Facile preparation of N-doped activated carbon produced from rice husk for CO₂ capture

Activated carbons (AC) were prepared by carbonization and KOH activation using rice husk as feedstock. The effects of impregnation ratios and activation temperatures on the properties of AC were investigated. Under optimum conditions, BET surface area, total pore volume and micropore volume of AC are as high as 1495.52 m²/g, 0.786 cm³/g and 0.447 cm³/g, respectively. Surface modification with chitosan as nitrogen source was performed simultaneously during KOH activation process. XPS and FT-IR analyses show that N-species was successfully incorporate into AC. Compared with AC-5 (general AC), CAC-5 (modified AC) exhibits better CO₂ adsorption performance, reaching 5.83 mmol/g at 273 K and 1 bar, which can be attributed to the formation of the CO₂-philic active sites on AC surface by N-species. The linear correlations between CO₂ uptake, micropore volume within specific size section and N-content was investigated. The isosteric heat of CO₂ adsorption for CAC-5 (average 30.21 kJ/mol) is much higher than that of AC-5 (average 14.48 kJ/mol). The adsorption behavior of CAC-5 can be well described by Freundlich model. The high IAST selectivity factor for N-doped ACs indicates their excellent adsorption selectivity for CO₂ over N₂. Both physisorption and chemisorption are present in CO₂ adsorption process of N-doped ACs.