WSO and WSeO Janus monolayers formation and their role for cation selection

2D transition metal dichalcogenides possess semiconductor characteristics and have environmental remediation and energy applications. Here, we conducted density functional theory studies to understand the Janus WSO and WSeO formation from their pristine counterparts WS₂ and WSe₂, respectively. The oxidation process is well-ordered in diagonal-like patterns. Each oxidation step is thermodynamically stable. A linear behavior in the lattice parameter reduction appears when going from WS₂/WSe₂ towards WSO/WSeO; a fact related to the electronegativity of the chalcogen species (Se>S>O). All oxidized structures possess bonds with mixed covalent and ionic characters. Also, oxidation produces a direct-to-indirect band gap transition (Gamma to K) at early oxidation steps and remains until the Janus monolayers formation. The oxidized part of the Janus monolayers is reactive towards electron donor species. Proof of that is the cation selection evidenced in both monolayers, which points to these 2D materials as potential anodes for water treatment.

We thank DGAPA-UNAM project IG101124 for its partial financial support. Calculations were performed in the DGCTIC-UNAM Supercomputing Center, Project LANCAD-UNAM-DGTIC-368. JGS acknowledges LNS-BUAP project 202201042N and THUBAT KAAL IPICYT supercomputing center project TKII-JGSA001 for their computational resources. We thank Aldo Rodriguez-Guerrero for their technical support and useful discussions.