Impact of solvents and surfactants on the self-assembly of nanostructured amine functionalized silica spheres for CO2 capture

摘要

Macroscopic SiO_2 spheres with a homogeneous amine distribution were synthesized by a one-step emulsion based synthesis approach in a flow column reactor. The CO_2 adsorption capacity of the nanostructured amine-functionalized silica spheres was studied in absence and presence of H_2O. The structural properties were adjusted by varying solvents and surfactants during the synthesis and, at constant amine loadings, were found to be the main factor for influencing the CO_2 sorption capacities. Under water-free conditions CO_2 is bound to the amino groups via the formation of carbamates, which require two neighboring amino groups to adsorb one CO_2 molecule. At constant amine concentrations sorbents with lower surface area allow to establish a higher amine density on the surface, which enhances the CO_2 uptake capacities under dry conditions. In presence of H_2O the CO_2 adsorption changes to 1:1 stoichiometry due to stabilization of carbamates by protonation of H_2O and formation of further species such as bicarbonates, which should in principle double the adsorption capacities. Low concentrations of physisorbed H2O(0.3 mmol/g) did not impair the adsorption capacity of the adsorbents for CO_2, while at higher water uptakes(0.6 and 1.1 mmol/g) the CO_2 uptake is reduced, which could be attributed to capillary condensation of H_2O or formation of bulky reaction products blocking inner pores and access to active sites.