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

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 MoS₂ quantum dots (QDs) at the S vacancies on a Zn facet in monolayered ZnIn₂S₄ (Vs-M-ZnIn₂S₄) to craft a two-dimensional (2D) atomic-level heterostructure (MoS₂QDs@Vs-M-ZnIn₂S₄). 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 ZnIn₂S₄ established an important link between the electronic manipulation and activities of ZnIn₂S₄. 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-ZnIn₂S₄, resulting in a highly efficient interface with low edge contact resistance. Photogenerated electrons could quickly migrate to MoS₂QDs through the intimate Zn-S bond interfaces. As a result, MoS₂QDs@Vs-M-ZnIn₂S₄ 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 ZnIn₂S₄, 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.