Polarization engineering of ether-embedded covalent organic frameworks for boosting photocatalytic H2O2 production from seawater

Visible light-driven hydrogen peroxide (H 2 O 2 ) production from natural seawater over covalent organic frameworks (COFs) is becoming a challenge. In this work, a polarization strategy via incorporating oxo-ether ( O ) functional groups into COFs architecture was attempted and demonstrated to significantly enhance photocarriers separation. The strategy interestingly transformed the COFs morphology from rod-like flower clusters to sheet-like flower clusters. Furthermore, the monomer 4,4′-oxydianiline (OD) of the oxo-ether functionalized COFs (TpOD-COF) obtained a cost efficiency that was about 1794 times higher than the monomer benzidine (BD) formed non-functionalized COFs (TpBD-COF). TpOD-COF in real seawater achieved 4598 μmol·g −1 ·h −1 of H 2 O 2 productivity, and 10.2% of apparent quantum yield (AQY) without electron-proton donors and pure oxygen (O 2 ), which was 1.91 times higher than TpBD-COF. Mechanism studies revealed that TpOD-COF not only satisfies the thermodynamic requirement for the 2e − oxygen reduction reaction, but also indirectly enhances H 2 O 2 production through water oxidation, thereby establishing a cycle system that goes from water (H 2 O) to O 2 and then indirectly to H 2 O 2 , which promotes the overall reaction kinetics. More importantly, the catalyst did not deactivate in seawater; instead, the presence of ions further promoted electron transfer. Furthermore, the polar oxygen atoms served as additional hydrogen bond acceptors, enhancing the hydrogen-bonding network architecture. The system suggested a powerful functional-groups-mediated polarization engineering for the development of highly efficient metal-free photocatalysts.