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Yolk-shell nanocrystals with movable gold yolk: Next generation of photocatalysts

June 7, 2022
Tokyo Institute of Technology
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 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.

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.

"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.

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Materials provided by Tokyo Institute of Technology. Note: Content may be edited for style and length.

Journal Reference:

  1. Jhen-Yang Wu, Ting-Hsuan Lai, Mei-Jing Fang, Jui-Yuan Chen, Ming-Yu Kuo, Yi-Hsuan Chiu, Ping-Yen Hsieh, Chun-Wen Tsao, Huai-En Chang, Yu-Peng Chang, Chien-Yi Wang, Chun-Yi Chen, Masato Sone, Wen-Wei Wu, Tso-Fu Mark Chang, Yung-Jung Hsu. Electronic Interactions and Charge-Transfer Dynamics for a Series of Yolk–Shell Nanocrystals: Implications for Photocatalysis. ACS Applied Nano Materials, 2022; DOI: 10.1021/acsanm.2c01529

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Tokyo Institute of Technology. "Yolk-shell nanocrystals with movable gold yolk: Next generation of photocatalysts." ScienceDaily. ScienceDaily, 7 June 2022. <>.
Tokyo Institute of Technology. (2022, June 7). Yolk-shell nanocrystals with movable gold yolk: Next generation of photocatalysts. ScienceDaily. Retrieved April 14, 2024 from
Tokyo Institute of Technology. "Yolk-shell nanocrystals with movable gold yolk: Next generation of photocatalysts." ScienceDaily. (accessed April 14, 2024).

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