Facile preparation of novel nickel sulfide modified KNbO3 heterojunction composite and its enhanced performance in photocatalytic nitrogen fixation

This work was designed to prepare a novel NiS/KNbO3 p-n heterojunction composite for efficient photocatalytic nitrogen fixation under simulated sunlight. The NiS/KNbO3 photocatalyst was prepared through a two-step hydrothermal method. X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy analyses proved that NiS nanoparticles were closely decorated on the surface of KNbO3 nanorods, to facilitate the migration of electrons between the two semiconductors. Mott-Schottky analysis indicated that the Femi level of KNbO3 is higher than that of NiS. Thus, the electron migration from KNbO3 to NiS occurs naturally. This migration elevates the band potential of NiS, makes NiS/KNbO3 form a type-II photocatalyst, and generates an internal electric field in the composite. The synergetic effect of the internal electric field and the type-II band structure endows NiS/KNbO3 with high efficiency in the spatial separation of photogenerated electron-hole pairs, verified by electrochemical impedance spectroscopy and transient photocurrent experiments. Therefore, NiS/KNbO3 presents good efficiency in photocatalytic N-2 reduction with an NH3 production rate of 155.6 mol (n) over tildeL(1)(n) over tildeg(1)(n) over tildeh(1), which is 1.9 and 6.8 times higher than those of KNbO3 and NiS, respectively. UVvisible diffuse reflectance spectroscopy and N-2-adsorption experiments were also performed to investigate the effect of light absorption and surface area on the photocatalytic reaction. Nevertheless, compared with the great promotion effect in charge separation, the contribution of the two factors can be ignored. (C) 2021 Elsevier Inc. All rights reserved.