Hydroxyl Radical Generation Depending on O_2 or H_2O by a Photocatalyzed Reaction in an Aqueous Suspension of Titanium Dioxide

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Photocatalytic production of the electron (e^-) and positive hole (h^+) in an aqueous suspension of TiO_2 (anatase form) under illumination by near-UV light (295-390nm) generated the superoxide (O^-_2) and hydroxyl radical (・OH), which both proceeded linearly with reaction time, while H_2O_2 accumulated non-linearly. Under anaerobic conditions (introduced Ar gas), the yields of three active species of oxygen were decreased to 10-20% of those detected in the air-saturated reaction. The electron spin resonance (ESR) signal characteristics of ・OH were obtained when a spin trap of 5,5-dimthyl-1-pyrroline-N-oxide (DMPO) was included in the illuminating mixture. The intensity of the ESR signal was increased by Cu/Zn superoxide dismutase, and decreased under anaerobic conditions, amounting to only 20% of the intensity detected in the aerobic reaction. The addition of H_2O_2 to the reaction mixture resulted in about an 8-fold increase of ・OH production in the anaerobic reaction, but only about 1.5-fold in the aerobic reaction, indicating that e^- generated by the photocatalytic reaction reduced H_2O_2 to produce ・OH plus OH^-. On the other hand, D_2O lowered the yield of ・OH generation to 18% under air and 40% under Ar conditions, indicating the oxidation of H_2O by h^+. The addition of Fe (III)-EDTA as an electron acceptor effectively increased ・OH generation, 2.3-fold in the aerobic reaction and 8.4-fold in the anaerobic reaction, the yield in the latter exceeding that in the air-saturated reaction.
社団法人日本農芸化学会の論文
1998-12-23

Hydroxyl Radical Generation Depending on O_2 or H_2O by a Photocatalyzed Reaction in an Aqueous Suspension of Titanium Dioxide

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