Facile Transformation of Imine Linkages and Functionalization of Aldehyde in the Covalent Organic Frameworks for Stable and Enhanced Photocatalytic Hydrogen Peroxide Production.

Imine-based covalent organic frameworks (COFs) have been widely applied in photocatalytic hydrogen peroxide (HO) production because of their highly crystalline properties and tunable chemical structures. However, the inherent polarization of C═N linkage brings a high energy barrier for π-electron delocalization, impeding the in-plane photoelectron transfer process, which leads to an inadequate efficiency of HO photosynthesis. In addition, the chemical stability of most imine-COFs remains insufficient due to the reversible nature of imine linkage. Herein, a quinoline-linked COF (Ald-TTB-TTA) bearing polar aldehyde groups was constructed by postsynthetic conversion of an imine COF (TTB-TTA). The expanded conjugate planes and the polar aldehyde groups facilitate the charge transfer, accelerating the proton-coupled electron transfer oxygen reduction reaction (ORR) process. As expected, Ald-TTB-TTA achieves a considerable photocatalytic HO production rate of 3169 μmol g h without a sacrificial agent, surpassing its imine-linked counterpart (1944 μmol g h). Therefore, this work provides a facile strategy for designing functional COFs and is expected to aid in the construction of high-performance catalysts for the photosynthesis of HO.