One-Step Process Using CO₂ for the Preparation of Amino-Functionalized Mesoporous Silica for CO₂ Capture Application

In this study, a novel and facile one-step method using CO₂ for the preparation of amino-functionalized mesoporous silica for CO₂ capture application was introduced. 3-Aminopropyltriethoxysilane (APTES, 30 wt % in water) was first bubbled with CO₂ and then mixed with sodium silicate to produce amino-functionalized mesoporous silica. Three adsorbents, namely, precipitated silica adsorbent (PSA), silicagel adsorbent (SGA), and condense silicagel adsorbent (C-SGA), were synthesized by tuning CO₂ pressure when preparing CO₂ absorbed APTES solution and aging temperatures of obtained hydrogel, respectively. PSA has large primary particles (200–1000 nm) with 73.4 m²/g in surface area and 0.1 cm³/g in pore volume. SGA has smaller silica primary particles (10–20 nm) with higher surface area (205.9 m²/g) and higher pore volume (0.70 cm³/g). When PSA and SGA hydrogels were aged at 110 °C, they transformed to a condensed silicagel adsorbent (C-SGA) with very low surface area (12.0 m²/g) and pore volume (0.05 cm³/g). The existence of amino-functional groups in the adsorbents was confirmed by Fourier transform infrared spectroscopy technique and energy dispersive spectroscopy coupled with a scanning electron microscope. PSA had the highest CO₂ loading with 45.1 mg/g at the adsorption temperature of 50 °C, and CO₂ loading decreased with the increase in adsorption temperature. This adsorbent has low CO₂ adsorption heat (66 kJ/mol) and heat capacity (1.25 kJ/kg °C) and is thermally stable, indicating that it could be suitable for CO₂ capture application. The success of the proposed one-step process does not only provide a facile method to synthesize solid adsorbent for CO₂ capture but also contributes an additional option to CO₂ utilization