Electronic Interactions and Charge-Transfer Dynamics for a Series of Yolk–Shell Nanocrystals: Implications for Photocatalysis

In recent years, yolk–shell nanocrystals have become the spotlight of research worldwide because of the fascinating structural properties such as a permeable shell, an interior void space, and a movable yolk. Numerous studies have reported various compositions of yolk–shell nanocrystals. Among them, yolk–shell nanocrystals comprising metal yolk and semiconductor shells are particularly interesting because they can be geared to mass transport-related utilizations, for example, photocatalysis. We reported a sequential ion-exchange process to prepare for metal–semiconductor yolk–shell nanocrystals comprising Au yolk associated with various semiconductor shells. The synthetic procedures involved delicate sulfidation on a Au@Cu2O core–shell nanocrystal template, followed by a kinetically controlled cation-exchange reaction that enabled the conversion of the shell composition into various metal sulfides. Four representative yolk–shell nanocrystal samples, including Au@Cu7S4, Au@CdS, Au@ZnS, and Au@Ni3S4, were synthesized for investigation. X-ray photoelectron spectroscopy and photoluminescence spectroscopy were used to explore the electronic interactions and charge-transfer dynamics between the yolk and shell components. Results showed that interfacial charge transfer between the metal yolk and semiconductor shell was significant for the four yolk–shell nanocrystals, leading to pronounced charge-carrier separation that can be utilized to demonstrate a multitude of photocatalysis applications, including environmental purification, hydrogen production, and carbon dioxide reduction.