Interaction of Cun, Agn and Aun (n = 1–4) nanoparticles with ChCl:Urea deep eutectic solvent

In this study, the interaction of noble metal nanoparticles (Mn, M = Cu, Ag, and Au; n = 1–4) with ChCl:Urea deep eutectic solvent was investigated using density functional theory (DFT) method. We find that ChCl:Urea mostly interact with the Mn nanoparticles through [Cl]- anion ([Cl]-…Mn) and nonconventional H-bonds of C–H⋯Mn and N–H⋯Mn. NBO, QTAIM, NCI and EDA analyses show that [Cl]-…Mn interactions are stronger than the nonconventional H-bonds interactions. Our results indicate that the nature of [Cl]-…Mn interactions is electrostatic, while the nonconventional H-bonds of C–H⋯Mn and N–H⋯Mn are van der Waals in nature. The negative values of enthalpy (ΔH) and free energy (ΔG) for the ChCl:Urea…Mn complexes reveal that the formation of ChCl:Urea…Mn complexes is exothermic and proceeds spontaneously. The calculation of binding energy (ΔEb) of Mn nanoparticles with ChCl:Urea shows that the strength of interaction of Aun nanoparticles with ChCl:Urea is more favorable than Cun and Agn, following the order ChCl:Urea…Aun > ChCl:Urea…Cun > ChCl:Urea…Agn. Furthermore, the ΔEb, ΔH and ΔG values enhance with increasing nanoparticle size from n = 1 to n = 4, ChCl:Urea…M4> ChCl:Urea…M3> ChCl:Urea…M2> ChCl:Urea…M1 (M = Cu, Ag, and Au).