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

Abstract

A series of Mo-doped Ca₂NiWO₆ (Ca₂NiW_1−xMo_xO₆, x = 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 Ca₂NiW_0.97Mo_0.03O₆ 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 Mo⁶⁺ ions were substituted into the W⁶⁺ 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.