Efficient and selective absorption of NH3 by supramolecular OHP[5]-based ternary deep eutectic solvents

Developing an efficient absorbent for selective ammonia capture is of significant importance in the recovery and utilization of ammonia resources. Herein, a series of supramolecular-based ternary deep eutectic solvents (DESs) was designed and prepared using per-hydroxy pillar[5]arene (OHP[5]) and ethylamine hydrochloride as the key components. It is found that the supramolecular-based ternary DES EaCl-Gly (1:2)-6% OHP[5] could be employed as an efficient absorbent for reversible absorption of NH3. The NH3 uptake capacity reached 2.39 mmol/g and 10.84 mmol/g at 298.2 K under the pressure of 10 kPa and 100 kPa, respectively. Meanwhile, a higher NH3/CO2 selectivity (84) was obtained at 298.2 K and 100 kPa owing to the low solubility of CO2 in EaCl-Gly (1:2)-6% OHP[5]. The results of 1H NMR and FTIR spectra further clarified the absorption mechanism of NH3 by EaCl-Gly (1:2)-6% OHP[5]. Accordingly, the chemical absorption and physical dissolution capacity of NH3 in EaCl-Gly (1:2)-6% OHP[5] were calculated on the basis of isotherm data and thermodynamic equations. This study offers a promising application of pillar[5]arene to form supramolecular-based DESs for efficient NH3 absorption.