Treated activated carbons, prepared by heat treatment of activated carbon sorbents under the protection of argon (Ar), were subjected to synthetic flue gases to investigate its elemental mercury (Hg-0) capture and the specific role of HCI and O-2. To elucidate the adsorption mechanisms & binding properties, subsequent sorbents were characterized by X-ray photoelectron spectroscopy and X-ray absorption fine structure spectroscopy. The results suggest that Hg-0 capture on the heat treated activated carbon (TAC) under HCI atmosphere mainly follows Eley-Rideal reaction mechanism, where, HCI reacts with the basic active carbon sites on the TAC leading to the formation of Cl-containing active sites, subsequently gaseous Hg-0 heterogeneously reacts with these Cl-containing active sites through electron-transfer and forms HgClx compounds. Both the 2.42 angstrom and 239 angstrom bonding distance of Hg-Cl shows that only one of the two valence electrons on mercury bond with Cl, while the other electron bonds with the basic active carbon site covalently. In presence of HCI and O-2, the synergistic effect of O-2 on Hg adsorption might attribute to the O-2 adsorption and the subsequent formation of oxygen-containing functional groups (OFGs) on TAC, which increase the amount of effective activated sites for Hg-0 adsorption and at the same time enhance the adsorbing kinetics of adjacent Cl-containing sites. (C) 2017 Elsevier B.V. All rights reserved.