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

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.