Chiral induction enhances hydrogen generation performance of CdS quantum dots

Chirality is ubiquitous in the nature. Chiral nanomaterials show wide application prospects owing to their special properties. In this study, chirality was introduced into photocatalysis. Chiral L-cysteine was introduced into photocatalytic materials for preparation of chiral CdS quantum dots (QDs) at room temperature. Then the CdS QDs were characterized by ultraviolet-visible spectra, infrared spectra and X-ray photoelectron spectroscopy. The hydrogen production activity was tested within the visible light range. Under visible light irradiation, the hydrogen yields of chiral CdS QDs at 298, 323, 333, 348, 358 K were all higher compared with the nonchiral CdS QDs. The hydrogen yield was maximized to 18.72 mmol/g/h at 333 K, which was significantly higher than that of the nonchiral CdS QDs (10.35 mmol/g/h). The reasons for the higher activity of chiral CdS QDs were that the introduction of the chiral ligand broadened the bandgap of CdS, and the more-negative conduction band strengthened the reducibility of photoelectrons. Moreover, the electron-donating groups that coordinated with the active Cd2+ directionally enhanced the electron density of CdS QDs. Theoretical calculation showed the conduction band electron density of CdS was significantly improved, which is consistent with the above results. For these reasons, the hydrogen production ability of chiral CdS QDs is considerably higher than that of nonchiral CdS QDs.