Density functional theory was applied to calculate the adsorption property of metal/hexa-vacancy defective graphene (denoted as HDG-M, M: Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) with O- and N-dopants. We investigate the adsorption properties of these complexes between gaseous molecules and HDG-M. Our results show that HDG-Cu has a high selectivity for O-2, but HDG-Fe has a good ability to capture many gases such as CO, NO and O-2. Our calculations could provide useful information for designing new graphene-based adsorbents to remove undesired gases, which may poison the metal catalysts in reaction processes. (C) 2016 Elsevier B.V. All rights reserved.