Investigation of protic NH4SCN-based deep eutectic solvents as highly efficient and reversible NH3 absorbents

Ammonia (NH 3 ) is not only a harmful gas to environmental problem, but also a fundamental raw material in chemical industry. The effective separation and recovery of NH 3 from exhaust gas at low cost still remains a challenge for a long time. In this study, a new strategy to construct protic deep eutectic solvents (DESs) by paring NH 4 SCN as hydrogen-bond acceptor with various hydrogen-bond donors [glycerol (G), ethylene glycol (EG), urea (U), acetamide (AT), and caprolactam (CL)] was proposed for efficient and reversible absorption of NH 3 . Results showed that all the DESs possessed exceptional NH 3 absorption capacity and high NH 3 /CO 2 selectivity. At 303 K and 0.10 MPa, the absorption capacity of NH 3 in NH 4 SCN-glycerol (2:3) is as high as 0.223 g NH 3 per g DES, which is much higher than all reported functional ILs and DESs up to date. The NH 3 saturated DES was easily regenerated and recycled 25 times with persistent absorption performance. The influences of DES composition, temperature, NH 3 partial pressure on NH 3 absorption performance were also explored in detail. The absorption mechanism was analyzed using NMR spectroscopy and quantum calculation. These protic NH 4 SCN-based DESs presented as promising absorbents for NH 3 because of their high absorption capacity and good reversibility.