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

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.