased at pH < 5 and pH > 11, indicating that the intermediate ・O₂^- is stabilized at the terminal OH site of the TiO₂ surface in the pH range of 5 < pH < 11. Eighteen commercially available TiO₂photocatalysts were compared on the formation of ¹O₂ and ・O₂^- in an aqueous suspensionsystem. The formation of ¹O₂ was increased with decreasing size of TiO₂ particles,indicating that a large specific surface area causes a higher possibility of reductionproducing ・O₂^- and then a large amount of ¹O₂ is formed. The difference in the crystal phase (rutile and anatase) did not affect the formation of ¹O₂.

doi:10.1016/j.apcata.2008.02.012

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