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

摘要

The effects of metal-ion doping or replacement on the photocatalytic performance for water splitting of d10 and d° metal oxides and d~(10) metal nitride were studied. The photocatalysts examined were (1) α-Ga_(2-2x)In_(2x)O_3 and ZnGa_(2-2x)In_(2x)O_4 in which In~(3+) was added to Ga_2O_3 and ZnGa_2O_4, respectively, (2) Y_xIn_(2-x)O_3 being a solid solution of In_2O_3 andY_2O_3, (3) metal ion doped CeO_2, and (4) metal ion doped GaN. The photocatalytic activity of 1 wt % RuO_2-loaded α-Ga_(2-2x)In_(2x)O_3 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-Ga_(2-2x)In_(2x)O_3 had the contribution of In 4d orbital to the valence band and of In5s orbital to the conduction band. Similar effects were observed for ZnGa_(2-2x)In_(2x)O_4. RuO_2-dispersed Y_xIn_(2-x)O_3 had a capability of producing H_2 and O_2 in the range x=1.0-1.5 in which the highest activity was obtained at x=1.3. The structures of both InO_6 and YO_6 octahedra were deformed in the solid solution,, and the hybridization of In5s5p and Y4d orbitals in the conduction band was enhanced. Undoped CeO_2 was photocatalytically inactive, but metal ion-doped CeO_2 showed a considerable photocatalytic activity. The activation occurred in the case that metal ions doped had larger ion sizes than that of Ce~(4+). The small amount doping of divalent metal ions (Zn~(2+) and Mg~(2+)) 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.