Stand-Alone CdS Nanocrystals for Photocatalytic CO₂ Reduction with High Efficiency and Selectivity

The development of a cost-effective photocatalyst is highly anticipated to achieve efficient photocatalytic CO2 reduction with superior selectivity, which is still facing the lack of valid settlements. Herein, 4-mercaptopyridine (PD) as the building block of a capping ligand is tightly decorated on the surface of CdS nanocrystals (CdS-PD) using a facile ligand-exchange strategy, to exploit a cost-effective photocatalyst for photocatalytic CO2 reduction without any cocatalysts. The conjugated structure of PD can facilitate the delocalization of photogenerated electrons in CdS nanocrystals, bringing forth an improved charge separation efficiency. More importantly, N-protonated PD can enable the easy formation of a six-membered ring intermediate with CO2 assisted by water, which can serve as the efficient active site to achieve photocatalytic CO2 reduction. In the absence of a cocatalyst, stand-alone CdS-PD nanocrystals exhibit an excellent CO yield of 20.35 mmol g–1 h–1 concomitant with a high selectivity of 95.3% for the CO2-to-CO conversion under visible light, which are remarkably superior than those of CdS nanocrystals possessing traditional alkyl-chain and other conjugated capping ligands.