Amine-based deep eutectic solvents (DESs) are promising alternatives to conventional amines for CO2 capture; however, the molecular design principle to achieve practical performance remains unclear. In response to this challenge, this licentiate thesis aims to develop DES-based solvents that achieve balanced performance in 30 wt% aqueous solutions, including high absorption capacity, efficient desorption, good thermal stability, and manageable viscosity, with ethanolamine (MEA) used as the reference. 

In the first part of this work, ethylenediamine (EDA) and diethylenetriamine (DETA) were selected as hydrogen-bond donors (HBD), while a series of hydrogen-bond acceptors (HBAs) were varied to evaluate their effects on CO2 absorption and desorption behaviors. The solvents were evaluated for absorption capacity and absorption rate at 22 °C and 1 bar, for desorption and cyclic loading at 110 °C, and for thermal stability using thermogravimetric (TG) and derivative thermogravimetric (DTG). From this side-by-side comparison, 30 wt% aqueous [TrizCl][DETA] was identified as the most practical candidate. It achieves a CO2 absorption capacity of 0.164 g-CO2/g-solvent and an absorption rate of 0.183 g-CO2/(g-solvent·min), provides the largest cyclic loading of 0.091 g-CO2/g-solvent, and exhibits an onset decomposition temperature (Tonset) of approximately 178.7 °C. Although EDA-based DESs demonstrate the highest capacity and rapid absorption, for example, a 30 wt% aqueous [N-1,2,4-TrizCl][EDA] solution reaches 0.203 g-CO2/g-solvent, they exhibit limited thermal stability.

Building on these findings, the second part of the study focused on structure-property relationships by fixing [TrizCl] as the HBA and varying the amine-based HBDs, including diamines, triamines, and alkanolamines. The comparison revealed that the balanced performance of [TrizCl][DETA] arises from the optimal combination of the triazolium-based HBA and the triamine HBD, which provides sufficient basicity and hydrogen-bonding capacity for CO2 activation. 

Additionally, [TrizCl][DETA] maintains workable viscosity after CO2 absorption at about 7.5 mPa·s, and exhibits stable absorption-desorption behaviors. Corrosion, oxidative degradation, and mechanistic analyses confirm its stability and explain the rise of moderate viscosity via carbamate and bicarbonate formation, indicating strong potential for CO2 capture and solvent recycling.