Three mesoporous silica materials with different pore sizes (33 angstrom for small pore size MCM-41; 38 angstrom for SBA-12; 71 angstrom for large pore size SBA-15) and pore connectivity (2D for MCM-41 and SBA-15-type materials: 3D for SBA-12 material) were prepared and functionalized with aminopropyl (AP) ligands by post-synthesis treatment. The materials were characterized by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and nitrogen adsorption/desorption experiments. The carbon dioxide sorption on modified mesoporous molecular sieves was investigated by using of microbalances at 25 C, and the influence of pore size and pore architecture on CO2 sorption was discussed. The large pore silica, SBA-15, showed the largest carbon dioxide sorption capacity (1.5 mmol/g), relating to highest amine surface density in this material. On the other hand, three-dimensional accessibility of amine sites inside the pores of SBA-12 silica resulted in a faster response to CO2 uptake in comparison with MCM-41 and SBA-15 molecular sieves. (C) 2008 Elsevier B.V. All rights reserved