▎ 摘　　要

Graphitic carbon nitride (g-C3N4) is an appealing visible-light photocatalyst for CO2 reduction; however, the high recombination rate of photogenerated electron-hole pairs as well as lack of efficient active sites severely restrict its photocatalytic activity. In this work, reduced graphene oxide (rGO) coordinated with single Co sites is integrated with the g-C3N4 to form van der Waals heterostructures, which offers an ideal interface for efficient charge separation and transfer as well as provide catalytically active sites for photocatalytic CO2 reduction. In such van der Waals heterostructures, the 7C-7C interaction formed at the interfacial of graphene and g-C3N4 can greatly expedite the transfer of photoinduced electrons from light-harvesting g-C3N4 to isolated Co catalytic sites whose coordination environment has been resolved by X-ray absorption near edge structure (XANES) spectroscopy. As a result, the two-dimensional van der Waals heterostructures (Co-rGO/C3N4) exhibit the remarkably enhanced photocatalytic efficiency for CO2 reduction to CO with a TON of 66 as compared with pristine g-C3N4. Remarkably, the ratio of CO/H2 in the produced syngas can be readily tuned ranging from 1:30 to 2:3 by adjusting the content of graphene. This work provides an up-and-coming strategy, which simultaneously improves charge transfer dynamics and creates highly efficient catalytic sites on van der Waals heterostructures, toward the design of efficient and tunable photocatalytic CO2 reduction systems.