Regulating the H 2 O 2 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 H 2 O 2 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 H 2 O 2 photosynthesis capability via dominant oxygen reduction reaction (ORR) paths (O 2 –O 2 •– –H 2 O 2 and O 2 –O 2 •– –O 2 1 –H 2 O 2 ) and feeble water oxidation reaction (WOR) paths. With no sacrificial agents in the air, the H 2 O 2 photosynthetic rates of TB-COF were 5186 μmol g –1 h –1 and 4111 μmol g –1 h –1 in water and natural seawater, respectively. The seawater-produced H 2 O 2 can be directly utilized for tetracycline degradation, manifesting a big picture for wastewater treatment by seawater-produced H 2 O 2 . 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 H 2 O 2 photosynthetic performance and may enlighten the design of catalysts for H 2 O 2 photosynthesis.