Amine-functionalized cellulose fiber sorbents via solvent-tuned aminosilane grafting for direct air capture

초록

In this study, aminosilane was grafted onto cellulose fibers under various solvent conditions to develop a low-cost CO2 sorbent for direct air capture (DAC). The grafting mechanism depended strongly on the solvent: in organic media (toluene, methanol), aminosilane reacted directly with cellulose hydroxyl (-OH) groups to form Si-O-C linkages, whereas in water, hydrolysis of the aminosilane preceded condensation with cellulose hydroxyl groups, also yielding Si-O-C bonds. Introducing a small amount of water into toluene combined the advantages of both systems by promoting hydrolysis while limiting self-condensation, giving the highest grafting efficiency and amine loading. Spectroscopic analyses (ATR-FTIR, solid-state 13C NMR) and morphological observations confirmed successful incorporation of aminosilane and showed that grafting prior to drying prevented hydrogenbond reformation and preserved the porous fiber structure. The toluene+water system achieved a high amine loading (1.63 mmol N/g) while maintaining structural integrity. CO2 adsorption experiments showed the highest uptake for aminosilane-grafted cellulose fibers in toluene+water mixture (A-GCF-Toluene+Water), reaching 0.81 mmol/g under pure CO2 and 0.27 mmol/g at 420 ppm CO2. Dual-site Langmuir model fitting indicated that both chemisorption and physisorption contributed to CO2 capture. A-GCF-Toluene+Water also maintained stable capacity over 20 adsorption-desorption cycles, demonstrating good durability. Overall, the optimized toluene+water grafting system enabled high amine incorporation, preserved porosity, and enhanced CO2 sorption performance, highlighting abundant, low-cost cellulose fibers as a viable platform for DAC sorbents.

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