One‐Pot Synthesis of Fully Conjugated Covalent Organic Frameworks via the Pictet–Spengler Reaction for Boosting H₂O₂ Photogeneration in Real Seawater

Abstract Photosynthesizing H₂O₂ from real seawater is a promising and green avenue but suffers from salt‐deactivated effects with limitations on stability and photocatalytic activity. Herein, by the Pictet–Spengler reaction, two fully conjugated thieno[3,2‐c]pyridine‐linked covalent organic frameworks (named TBA‐COF and TCA‐COF) are synthesized for seawater H₂O₂ photoproduction for the first time. Without sacrificial agents in real seawater and O₂, TBA‐COF and TCA‐COF exhibit impressive H₂O₂ generation rates of 8878 and 6023 µmol g⁻¹ h⁻¹ with the solar‐to‐chemical conversion efficiency of 0.62% and 0.42%, respectively, superior to their Schiff base analogs. Further experimental and theoretical investigations reveal that, compared to the imine‐linkage counterparts, in one‐pot cyclized TBA‐COF and TCA‐COF, the Pictet–Spengler reaction improves their charge carrier separation efficiency, alters the photoreduction center from the triazine and benzene parts to the pyridine units, modulates the energy band structures to drive the H₂O₂ photoproduction by 2e⁻ oxygen reduction reaction and 2e⁻ water oxidation reaction, and thereby enhances the H₂O₂ photosynthetic activity. Notably, seawater‐produced H₂O₂ by flow reactors packed with TBA‐COF can be directly utilized for E. coli sterilization. The present study highlights the one‐pot construction of robust COFs with thieno[3,2‐c]pyridine linkage via the Pictet–Spengler reaction and sustainable producing H₂O₂ from seawater.