Exceptional Gas Adsorption Properties by Nitrogen-Doped
Porous Carbons Derived from Benzimidazole-Linked Polymers
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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 m<sup>2</sup> g<sup>–1</sup> and 1.51 cm<sup>3</sup> g<sup>–1</sup>, respectively, while
low temperature activated CPC-550 exhibits the highest ultramicropore
volume of 0.35 cm<sup>3</sup> g<sup>–1</sup>. 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 CO<sub>2</sub> uptake capacities
of 5.8 mmol g<sup>–1</sup> (1.0 bar) and 2.1 mmol g<sup>–1</sup> (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 CO<sub>2</sub> (25.7 mmol g<sup>–1</sup> at 298 K and 30 bar) and CH<sub>4</sub> (20.5 mmol
g<sup>–1</sup> 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