Improved CO₂ Sorption in Freeze-Dried Amine\nFunctionalized Mesoporous Silica Sorbent

Abstract

This work investigates the structural\nand CO₂ sorption\nproperties of amine-functionalized mesoporous silica prepared by a\nfreeze-drying method. It was found that the freeze-dried samples delivered\nsignificantly higher CO₂ sorption capacities up to a factor\nof 18 times as compared to samples prepared by the conventional oven-drying\nevaporation method. The improved performance of the freeze-drying\nmethod was attributed to a higher surface area and access to active\namine sites for CO₂ sorption. The freeze-dried samples\nalso exhibited good stability at a relatively high sorption temperature\n(90 °C) and flue gas CO₂ partial pressure (15 kPa).\nThe freeze-drying method reached the best CO₂ sorption\ncapacity of 4.71 mmol g^–1 for samples with 70 wt\n% amine loading. Higher loading (80 and 90 wt %) led to excess amine\nnot being incorporated into the mesoporous silica structure, thus\ncovering active sites and limiting CO₂ diffusion.