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

Abstract

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.