ELECTRON-SPIN-RESONANCE STUDIES OF PHOTOCATALYTIC INTERFACE REACTIONSOF SUSPENDED M TIO(2) (M=PT, PD, IR, RH, OS, OR RU) WITH ALCOHOL AND ACETIC-ACID IN AQUEOUS-MEDIA/

We present here the results of photocatalytic interface reactions betw een the catalysts shown in the title and acetic acid or alcohol (metha nol, ethanol, and 2-propanol) in aqueous solution. Irrespective of loa ded metal species in the platinum group, the same radical intermediate s, a methyl radical (.CH3) and a carboxymethyl radical (.CH2COOH), wer e recognized by observation of their ESR absorption from aqueous solut ion of the acetic acid at room temperature. Moreover transient interme diates of alpha-hydroxymethyl radical (.CH2OH), alpha-hydroxyethyl rad ical (CH3.CHOH), and alpha-hydroxypropyl radical (CH3.COHCH3) were obs erved in reactions with organic ingredients of methanol, ethanol and 2 -propanol, respectively. Our results suggest that a photocatalytic act ive site in the generation of the radical intermediates under UV illum ination is not on the metal surface but the TiO2 surface of the photoc atalysts. As a ''preintermediate'', existence of a hydroxyl radical (. OH) was presumed on the surface of the photocatalyst; the radical is c reated by electron transfer from a hydroxy anion (OH-) to an electron hole (p+) of TiO2. Thus, the most probable photocatalytic reaction mec hanism has been proposed which indicates the resultant electron transf er from OH- to H+ over the photoexcited M/TiO2.