Designed Synthesis of Mesoporous sp2 Carbon-Conjugated Benzothiadiazole Covalent Organic Frameworks for Artificial Photosynthesis of Hydrogen Peroxide

Abstract

Artificial photosynthesis of hydrogen peroxide (H₂O₂) from ambient air, water, and sunlight has attracted considerable attention recently. Despite being extremely challenging to synthesis, sp² carbon-conjugated covalent organic frameworks (COFs) can be powerful and efficient materials for the photosynthesis of H₂O₂ due to desirable properties. Herein, we report the designed synthesis of an sp² carbon-conjugated COF, BTD-sp²c-COF, from benzothiadiazole and triazine units with high crystallinity and ultralarge mesopores (∼4 nm). The sp² carbon-conjugated skeletons guarantee BTD-sp²c-COF superior optoelectronic properties and chemical stability. BTD-sp²c-COF exhibits an exceptional efficiency of 3066 μmol g^–1 h^–1 from pure water and air, much better than that of BTD-imine-COF. In contrast, the resilience of BTD-imine-COF is compromised due to the participation of imine linkages in the oxygen reduction reaction. Importantly, in situ characterization and theoretical calculation results reveal that both benzothiadiazole and triazine units serve as oxygen reduction reaction centers for H₂O₂ photosynthesis through a sequential electron transfer pathway, while the vinylene bridged phenyls serve as water oxidation reaction centers. The sp² carbon-conjugated COFs pave the way for potent artificial photosynthesis.