N, S doped graphene-based materials have been recently recognized as promising adsorbents for CO2 capture, but understanding of the adsorption mechanism at the atomic level is still limited. Herein, the local structures and promotion mechanism of CO2 capture by N, S doped graphene were investigated by combining density functional theory and ab initio thermodynamics. A single vacancy defected graphene involving N, S dual-doping was found to be a superior adsorbent for CO2 capture under mild conditions (<100 degrees C, 1 atm). The enhanced CO2 adsorption performance should be ascribed to a charge delivery channel along the S N CO2 path, leading to extra charge transfer from graphene to CO2. It is worth mentioning that the extra charge transfer was stimulated by the unique sp(2) hybridization of pyridine N and further enhanced by S in N, S dual-doped graphene. A possible mechanism has been proposed to explain the high adsorption performance of CO2 by N, S dual-doped graphene, which offers insights for the design of new graphene-based adsorbents. (C) 2016 Elsevier B.V. All rights reserved.