Insights into CO2 adsorption in amino-functionalized SBA-15 synthesized at different aging temperature

Mesoporous silica SBA-15 solids have been synthesized at different aging temperature with the goal of obtaining materials with different textural properties. The synthesized samples have been evaluated for their CO2 adsorption capacity. In order to increase the CO2 adsorption capacity and the CO2/N2 selectivity, the SBA-15 synthesized at different aging temperatures were functionalized via grafting with 3-aminopropyltriethoxysilane (APTES) and via impregnation with polyethyleniminethylenediamine branched (PEI) or tetraethylenepentamine (TEPA). In all cases, the adsorption isotherms of the amine functionalized silica are fitted to the Dualsite-Langmuir model, where physical and chemical adsorption sites are reported. The isotherms reveal that grafted-silicas with APTES displayed the coexistence of both adsorption sites, while the adsorption process of PEI or TEPA impregnated-silicas are mainly governed by chemical interactions. The adsorption isotherms show that the most promising adsorbent for CO2 capture in terms of CO2 adsorption capacity and CO2/N2 selectivity is the SBA synthesized at 393 K (aging temperature) and functionalized with TEPA (50 wt%) (SBA-393-50T). This sample reached a CO2 adsorption capacity of 2.83 mmol g−1 at 100 kPa and 338 K. The CO2 adsorption capacity of this material decreased around 5% after the first adsorption/desorption cycle, maintaining a constant value for successive cycles. SBA-393-50T also showed an outstanding CO2/N2 selectivity, increasing significantly as the CO2 concentration decreases.