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

Abstract

Zn-doped and Pb-doped β-Ga₂O₃-based photocatalysts were prepared by an impregnation method. The photocatalyst based on the Zn-doped β-Ga₂O₃ shows a greatly enhanced activity in water splitting while the Pb-doped β-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–β-Ga₂O₃ heterojunction is formed in the surface region of the Zn-doped β-Ga₂O₃ and a slower decay of photogenerated electrons is observed. The ZnGa₂O₄–β-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 β-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.