Larger Pore Size and Higher Intrawall Pore Volume of the Support Enhance the CO_2 Adsorption Performance of Amine-Tethered SBA-15 Silica

摘要

Amine-functionalized silicas have drawn tremendous attention for adsorptive CO_2 capture, owing to their high CO_2 uptake at low partial pressures, fast CO_2 adsorption kinetics, favorable CO_2/N_2 selectivity, thermal stability, and tolerance to humid conditions. Herein, the impact of the support pore structure on the CO_2 adsorption performance of triarnine-tethered SBA-15 silica is investigated. Four SBA-15 silica supports with different pore sizes and intrawall pore volumes were synthesized, followed by triamine grafting. CO_2 adsorption measurements showed the positive impact of support large pore size and high intrawall pore volume on adsorptive properties, with the former being dominant. Large-pore supports exhibited the highest surface density of amine groups (up to 30 μmol/m~2), highest CO_2 uptakes (up to 1.88 mmol CO_2/g) and CO_2/N ratios (up to 0.33 mol CO_2/mol N), and fastest adsorption kinetics. When the intrawall pore volume decreased by 53% for samples with identical pore sizes, lower CO_2 uptakes (up to 63%) and CO_2/N ratios (up to 62%), and slower adsorption kinetics were observed, particularly for the lowest adsorption temperature (i.e., 25 °C). It was inferred that large pore size and/or high intrawall pore volume of the support improve the adsoiptive properties via enhanced amine accessibility. Large-pore supports also allowed higher surface amine density to be achieved because of reduced steric hindrance between the grafted triamine species.