Susceptible Surface Sulfide Regulates Catalytic Activity of CdSe Quantum Dots for Hydrogen Photogeneration

Semiconducting quantum dots (QDs) have recently triggered a huge interest in constructing efficient hydrogen production systems. It is well established that a large fraction of surface atoms of QDs need ligands to stabilize and avoid them from aggregating. However, the influence of the surface property of QDs on photocatalysis is rather elusive. Here, the surface regulation of CdSe QDs is investigated by surface sulfide ions (S^2- ) for photocatalytic hydrogen evolution. Structural and spectroscopic study shows that with gradual addition of S^2- , S^2- first grows into the lattice and later works as ligands on the surface of CdSe QDs. In-depth transient spectroscopy reveals that the initial lattice S^2- accelerates electron transfer from QDs to cocatalyst, and the following ligand S^2- mainly facilitates hole transfer from QDs to the sacrificial agent. As a result, a turnover frequency (TOF) of 7950 h^-1 can be achieved by the S^2- modified CdSe QDs, fourfold higher than that of original mercaptopropionic acid (MPA) capped CdSe QDs. Clearly, the simple surface S^2- modification of QDs greatly increases the photocatalytic efficiency, which provides subtle methods to design new QD material for advanced photocatalysis.