Study on mechanism and thermodynamics of NO absorption by acetylcholine-chloride type deep eutectic solvents

NO absorption by using deep eutectic solvents (DESs) from flue gas has become one of great research interest. In this work, different DESs were prepared with acetylcholine chloride as a hydrogen-bond acceptor. The effect of molar ratio of the hydrogen-bond acceptor and different hydrogen-bond donor, temperature, and different hydrogen-bond donors on NO absorption by acetylcholine chloride DESs was investigated systematically. The absorption experiment of NO by acetylcholine-methyl urea DES at an absorption capacity of 0.119 (g NO/g DES) when the molar ratio of acetylcholine chloride to methyl urea was 1 : 2 at 30–40 °C. The absorption mechanism of NO by acetylcholine chloride DESs was determined by Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance combined with quantum chemical calculation. The results indicated that NO with acetylcholine-methyl urea DESs by chemical absorption to form NONO structure, nitrogen-oxygen double bonds (N=O), nitrogen-oxygen single bonds (N−O), and nitrogen-nitrogen single bonds (N−N). The simulation results showed that nitric oxide formed two hydrogen bonds with N atoms on methyl urea: C−N⋅⋅⋅N and O=N⋅⋅⋅N=O. Thermodynamic properties showed that the ▵_rH^o_m for NO absorption in acetylcholine-chloride-type DES was −15.39 kJ/mol, which was more efficient for NO absorption/desorption.