Electrochemical behavior of Eu(III) in imidazolium ionic liquid containing tri-n-butyl phosphate and N,N-dihexyloctanamide ligands

The electrochemical behavior of Eu( III) in room temperature ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide (C(6)mimNTf(2)), was studied in the presence and absence of ligands such as tri-n-butyl phosphate (TBP) and N,N-dihexyloctanamide (DHOA) by cyclic voltammetry. The cyclic voltammogram of Eu(III) in C(6)mimNTf(2), recorded at glassy carbon electrode, exhibited a prominent quasi-reversible reduction wave occurring at the onset of -0.25 V (Vs Fc/Fc(+)), culminating in a peak at -0.84V (Vs Fc/Fc(+)) was due to the reduction of Eu(III) to Eu(II). The cathodic peak current was lowered and the peak potential shifted cathodically in the presence of ligands, due to the co-ordination of Eu(III) with ligands in ionic liquid phase. The diffusion coefficient (D, cm(2)/s) of Eu(III) and the rate constant (k(s), cm/s) for the electron transfer reaction across the electrode-electrolyte inter-phase in various systems were determined and they increased with increase of temperature. The stability constant and stoichiometry of Eu(III)-ligand complex were determined from the voltammograms recorded at various ligand concentrations. The emission spectra of Eu(III) in ionic liquid phase suggested that the coordination environment of Eu(III) in TBP was different from that in DHOA. (C) 2015 Elsevier B.V. All rights reserved.