Effects of Vacancy Defects and the Adsorption of Toxic Gas Molecules on Electronic, Magnetic, and Adsorptive Properties of g−ZnO: A First-Principles Study

Abstract

Using first principles based on density functional theory (DFT), the CO, NH3, NO, and NO2 gas adsorbed on intrinsic Graphite-like ZnO (g−ZnO) and vacancy-deficient g−ZnO were systematically studied. For intrinsic g−ZnO, the adsorption energy of NH3, NO, and NO2 adsorption defective g−ZnO systems increased significantly due to the introduction of Zn vacancy (VZn). Especially, for NH3, NO, and NO2 adsorbed Zn-vacancy g−ZnO (VZn/g−ZnO) systems increased to 1.366 eV, 2.540 eV and 2.532 eV, respectively. In addition, with the introduction of vacancies, the adsorption height of the gases adsorbed on VZn/g−ZnO system is significantly reduced, especially the adsorption height of the NH3 adsorbed on VZn/g−ZnO system is reduced to 0.686 Å. It is worth mentioning that the introduction of O-vacancy (VO) significantly enhances the charge transfer between NO or NO2 and VO/g−ZnO. This suggest that the defective g−ZnO is more suitable for detecting NH3, NO and NO2 gas. It is interesting to note that the adsorption of NO and NO2 gases gives rise to magnetic moments of 1 μB and 0.858 μB for g−ZnO, and 1 μB and 1 μB for VO/g−ZnO. In addition, VZn induced 1.996 μB magnetic moments for intrinsic g−ZnO, and the CO, NH3, NO and NO2 change the magnetic of VZn/g−ZnO. The adsorption of NO2 causes the intrinsic g−ZnO to exhibit metallic properties, while the adsorption of NH3 gas molecules causes VZn/g−ZnO also to show metallic properties. The adsorption of NO and NO2 causes VZn/g−ZnO to display semi-metallic properties. These results facilitate the enrichment of defect detection means and the design of gas detection devices.