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.