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.