Abstract
We intend to report an interesting phenomenon related to the different interfacial transfer processes between ellipsoidal-like ZnO (E-ZnO) and rod-like ZnO (R-ZnO) nanoheterojunctions witness by the nanosecond time-resolved transient photoluminescence (NTRT-PL) spectra. Fristly, E-ZnO and R-ZnO nanoarchitectures were fabricated via facilitating the electrochemical route; and then, they decorated it with dispersed Au nanoparticles (NPs) by the methods of ion-sputtering deposition, constituting Au/E-ZnO and Au/R-ZnO Schottky-heterojunction nanocomplex, which is characterized by SEM, XRD, Raman analysis, and UV-vis absorption spectra. Steady-state photoluminescence and NTRT-PL spectra of as-fabricated Au/E-ZnO and Au/R-ZnO nanocomposites were probed for interfacial charge transfer process under 266 nm femtosecond (fs) light irradiation. Simultaneously, a distinct diversification for the NTRT-PL spectra is observed, closely associating with oxygen vacancies (Vo), which is confirmed by X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) spectra. Furthermore, Au NPs act as an “annular bridge” and “transit depot” for interfacial charge transfer through local surface plasmon resonance (LSPR) effect and Schottky barrier, respectively, which is identified by NTRT-PL and time-resolved PL (TRPL) decay spectrum. Moreover, this mechanism is responsible for the enhanced photoelectrochemical (PEC) performances of methyl orange (MO) photodegradation under UV light irradiation.
Highlights
Zinc oxide (ZnO), which is a representative II-VI semiconductor with a wide direct bandgap of 3.3 eV and a large excitation binding energy of 60 meV, has attracted considerable attention because of its unique optical and electrical properties
These issues are reported to be settled by coupling wide bandgap semiconductors (WBGs) with plasmonic metal nanocrystals (e.g., Au, Ag, and Pt), i.e., M/S Schottky contact, as they could improve the concentration of PEC active electrons and facilitate the photogenerated e--h+ pair separation, which originated from local surface plasmon resonance (LSPR) effect and built-in electric field of Schottky nanoheterojunction, respectively
The size of the surface-attached Au NPs increased with increasing Au sputtering time, which was homogenously distributed on the ZnO nanorod arrays
Summary
Zinc oxide (ZnO), which is a representative II-VI semiconductor with a wide direct bandgap of 3.3 eV and a large excitation binding energy of 60 meV, has attracted considerable attention because of its unique optical and electrical properties. It is well known that the pristine ZnO semiconductor is intrinsically not a good candidate for PEC implementation, which is limited by light absorption and higher electron-hole (e--h+) pair recombination rate These issues are reported to be settled by coupling wide bandgap semiconductors (WBGs) with plasmonic metal nanocrystals (e.g., Au, Ag, and Pt), i.e., M/S Schottky contact, as they could improve the concentration of PEC active electrons and facilitate the photogenerated e--h+ pair separation, which originated from local surface plasmon resonance (LSPR) effect and built-in electric field of Schottky nanoheterojunction, respectively. Nanosecond timeresolved transient photoluminescence (NTRT-PL) spectra present direct evidence that the interfacial transfer mechanism of the photoinduced electrons in the Au/ZnO nanoheterojunction associated with intrinsic defect states. To the best of our knowledge, there are only few reports for this interesting phenomenon, which is better understood by introducing competing mechanisms between the photogenerated carrier defect trapping and PEC redox process in the interfaces of the Au/ZnO Schottky heterostructure
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