Diethylenetriamine[propyl(silyl)]-Functionalized (DT) Mesoporous Silicas as CO₂ Adsorbents

Mesoporous silica substrates were functionalized with N -[3-(trimethoxysilyl)propyl]diethylenetriamine to form diethylenetriamine[propyl(silyl)]- (DT-) functionalized hybrid products suitable for CO 2 adsorption. The materials prepared were characterized by N 2 adsorption/desorption at 77 K, C and N elemental analysis, helium pycnometry, X-ray diffraction (XRD), CO 2 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. CO 2 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 CO 2 adsorption capacities at 20 °C under anhydrous conditions. Higher temperature led to reduced adsorption capacities but higher heats of adsorption ( H ads ) of CO 2, thought to be due to the reduced role of weak physisorption sites. When CO 2 was supplied in a moist gas stream, the adsorption capacity was reduced, but the value of H ads (CO 2 ) was essentially unchanged. The thermal stabilities of one substrate and its AP-, ED-, and DT-functionalized products both in N 2 and in mildly oxygenated N 2 were also characterized by combined TGA/DTA. These materials were found to be stable up to 170 °C in both atmospheres and, furthermore, had no particular affinity for either N 2 or O 2 over this temperature range. Oxidative decomposition data from TGA at higher temperature were found useful for estimating the N content of these materials.