Amine functionalized silica microspheres were synthesised via a modified Stober reaction for carbon dioxide (CO2) adsorption. A number of adsorbents were synthesized by co-condensation and post synthesis immobilization of amines on porous silica spheres. CO2 adsorption studies were carried out on a fixed bed gas adsorption rig with online mass spectrometry. Amine co-condensed silica spheres were found to adsorb up to 66 mg CO2 g(-1) solid in a 0.15 atm CO2 stream at 35 degrees C. Simple post-synthesis addition of aminopropyltriethoxysilane to amine co-condensed silica was found to significantly increase the uptake of CO2 to 211 mg CO2 g(-1) under similar conditions, with CO2 desorption commencing at temperatures as low as 60 degrees C. The optimum temperature for adsorption was found to be 35 degrees C. This work presents a CO2 adsorbent prepared via a simple synthesis method, with a high CO2 adsorption capacity and favorable CO2 adsorption/desorption performance under simulated flue gas conditions. (C) 2016 American Institute of Chemical Engineers