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

- Fe3+ is recyclable with all catalysts except WO3.
- Cu2+ is recyclable with all catalysts except P25.
- Fe3+ is regenerated through H2O2 photogenerated from TiO2.
- Cu2+ is regenerated through dissolved O2 in water.