Topology-Optimized 3D Metalloporphyrin Covalent Organic Framework for Photocatalytic CO₂ Fixation

Three-dimensional (3D) covalent organic frameworks (COFs) represent promising photocatalytic platforms with accessible active sites, yet their development faces challenges in terms of structural diversity and synthetic complexity. Herein, a robust 3D metalloporphyrin COF with scu topology and 2-fold interpenetration is achieved by using high-connectivity metalloporphyrin, and different metal centers within the porphyrin units of 3D COFs lead to intriguing structural variations. Particularly, the 3D cobalt-porphyrin-based COF achieves efficient photocatalytic CO2-to-CO conversion with a rate of 21 251.0 μmol g-1 h-1, 94.2% selectivity, and a cycle stability up to 6 cycles for 30 h. The accessible active sites of 3D COF deliver an exceptional turnover frequency (TOF) and conversion rate compared with reported pristine COFs for photocatalytic CO2 fixation. Density functional theory (DFT) calculations demonstrate the efficient donor-acceptor (D-A) system constructed in the framework, and the temperature-programmed desorption (TPD) measurement confirms the superiority of the 3D network for CO2 chemisorption. In contrast, the two-dimensional (2D) counterpart with similar composition and D-A system is restricted by the buried metal centers. Taking the high efficiency and selectivity of CO2-to-CO conversion, the robust metalloporphyrin-based 3D COF has been further incorporated into tandem reaction toward higher value-added chemical products.