Ab initio investigation of the adsorption properties of molecules on MoS2 pristine and with sulfur vacancy

MoS2 is a key two-dimensional material with a broad range of potential technological applications, which includes flexible nanoelectronics, sensors, support for catalysts, photovoltaics, etc. During device operation, the interactions of gas molecules with the MoS2 surface can significantly affect its performance. In this study, we report a theoretical study based on density functional theory of the impact of sulfur vacancies, a common point defect in MoS2 monolayers, on the adsorption properties of 12 relevant molecules on MoS2 monolayers. Our findings reveal that H2O, N2, CO, O2, NO, and SO2 exhibit the lowest interaction energies when adsorbed in proximity to sulfur vacancies, leading to a modification in their adsorption orientation compared to the pristine surface of MoS2. In contrast, the remaining investigated molecules (H2, NH3, CH4, N2O, CO2, and NO2) preferentially adsorb on pristine regions of MoS2. We attribute these results to differences in charge transfer between the molecules and the surface, with sulfur vacancies inducing more significant charge transfer for the first set of molecules. Notably, the adsorption of NO stands out from the others as it leads to an increase in the work function of MoS2 by 1.25 eV due to the creation of energy levels within the MoS2 band gap. Additionally, NO passivates sulfur vacancies through covalent bonds. Among the remaining 11 molecules, only NO2 and SO2 induce modifications in the electronic structure around the MoS2 bandgap region, showcasing the potential of MoS2 for sensing these molecules, whereas sulfur vacancies enhance only the SO2/monolayer interaction energy, suggesting a promising avenue for selective sensing.