Halogen-free deep eutectic solvents with multiple active sites for efficient absorption of ammonia

Abstract

The use of reversible absorbents such as ionic liquids (ILs) and deep eutectic solvents (DESs) has recently garnered significant attention for NH3 absorption. Nonetheless, absorbents containing halogen ions, which are often presented in ILs or DESs, impose limitations on their practical applications due to increased corrosiveness. Consequently, there is a strong demand for the development of halogen-free and sustainable absorbents. In this study, a series of halogen-free DESs were synthesized using amino-2-propanol nitrate ([APH]NO3) as a hydrogen bond acceptor, and resorcinol (Res), phenol (PhOH), glycerol (Gly), and ethylene glycol (EG) as hydrogen bond donors. Remarkably, [APH]NO3-Res(2:1) exhibited outstanding NH3 absorption performance of 0.253 g·g−1 at 293 K and 1 bar, which is comparable to, or even exceeds, the absorption capacities of previously reported absorbents. Furthermore, it also showed the ability to be recycled multiple times without a significant decreased in NH3 adsorption performance. Further insight into the NH3 absorption mechanism was gained through quantum chemical calculations and spectral studies, suggesting that the high solubility of NH3 in DESs is facilitated by the multi-site hydrogen bond interaction. The DESs developed in this study have the potential to be viable options for halogen-free and environmentally friendly NH3 capture.