Selective CO2 Reduction Catalyzed by Single Cobalt Sites on Carbon Nitride under Visible-Light Irradiation

Framework nitrogen atoms of carbon nitride (C 3 N 4 ) can coordinate with and activate metal sites for catalysis. In this study, C 3 N 4 was employed to harvest visible light and activate Co 2+ sites, without the use of additional ligands, in photochemical CO 2 reduction. Photocatalysts containing single Co 2+ sites on C 3 N 4 were prepared by a simple deposition method and demonstrated excellent activity and product selectivity toward CO formation. A turnover number of more than 200 was obtained for CO production using the synthesized photocatalyst under visible-light irradiation. Inactive cobalt oxides formed at relatively high cobalt loadings but did not alter product selectivity. Further studies with X-ray absorption spectroscopy confirmed the presence of single Co 2+ sites on C 3 N 4 and their important role in achieving selective CO 2 reduction.