Density Function theory (DFT) calculation used to employed ground and excitation states for graphene ribbons, types of adsorption, energy gap, maximum wave length and optical band gap. Adsorption energy showed that CO2 gas molecule have chemical adsorption in distance 1 and 1.5 Angstrom, distance 2 and 2.5 Angstrom appear physical adsorption, adsorption energy decreased when distance between surface and gas molecule increasing. Resulting from chemical adsorption energy gap change with distance 1 and 1.5 Angstrom because attract gas molecule with surface. Excitation energy for nano system in sample 1 and 4 shifted to low wavelength (blue shift) change from 1018 nm to 993 nm and 718 nm on series. Other sample have red shift and energy gap becoming open. Result showed that graphene ribbon sense carbon dioxide gas (CO2).