Highly porous N-doped carbons impregnated with sodium for efficient CO2 capture

Abstract

Highly porous sodium-impregnated and N-doped carbon sorbents (SNSs) were prepared by KOH activation of polyacrylonitrile (PAN), followed by NaOH impregnation of the activated N-doped carbons. These new types of materials were investigated as sorbents for CO₂ capture. Particularly, SNS2-20 prepared with the KOH/PAN ratio of 2 at 700 °C and 20 wt% NaOH based on the weight of the activated carbon exhibited the adsorption capacity of 6.84 and 4.48 mmol g⁻¹ at 0 and 25 °C under ambient pressure. Among the carbon sorbents reported to date, it showed the highest CO₂ uptake of 3.03 and 1.90 mmol g⁻¹ at 0 and 25 °C under a typical pressure condition of post-combustion flue gas (0.15 bar CO₂). The enhanced CO₂ uptake is due to high porosity caused by KOH activation, enriched pyridonic/pyrrolic nitrogen contents, and strong basic sites generated by NaOH impregnation. Moreover, CO₂/N₂ selectivities of 59.5, 68.9 and 79.4 at 0, 25 and 50 °C were achieved for the gas mixture (CO₂ : N₂ = 15 : 85) according to the ideal adsorbed solution theory (IAST). The consecutive adsorption–desorption cycle experiments using SNS2-20 showed almost unaltered CO₂ uptake capacities. Combined with its simple preparation, the high CO₂ adsorption capacity and selectivity of the synthesized SNS2-20 could provide potential for practical applications of CO₂ capture and storage.