Symmetry Basis Engineered Covalent Organic Frameworks for Water Purification Under Ultralow Light Intensity

Abstract

Achieving efficient solar‐to‐chemical energy conversion of low‐intensity and natural sunlight is a promising but challenged for sustainable water purification. Herein, an electron‐deficient pyridine units into functional basis with symmetric and asymmetric is newly pre‐designed to form covalent organic frameworks (COFs). It is found that the bidirectional push‐pull effect of the bipyridine units in the symmetric Bby‐COF induces an increase in charge density and enhances the electron sink effect. This transformation optimizes the activation pathway of dissolved oxygen, establishing a pathway of micropollutants decomposition mediated by superoxide free radicals and photoexcited holes oxidation. Specifically, the first‐order rate constant of ofloxacin (OFL) removal for Bby‐COF for is 28.14 × 10−2 min−1, surpassing that of asymmetric Bpy‐COF by 6.3‐times (4.45 × 10−2 min−1). Remarkably, Bby‐COF can achieve complete OFL removal within 30–40 min under winter sunlight conditions, demonstrating unprecedented ultra‐low‐light‐intensity (36 mW cm−2) catalytic performance. In this mode, an array‐type plate‐and‐frame flow‐through reactor can be consecutively operated for treating a total volume of 58.8 L wastewater using outdoor sunlight, meeting the potentiality of large‐scale applications. This study pioneers a symmetry‐engineered molecular strategy for developing high‐performance organocatalysts, bridging the critical gap between laboratory photocatalysis and real‐world solar wastewater treatment applications.