A simple solid-state dechlorination route has been demonstrated to synthesize few layered functionalized carbon nanosheets (FCNS) utilizing hexachloroethane as carbon source and copper as reducing agent under the autogenic pressure at 300°C. The obtained FCNS possesses the sheet thickness of 6–12nm as analyzed by transmission electron microscopy. The particle nature of the FCNS provides the excess porosity having the surface area 836m2/g. The equilibrium gas adsorption study of FCNS for greenhouse gases (CO2 and CH4), toxic gas (CO) and light gas (N2) showed the maximum adsorption capacity for CO2 (2.95mmol/g; at 288K) with maximum capacity selectivity of 10.1 at 318K. The very strong adsorbate–adsorbent interaction was observed in case of CO compare to other gases resulted in higher heat of adsorption for CO. The gas adsorption and FT-IR study showed that the interaction of CO with copper present in minute quantities in FCNS improves the CO adsorption due to π complexation. The FCNS obtained under present methodology showed the very high equilibrium selectivity for CO over N2 (197) followed by CH4 (61) and CO2 (7.3) at 288K.