Capped CuInS2 quantum dots for H2 evolution from water under visible light illumination

Highlights: ► Dispersed CuInS2 quantum dots showed remarkable photosynthetic activity using visible light. ► Photogenerated electrons in CuInS2 were effective in H2 production from aqueous solution. ► The bifunctional capping reagent effectively transported photogenerated electrons for reaction. ► Ru-loaded CuInS2 quantum dots showed a quantum efficiency of 4.7% in H2 evolution. ► Attaching CuInS2 to TiO2 with CdS passivation achieved a quantum efficiency of 41%. - Abstract: This study demonstrates H2 evolution from water decomposition catalyzed by capped CuInS2 quantum dots (QDs) that are highly dispersed in a polysulfide aqueous solution. The CuInS2 QDs, which are obtained from solvothermal synthesis, have a size of 4.3 nm and a band gap of 1.97 eV. For photosynthetic H2 evolution in the aqueous solution, the QDs are capped with a multidentate ligand (3-mercaptopropionic acid), which has a thiol end for attaching the QDs and a hydrophilic carboxylic end for dispersion in water. The capped QDs exhibit low activity in catalyzing H2 evolution under visible illumination. After photodepositing 0.5 wt.% Ru, the capped QDs are active in producing H2 with illumination. This demonstrates that the photogenerated electrons travel through the capping reagent to generate deposited Ru, which subsequently serves as an electron trap for H2 evolution. A heterostructure formed by attaching the capped QDs on TiO2 nanoparticles, followed by coating CdS with photodeposition, exhibits a high quantum efficiency of 41% for H2 evolution from the polysulfide solution. These results demonstrate the potential for photosynthesis and phototherapy in biologic in vivo or microfluidic systems based on this capped QD material.