Enhanced built-in electric fields in novel Bi₂MoO₆/graphdiyne S-scheme heterojunction enable superior molecular oxygen activation for broad-spectrum antibiotic degradation

Efficient activation of molecular oxygen under visible light is essential for generating reactive oxygen species (ROS) toward environmental remediation but remains challenging due to rapid electron-hole recombination. Herein, a novel S-scheme Bi₂MoO₆/graphdiyne (BMO/GDY) heterojunction was successfully constructed via a hydrothermal route. The intimate interfacial contact and built-in internal electric field between BMO and GDY facilitate effective spatial charge separation, while retaining strong redox ability. Density functional theory calculations indicate that BMO/GDY significantly enhances the adsorption of molecular oxygen, which can lower the adsorption energy from 0.19 eV (BMO) to -0.82 eV. Meanwhile, the OO bond in BMO/GDY is elongated and the electron density on the adsorbed O₂ molecule is increased, which facilitates the O₂ activation to produce ROS. Mechanistic studies also reveal that O₂ is effectively activated on the BMO/GDY interface to generate superoxide radical, which subsequently serve as the key intermediate species for the formation of singlet oxygen and hydroxyl radical. These ROS, together with photogenerated holes, synergistically drive the degradation of tetracycline (TC), the optimal BMO/GDY-4 heterojunction achieves nearly 100 % TC removal within 18 min and maintains excellent photostability. This work not only elucidates the mechanism of molecular oxygen activation over S-scheme heterojunctions, but also offers a strategically guided pathway for engineering high-activity photocatalysts for antibiotic pollution control.