A Metal‐Free Donor–Acceptor Covalent Organic Framework Photocatalyst for Visible‐Light‐Driven Reduction of CO2 with H2O

Abstract

Visible‐light‐driven CO 2 reduction to valuable chemicals without sacrificial agents and cocatalysts remains challenging, especially for metal‐free photocatalytic systems. Herein, a novel donor–acceptor (D–A) covalent organic framework (CT‐COF) 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 abundant nitrogen sites. CT‐COF as a metal‐free photocatalyst could reduce CO 2 with gaseous H 2 O to CO as the main carbonaceous product with approximately stoichiometric O 2 evolution under visible‐light irradiation and without cocatalyst. The CO evolution rate (102.7 μmol g−1 h−1) was 68.5 times that of g‐C 3 N 4 under the same conditions. In situ Fourier‐transform (FT)IR analysis indicated 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 suggested that nitrogen atoms in the triazine rings may be photocatalytically active sites.