Most commonly studied wide bandgap semiconductors have conduction band minima  positive enough for the photoreduction of Cr(VI) to occur ( Fig. 1C). During light irradiation, photogenerated holes are also produced, which can be used to oxidize water or a sacrificial agent, Dn ( Fig. 1A). To be able to oxidize water, the valence band edge of the semiconductor must be more positive than the reduction potential for OH−/O2. The net reaction for Cr(VI) reduction and concurrent water oxidation in acidic and neutral environments are shown in Eqs.