Highly efficient and regenerable amine-impregnated adsorbents: Mechanistic insights into glycerol modification for enhanced direct air capture

Amine-impregnated adsorbents play a crucial role in direct air capture (DAC) technologies, however, challenges remain in balancing high amine loading, enhanced amine efficiency and long-term stability against urea formation. This study introduces a highly efficient and regenerable GI-PEI@MSF adsorbent, synthesized by impregnating glycerol-modified polyethyleneimine (GI-PEI) onto a mesoporous silica foam (MSF) support with ultra-large pore structure derived from coal fly ash (CFA). The 30 %GI-PEI@MSF adsorbent exhibited a remarkable CO 2 uptake of 9.70 mmol·g PEI −1 with an enhanced amine efficiency of 115.9 %, while maintaining excellent cyclic stability under harsh regeneration conditions. Hydroxyl-rich GI formed the intermolecular hydrogen bonds with PEI and facilitated the PEI dispersion, enabling a lower optimal adsorption temperature and faster adsorption kinetics, which are critical for lowering DAC energy demands. Characterization and Density Functional Theory (DFT) analysis provided molecular-level insights into the dual-functionality mechanism of GI modification: The secondary hydroxyl groups of GI, acting as Bronsted bases, can partially replace the primary or secondary amines of PEI in CO 2 adsorption, thereby enhancing the amine efficiency and inhibiting the urea formation. These findings demonstrate the feasibility of CFA recycling and GI modification for enhanced CO 2 adsorption, providing a promising strategy for scalable and cost-effective DAC applications.