Abstract

Two silica-based nanomaterials, SBA15 and HMS, were modified via surface impregnation with ternary Natural Deep Eutectic Solvents (NADES) composed of choline chloride, glycerol, and urea in varying molar proportions. A design of experiments (DoE) methodology was employed to optimize the NADES composition. The effects on the porous structure and CO₂ adsorption capacity of the nanomaterials were evaluated using FTIR, TGA, N₂ adsorption/desorption isotherms, TEM, and SAXS, both before and after impregnation. These analyses confirmed the successful incorporation of NADES onto the nanomaterials' surfaces while preserving their porous structure, pore size distribution, and surface area. Functionalization enhanced CO₂ uptake, achieving 40.0 mg g⁻1 for SBA-15 impregnated at 15 wt% and 48.8 mg g⁻1 for HMS impregnated at 5 wt%, corresponding to increases of 17.4% and 25.2%, respectively. CO₂ adsorption mechanisms were investigated through gravimetry, FTIR, TGA, NMR, and CO₂ isotherms, revealing both physical adsorption via the nanomaterials’ surface area and chemical adsorption through carbamate/bicarbonate formation from amine and hydroxyl groups interacting with CO₂. The isosteric heat of adsorption ranged from 22.7 to 32.5 kJ mol⁻1 also confirmed these adsorption mechanisms. The nanomaterials exhibited stable adsorption capacity over five adsorption–desorption cycles, with a slight decrease in CO₂ uptake. However, heating to 100 °C restored the original weight, indicating effective CO₂ desorption during each cycle. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.