Effects of doping on photocatalytic activity for water splitting of metal oxides and nitride

摘要

The effects of metal-ion doping or replacement on the photocatalytic performance for water splitting of d10 and d0 metal oxides and d10 metal nitride were studied. The photocatalysts examined were (1) α-Ga2-2xIn2xO3 and ZnGa2-2xIn2xO4 in which In3+ was added to Ga2O3 and ZnGa2O4, respectively, (2) YxIn2-xO3 being a solid solution of In2O3 and Y2O3, (3) metal ion doped CeO2, and (4) metal ion doped GaN. The photocatalytic activity of 1 wt % RuO2-loaded α-Ga2-2xIn2xO3 increased sharply with increasing x, reached a maximum at around x=0.02, and considerably decreased with further increase in x. The DFT calculation showed that the band structures of α-Ga2-2xIn2xO3 had the contribution of In 4d orbital to the valence band and of In5s orbital to the conduction band. Similar effects were observed for ZnGa2-2xIn2xO4. RuO2-dispersed YxIn2-xO3 had a capability of producing H2 and O2 in the range x=1.0-1.5 in which the highest activity was obtained at x=1.3. The structures of both InO6 and YO6 octahedra were deformed in the solid solution,, and the hybridization of In5s5p and Y4d orbitals in the conduction band was enhanced. Undoped CeO2 was photocatalytically inactive, but metal ion-doped CeO2 showed a considerable photocatalytic activity. The activation occurred in the case that metal ions doped had larger ion sizes than that of Ce4+. The small amount doping of divalent metal ions (Zn2+ and Mg2+) converted photocatalytically inactive GaN to an efficient photocatalyst. The doping was shown to produce p-type GaN which had the large concentration and high mobility of holes. The roles of metal ion doping and replacement in the photocatalytic properties are discussed.