Dual Metallosalen-Based Covalent Organic Frameworks for Artificial Photosynthetic Diluted CO₂ Reduction

Directly converting CO₂ in flue gas using artificial photosynthetic technology represents a promising green approach for CO₂ resource utilization. However, it remains a great challenge to achieve efficient reduction of CO₂ from flue gas due to the decreased activity of photocatalysts in diluted CO₂ atmosphere. Herein, we designed and synthesized a series of dual metallosalen-based covalent organic frameworks (MM-Salen-COFs, M: Zn, Ni, Cu) for artificial photosynthetic diluted CO₂ reduction and confirmed their advantage in comparison to that of single metal M-Salen-COFs. As a results, the ZnZn-Salen-COF with dual Zn sites exhibits a prominent visible-light-driven CO₂-to-CO conversion rate of 150.9 μmol g^-1 h^-1 under pure CO₂ atmosphere, which is ~6 times higher than that of single metal Zn-Salen-COF. Notably, the dual metal ZnZn-Salen-COF still displays efficient CO₂ conversion activity of 102.1 μmol g^-1 h^-1 under diluted CO₂ atmosphere from simulated flue gas conditions (15 % CO₂), which is a record high activity among COFs- and MOFs-based photocatalysts under the same reaction conditions. Further investigations and theoretical calculations suggest that the synergistic effect between the neighboring dual metal sites in the ZnZn-Salen-COF facilitates low concentration CO₂ adsorption and activation, thereby lowering the energy barrier of the rate-determining step.