Integrating Multifunctionalities into a 3D Covalent Organic Framework for Efficient CO₂ Photoreduction

Fabrication of highly efficient photocatalysts for CO₂ conversion is still challenging. Herein, integrating nitrogen-rich organic cages and the photoactive porphyrin moieties together, a 3D covalent organic framework (COF), Cage-PorCOF, is successfully synthesized. After incorporating metal ions (Co²⁺ and Ni²⁺) into the cage-based COF, Cage-PorCOF(Co) and Cage-PorCOF(Ni) are subsequently constructed for the CO₂ photoreduction. Catalytic experiments show impressive performance in CO₂ photoreduction with CO generation rates of up to 48 748 and 28 446 µmol g^-1 h^-1 in the first initiating hour for Cage-PorCOF(Co) and Cage-PorCOF(Ni), respectively, which is attributed to the synergistic effects from CO₂-affinity of the porous frameworks and incorporated metal atoms, the light-absorption and charge separation ability of metalloporphyrin groups as well as the fully exposed single-atomic catalytic sites confirmed by both experimental and theoretical analyses. This study demonstrates that by the integration of multiple functionalities into 3D porous solids, highly effective photocatalysts for CO₂ conversion can be achieved.