Indole-Linkages as Base-Activated Sites in a Covalent Organic Framework for Efficient Photosynthesis of Hydrogen...

The photocatalytic production of hydrogen peroxide (H₂O₂) under alkaline conditions is very important for biomass pretreatment and electronic industry. However, the proton-deficient nature of alkaline water and the intolerance of COF linkages in strong alkaline conditions lead to insufficient H₂O₂ production by most COF-based catalysts. Thus, developing novel COFs containing base-triggered active sites is an effective strategy to maintain structural rigidity and photocatalytic efficiency. Herein, an indole-linked COF (CityU-45) was prepared through the Cadogan-Sundberg post-synthetic reaction in a nitro-containing sp²-carbon COF (CityU-44). The formation of the indole linkage maintains its crystallinity, reduces the bandgap, and results in the redshift of fluorescent emission. Moreover, CityU-45 reveals an alkaline-activated characteristic with a photocatalytic H₂O₂ rate up to 4854 µmol g^-1 h^-1 at pH = 13, which is six times higher than that in neutral conditions. This research demonstrated that indole-linked COFs can be promising catalysts for photocatalytic H₂O₂ generation under alkaline conditions.