Improved CO₂ Sorption in Freeze-Dried Amine Functionalized Mesoporous Silica Sorbent

Abstract

This work investigates the structural and CO2 sorption properties of amine-functionalized mesoporous silica prepared by a freeze-drying method. It was found that the freeze-dried samples delivered significantly higher CO2 sorption capacities up to a factor of 18 times as compared to samples prepared by the conventional oven-drying evaporation method. The improved performance of the freeze-drying method was attributed to a higher surface area and access to active amine sites for CO2 sorption. The freeze-dried samples also exhibited good stability at a relatively high sorption temperature (90 °C) and flue gas CO2 partial pressure (15 kPa). The freeze-drying method reached the best CO2 sorption capacity of 4.71 mmol g–1 for samples with 70 wt % amine loading. Higher loading (80 and 90 wt %) led to excess amine not being incorporated into the mesoporous silica structure, thus covering active sites and limiting CO2 diffusion.