Construction of ultramicropore-enriched N-doped carbons for CO₂capture: Self-decomposition of polyethyleneimine-based precursor to promote pore formation and surface polarity

N-doped porous carbons have been regarded as competitive candidates for CO2 adsorption by virtue of tunable micropores and basic nitrogen sites. Herein, we synthesized the ultramicropore-enriched N-doped carbon by pyrolysis of polyethyleneimine-based polymer network which was formed by nucleophilic substitution reaction of polyethyleneimine and p-dichloroxylene. The precursor with evenly anchored amine groups on the surface and interior could not only serve as pore-forming agent by self-decomposition, but also generate abundant nitrogen sites to enhance the surface polarity. By adjusting carbonization temperatures (500, 600, 700 and 800 °C) and amounts of KOH activator, the texture properties and nitrogen contents of the N-doped porous carbons (denoted as CPDs) were tuned finely. Impressively, the CPD-600 pyrolyzed at 600 °C possessed large surface area (1638 m2/g), narrow-distributed ultramicropores (d < 0.7 nm) and high nitrogen content (6.16 wt%). The sufficient nitrogen species (especially pyrrolic-N) as the basic "CO2-philic"sites could strengthen the affinity of polar surfaces toward CO2 molecules. Moreover, the well-developed ultramiropores offered restricted spaces that could capture CO2 by superposition effect of Van der Waals' force. These advantages endowed CPD-600 with high-performance of CO2 uptake (4.92 mmol/g), CO2/N2 (15/85, v/v) selectivity (31) and regenerability at 298 K and 1 bar. The rational design of polymer-derived porous carbons with tailoring structural and functional properties could be applied not only to CO2 capture from gas mixtures but also to other advanced fields.