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A Metal-free Donor-Acceptor Covalent Organic Framework Photocatalyst for Visible-Light-Driven Reduction of CO2 with H2O.

Visible-light-driven CO 2 reduction to valuable chemicals without sacrificial agents and co-catalysts remains challenging, especially for metal-free photocatalytic systems. Herein, we report a novel donor-acceptor (D-A) COF (CT-COF) that was constructed by the Schiff base reaction of carbazole-triazine based D-A monomers and possessed a suitable energy band structure, strong visible-light-harvesting and rich nitrogen sites. CT-COF used as a metal-free photocatalyst can reduce CO 2 with gaseous H 2 O to CO as the main carbonaceous product with the approximate stoichiometric O 2 evolution under visible light irradiation and co-catalysts free conditions. The CO evolution rate (102.7 μmol g -1 h -1 ) is 68.5 times that of g-C 3 N 4 under the same test conditions. In situ FT-IR analysis indicates that CT-COF could adsorb and activate the CO 2 and H 2 O molecules and that COOH* species may be a key intermediate. DFT calculations suggest that nitrogen atoms in the triazine rings may be photocatalytic active sites.