The adsorption and desorption of CO2 on diamine-grafted SBA-15 have been studied by infrared spectroscopy coupled with mass spectrometry. Diamine was grafted onto the SBA-15 surface by the reaction of [N-(2-aminoethyl)-3-aminopropyl]trimethoxysilane with the surface OH. CO2 is adsorbed on the diamine-grafted SBA-15 as bidentate carbonate and bidentate and monodentate bicarbonates at 25 °C. Bidentate carbonate and monodentate bicarbonates are the major surface species formed and decomposed during the concentration-swing adsorption/desorption process at 25 °C. Temperature-programmed desorption revealed that the monodentate and bidentate bicarbonates bound stronger to the diamine-grafted SBA-15 surface than the bidentate carbonate. The amount of CO2 desorbed from the carbonate and bicarbonate between 30 and 120 °C is 2 times more than that of CO2 adsorbed/desorbed during each cycle of the concentration-swing adsorption/desorption. Desorption at 120 °C removes the majority of the captured CO2 and regenerates the sorbent for CO2 capture at low temperature. Regeneration of the sorbent with temperature-swing adsorption gives a significantly higher CO2 capture capacity than concentration-swing adsorption. The use of a diamine-grafted sorbent, with an adsorption capacity of more than 1000 μmol/g of sorbent and a temperature-swing adsorption process, could be a cost-effective alternative to capture CO2 from power plant flue gases.