Keto-enamine-based covalent organic framework with controllable anthraquinone moieties for superior H₂O₂ photosynthesis from O₂ and water

Photocatalytic H₂O₂ production is a promising strategy for decentralized applications, but to realize efficient H₂O₂ production in the ambient conditions and absence of organic sacrifice remains challengeable. Herein, anthraquinone functionalized covalent organic frameworks (TpAQ-COFs) were fabricated by β-ketoenamines links of 2,6-diaminoanthraquinone (AQ) and 2, 4, 6-triformylphloroglucinol (Tp), and the structures and compositions were tuned by controlling the condensation time. The increase of time favors the assembly of TpAQ-COFs into more ordered lamellar stacking structure, and induces the increase of enol-imine form. The critical role of anthraquinone moieties as the active sites for oxygen reduction was proved, that is, facilitating charge separation and enhancing the activity and selectivity of H₂O₂ production. Upon visible light irradiation, the TpAQ-COF synthesized after 12 h reaction has the highest content of anthraquinone moieties and the best performance for H₂O₂ production (420 μmol h⁻¹ g⁻¹) in the absence of organic sacrificial agents. These findings bring insights to incorporate anthraquinone chemistry into photocatalysts at molecular levels for efficient H₂O₂ production.