Effects of Zn2+ and Pb2+ dopants on the activity of Ga2O3-based photocatalysts for water splitting

Zn-doped and Pb-doped beta-Ga2O3-based photocatalysts were prepared by an impregnation method. The photocatalyst based on the Zn-doped beta-Ga2O3 shows a greatly enhanced activity in water splitting while the Pb-doped beta-Ga2O3 one shows a dramatic decrease in activity. The effects of Zn2+ and Pb2+ dopants on the activity of Ga2O3-based photocatalysts for water splitting were investigated by HRTEM, XPS and time-resolved IR spectroscopy. A ZnGa2O4-beta-Ga2O3 heterojunction is formed in the surface region of the Zn-doped beta-Ga2O3 and a slower decay of photogenerated electrons is observed. The ZnGa2O4-beta-Ga2O3 heterojunction exhibits type-II band alignment and facilitates charge separation, thus leading to an enhanced photocatalytic activity for water splitting. Unlike Zn2+ ions, Pb2+ ions are coordinated by oxygen atoms to form polyhedra as dopants, resulting in distorted surface structure and fast decay of photogenerated electrons of beta-Ga2O3. These results suggest that the Pb dopants act as charge recombination centers expediting the recombination of photogenerated electrons and holes, thus decreasing the photocatalytic activity.