Efficient and reversible absorption of NH3 by functional azole–glycerol deep eutectic solvents

Abstract

The hydrogen bond donor (HBD) glycerol (Gly) and hydrogen bond acceptors (HBA) selected among 1,2,4-triazole (Tri), imidazole (Im), tetrazole (Tz), 1-methyl-triazole (Tri-Me), 3-mercapto-1,2,4-triazole (Tri-SH), 3-amino-1,2,4-triazole (Tri-NH₂), 3-cyano-1,2,4-triazole (Tri-CN), and 4-formalimidazole (Im-CHO) were paired to construct functional deep eutectic solvents (DESs) that were then utilized as ammonia (NH₃) absorbents. The influences of the HBA in DESs, temperature, and partial pressure of NH₃ on the NH₃ absorption performance were systematically investigated. The results illustrated that all the DESs exhibited efficient and reversible absorption for NH₃, and Tri–Gly possessed higher absorption capacity than Im–Gly, with the maximum absorption capacity of 0.115 gram NH₃ per gram DES of Tri–Gly (1 : 3) at 313.15 K and 1.0 bar. The NH₃-saturated DES could be easily recycled five times with a persistent absorption performance. The absorption mechanism was further deduced by the NMR and FTIR spectroscopy. These DESs acted as potential absorbents for NH₃ due to their good absorption performance and reversibility.