Effect of micropore and mesopore structure on CO₂ adsorption by activated carbons from biomass

Activated carbons (ACs) were produced by a one step process with CO₂ as the physical activation agent at 800 ℃. The ACs were further activated chemically using KOH, HNO₃ or CH₃COOH and heat-treated at 300 or 600 ℃ for 1 or 2 h to modify their properties. The effect of CO₂ concentration, activation time, types of chemical agents and the post heat-treatment conditions on CO₂ capture were investigated. Results showed that the optimum conditions for AC production from corn stalks was at 800 ℃ for 30 min with a CO₂ concentration of 20% during the physical activation. Chemical agents and further heat-treatment modified the pore structure of the ACs, resulting in a performance improvement for CO₂ adsorption. The BET surface area of one sample (HNO₃ activation +100 ℃ water bath 1 h + post heat-treatment at 600 ℃ for 2 h) was 639. 8 m²/g. The maximum CO₂ adsorption capacity of the sample was 7.33%, which is higher than that of a commercial AC (6.55%). The CO₂ adsorption is dominantly dependent on the mesopore volume when the BET surface area is smaller than 500 m²/g while the adsorption is closely associated with micropore area when the BET surface area is larger than 500 m²/g. The adsorption kinetics agreed well with the Bangham kinetic model.