Abstract
A sustainable and integrated strategy is developed for the synthesis of nitrogen-doped porous carbons (HNPCs) using organically modified CaCO₃ nanofluids as multifunctional precursors, and their CO₂ separation performance is systematically evaluated. Cubic and spherical CaCO3 nanofluids were prepared using M2070 and KH560 as organic modifiers to form an organic crown-like structure, followed by programmed pyrolysis at 800 °C to obtain HNPCs. The obtained HNPCs exhibit well-developed porous structures with a high BET surface area of 777.3 m2·g−1, a micropore volume of 0.0928 cm3·g−1, and a nitrogen content of 2.79 wt% (elemental analysis). XPS analysis reveals that pyrrolic N (48.98%) and pyridinic N (26.47%) are the dominant nitrogen species, contributing to enhanced CO₂ adsorption affinity. The spherical CaCO₃-derived sample (SNPC(II)) shows superior CO₂ uptake capacities of 2.85 mmol·g−1 at 25 °C and 3.98 mmol·g−1 at 0 °C under 1 bar. The isosteric heat of adsorption ranges from 17.3 to 36.5 kJ·mol−1, indicating a physisorption-dominated and energy-efficient process. Ideal Adsorbed Solution Theory predicts a CO2/N2 selectivity of 34.19 at 298 K and 1 bar. Fixed-bed breakthrough experiments using simulated flue gas (15 vol% CO₂/85 vol% N₂) demonstrate a CO₂ breakthrough time of 4631 s·g−1, markedly longer than that of N₂ (342 s·g−1). Moreover, SNPC(II) retains 98.7% of its initial CO₂ capacity after eight adsorption–desorption cycles, highlighting excellent cyclic stability.
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