Silica-alumina aerogels functionalized with amino-groups for the adsorption of CO2

Abstract

To overcome climate challenges, emerging CO₂ capture technologies focus on innovative solid sorbents, like aerogels. Silica aerogels, in particular, have emerged as an exceptional class of materials with unique properties even though their adsorption selectivity towards CO₂, and their thermal and mechanical properties are limited. In this research, a hybrid silica-alumina aerogel has been prepared, to merge the elevated surface area typical of silica with the basic character (favorable to CO₂ adsorption) and the high thermal and mechanical resistance typical of alumina. For the first time, these silica-alumina aerogels were functionalized with 3-aminopropyltriethoxysilane (APTES) amino groups through a one-pot process. This approach was chosen to directly introduce functional groups during gel formation, reducing the number of post-synthesis steps. The functionalization with amino groups aims to strengthen the interactions with CO₂ molecules via acid–base interactions, thus enhancing adsorption capacity and selectivity. Three samples with increasing APTES content as well as a reference without any functionalization were prepared and characterized in terms of physico-chemical and adsorption properties. The results of CO₂ and N₂ adsorption tests as well as in situ FTIR suggest that low functionalization does not confer a significant advantage in CO₂ capture. Higher APTES contents, instead, lead to a significant increase in the total quantity of adsorbed CO₂ and in higher selectivity over N₂ (calculated according to the Ideal Adsorbed Solution Theory). Moreover, also the strength of interaction increases, since not only physisorption, but also chemisorption takes place.