CdS Nanoparticles Exhibiting Quantum Size Effect by Dispersion on TiO2: Photocatalytic H2 Evolution and Photoelectrochemical Measurements

Uniformly sized CdS nanoparticles exhibiting quantum size effect have been synthesized as a suspension in hexane solution containing oleic acid and 9-octadecenylamine as protective ligands. Our study focuses on utilizing the intrinsic optical property of the nanoparticles for photocatalytic H2 evolution and photoelectrochemical reaction by immobilizing oxide substrate and removing protective ligands. Immobilized CdS nanoparticles on TiO2 were found to maintain their original particle size and optical property after impregnation and removal of the protective ligands by oxidative heat treatment and/or alkali treatment. The photocatalytic H2 evolution rates in Na2S–Na2SO3 solution under visible light were strongly affected by the CdS particle size (quantum size effect), CdS loading amount, and TiO2 surface area. High photoanodic current was observed for CdS/TiO2 sprayed on a fluoride-doped tin oxide (FTO) electrode, functioning as an n-type semiconductor. The knowledge acquired in this study can be extended for further development in the field of nanoparticle materials covered with protective ligands.