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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 (V_Zn). Especially, for NH₃, NO, and NO₂ adsorbed Zn-vacancy g−ZnO (V_Zn/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 V_Zn/g−ZnO system is significantly reduced, especially the adsorption height of the NH₃ adsorbed on V_Zn/g−ZnO system is reduced to 0.686 Å. It is worth mentioning that the introduction of O-vacancy (V_O) significantly enhances the charge transfer between NO or NO₂ and V_O/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 <i>μ</i>_B and 0.858 <i>μ</i>_B for g−ZnO, and 1 <i>μ</i>_B and 1 <i>μ</i>_B for V_O/g−ZnO. In addition, V_Zn induced 1.996 <i>μ</i>_B magnetic moments for intrinsic g−ZnO, and the CO, NH₃, NO and NO₂ change the magnetic of V_Zn/g−ZnO. The adsorption of NO₂ causes the intrinsic g−ZnO to exhibit metallic properties, while the adsorption of NH₃ gas molecules causes V_Zn/g−ZnO also to show metallic properties. The adsorption of NO and NO₂ causes V_Zn/g−ZnO to display semi-metallic properties. These results facilitate the enrichment of defect detection means and the design of gas detection devices.