Gas Molecules on Defective and Nonmetal-Doped MoS₂ Monolayers

The adsorption and reaction behaviors of a series of common gas molecules (CO, CO₂, NH₃, SO₂, NO, NO₂, and O₂) over defective and nonmetal (C, N, and O)-doped MoS₂ monolayers in both the 2H and 1T′ phases have been systematically investigated using first-principles calculations. The most common defect (S vacancy) can significantly enhance the adsorption strength of all gas molecules. For defective 2H-MoS₂ monolayers, the S vacancies can be doped with C, N, and O atoms by passing the corresponding gases of CO, NO, and NO₂/CO₂ at room temperature. However, this doping approach does not apply to defective 1T′-MoS₂ monolayers because of the high dissociation barrier of the adsorbed gases and other means such as electron beam irradiation has to be pursued. Moreover, O₂ and NO₂ catalytically dissociate over the defective and doped 2H and 1T′-MoS₂ monolayers. The O-doped sites in 1T′-MoS₂ monolayers can be reverted back to S vacancies by the CO adsorption.