Modification of CO ₂ Separation Properties of Choline Chloride-Based Deep Eutectic Solvents Using Nanoparticles of Fe ₃ O ₄ : Experimental Analysis by Response Surface Methodology

This study examines the synergistic effects of choline chloride (ChCl) and ethylene glycol (EG) as deep eutectic solvents (DESs), in combination with Fe3O4 nanoparticles, for enhanced CO2 capture. The effects of temperature, the molar ratio of EG to ChCl, and the mass fraction of Fe3O4 were investigated using Design Expert software (version 11) based on the Box–Behnken design (BBD) methodology. The ANOVA table identified a transformed cubic model with an optimal lambda value of 1.46 and an insignificant lack of fit. Optimization of the operating parameters yielded a maximum CO2 absorption efficiency of 99.86% at a nanoparticle dosage of 0.074, a temperature of 27.9 °C, and an HBD to HBA ratio of 4.98. These conditions exhibited strong agreement with the experimental observation (99.5%). The incorporation of Fe3O4 nanoparticles enhanced the CO2 absorption capacity of neat DES by 57%. Furthermore, the consistent absorption performance over ten consecutive cycles demonstrated the excellent stability and reusability of the developed DES–nanoparticle system.