MoS₂ Quantum Dot Growth Induced by S Vacancies in a ZnIn₂S₄ Monolayer: Atomic-Level Heterostructure for Photocatalytic Hydrogen Production

Abstract

It is highly demanded to steer the charge flow in photocatalysts for efficient photocatalytic hydrogen reactions (PHRs). In this study, we developed a smart strategy to position MoS 2 quantum dots (QDs) at the S vacancies on a Zn facet in monolayered ZnIn 2 S 4 (Vs-M-ZnIn 2 S 4 ) to craft a two-dimensional (2D) atomic-level heterostructure (MoS 2 QDs@Vs-M-ZnIn 2 S 4 ). The electronic structure calculations indicated that the positive charge density of the Zn atom around the sulfur vacancy (Vs) was more intensive than other Zn atoms. The Vs confined in monolayered ZnIn 2 S 4 established an important link between the electronic manipulation and activities of ZnIn 2 S 4 . The Vs acted as electron traps, prevented vertical transmission of electrons, and enriched electrons onto the Zn facet. The Vs-induced atomic-level heterostructure sewed up vacancy structures of Vs-M-ZnIn 2 S 4, resulting in a highly efficient interface with low edge contact resistance. Photogenerated electrons could quickly migrate to MoS 2 QDs through the intimate Zn–S bond interfaces. As a result, MoS 2 QDs@Vs-M-ZnIn 2 S 4 showed a high PHR activity of 6.884 mmol g –1 h –1, which was 11 times higher than 0.623 mmol g –1 h –1 for bulk ZnIn 2 S 4, and the apparent quantum efficiency reached as high as 63.87% (420 nm). This work provides a prototype material for looking into the role of vacancies between electronic structures and activities in 2D photocatalytic materials and gives insights into PHR systems at the atomic level.