Ab-initio investigation of adsorption of CO and CO2 molecules on graphene: Role of intrinsic defects on gas sensing

•Absorptions of CO and CO2 molecules on graphene are studied using DFTB and QE.•CO and CO2 molecules can alter chemisorption on vacancy of graphene.•Vacancy-defected graphene is highly sensitive and selective toward detection of CO.•Normalized Conductance varies linearly with CO or CO2 gas doses in consistency with experimental data.