The other methods for enhancement of photocatalytic activity are grafting co-catalysts. There are two kinds of co-catalysts in terms of its function: one is for separation of electrons and the other is for separation of holes. The former representative co-catalysts are Pt, Fe3+, and Cu2+ [9–12]. It was reported that Fe3+ and Cu2+ were grafted as amorphous oxide cluster [9,10], and reduced into Fe2+ and Cu+ by receiving one electron, respectively [11,12]. The reduced metal oxide cluster with reduced ions could return into the original state by giving more than one electron to molecular oxygen. The latter ones are CoOx, CoPi (CoPOx), IrOx, and RuOx which are used for water oxidation, among which CoPi is reported to be the most effective co-catalyst for water oxidation [13]. However, there were few reports concerning co-grafting effects on photocatalytic activity especially in gaseous phase. We expected that by co-grafting of both co-catalysts for separations of electrons and holes, photocatalytic activity in gaseous phase would be further enhanced. Moreover, complex of BiVO4 with the other materials of p-type semiconductor is also effective for enhancing photocatalytic activity.
