Efficient Photon Conversion via Double Charge Dynamics CeO₂–BiFeO₃ p–n Heterojunction Photocatalyst Promising toward N₂ Fixation and Phenol–Cr(VI) Detoxification

For better exciton separation and high catalytic activity, the most trailblazing stratagem is to construct defect engineered low-dimensional p–n heterojunction framed photocatalytic systems. In this context, we have developed a rod–sheet (1D–2D) p–n heterojunction of MCeO₂–BiFeO₃ by a simple hydrothermal method and scrutinized its photocatalytic performance toward N₂ fixation and phenol/Cr­(VI) detoxification. The intimate contact between MCeO₂ and BiFeO₃ in the junction material is well established via X-ray diffraction (XRD), UV–vis diffuse reflectance spectrosopy (DRS), transmission electron microscopy (TEM), and photoelectrochemical studies. Further, scanning electron microscopy (SEM) and TEM pictures clearly support the decoration of MCeO₂ nanorods over BiFeO₃ sheets and also depict the junction boundary. Additionally, photoluminescence (PL), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and Raman measurements give solid evidence toward the presence of an oxygen vacancy. Moreover, the Mott–Schottky result indicates a feasible band edge potential favoring the p–n heterojunction with a built-in electric field between BiFeO₃ and MCeO₂ favoring a double charge dynamic. The MCeO₂–BFO p–n junction displays a notable catalytic activity, i.e., 98.2% Cr­(VI) reduction and 85% phenol photo-oxidation, and produces 117.77 μmol h^–1 g^–1 of ammonia under light irradiation. Electrochemical analysis suggests a four-electron/five proton-coupled N₂ photoreduction pathway. The designed oxygen vacancy oriented p–n heterojunction suffering double charge migration shows significant catalytic performance due to effective electron–hole separation as justified via PL, electrochemical impedance spectra (EIS), and Bode phase analysis.