Microwave-DES activation of poplar-derived ultramicroporous carbon for efficient CO2/N2 separation with extremely high pore utilization rate

Abstract

Poplar wood was employed as the precursor to develop a coupled “microwave self-gasification & aqueous post-modification” protocol that enables instantaneous activation within a microwave field, yielding activated carbon dominated by ultra-micropores (< 0.7 nm). Despite a modest BET surface area of ~ 900 m²/g, the material exhibits an exceptional CO₂ uptake of 180.4 mg/g at 0 °C and 1 bar—1.6-fold higher than at 25 °C—while N₂ uptake remains below 30 mg/g under the same conditions. On a pore-volume basis, the carbon stores 443.79 mg CO₂ per cm³ at 0 °C and 278.62 mg/cm³ at 25 °C. CO₂ adsorption proceeds via a multilayer mechanism with the isosteric heat (Qst) decreasing from 45 to 23 kJ mol⁻¹, whereas N₂ follows a monolayer pathway with Qst held between 20 and 24 kJ mol⁻¹. IAST calculations reveal that CO₂/N₂ selectivity rises from 70 to 90 with increasing pressure at 0 °C and levels off around 50 at 25 °C. Dynamic breakthrough experiments deliver a separation factor of 8.28 for a 15% CO₂/85% N₂ mixture. GCMC simulations further indicate that O–C = O-functionalized surfaces confer the highest CO₂ capacity, while C–S–C motifs are the least favorable in competitive adsorption.