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

Abstract Photosynthesizing H 2 O 2 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 thieno3,2‐cpyridine‐linked covalent organic frameworks (named TBA‐COF and TCA‐COF) are synthesized for seawater H 2 O 2 photoproduction for the first time. Without sacrificial agents in real seawater and O 2 , TBA‐COF and TCA‐COF exhibit impressive H 2 O 2 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 H 2 O 2 photoproduction by 2e − oxygen reduction reaction and 2e − water oxidation reaction, and thereby enhances the H 2 O 2 photosynthetic activity. Notably, seawater‐produced H 2 O 2 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 thieno3,2‐cpyridine linkage via the Pictet–Spengler reaction and sustainable producing H 2 O 2 from seawater.