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.