Preparation of N, O co-doped carbon nanotubes and activated carbon composites with hierarchical porous structure for CO2 adsorption by coal pyrolysis

Coal pyrolysis was employed to create nitrogen-oxygen co-doped CNTs/AC composites for CO2 adsorption in this work. In comparison to previous publications on carbon nanotube surface modification and direct fabrication of CO2 adsorption materials, the approach developed in this work is simpler, more cost-effective, and has a better CO2 adsorption capability. The synthesized functional composites have high specific surface area (1003-1443 m2/g), high oxygen content (16.1 %) and nitrogen content (2.37 %).Among them, NCNTs/AC-1 exhibited a CO2 adsorption capacity of 3.77 mmol/g and a high CO2/N2 selectivity (25.05) at 298 K and 1 bar. The adsorption behavior of NCNTs/AC-1 can be well described by the Freundlich model. The linear correlation between CO2 absorption capacity, micropore volume of specific size (V < 0.7 nm and V < 0.9 nm), O content and N content was investigated. At 298 K, the contribution of O content to CO2 adsorption is comparable to or even higher than that of N content. Interestingly, micropores in the range of V < 0.9 nm have a good correlation with CO2 adsorption capacity at 273 K. This study offers new perspectives for the high added value and environmental protection of bituminous coal.