Different recycle behavior of Cu2+ and Fe3+ ions for phenol photodegradation over TiO2 and WO3

Abstract

Photocatalytic degradation of organic pollutants on TiO2 and WO3 have been widely studied, but the effects of Cu2+ and Fe3+ ions still remain unclear. In this work, we have found that the recycle behavior of Cu2+ and Fe3+ are greatly dependent on the photocatalytic activity of metal oxide used. With TiO2 (P25, anatase, and rutile), all the time profiles of phenol degradation in water under UV light well fitted to the apparent first-order rate equation. On the addition of Cu2+, phenol degradation on anatase, rutile and WO3 also followed the first-order kinetics. On the addition of Fe3+, the initial rate of phenol degradation on each oxide was increased, but only the reactions on three TiO2 became to follow the first order kinetics after half an hour. The relevant rate constants for phenol degradation in the presence of Cu2+ or Fe3+ were larger than those in the absence of metal ions. Under visible light, phenol degradation on WO3 was also accelerated on the addition of Fe3+ or Cu2+. Moreover, several influencing factors were examined, including the metal ion photolysis in solution. It becomes clear that as electron scavengers of TiO2 and WO3, Fe3+ is better than Cu2+, while they are better than O2. We propose that Fe3+ recycle occurs through H2O2, photogenerated from TiO2, not from WO3, while Cu2+ regeneration on a moderate photocatalyst is through the dissolved O2 in water.