Mesoporous silica substrates were functionalized with N-[3-(trimethoxysilyl)propyl]diethylenetriamine to form diethylenetriamine[propyl(silyl)]- (DT-) functionalized hybrid products suitable for CO2 adsorption. The materials prepared were characterized by N2 adsorption/desorption at 77 K, C and N elemental analysis, helium pycnometry, X-ray diffraction (XRD), CO2 adsorption, and thermal decomposition and were compared to analogous aminopropylsilyl- (AP-) and ethylenediamine[propyl(silyl)]- (ED-) functionalized materials. The extent of surface functionalization varied with substrate morphology. CO2 adsorption capacities and heats of adsorption were determined via combined thermogravimetric analysis and differential thermal analysis (TGA/DTA). Functionalization of the substrates was found to enhance their CO2 adsorption capacities at 20 °C under anhydrous conditions. Higher temperature led to reduced adsorption capacities but higher heats of adsorption (Hads) of CO2, thought to be due to the reduced role of...