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 O-2) 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'-MoS 2 monolayers because of the high dissociation barrier of the adsorbed gases and other means such as electron beam irradiation has to be pursued. Moreover, O-2 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.