Regulating the H₂O₂ Photosynthetic Activity of Covalent Organic Frameworks through Linkage Orientation

Imine-linked isomeric covalent organic frameworks (COFs) with opposite linkage orientations are not rare, but their structure and photocatalytic property corrections are still puzzling, let alone the emerging photosynthetic H2O2 performance. Herein, a pair of isomeric COFs (TB-COF and TA-COF) with reversed imine linkages was fabricated. Compared to TA-COF, TB-COF exhibited larger dipole moments and better charge carrier separation efficiency, resulting in superior H2O2 photosynthesis capability via dominant oxygen reduction reaction (ORR) paths (O-2-O-2(center dot-)-H2O2 and O-2-O-2(center dot-)-O-2(1)-H2O2) and feeble water oxidation reaction (WOR) paths. With no sacrificial agents in the air, the H2O2 photosynthetic rates of TB-COF were 5186 mu mol g(-1) h(-1) and 4111 mu mol g(-1) h(-1) in water and natural seawater, respectively. The seawater-produced H2O2 can be directly utilized for tetracycline degradation, manifesting a big picture for wastewater treatment by seawater-produced H2O2. Theoretical calculations revealed that in TB-COF and TA-COF, the hydroxyl-rich benzene ring was the photooxidation part and the triazine unit was the primary photoreduction part. Through linkage-orientation regulation, the electronic structures, charge migration property, and energy barrier of the rate determination step in the 2e(-) ORR and 2e(-) WOR paths can be well-modulated. The current work provides insight into the effect of the linkage orientation on H2O2 photosynthetic performance and may enlighten the design of catalysts for H2O2 photosynthesis.