Preparation of a NiO/KNbO3 nanocomposite via a photodeposition method and its superior performance in photocatalytic N2 fixation

Abstract

This paper reports the synthesis of a NiO loaded KNbO₃ nanocomposite via a photodeposition method and its application in photocatalytic N₂ fixation for the first time. Results indicated that the NiO/KNbO₃ composite displayed superior photocatalytic efficiency in NH₃ production under simulated sunlight illumination. The optimal NiO/KNbO₃ sample showed an NH₃-generation rate of 470.6 μmol g⁻¹ h⁻¹, which reaches 4.8 times that of pristine KNbO₃. Various characterization techniques including powder X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflection spectroscopy (DRS), transient photocurrent, electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) were applied to reveal the mechanism behind the high photoactivity of NiO/KNbO₃. The addition of NiO nanoparticles showed a slight effect on the specific surface area and the optical properties of KNbO₃, but elevated the charge separation efficiency which was verified to be the key role in affecting the photocatalytic reaction. The introduced NiO fabricated a p–n heterojunction structure with KNbO₃ and hence achieved enhanced efficiency in separating electrons and holes via a type-II mechanism. The cycling test further demonstrated that the NiO/KNbO₃ sample has high photocatalytic stability, indicating its good potential in photocatalytic nitrogen fixation.