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.