Markedly different adsorption behaviors of gas molecules on defective monolayer MoS2: a first-principles study

Sulfur vacancy (SV) is one of the most typical defects in two-dimensional monolayer MoS2, leading to reactive sites. We presented a systematic study of the adsorption behaviors of gas molecules, CO2, N-2, H2O, CO, NH3, NO, O-2, H-2 and NO2, on monolayer MoS2 with single SV by first-principles calculations. It was found that CO2, N-2 and H2O molecules physisorbed at the proximity of single SV. Our adsorption energy calculations and charge transfer analysis showed that the interactions between CO2, N-2 and H2O molecules and defective MoS2 are stronger than the cases of CO2, N-2 and H2O molecules adsorbed on pristine MoS2, respectively. The defective Mo(S)2 based gas sensors may be more sensitive to CO2, N-2 and H2O molecules than pristine MoS2 based ones. CO, NO, O-2 and NH3 molecules were found to chemisorb at the S vacancy site and thus modify the electronic properties of defective monolayer MoS2. Magnetism was induced upon adsorption of NO molecules and the defective states induced by S vacancy can be completely removed upon adsorption of O-2 molecules, which may provide some helpful information for designing new MoS2 based nanoelectronic devices in future. The H-2 and NO2 molecules were found to dissociate at S vacancy. The dissociation of NO2 molecules resulted in O atoms located at the S vacancy site and NO molecules physisorbed on O-doped MoS2. The calculated results showed that NO2 molecules can help heal the S vacancy of the MoS2 monolayer.