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. 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 At constant amine concentrations sorbents with lower surface area allow to establish 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 furth 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.