A range of mesoporous silica substrates were functionalized with 3-aminopropyltrimethoxysilane to form hybrid products suitable for carbon dioxide adsorption. A 'cylindrical pore' model was employed to characterize the extent of surface modification per unit substrate surface area and to permit its comparison on a common basis. The extent of surface functionalisation varied with substrate morphology. Combined DTA/TGA was used to characterise CO2 adsorption. Substantial reversible CO2 adsorption capacities were observed under anhydrous conditions (at 20 degrees C). In the presence of water, CO2 capacity was enhanced, but the rate of desorption was diminished. (c) 2005 Elsevier B.V. All rights reserved.