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Tokyo Tech News
Published: June 7, 2022
Owing to their unique permeable, hollow shell structures with inner, movable cores, yolk-shell nanocrystals are suitable for a wide variety of applications. Yolk-shell nanocrystals consisting of a gold core with various semiconductor shells have been developed by Tokyo Tech researchers, using a novel sequential ion-exchange process. These metal-semiconductor yolk-shell nanocrystals can serve as highly effective photocatalysts for many applications.
Yolk-shell nanocrystals are unique materials with fascinating structural properties, such as a permeable shell, interior void space, and movable yolk. These nanocrystals are suitable for a variety of applications, depending on the choice of materials used for their fabrication.
For example, if the inner surface of their shells are reflective, yolk-shell nanocrystals can make for a reliable photovoltaic device. A mobile core can can act as a stirrer, capable of mixing solutions held within the shell. The inner and outer surfaces of the shell provide plenty of active sites for reactions, and the yolk-shell structure's fascinating properties (a result of electronic interactions and charge-transfer between the surfaces of the structure) make these nanocrystals ideal for photocatalysis applications. Understandably, yolk-shell nanocrystals have earned the attention of researchers worldwide.
Now, in a collaborative study published in ACS Applied Nano Materials, which was also selected as the ACS Editors' Choice, an international research team led by Associate Professor Tso-Fu Mark Chang and Assistant Professor Chun-Yi Chen at Tokyo Institute of Technology (Tokyo Tech) and Professor Yung-Jung Hsu at the National Yang Ming Chiao Tung University in Taiwan have developed several yolk-shell structures containing a metallic gold (Au) yolk with various semiconductor shells. Such structures have risen in popularity worldwide because of their fascinating properties, owing to their Au cores.
"Yolk-shell nanocrystals comprising of a metal yolk and semiconductor shells are particularly interesting because they can be geared to mass transport-related utilizations, for example, photocatalysis," says Professor Chen.
To make the nanocrystals, the researchers employed a sequential ion-exchange process. The procedure involves delicate sulfidation on an Au@Cu2O core-shell nanocrystal template (where Au contributes to the core, and Cu2O to the shell formation), followed by a kinetically controlled cation exchange reaction that enables conversion of the shell composition (i.e., Cu2O) into various metal sulfides, which are semiconductors. Four representative yolk-shell nanocrystal samples, including Au@Cu7S4, Au@CdS, Au@ZnS, and Au@Ni3S4, were synthesized for investigation in this way, as shown in Figure 1.
The performance of these yolk-shell structures as photocatalysts was evaluated using x-ray photoelectron spectroscopy (XPS) and steady-state photoluminescence (PL) spectroscopy.
Using XPS, the researchers found the metal cores and semiconducting shells of the nanocrystals to have electronic interactions favorable for photocatalysis applications. Time-resolved PL spectroscopy revealed the nanostructures to have high PL intensity, indicating high photocatalytic activity, implying that they were highly capable of absorbing light and generating electron-hole charge carriers (as shown in Figure 2).
"In a real-world scenario, the reactions facilitated by separated photoexcited electrons and holes play a role in environmental purification, by producing reactive oxygen species," explains Prof. Chen, describing one scenario in which their novel yolk-shell photocatalysts could be used. These photoexcited electrons and holes can facilitate a multitude of reactions, making yolk-shell nanocrystals applicable in many fields such as environmental purification, hydrogen production, and carbon dioxide reduction.
Reference
Authors : |
Jhen-Yang Wu1, Ting-Hsuan Lai2, Mei-Jing Fang2, Jui-Yuan Chen3, Ming-Yu Kuo2, Yi-Hsuan Chiu2, Ping-Yen Hsieh2, Chun-Wen Tsao2, Huai-En Chang2, Yu-Peng Chang2, Chien-Yi Wang2, Chun-Yi Chen1, Masato Sone1, Wen-Wei Wu2, Tso-Fu Mark Chang1*, and Yung-Jung Hsu2* |
Title of original paper : |
Electronic Interactions and Charge-Transfer Dynamics for a Series of Yolk–Shell Nanocrystals: Implications for Photocatalysis |
Journal : |
ACS Applied Nano Materials |
DOI : |
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Affiliations : |
1 Tokyo Institute of Technology, Japan 2 National Yang Ming Chiao Tung University, Taiwan 3 National United University, Taiwan |
* Corresponding author's email: Tso-Fu Mark Chang: chang.m.aa@m.titech.ac.jp
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Specially Appointed Assistant Professor Chun-yi Chen
Institute of Innovative Research, Tokyo Institute of Technology
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