Turning Au Nanoclusters Catalytically Active for Visible-Light-Driven CO2 Reduction through Bridging Ligands

Development of visible-light photocatalytic materials is an ultimate goal for solar-driven CO, conversion. Au nanoclusters (NCs) may potentially serve as components for harvesting visible light but can hardly perform solar-driven CO, reduction due to the lack of catalytic sites. Herein, we report an effective strategy for turning Au nanoclusters catalytically active for visible-light CO, reduction, in which metal cations (Fe2+, Co2+, Ni2+, and Cu2+) are grafted to the Au NCs using L-cysteine as a bridging ligand. The metal-S bonding bridge facilitates the electron transfer from Au NCs to metal cations so that the grafted metal cations can receive photoinduced electrons and work as catalytic sites for CO, reduction. The varied d-band centers and binding energies with CO, for different metal cations allow tuning electron transfer efficiency and CO, activation energy. Furthermore, the photostability of Au NCs-based catalyst can be significantly enhanced through the encapsulation with metal organic frameworks. This work opens a new door for the photocatalyst design based on metal clusters and sheds light on the surface engineering of metal clusters toward specific applications.