Reaction Mechanism of Cu(II)-Grafted Visible-Light Responsive TiO2 and WO3 Photocatalysts Studied by Means of ESR Spectroscopy and Chemiluminescence Photometry

The reaction mechanism of visible-light responsive Cu(II)-grafted TiO 2 and WO 3 photocatalysts was analyzed by detecting trapped holes and electrons by means of electron spin resonance (ESR) spectroscopy and O 2 •- and H 2 O 2 by chemiluminescence photometry. At first, the photocatalytic activities were confirmed for acetaldehyde decomposition in gas phase under 470 nm light emitting diode (LED) irradiation. The reduction of grafted Cu 2+ ions and the alternative reduction of O 2 by the resultant Cu + ions were shown by ESR measurements at 77 K for both photocatalysts under irradiation of visible light (500 W high pressure Hg-lamp with a 500 nm sharp-cut-filter). One-electron reduction product for O 2, that is, O 2 •-, was detected in aqueous suspension by 442 nm irradiation for Cu(II)/TiO 2 . On the other hand, only two-electron reduction was observed for Cu(II)/WO 3 where Cu 2+ species mainly act as a catalyst since the optical absorption mainly causes band gap excitation. Based on these observations, the difference in the reaction mechanism of Cu(II)/TiO 2 photocatalyst and Cu(II)/WO 3 photocatalysts was discussed.