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 m² g⁻¹), ultra-micropores (<0.63 nm), high micropore volume (0.5718–1.6247 cm³/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 (ΔH_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.