An insight into the complexation of UO2 2+ with diglycolamide-functionalized task specific ionic liquid: kinetic, cyclic voltammetric, extraction and spectroscopic investigations

A systematic study was carried out to understand the complexation of a diglycolamide functionalized task-specific ionic liquid (DGA-TSIL) and its molecular analogue, (tetraoctyldiglycolamide) TODGA with uranyl ion by cyclic voltammetry, solvent extraction and UV–Vis spectroscopy. Significant shifts of cathodic peak potential towards more positive values as compared to the uranyl ion in a room temperature ionic liquid-diluent, [C8mim][Br] were attributed to the complexation of it with the ligands. The order of diffusion coefficient values determined gave the idea of the bulkiness of the U bearing species. In the case of DGA-TSIL, the measurable, relatively slower kinetics in ionic liquid observed by both electrochemical and biphasic extraction techniques was attributed to high viscosity coefficient of the ionic liquid. The complexation reaction with U(VI) was found to follow the first order kinetics with a rate constant of 4.8 × 10−4 s−1. Titration data from cyclic voltammograms for a series of additions of the ligand to a fixed concentration of uranyl ion indicated that uranyl ion forms 1:1 complexed species with DGA-TSIL with the formation constant of 1.0 × 103 M−1 which agreed well with that obtained by slope analysis from biphasic extraction results. Difference in the UV–Vis spectra in terms of shifts of peak positions and relative peak intensities could possibly indicate the presence of different species of the uranyl ion in the RTIL with and without the ligand. It was also proposed that the bond (Odouble bond; length as m-dashUdouble bond; length as m-dashO) becomes weaker on complexation due to the approach of the ligand towards the metal ion, partially neutralizing the charge on the uranyl moiety. The symmetric stretching frequency calculated from UV–Vis spectra was in conformity of the above fact