Rational design of deep eutectic solvents with low viscosities and multiple active sites for efficient recognition and selective capture of NH3.

Abstract

Efficient recognition and selective capture of NH₃ is not only beneficial for increasing the productivity of the synthetic NH₃ industry but also for reducing air pollution. For this purpose, a group of deep eutectic solvents (DESs) consisting of glycolic acid (GA) and phenol (PhOH) with low viscosities and multiple active sites was rationally designed in this work. Experimental results show that the GA + PhOH DESs display extremely fast NH₃ absorption rates (within 51 s for equilibrium) and high NH₃ solubility. At 313.2 K, the NH₃ absorption capacities of GA + PhOH (1:1) reach 6.75 mol/kg (at 10.7 kPa) and 14.72 mol/kg (at 201.0 kPa). The NH₃ solubility of GA + PhOH DESs at low pressures were minimally changed after more than 100 days of air exposure. In addition, the NH₃ solubility of GA + PhOH DESs remain highly stable in 10 consecutive absorption-desorption cycles. More importantly, NH₃ can be selectively captured by GA + PhOH DESs from NH₃/CO₂/N₂ and NH₃/N₂/H₂ mixtures. ¹H-NMR, Fourier transform infrared and theoretical calculations were performed to reveal the intrinsic mechanism for the efficient recognition of NH₃ by GA + PhOH DESs.