Direct Carbonization of Cyanopyridinium Crystalline Dicationic Salts into Nitrogen-Enriched Ultra-Microporous Carbons toward Excellent CO₂ Adsorption

A family of nitrogen-enriched ultramicroporous carbon materials was prepared by direct carbonization of task-specifically designed molecular carbon precursors of cyanopyridinium-based crystalline dicationic salts (CISs). Varying the molecular structure of CISs, large surface area (918 m² g^-1), high N content (20.10 wt %), and narrow distributed ultramicropores (0.59 nm) can be simultaneously achieved on the sample PCN-14 derived from methyl-linked 4-cyanopyridinium D[4-CNPyMe]Tf₂N. It therefore exhibited exceptional performance in greenhouse gas CO₂ capture, i.e., simultaneously possessing (1) high CO₂ adsorption uptakes: 5.33 mmol g^-1 at 273 K, and 3.68 mmol g^-1 at 298 K (both at 1.0 bar); (2) unprecedented selectivity of CO₂ versus N₂: 156; and (3) a high adsorption ratio of CO₂ to N₂: 148 (at 1.0 bar). This is the first time such a high selectivity and adsorption ratio over carbon materials has been achieved, which is among the highest values over solid adsorbents. (Chemical Equation Presented).