Role of Amine Structures in CO2 Adsorption Performance and Stability of Amine-Modified Bimodal Porous Silica

This study provides insights into how various parameters─including amine type (DETA, TEPA, PEI), amine loading, drying conditions (duration of 0.5 versus 12 h and drying atmosphere of ambient air versus N₂ flow), and adsorption temperature─influence CO₂ capture performance using bimodal porous silica (BS) sorbents. Increasing the drying time from 0.5 to 12 h notably reduced the amine content in DETA-loaded sorbents, had a moderate effect on TEPA-loaded sorbents, and minimally affected PEI-loaded sorbents. Drying under N₂ flow accelerated amine loss in DETA-loaded sorbents but slightly improved amine retention in PEI-loaded sorbents. Adsorption kinetics described by the Avrami fractional-order model indicated internal diffusion limitations dependent upon amine type and adsorption temperature with the strongest diffusion constraints occurring in DETA-loaded sorbents, while PEI-loaded sorbents exhibited balanced adsorption dynamics. A PEI-loaded BS sorbent achieved a high initial CO₂ adsorption capacity of 122.6 mg CO₂ g^–1, maintaining excellent stability with a capacity of 120.2 mg CO₂ g^–1 after ten cycles. Furthermore, the PEI-loaded BS sorbent exhibited only minor degradation when exposed to oxygen under ambient conditions, underscoring its potential for practical, sustainable CO₂ capture applications.