Enhanced photocatalytic nitrogen fixation over MnOx-modified O-KNbO3: impact of oxygen vacancies and MnOx loading

Abstract

KNbO₃, long recognized for its applications in photocatalytic hydrogen production, has recently emerged as a highly promising candidate for photocatalytic nitrogen fixation. This study aims to enhance the photocatalytic nitrogen fixation performance of KNbO₃ by introducing oxygen vacancies and loading manganese oxide (MnO_x) nanoparticles. The catalyst was prepared using a combination of sodium borohydride reduction and photodeposition methods. The morphology, structure, and physicochemical properties of the synthesized MnO_x/O-KNbO₃ composite were systematically investigated using various characterization techniques and density functional theory calculations. The results show that the introduced oxygen vacancies, as active sites, are beneficial to the adsorption and activation of N₂, while promoting the migration of bulk carriers through the adjustment of the electronic structure. The loading of MnO_x further promotes the effective separation of surface photo-generated electrons and holes, resulting in significantly enhanced catalytic activity during the nitrogen fixation reaction. The photocatalytic nitrogen fixation rate of MnO_x/O-KNbO₃ reached 352 μmol L⁻¹ g⁻¹ h⁻¹, which is 5.4 times that of KNbO₃ and 2.6 times that of O-KNbO₃. This work offers new insights into improving the application of KNbO₃ in photocatalytic nitrogen fixation and demonstrates the synergistic effects of oxygen vacancies and co-catalysts, highlighting significant scientific value and application prospects for the future development of efficient nitrogen fixation materials.