Enhanced photocatalytic oxygen evolution over Mo-doped Ca2NiWO6 perovskite photocatalyst under visible light irradiation

Ying Luo, Jiawei Xue, Xiaodi Zhu, Jose Daniel, Xiang Gao, Song Sun,* Chen Gao* and Jun Bao* A series of Mo-doped Ca2NiWO6 (Ca2NiW1 xMoxO6, x1⁄4 0–0.05) samples were synthesized by a solid-state reaction. The physical and optical properties of these photocatalysts were characterized by X-ray diffraction, X-ray absorption fine structure, UV-visible diffuse reflectance spectra, and the band structure along with density of states were calculated by the plane-wave-based density functional theory. The photocatalytic activity of oxygen evolution from water was evaluated under visible light irradiation. The Mo doping significantly increased the photocatalytic activity of Ca2NiWO6. The optimal Ca2NiW0.97Mo0.03O6 showed an oxygen evolution rate approximately 2 times higher than that of the pure Ca2NiWO6. The characterization results indicated that the Mo-doped Ca2NiWO6 maintained the double perovskite structure. The Mo ions were substituted into the W sites in the lattice, causing a certain amount of lattice distortion and promoting the formation of oxygen vacancies. Furthermore, the Mo doping introduced impurity energy levels into the band structure of Ca2NiWO6. Consequently, the conduction band changed from discrete to continuous and the bottom of the conduction band was shifted to more positive potential, compared to that of pure Ca2NiWO6, leading to a lower band gap and higher absorbance in the wider visible light region. These characteristics are responsible for the high photocatalytic activity of the oxygen evolution reaction.