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 (H₂O₂) 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 H₂O₂ 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 H₂O₂ generation rate. The highest H₂O₂ production rate of the prepared COFs with the longest amine linker reached 1164 μmol h⁻¹ g_cat⁻¹ in O₂-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.