Adsorption of CO2 onto amine-grafted mesoporous silicas

The characteristics and CO2 adsorption of mesoporous silicas including MCM-41, SBA-15, and pore-expanded MCM-41 with pore size in a range of 2–17 nm, modified by mono-, di-, and tri-aminosilanes were examined in this study. The adsorption data show that SBA-15 possessing a proper pore size accommodated amines exhibit the best CO2 adsorption capacity as 2.41 mmol CO2/g at 333 K. The corresponded CO2 adsorption efficiencies, represented by CO2/N molar ratios, were as high as of 0.5–0.7, an indication of the adsorption being sufficiently close to thermodynamic equilibrium. The CO2 adsorption mechanism of the amine-functionalized mesoporous silica is proposed. The adsorption of the grafted amine under anhydrous CO2 can be considered to proceed through carbamate intermediate and zwitterion mechanism.