Tridentate Coordination-Driven Covalent Organic Frameworks Incorporating Recycled Cobalt(II) for Enhanced...

Photocatalytic CO₂ reduction represents a promising route toward carbon neutrality and renewable fuel production. Covalent organic frameworks (COFs) are attractive photocatalytic platforms because their tunable structures can stabilize isolated metal sites and regulate the local environment of catalytic centers. Herein, a series of COFs featuring N₁O₂-tridentate coordination sites were synthesized by condensing 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde with hydrazide- or amine-containing building blocks. Combined experimental and theoretical results show that the hydrazone-linked N₁O₂-tridentate environment enables stronger Co anchoring and a more favorable local Co-site environment, which together promote charge transfer and lower the free-energy barrier for key CO₂RR intermediates. Among the three Co-loaded COFs, Co-AH-COF exhibits the best photocatalytic CO₂RR performance, affording a CO production rate of 34.2 mmol g^-1 h^-1. AH-COF was further used to capture cobalt species from spent lithium-ion battery leachate under mild conditions to prepare Co_R-AH-COF, which delivers a CO production rate of 33.6 mmol g^-1 h^-1 under identical conditions. These results demonstrate the feasibility of employing waste-battery-derived cobalt species as a precursor for efficient COF-based photocatalysts and provide a route for integrating CO₂ conversion with waste-metal reuse.