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Visible-light-driven CO2 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 CO2 with gaseous H2 O to CO as the main carbonaceous product with approximately stoichiometric O2 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-C3 N4 under the same conditions. In situ Fourier-transform (FT)IR analysis indicated that CT-COF could adsorb and activate the CO2 and H2 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.

Visible-light-driven CO

Photocatalytic selective oxidative coupling of amines is a promising method for imine synthesis. Bismuth-rich bismuth oxybromide photocatalysts have been found to exhibit improved conversion and selectivity for the visible-light-driven selective oxidative coupling of amines to imines in water. Benzylamines with either electron-withdrawing or electron-donating groups undergo good conversion (94-99 %) and excellent selectivity (93-98 %) to the corresponding imines. The average apparent quantum efficiency at 455 nm is 57.4 %. Active species trapping experiments, isotope experiments, and in situ infrared spectroscopy reveal that water both serves as solvent and participates in the coupling reaction as a reactant. This work provides a green and environmentally friendly method for the efficient synthesis of imines with bismuth-rich bismuth oxyhalides and reveals water is involved in the oxidative coupling mechanism of benzylamines.