Hierarchical nanostructured carbons as CO₂ adsorbents

Synthesis and characterization of hierarchical carbon materials, CMK-5 type, with high specific surface areas and large pore volumes is reported and tested in CO₂ adsorption. These materials were successfully synthesized by the nanocasting process using a hard silica template SBA-15, furfuryl alcohol (FA) as carbon precursor, and 1,3,5-trimethylbenzene (TMB) as solvent. The percentage of FA, and the FA:TMB volume ratio were the synthesis parameters evaluated to determine the accurate amounts to impregnate the pore walls of the template. Both parameters influence the formation of carbon materials with a 2D porous structure and hexagonal tube array. CMK-5 materials achieved specific surface areas up to 2200 m²/g and total pore volumes ca. 2 cm³/g. The characterization techniques allowed us to establish a correlation between the different textural, structural and morphological properties and the carbon dioxide adsorption capacity. The CO₂ adsorption capacity at 308 K up to 1 bar has a strong relationship only with the micropore volume, but at higher pressure (up to 10 bar) the CO₂ adsorption capacity depends not simply on the amount of micropores but also of the small mesopores present in these carbons, reaching a maximum value of 7 mmol/g, at 308 K and up to 10 bar.