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. The N-doped 2H-MoS2 monolayers are found to be a promising candidate for sensing CO and SO2.