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.