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