Nitrogen doping of porous carbons derived from CaCO3 nanofluids for enhanced CO2 adsorption.

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 CaCO 3 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 m 2 ·g −1 , a micropore volume of 0.0928 cm 3 ·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 CO 2 /N 2 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.