title: Electron-transfer dependent photocatalytic hydrogen generation over cross-linked CdSe/TiO2type-II heterostructure.
abstract: Developing type-II heterostructures with a spatial separation of photoexcited electrons and holes is a useful route to promote photocatalytic hydrogen generation. However, few investigations on the charge transfer process across the heterojunction have been carried out, which can allow us to uncover the reaction mechanism. Herein, CdSe quantum dots (QDs) and TiO2nanocrystals were synthesized and combined in water yielding CdSe/TiO2type II heterostructures. It was found that mercaptopropionic acid as bifunctional molecules could bind with CdSe and TiO2to form a cross-linked morphology. The charge carrier dynamics of bare CdSe and CdSe/TiO2were detected using femtosecond transient absorption spectroscopy. In the presence of TiO2, the average exciton lifetime of CdSe QDs was apparently decreased, owing to the electron transfer from photoexcited CdSe to TiO2. Particularly, the electron-transfer rate from small CdSe QDs (3.0 nm) was much faster than that from big CdSe QDs (4.2 nm). The improved photocatalytic hydrogen generation was observed for CdSe/TiO2compared to bare CdSe QDs. The enhancement factor for small CdSe QDs was higher than that for big CdSe QDs, which was in good agreement with the electron-transfer rates. This result indicated that the electron transfer between CdSe and TiO2played an important role in photocatalytic hydrogen generation on CdSe/TiO2type-II heterostructure. Our study provides a fundamental guidance to construct efficient heterostructured photocatalysts by delicate control of the band alignment.
authors.affiliation: International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Shaanxi 710049, People's Republic of China.
authors.forename: Yubin
authors.initials: Y
authors.lastname: Chen
authors.forename: Chi-Hung
authors.initials: CH
authors.lastname: Chuang
authors.forename: Zhixiao
authors.initials: Z
authors.lastname: Qin
authors.forename: Shaohua
authors.initials: S
authors.lastname: Shen
authors.forename: Tennyson
authors.initials: T
authors.lastname: Doane
authors.forename: Clemens
authors.initials: C
authors.lastname: Burda