Interaction of Cu, Ag and Au (n = 1-4) nanoparticles with ChCl:Urea deep eutectic solvent.

In this study, the interaction of noble metal nanoparticles (M, 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 M nanoparticles through [Cl] anion ([Cl]…M) and nonconventional H-bonds of C-H⋯M and N-H⋯M. NBO, QTAIM, NCI and EDA analyses show that [Cl]…M interactions are stronger than the nonconventional H-bonds interactions. Our results indicate that the nature of [Cl]…M interactions is electrostatic, while the nonconventional H-bonds of C-H⋯M and N-H⋯M are van der Waals in nature. The negative values of enthalpy (ΔH) and free energy (ΔG) for the ChCl:Urea…M complexes reveal that the formation of ChCl:Urea…M complexes is exothermic and proceeds spontaneously. The calculation of binding energy (ΔE) of M nanoparticles with ChCl:Urea shows that the strength of interaction of Au nanoparticles with ChCl:Urea is more favorable than Cu and Ag, following the order ChCl:Urea…Au > ChCl:Urea…Cu > ChCl:Urea…Ag. Furthermore, the ΔE, ΔH and ΔG values enhance with increasing nanoparticle size from n = 1 to n = 4, ChCl:Urea…M> ChCl:Urea…M> ChCl:Urea…M> ChCl:Urea…M (M = Cu, Ag, and Au).