Thermodynamic analysis of nitric oxide absorption in deep eutectic solvents comprising 1,1,3,3-tetramethylguanidine

Four deep eutectic solvents (DESs) based on 1,1,3,3-tetramethylguanidine (TMG) and N-heterocycles (succinimide, 2-pyrrolidinone, 2-oxazolidone, N -methylurea) were prepared and assessed for NO capture. At 313.2 K and 1 bar, the viscosities of TMG/succinimide (TMG-Succ) and TMG/2-pyrrolidinone (TMG-Pyrr) were measured as 49.23 mPa·s and 2.85 mPa·s, respectively, while their corresponding nitric oxide (NO) uptake capacities reached 1.62 Mol·kg −1 and 1.10 Mol·kg −1 under identical conditions. Spectroscopic analysis confirmed chemisorption in TMG-Succ versus physical dissolution in TMG-Pyrr. Thermodynamic fits yielded the absorption enthalpy ΔH = −16.94 kJ·Mol −1 for TMG-Succ and − 70.1 kJ·Mol −1 for TMG-Pyrr DES. In addition, the absorption capacities of both DESs remained almost unchanged during the 10 cycles of absorption-desorption experiments, highlighting their low-viscosity, high-capacity, and energy-efficient reversible NO capture performance