Partitioning of Cs⁺ and Na⁺ ions by dibenzo-18-crown-6 ionophore in biphasic aqueous systems of octanol and ionic liquid

Molecular dynamics (MD) simulations were carried out to obtain molecular level insights on the behavior of Cs⁺/Na⁺ ions at the water-ionic liquid and water-octanol interface in the presence of dibenzo-18-crown-6 (DB18C6) ionophore with an aim to compare an ionic liquid (IL) to a octanol as receiving organic solvent phase. It was observed that the rate of phase separation for the octanol system was rapid as compared to the IL system. The free crown ethers (CE) were found to be highly solvated by the IL phase. A dual cationic exchange mechanism was observed at the [BMIM]/water interface. The [BMIM]⁺ cation was found to exchange with both the metal ions in aqueous phase as well as with the metal ion aided by the ionophore. The self-diffusion coefficient of the 1:2 complex (0.07 x 10^-9 m²/s) at the octanol/water interface were found to be smaller than that of 1:1 complex (0.37 and 0.14 x 10^-9 m²/s). It was observed that the surface tension of ILs decreased in the presence of complexes and free CE, whereas the surface tension of water was found to increase in presence of salts (Cs⁺NO₃^- and Na⁺NO₃^-). The experimentally determined value of D_Cs was found to be quite high in IL phase (1.595) compared to the octanol phase (0.139) in presence of CE. The kinetics of Cs⁺ was found to be very fast having rate with values of k₁=1.79 x 10^-12 s^-1 and k₂=0.205 x 10^-12 s^-1 in IL and water phase, respectively. The present results may help us in understanding the role of diluents in the assisted metal ion extraction but also in the future design of diluents and ionophore.