Tetrazole-Based Deep Eutectic Solvents with Multiple Hydrogen Bonding Sites for Highly Efficient Uptake of NH₃

It has been of long concern that the separation and recovery of NH₃ from industrial processes, in addition to attracting huge economic interest, also reduce environmental pollution. So, it is very urgent to develop novel absorbents for highly efficient capture of NH₃. In this study, several novel tetrazole (TetrZ)-based binary deep eutectic solvents (DESs) were formed by mixing TetrZ with 1,2,3-triazole (1,2,3-Tri), ethylene glycol (EG), 2-morpholinoethanol (2-Mor), or N-methyldiethanolemine (MDEA) to absorb NH₃. TetrZ + 1,2,3-Tri (1:4, mole ratio) not only exhibits higher NH₃ absorption ability of 0.239 g_NH3·g_DES^–1 than that of most absorbents reported to date at 313.15 K and 101.3 kPa, but also shows elevated selectivities of 592.7 for NH₃/CO₂, 654.5 for NH₃/N₂, and 1033.7 for NH₃/O₂. Meanwhile, TetrZ + 1,2,3-Tri (1:4) can be reused 10 times with good absorption capacity retained. Additionally, the solubility data of NH₃ were correlated by the reaction equilibrium thermodynamic model. The NMR and FTIR spectroscopic characterizations were also used to study the absorption mechanism, and quantum chemistry calculation was utilized to further investigate the interactions between NH₃ and DESs from an atomic level perspective. The DESs developed in the present work have the potential to capture NH₃ sustainably, owing to their high solubility, superior selectivity, and desirable reversibility.