Elemental mercury oxidation mechanism by gaseous advanced oxidation method was studied using density functional theory on Fe3O4 (111) surface containing H2O2 molecule. Fe-tet1- and Fe-oct2-terminated Fe3O4 (111) surfaces have been simultaneously considered both in H2O2 decomposition and hydroxyl pre-adsorbed Fe3O4 (111) interfaces. It is found that the Fe-oct2-terminated surface was more favored for H2O2 decomposition, and H2O2 was easier to decompose and generate two hydroxyls than Fe-tet1-terminated surface. Through the discussion of Fe-tet1- and Fe-oct2-terminal mechanisms, the Mulliken charge population, and the partial density of states, we found that OH had different reaction activity generated on different Fe-terminal. Hg strongly interacted with the free state OH mainly due to the highly reactive and strong electrophilic ability of OH radical. The oxidation of Hg formed stable oxidized mercury species on Fe-terminated surface and most of the lost electron transferred from Hg to unbonded hydroxyl during Hg oxidation. The result showed that the combination of Hg and hydroxyl was exothermic reaction, which was favorable to spontaneous processes of Hg oxidation. The OH-Hg-OH and Hg-OH intermediates had a lower desorption energy when they detached from the surface and was the major reaction pathway. (C) 2017 Elsevier Ltd. All rights reserved.