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.