Development and identification of diamine-based functional deep eutectic solvents for CO2 capture

The development of advanced absorbents for efficient CO 2 capture is crucial for mitigating greenhouse gas emissions. This study designed and prepared diamine-based functional deep eutectic solvents (DESs), combining ethylenediamine (EDA) as a hydrogen bond donor (HBD) with various organic ammonium halides as a hydrogen bond acceptor (HBA) to achieve desirable absorption performance and overcome the poor thermal stability of EDA. Subsequently, a novel stepwise methodology was proposed to identify the most promising one from this series of DESs, including the ones studied in this work and those reported previously, based on the absorption capacity, absorption rate, stability, and desorption rate. Additionally, FTIR and NMR analyses were conducted to confirm the formation of carbamate species, elucidating the chemical absorption mechanism of DESs for CO 2 , and density functional theory (DFT) calculations were further used to reveal the molecular-level interactions between the DESs and CO 2 . It was found that the HBA structure significantly influences the DES performance, with the triazole-based amines, i.e., the DESs of ([N-1,2,4-TrizCl][EDA] (1:5) and [TrizCl][EDA] (1:5)), providing better overall performance. Compared to the conventional monoethanolamine (MEA), [N-1,2,4-TrizCl][EDA] (1:5) and [TrizCl][EDA] (1:5) exhibited significantly improved performance, with CO 2 absorption capacity by 65 % and 43 %, absorption rates by 13 % and 22 %, thermal stabilities by 18 % and 19 %, and cyclic loadings by 19 % and 18 %, respectively. These findings provide critical insights into the design of DESs and emphasize the importance of balancing the absorption and desorption performance for industrial CO 2 capture applications, offering a promising pathway for developing high-performance CO 2 absorbents. • Proposed a step-by-step screening methodology that compared five literature DESs with five newly synthesised EDA-based DESs. • [N-1,2,4-TrizCl][EDA] (1:5) and [TrizCl][EDA] (1:5) emerged as top DES with capacity, rate, stability, and regenerability. • Relative to 30 wt% MEA, [N-1,2,4-TrizCl][EDA] (1:5) showed 65% higher capacity, 13% faster rate, 18% more stable, and 19% higher cyclic loading. • -FTIR/ 13 C NMR confirmed carbamate formation, while DFT calculations revealed key H-bond/electrostatic interactions.