Enhanced photocatalytic N2 fixation using KNbO3/Bi4O5Br2 type II heterojunction

The fabrication of heterojunction catalysts is an effective strategy to enhance charge separation efficiency, thus boosting the performance of photocatalysts. This work presents the synthesis and investigation of a novel KNbO₃/Bi₄O₅Br₂ heterostructure catalyst for photocatalytic N₂–to–NH₃ conversion under light illumination. While morphology analysis revealed KNbO₃ microcubes embedded within Bi₄O₅Br₂ nanosheets, the composite exhibited no significant improvement in specific surface area or optical property compared to Bi₄O₅Br₂ due to the relatively wide band gap and low surface area of KNbO₃. The main contribution lies in the enhanced separation efficiency of photogenerated electrons and holes. Besides, the band structure analysis suggests that KNbO₃ and Bi₄O₅Br₂ exhibit suitable band potentials to form a type II heterojunction. Benefiting from the higher Fermi level of KNbO₃ than Bi₄O₅Br₂, the electron drift at the contact region thus occurs and leads to the formation of a built-in electric field with the direction from KNbO₃ to Bi₄O₅Br₂, accelerating electron migration and improving the operational efficiency of the photocatalysts. Consequently, the KNbO₃/Bi₄O₅Br₂ catalyst shows an increased photoactivity, achieving an NH₃ generation rate 1.78 and 1.58 times those of KNbO₃ and Bi₄O₅Br₂, respectively. This work may offer valuable insights for the design and synthesis of heterojunction composite photocatalysts.