Ultrafine ZnO quantum dot-modified TiO2 composite photocatalysts: the role of the quantum size effect in heterojunction-enhanced photocatalytic hydrogen evolution

Quantum dot (QD) modification has been recently demonstrated to be a highly efficient strategy to improve the photocatalytic performance of wide band gap semiconductor nanocrystals like TiO2. However, it remains a great challenge to controllably construct QD-modified composite photocatalysts via facile processes, which limits our understanding of the role of QDs in heterojunction-enhanced photocatalysis to some extent. In this work, we reported the fabrication of ZnO QD-modified TiO2 nanowire (NW)-based composite photocatalysts via a facile calcination treatment method. The structure analysis indicated that ZnO QDs were uniformly loaded onto the surface of TiO2 NWs and their particle size could be tuned by simply adjusting the amount of the zinc precursor added. Under simulated solar irradiation, the as-prepared ZnO QD-decorated TiO2 NWs exhibited remarkably enhanced photocatalytic activity in water splitting reaction compared to the bare TiO2 NWs and commercial photocatalyst P25. The rate of hydrogen evolution on the optimal sample TZ-0.6% was double and four times that obtained on the bare TiO2 NWs and P25, respectively. Based on systematic photoelectric characterization, it can be concluded that the excellent photocatalytic performance of these composite photocatalysts was attributed to the synergism between heterojunction-induced effective interfacial charge carrier migration and the size-dependent quantum confinement effect.