2D MoO_3-S/MoS₂ van der Waals Assembly: A Tunable Heterojunction with Attractive Properties for Photocatalysis

Two-dimensional (2D) van der Waals (vdW) heterostructures currently have attracted much attention in widespread research fields where semiconductor materials are key. With the aim of gaining insights into photocatalytic materials, we use density functional theory (DFT) calculations within the HSE06 functional to analyze the evolution of optoelectronic properties and high-frequency dielectric constant profiles of various 2D MoO_3-S/MoS₂ heterostructures modified by chemical and physical approaches. Although the MoO₃/MoS₂ heterostructure is a type III heterojunction associated with a metallic character, we found that exchanging the terminal oxo atoms of the MoO_3-S single layer (SL) with sulfur enables shifting its CB position above the VB position of the MoS₂ SL. This trend gives rise to a type II heterojunction where the band gap and charge transfer within the two layers are driven continuously by the S concentration in the MoO_3-S SL. This fine-tuning leads to a versatile type II heterostructure proposed to provide a direct Z-scheme system valuable for photocatalytic water splitting.