Linker length-dependent hydrogen peroxide photosynthesis performance over crystalline covalent organic frameworks

Molecular engineering-tuned covalent organic frameworks (COFs) have been demonstrated as promising photocatalysts for photocatalytic hydrogen peroxide (H 2 O 2 ) production by a two-electron oxygen reduction in water. Herein, a simple strategy by altering the linker length of the building units is developed to harvest efficient COF catalysts for H 2 O 2 photosynthesis. Three imine-linked COFs with similar structures but varied amine linker lengths were prepared by the amine aldehyde condensation reactions. It was found that the resultant COF with a longer linker exhibited a higher H 2 O 2 generation rate. The highest H 2 O 2 production rate of the prepared COFs with the longest amine linker reached 1164 μmol h −1 g cat −1 in O 2 -presaturated pure water, together with better stability. The rising photocatalytic performance of COFs with longer linkers could be attributed to the tuning of their molecular structures and morphologies, including a more negative conductor band, higher specific surface area, and separation efficiency of photogenerated carriers. This study provides a simple strategy by facially varying linker lengths for gaining COF-based photocatalysts. The imine COFs with longer linkers exhibited higher H 2 O 2 photoproduction rate in pure water, owing to their more negative conductor band and better separation efficiency of photogenerated carriers.