Changing Benzoxazole Ring into Nonring Imine Linkages on Covalent Organic Frameworks with Tuning H 2 O 2 Photosynthesis Performance.

Two π-conjugated covalent organic frameworks (COFs) with nonring imine or benzoxazole ring linkages were prepared by reacting 3,3'-dihydrooxybenzidine (BDOH) with 3,5-triformylbenzene (Tb) in the presence or absence of benzimidazole (BDOH-Tb- IM and BDOH-Tb- BO ). Although two COFs indicated similar composition, crystalline structures, and morphologies, imine-based BDOH-Tb- IM exhibited a photocatalytic H ₂ O ₂ production rate of 2490 μmol·g ^-1 ·h ^-1 in sacrificial reagent-free pure water, higher than that of benzoxazole-based BDOH-Tb- BO-a (1168 μmol·g ^-1 ·h ^-1 ). The higher photocatalytic activity of BDOH-Tb- IM was attributed to its more efficient photoinduced charge separation and utilization efficiency and different 2e ^- ORR active sites over the two COFs. This study demonstrated an available ring effect to adjust photocatalytic performance between π-conjugated COFs.