Spatially Manipulating Polar Centers of Covalent Organic Frameworks for Boosting Hydrogen Peroxide Photosynthesis and Water Purification.
Hydrogen peroxide (H2O2) photosynthesis from H2O and O2 using covalent organic frameworks (COFs) is a sustainable approach, yet its efficiency is restricted by a sluggish water oxidation reaction (WOR) due to insufficient water adsorption and charge separation. Herein, we propose a facile and universal polar center spatial-manipulation strategy to enable efficient H2O2 photosynthesis by COFs via converting high-polarity C═N linkages into 4-carboxyl-quinolyl linkages with weakened-polarity quinoline backbones and ultra-polar carboxyl side chains (forming COF-TBC). This polar-center side-shifting strategy concurrently enhances water adsorption (via the polar carboxyl side chain) and water activation (enabled by efficient exciton formation and separation along the low-polarity quinoline backbone) by COF-TBC, lowering the energy barrier of the rate-determining WOR and achieving outstanding and stable H2O2 photosynthesis from O2 and H2O without sacrificial agents (5624 µmol g-1 h-1, accumulating to 41 mM, solar-to-chemical efficiency of 0.72%). The polar-center side-shifting strategy can be extended to modify other COFs for enhancing H2O2 photosynthesis, indicating its universality. COF-TBC maintains high H2O2 yield in complex real-water matrices and can be integrated into membrane-based and continuous-flow reactors for successive H2O2 generation under natural sunlight. COF-TBC also exhibits efficient photocatalytic performance toward organic contaminant degradation and microorganism inactivation, highlighting its broad potential for water purification.