3-1 Conclusions
A facile and reproducible approach for preparing Au-CdS core-shell nanocrystals with controllable shell thickness was developed. The photoinduced charge separation property was demonstrated and revealed in the as-synthesized Au-CdS nanocrystals due to the difference in band structures between Au and CdS. A pronounced photoinduced charge separation took place at the interface of Au and CdS, resulting in the electron-charged Au core and the hole-enriched CdS shell. The electron-charging of Au core in Au-CdS nanocrystals was revealed with the corresponding XPS analysis and photocurrent measurement. Time-resolved PL data showed that a higher electron-transfer rate constant was observed for Au-CdS nanocrystals with thicker CdS shell. On the other hand, the hole-enriched CdS shell of Au-CdS nanocrystals upon light illumination was characterized with a photocatalytic process. The photocatalytic activity of Au-CdS nanocrystals was found to increase with increasing shell thickness, consistent with the result of electron-transfer rate constant variation.
To further improve the recyclability and durability, Zn was doped into the shell of Au-CdS to produce Au-Cd1-xZnxS nanocrystals that showed relatively high long-term stability in photocatalysis. The present synthetic route can be readily extended to obtain other sulfide-semiconductor-coated Au nanocrystals such as Au-ZnS. The as-obtained Au-ZnS nanocrystals showed promising potential as efficient photoanode in relevant photoelectrochemical processes such as photocatalytic methanol oxidation.
The present study also gives rise to a new class of highly efficient metal-semiconductor hybrid photocatalysts which may effectively utilize the solar power.
3-2 Future Work
Though the potential of Au-ZnS nanocrystals as photoanode in photoelectrochemical cell has been successfully demonstrated, the serious photocorrosion when subjected to white light illumination is a big concern. The durability of Au-ZnS nanocrystals in the photoelectrochemical processes should be further improved to enhance their practical significance. Besides, to comprehend the charge transfer behavior for Au-ZnS nanocrystals, the interfacial charge carrier dynamics are needed to be studied by using time-resolved PL and transient absorption spectroscopy in the future.
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