Photocatalytic Hydrogen Evolution from Glycerol and Water over Nickel-Hybrid Cadmium Sulfide Quantum Dots under Visible-Light Irradiation

Natural photosynthesis offers the concept of storing sunlight in chemical form as hydrogen (H-2), using biomass and water. Herein we describe a robust artificial photocatalyst, nickel-hybrid CdS quantum dots (Ni-h-CdS QDs) made insitu from nickel salts and CdS QDs stabilized by 3-mercaptopropionic acid, for visible-light-driven H-2 evolution from glycerol and water. With visible light irradiation for 20h, 403.2mol of H-2 was obtained with a high H-2 evolution rate of approximately 74.6molh(-1)mg(-1) and a high turnover number of 38405 compared to MPA-CdS QDs (mercaptopropionic-acid-stabilized CdS quantum dots). Compared to CdTe QDs and CdSe QDs, the modified CdS QDs show the greatest affinity toward Ni2+ ions and the highest activity for H-2 evolution. X-ray photoelectron spectroscopy (XPS), inductively-coupled plasma atomic emission spectrometry (ICP-AES), and photophysical studies reveal the chemical nature of the Ni-h-CdS QDs. Electron paramagnetic resonance (EPR) and terephthalate fluorescence measurements clearly demonstrate water splitting to generate OH radicals. The detection of DMPO-H and DMPO-C radicals adduct in EPR also indicate that H radicals and C radicals are the active species in the catalytic cycle.