Alumina-silica aerogels functionalized with amino groups for CO2 capture

To overcome climate challenges, emerging CO2 capture technologies focus on innovative solid and chemical adsorbents like aerogels. Aerogels, in particular silica aerogel, have emerged as an exceptional class of materials with unique properties. In particular, functionalizing the silica matrix with metal oxides can significantly enhance their adsorption capacity and selectivity. For this reason, in this research, alumina is added to the aerogels to improve both mechanical and adsorption properties (due to the basic character of alumina). Furthermore, functionalizing alumina-silica aerogels with amino groups could improve their ability to adsorb CO2. Alumina-silica aerogels functionalised with amino groups (AlSi with (3-aminopropyl) trimetossisilano, also called APTES) for CO2 capture are here synthesized for the first time by a one-pot process. Various samples of AlSi-APTES were prepared by varying the number of APTES moles added during the synthesis: 2.5 mmol, 7.5 mmol, and 22.5 mmol (moles of APTES relative to 30 mmol of silica). Characterization results show that the increase in APTES content leads to an increase in the number of amino groups present in the aerogel. The analyses demonstrate that the incorporation of amino groups significantly changes the properties of the alumina-silica aerogels, reducing both the surface area and pore volume. Regarding CO2 adsorption, no significant differences are observed between the samples with 2.5 and 7.5 mmol of APTES, suggesting that low functionalization does not confer a significant advantage in this molar range. An interesting result is obtained with the sample with the highest amine content (22.5 mmol of APTES) where the absorption of CO2 far exceeds other samples demonstrating that with enough APTES, it is possible to absorb significant quantities of CO2. It is worth noting that at low CO2 partial pressures, even samples with a lower amine content are advantageous with respect to the non-functionalized sample as they absorb more CO2 than the reference sample.