Density functional theory calculations were employed for investigation of three transition metals (TMs), i.e. Co, Rh and Ir binding to armchair (5,5) single-walled carbon nanotubes (SWCNTs) and adsorption of CO2 and NO2 onto TM-doped SWCNTs. It was found that the binding abilities of TMs to the SWCNT are in order: Ir > Rh > Co. The adsorption abilities of CO2 and NO2 gases individually on the pristine and TM-doped SWCNTs were found as orders: Co-doped > Ir-doped > Rh-doped >> pristine SWCNTs and Ir-doped > Co-doped > Rh-doped >> pristine SWCNTs for adsorptions of CO2 and NO2, respectively. The Ir-doped SWCNT was found to be the best NO2 storage. Either the Ir-doped SWCNT or Co-doped SWCNT or Rh-doped SWCNT can also be used as the NO2 storage. (C) 2013 Elsevier B.V. All rights reserved.