Thiocyanate-capped CdSe@Zn1-XCdXS gradient alloyed quantum dots for efficient photocatalytic hydrogen evolution

Abstract

CdSe@Zn1-XCdXS QDs possessing a gradient alloy composition structure with an energy level width continuous increasing along the radial direction from the center to the surface were prepared and employed as a photocatalyst in a hydrogen generation system. Thiocyanate or mercaptopropionic acid capped QDs was adopted for assembling CdSe@Zn1-XCdXS QDs onto TiO2 film. Using as photocatalysts for hydrogen generation, it’s found that these gradient alloyed QDs/TiO2 photocatalysts exhibit excellent hydrogen production rates of 94 mmol/gh for MPA capped QDs and 951 mmol/gh for SCN capped QDs at 100 mW/cm2 AM 1.5 illumination without co-catalysts. Moreover, the SCN capped QDs demonstrate remarkably higher hydrogen evolution rate than that of the reference MPA capped QDs due to a higher ligand induced hole trap level, resulting in a much faster electron-hole separation and charge transfer rate compared with those of MPA capped QDs.