Pollen-derived porous carbon by KOH activation: Effect of physicochemical structure on CO ₂ adsorption

Novel microporous carbons were prepared from bee-collected pollens through carbonization and KOH activation. In the activation, various mass ratios of KOH/carbonized pollen from 1:3 to 3:1 were tested, and their effect on the physicochemical properties and CO ₂ adsorption performance was analyzed. As the KOH amount increased, the specific surface area and total pore volume increased because of the development of micropores during activation. Among the developed porous carbons, the sample activated with a high ratio (3:1) of KOH/carbonized pollen showed the highest CO ₂ adsorption uptake at 1 bar. However, the sample activated with a KOH/carbonized pollen mass ratio of 1:1 exhibited the highest CO ₂ adsorption uptake at 0.15 bar owing to different micropore distributions and nitrogen contents originating from the pollen precursor. Because narrower micropores are more important in the low-pressure region, cumulative pore volumes with pore sizes of less than 0.6 and 0.8 nm were well correlated with the CO ₂ adsorption uptake at 0.15 and 1 bar, respectively. Further, samples with residual nitrogen content showed high CO ₂ /N ₂ selectivity. The developed microporous carbons also showed excellent adsorption-desorption cyclic stability during regeneration by simple N ₂ purging or by temperature-swing operation.