Preparation of porous carbons with high low-pressure CO2 uptake by KOH activation of rice husk char

Porous carbons for CO2 capture at low pressures were prepared by KOH activation of rice husk char. Low activation temperature (640–710 °C) and small KOH/char ratio (1:1) favored the increase in low-pressure CO2 uptake. The CO2 uptakes at 0.1 bar (0 °C) reached 2.11 mmol/g, which were probably the highest value ever reported for porous carbons prepared from lignocellulosic biomass. The high CO2 uptakes at low pressures were ascribable to the presence of micropores (<0.7 nm or <1 nm), the narrow micropore size distribution, or the existence of nitrogen. The obtained porous carbons also exhibited a large CO2 uptake at 1 bar (6.24 mmol/g at 0 °C) and good CO2-over-N2 selectivity. No noticeable change in CO2 uptake was observed after five successive runs of adsorption–desorption. The excellent recyclability, high CO2 uptakes, and good selectivity show that high-performance porous carbons for capturing CO2 at low pressures can be prepared by KOH activation of rice husk char.