Amino acid-based deep eutectic solvent functionalized NH₂-UiO-66 for selective CO₂ capture from flue gas

Efficient CO₂ capture from flue gas is a critical step toward mitigating greenhouse gas emissions and enabling its subsequent utilization. The relatively low CO₂ partial pressure in flue gas necessitates the development of highly selective adsorbents capable of producing pure CO₂ in a single step with minimal energy input. In this study, an amino acid-based deep eutectic solvent (DES) was immobilized onto NH₂-UiO-66 using impregnation to enhance CO₂ capture performance. Herein, proline (Pro) and glycine (Gly), two amino acids, were used as HBAs and monoethanolamine (MEA) was employed as an HBD. The DES provides high CO₂ solubility through amine-CO₂ interactions, while the MOF framework serves as a microporous reservoir for gas storage. Structural and physicochemical analyses, including Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (FESEM) with Energy-Dispersive X-ray Spectroscopy (EDX), Thermogravimetric Analysis (TGA), and Brunauer-Emmett-Teller (BET) surface area analysis confirmed successful DES loading without compromising the intrinsic microporosity of NH₂-UiO-66. CO₂ adsorption was evaluated using a quartz crystal microbalance (QCM) at pressures up to 1 bar and 288.15-308.15 K. The adsorption isotherms were well-described by a hybrid Redlich-Peterson model, indicating a predominant chemisorption mechanism. DES functionalization increased the CO₂ adsorption capacity of the MOF by factors of 1.54 (DES1@MOF) and 0.75 (DES2@MOF) despite a reduction in pore volume, due to enhanced adsorbate-DES interactions. The composites exhibited improved CO₂/N₂ selectivity, favorable adsorption thermodynamics, and maintained over 98% of their initial capacity after 10 adsorption/desorption cycles. These results highlight amino acid-based DES@MOF composites as promising candidates for energy-efficient CO₂ capture and utilization from flue gas.