Tunable nitrogen-doped microporous carbons: Delineating the role of optimum pore size for enhanced CO2 adsorption

In the current study, a series of nitrogen-doped carbons was designed which possess high surface area (1047-3247 m(2) g(-1)), ultra-micropores (< 0.63 nm), high micropore volume (0.5718-1.6247 cm(3)/g) and optimum nitrogen content (2.07-13.8 at%). At 1 bar, all the prepared samples exhibits an outstanding CO2 uptake of 228-355 mg g(-1) at 273 K and 162-218 mg g(-1) at 298 K, which commensurate to the highest reported adsorption data for the carbon-based materials. The isosteric heat of adsorption (Delta H-ads) lies in the range (26.5-42.0 kJ/mol), suggesting the predominantly physisorption mechanism of adsorption. To investigate the effect of narrow micropores and nitrogen content on CO2 adsorption, the amount of CO2 adsorbed at 273 K/1 bar, micropore volume < 0.63 nm and pyrrolic nitrogen content were normalized and compared. Results declared that the presence of micropores of about 0.63 nm in diameter were primarily responsible for CO2 adsorption by micropore filling mechanism with the pyrrolic content playing a secondary role.