Size-dependent properties of amino-functionalized single walled carbon nanotubes

► We present ab initio study of covalently amino-functionalized carbon nanotubes. ► Relationship between size of CNT and their properties was analyzed and discussed. ► Binding energies, charge transfer and structural properties were calculated. ► The stability of amine group is favored for narrower nanotubes. ► The addition of NH2 group changes drastically the electronic structure of CNT.