Donor–acceptor-type β-ketoenamine-linked covalent organic frameworks for enhanced photocatalytic hydrogen peroxide production

Abstract

Covalent organic frameworks (COFs) have become increasingly prominent in photocatalytic synthesis of hydrogen peroxide (H₂O₂), owing to their structural versatility, functional tenability, and photoelectric properties. Herein, we report CN-functionalized β-ketoenamine-linked COFs with donor–acceptor (D–A) architectures for enhanced photocatalytic H₂O₂ production. The rational integration of hydroxyl groups and cyano groups into the D–A architecture of COFs is a promising strategy to enhance their electron/proton transfer capabilities and modulate the electronic environment of catalytically active sites. The resulting COF-TpDb and COF-HbDb exhibit high crystallinity, moderate specific surface area, and superior hydrophilicity. Notably, COF-TpDb achieved efficient H₂O₂ generation with a high rate of 3272 µmol g⁻¹ h⁻¹ and an apparent quantum yield (AQY) of 3.31% under simulated sunlight (AM 1.5 G) irradiation in pure water, without the addition of any sacrificial agents. Compared with COF-HbDb, COF-TpDb demonstrated faster charge separation and prolonged photogenerated carrier lifetimes, thereby exhibiting higher catalytic efficiency. Electron paramagnetic resonance (EPR) and other characterization studies confirm the generation of superoxide radical anion (O₂˙⁻) intermediates during the photocatalytic reaction. Theoretical calculations further reveal robust charge transfer efficiency and enhanced oxygen adsorption capacity of the two COFs. This work highlights the synergistic effect of β-ketoenamine linkages and cyano groups in enhancing photocatalysis. Moreover, the findings of this study provide valuable insights into development of high-efficiency COF photocatalytic systems for sustainable H₂O₂ production.