Exceptional Gas Adsorption Properties by Nitrogen-Doped Porous Carbons Derived from Benzimidazole-Linked Polymers

Abstract

Heteroatom-doped porous carbons are emerging as platforms for use in a wide range of applications including catalysis, energy storage, and gas separation or storage, among others. The use of high activation temperatures and heteroatom multiple-source precursors remain great challenges, and this study aims to addresses both issues. A series of highly porous N-doped carbon (CPC) materials was successfully synthesized by chemical activation of benzimidazole-linked polymers (BILPs) followed by thermolysis under argon. The high temperature synthesized CPC-700 reaches surface area and pore volume as high as 3240 m² g^–1 and 1.51 cm³ g^–1, respectively, while low temperature activated CPC-550 exhibits the highest ultramicropore volume of 0.35 cm³ g^–1. The controlled activation process endows CPCs with diverse textural properties, adjustable nitrogen content (1–8 wt %), and remarkable gas sorption properties. In particular, exceptionally high CO₂ uptake capacities of 5.8 mmol g^–1 (1.0 bar) and 2.1 mmol g^–1 (0.15 bar) at ambient temperature were obtained for materials prepared at 550 °C due to a combination of a high level of N-doping and ultramicroporosity. Furthermore, CPCs prepared at higher temperatures exhibit remarkable total uptake for CO₂ (25.7 mmol g^–1 at 298 K and 30 bar) and CH₄ (20.5 mmol g^–1 at 298 K and 65 bar) as a result of higher total micropores and small mesopores volume. Interestingly, the N sites within the imidazole rings of BILPs are intrinsically located in pyrrolic/pyridinic positions typically found in N-doped carbons. Therefore, the chemical and physical transformation of BILPs into CPCs is thermodynamically favored and saves significant amounts of energy that would otherwise be consumed during carbonization processes