Framework nitrogen atoms of carbon nitride (C3N4) can coordinate with and activate metal sites for catalysis. In this study, C3N4 was employed to harvest visible light and activate Co2+ sites, without the use of additional ligands, in photochemical CO2 reduction. Photocatalysts containing single Co2+ sites on C3N4 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 Co2+ sites on C3N4 and their important role in achieving selective CO2 reduction.
