Functionalization of hollow silica microspheres by impregnation or grafted of amine groups for the CO2 capture

Hollow silica microspheres have been synthesized with high surface area and homogenous porous size distribution to be evaluated for their CO2 adsorption capacity. All adsorbents were well fitted to the Henry model, except HMS-F that displays the highest CO2 adsorption capacity, which was adjusted to the Langmuir model. In order to increase the CO2 capture, the hollow silica microspheres were functionalized via grafting 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 Dual-Langmuir model, where physical and chemical adsorption sites are described. The isotherms reveal that grafted-silicas with APTES display the coexistence of both adsorption sites, while the adsorption process of impregnated-silicas with PEI or TEPA are governed by chemical interactions. The adsorption isotherms show that the most promising adsorbent for CO2 capture is HMS-F-TiPB, which reached a CO2 adsorption capacity of 3.4 mmol g−1 at 760 mmHg and 25 °C, maintaining this adsorption capacity 5 cycles.