Standing out the key role of ultramicroporosity to tailor biomass-derived carbons for CO2 capture

Abstract

The successful tailoring of the ultramicroporosity remarkably increases the CO2 uptake capacity of low cost-carbons derived by a simple one-pot physical activation of olive stones, coffee grounds, almond shells and grape seeds. A porous network dominated by ∼40–46% of ultramicropores below 0.5 nm and no significant presence of pores above 0.7 nm boosts the CO2 uptake at 1 bar and 298 K around 40% compared to materials with similar micropore volume. A slight ultramicropore widening causes the drop to a standard pattern that depends mainly on the micropore volume.

The detailed analysis of the CO2 isotherms within the Dubinin´s theory provides simple clues for the optimization of carbons for CO2 capture at ambient temperature and atmospheric pressure. Thus, a general pattern of around 7.2 mmol of CO2 captured per cm3 of ultramicropores is found for a variety of activated carbons and carbide derived-carbons with characteristic energy Eo of 29–22 kJ/mol. This feature is typical of materials with average micropore sizes from 0.65 to 1 nm. An enhancement of up to 10 mmol CO2/cm3 is achieved by carbons with Eo ranging between 30 and 32 kJ/mol which correlates with an extremely homogeneous porosity with average dimensions around 0.5 nm. The excellent fit of the present carbons into general patterns exclusively based on the textural features reveals no significant influence of their surface functionalities on the CO2 adsorption performance.