Azobenzene-Bridged Covalent Organic Frameworks Boosting Photocatalytic Hydrogen Peroxide Production from Alkaline Water: One Atom Makes a Significant Improvement

Covalent organic frameworks (COFs) have been demonstrated as promising photocatalysts for hydrogen peroxide (H₂O₂) production. However, the construction of COFs with new active sites, high photoactivity, and wide-range light absorption for efficient H₂O₂ production remains challenging. Herein, we present the synthesis of a novel azobenzene-bridged 2D COF (COF-TPT-Azo) with excellent performance on photocatalytic H₂O₂ production under alkaline conditions. Notably, although COF-TPT-Azo differs by only one atom (-N=N- vs. -C=N-) from its corresponding imine-linked counterpart (COF-TPT-TPA), COF-TPT-Azo exhibits a significantly narrower band gap, enhanced charge transport, and prompted photoactivity. Remarkably, when employed as a metal-free photocatalyst, COF-TPT-Azo achieves a high photocatalytic H₂O₂ production rate up to 1498 μmol g^-1 h^-1 at pH = 11, which is 7.9 times higher than that of COF-TPT-TPA. Further density functional theory (DFT) calculations reveal that the -N=N- linkages are the active sites for photocatalysis. This work provides new prospects for developing high-performance COF-based photocatalysts.