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 CO₂ conversion. Au nanoclusters (NCs) may potentially serve as components for harvesting visible light but can hardly perform solar-driven CO₂ reduction due to the lack of catalytic sites. Herein, we report an effective strategy for turning Au nanoclusters catalytically active for visible-light CO₂ 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 CO₂ reduction. The varied d-band centers and binding energies with CO₂ for different metal cations allow tuning electron transfer efficiency and CO₂ 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.