Abstract: Defect engineering represents a potent strategy for the modification of electronic properties by introducing atomic vacancies in photocatalysts. However, the synergistic enhancement attributable to different types of atomic vacancies within a heterojunction, as well as their underlying mechanisms, remains sparsely studied. Here, the flexible g-C₃N₄ materials with varying nitrogen vacancies were prepared via a facile calcination method under different atmospheric conditions and then composited with CeO₂ nanocubes to construct Z-scheme heterojunction. It was observed that CeO₂ has abundant O vacancies, and the g-C₃N₄ form tertiary nitrogen defects at the center of the heptazine units under an NH₃ atmosphere treatment. The resulting enhancement in the interfacial built-in electric field, coupled with the synergistic effect of O and N vacancies within the Z-scheme heterojunction, has been demonstrated to significantly enhance charge transfer efficiency. This results in an optimized photoactivity with a H₂O₂ generation rate of 2.01 mmol g^-1 h^-1. This work opens an avenue for constructing and optimizing the heterogeneous photocatalysts by defect engineering technology, and provides deep insight to understand the nature of vacancy engineering in designing effective catalysts for solar energy conversion.

Key words: Photocatalysis, H₂O₂ production, Z-scheme, Defect engineering, Synergy effect