Molecular fusion in covalent organic frameworks promotes oxygen reduction and water oxidation for efficient photocatalytic H₂O₂ production

Covalent organic frameworks (COFs) have attracted much attention as photocatalysts for efficient hydrogen peroxide (H₂O₂) production. Herein, we propose a molecular fusion strategy to extend planar conjugated structures to significantly enhance H₂O₂ production performance from O₂ and H₂O. We synthesized BTS-COF and BTT-COF using 5,5′,5″-(benzene-1,3,5-triyl)tris(thiophene-2-carbaldehyde) and benzo[1,2-b:3,4-b′:5,6-b″]trithiophene-2,5,8-tricarbaldehyde as building blocks. BTT-COF exhibits excellent photocatalytic performance with a H₂O₂ production rate of 2904 µmol g⁻¹ h⁻¹, which is higher than that of BTS-COF (1786 µmol g⁻¹ h⁻¹). Experimental and theoretical investigations show that the fused ring structure in BTT-COF can greatly enhance the photoexcited charge transfer and change the local electronic structure. BTT-COF adopts the Pauling-type oxygen adsorption, which has lower adsorption energy. Unexpectedly, the water oxidation reaction (WOR) process of BTS-COF adopts a 4e⁻ pathway. The WOR process of BTT-COF is transformed from 4e⁻ to 2e⁻, thus improving the atom utilization efficiency and enhancing the photocatalytic H₂O₂ production performance. In addition, the antipathogenic concentration of H₂O₂ produced by BTT-COF at minimum inhibitory concentrations (MICs) can kill E. coli and S. aureus (100 µg mL⁻¹) by destroying the bacterial membranes, making BTT-COF a strong candidate as a novel nano-based antimicrobial material. This work provides valuable insights into the design and synthesis of efficient COF-based photocatalysts, and broadens the application of COFs in the antibacterial field, providing new strategies for developing advanced anti-infective materials in the future.