Engineering Metal-Salen Covalent Organic Polymers for Boosted H₂O₂ Photosynthesis and Coupled Environmental...

Photocatalytic oxygen reduction reaction (ORR) is a promising route for sustainable H₂O₂ synthesis, enabling on-demand production and in situ water remediation, yet it is still hampered by poor charge separation and migration, as well as sluggish O₂ adsorption and activation. Herein, salen-based covalent organic polymers (COPs) possessing tunable metal site numbers and coordination environments are designed for photocatalytic H₂O₂ synthesis. Among them, ZnZn-salen-COP achieves an efficient H₂O₂ production rate of 8577 µmol g^-1 h^-1 in 10% benzyl alcohol (BA) without oxygen aeration, generating high-value compound, benzaldehyde (BAD) with a production rate of 24 mmol g^-1 h^-1. The experimental study and theoretical calculation confirm that the dual metallosalen structure promotes visible-light absorption and charge carrier separation efficiency, boosting O₂ adsorption and lowering the reaction potential barrier, enabling H₂O₂ production mainly via indirect 2e^- ORR. Furthermore, ZnZn-salen-COP enables efficient H₂O₂ production for in situ uranium extraction (98% efficiency) and organic degradation (methyl orange ∼100%, BPA∼98.4% and tetracycline ∼94.1%). This work provides insight into designing highly efficient photocatalysts for water treatment via in situ H₂O₂ generation by engineering metal sites and coordination environments.