First-Principles Study of Hazardous Gas Molecule Adsorption on Janus MoSTe Monolayer Modified with Surface Vacancy Defect

Novel highly sensitive two-dimensional gas-sensing materials for detecting hazardous gases are crucial for human health, climate protection, and industrial development. In this study, density functional theory (DFT) was employed to investigate the adsorption and sensing properties of four representative hazardous gas molecules (NO, NO2, F2, and Cl2) on pristine and vacancy-defective (S vacancy and Te vacancy) Janus MoSTe monolayer. The introduction of a vacancy into the MoSTe monolayer significantly reduces the adsorption distances and enhances the adsorption energies and charge transfers. Notably, an S vacancy induces a transition in the adsorption behaviors of NO, NO2, and Cl2 on MoSTe from physisorption to chemisorption, and a Te vacancy leads to strong physisorption of NO and NO2 on the MoSTe monolayer. Electronic structure analysis further reveals that gas molecule adsorption can modulate band gaps. Adsorption of F2 and Cl2 on the Te surface of pristine MoSTe converts the indirect bandgap into a direct bandgap. However, the calculation results for O2 adsorption indicate that the S and Te vacancies in Janus MoSTe may be readily occupied by O2, suggesting that it is not a good sensing material under atmospheric conditions. This study provides valuable theoretical insights and guidance for future experiments on vacancy-defective Janus MoSTe monolayer.