Amine-modified mesoporous SiO₂ spheres (MSS-(x) APTMS) as a promising CO₂ sorbent

The design of effective CO2 adsorbents requires high adsorption capacity and selectivity. In this study, we developed a hybrid organic-inorganic sorbent by functionalizing mesoporous silica spheres (MSS) with aminopropyltriethoxysilane (APTMS) to address common challenges, such as limited selectivity and low adsorption capacity. MSS-(x%) APTMS (where x = 0, 1.5, 7.5, and 15) were synthesized, with x representing the APTMS loading percentage in the MSS framework. Thermogravimetric analysis (TGA) revealed that MSS-(15%) APTMS exhibited the highest adsorption capacity of 2.5 w.t.% (0.57 mmol/g) under 10% CO2 at 35 °C. Cyclic adsorption tests confirmed the stability and reproducibility of this sample over multiple cycles. CO2 adsorption was further assessed under pressures ranging from 0 to 120 kPa at 0°C, with MSS-(15%) APTMS achieving the highest uptake of 2.33 mmol/g at 120 kPa. Comprehensive characterization using FTIR and TEM highlighted the presence of amine functional groups and the preserved morphology of the MSS framework. Adsorption kinetics at varying temperatures were analyzed using pseudo-first-order and pseudo-second-order models, providing insights into the interaction mechanisms between CO2 and the functionalized adsorbents. Comparative studies with SBA-15 and fumed silica functionalized with the same APTMS concentration demonstrated the superior adsorption performance of MSS-(15%) APTMS. These findings establish MSS-(x%) APTMS as a promising material for efficient CO2 capture, particularly under near ambient conditions.