Complexation of Eu(III) in a Completely Incinerable Ionic Liquid System: A Luminescence Spectroscopy Approach

Abstract

Luminescence study of europium(III) ion has been carried out in a completely incenerable (CHON based) ionic liquid system. The ionic liquid used in the study was trioctylmethylammonium nitrate ([N 1888 ][NO 3 ] while the extractant used was N,N-dioctyl-2-hydroxyacetamide (DOHyA). The complexation of europium (III) in such type of ionic liquid system and its elaboration by luminescence study is highlighted for the first time in this paper. The luminescence behaviour of europium(III) was ascertained as a function of various parameters, such as aqueous phase acidity, extractant concentration, initial metal ion concentration, types of ionic liquid diluents etc. The luminescence intensity of Eu(III) was remarkably high in the ionic liquid medium at all aqueous phase acidity (0.1 M to 5 M HNO3) as compared to that of in aqueous phase. The luminescence lifetime of Eu(III) in this complex is in the range of 360 ms -550 ms which is quite higher than that of aqueous phase (107 ms -130 ms), suggesting the luminescence enhancement is a result of reduction in non-radiative decay channels in ionic liquid medium. The emission peak of Eu(III) in DOHyA was compared with that of DOMeA (N,N-dioctyl-2methoxyacetamide) in ionic liquid medium in order to highlight the presence of -OH group in DOHyA. The luminescence spectra of Eu(III) was also investigated by changing the type of aqueous phase acidity from nitrate ion to chloride ion and the results are detailed in the paper.

Europium(III) Coordination in a Combined Ligand System: A Luminescence Spectroscopy Study

“…A similar observation has been reported elsewhere with a high concentration of Eu(III). [16] At low acidity (0.1 M), the electric dipole transition occurred at 615 nm is less intense in contrast to the magnetic dipole transition occurred at 592 nm and as the acid strength increases in the aqueous phase the intensity of electric dipole transition increases and becomes more intense than its corresponding transition at 592 nm. This is attributed to the availability of more nitrate ion which eventually perturbs the degeneracy of the [Eu(H 2 O) 9 ] 3 + complex by expelling out the inner sphere water molecules by nitrate ions.…”

Unraveling the coordination approach of Eu(iii) in cyphos nitrate ionic liquid – a comprehensive luminescence spectroscopy study

“…For instance, the presence of an OH group oscillator, i.e., an OH • radical, which is formed either by the reaction of an H • radical (generated from [P 66614 ] + and an O • radical generated from the NO 3 − ion) or from the residual water molecules present in the ionic liquid, decreases sharply the decay time of Eu(III) emission. 36,65 To evaluate the loading capacity of the irradiated ionic liquid, the concentration of Eu (III) was varied from 5 g L −1 to 80 g L −1 in the feed phase and the extraction was performed using [P 66614 ][NO 3 ] irradiated at 500 kGy. A similar trend was obtained as portrayed in Fig.…”

“…[27][28][29][30][31][32] Among these, luminescence spectroscopy assisted Ln(III) extraction chemistry is proven to be a promising area as it offers fundamental comprehension of the metal-ligand coordination process. [32][33][34][35][36][37][38][39][40][41][42] Change in the local environment of the target metal ion, asymmetry ratio (AR) values (the ratio of intensity (I 615 /I 592 ) due to the 5 D 0 → 7 F 2 transition to 5 D 0 → 7 F 1 transition), the number of water molecules present in the primary coordination sphere of the metal-solvate species and decay profile or lifetime of the metal transition are the primary parameters to realize the essence of luminescence spectroscopy in evaluating the nature of the Eu (III)-solvate species formed in a complexation process. [31][32][33][34][35][36][37][38][39][40][41] In the lanthanide series, the Eu(III) ion is most often being used as a fluorescent probe to understand the coordination behavior of the trivalent Ln(III)/An(III) complex with various ligands.…”

“…[32][33][34][35][36][37][38][39][40][41][42] Change in the local environment of the target metal ion, asymmetry ratio (AR) values (the ratio of intensity (I 615 /I 592 ) due to the 5 D 0 → 7 F 2 transition to 5 D 0 → 7 F 1 transition), the number of water molecules present in the primary coordination sphere of the metal-solvate species and decay profile or lifetime of the metal transition are the primary parameters to realize the essence of luminescence spectroscopy in evaluating the nature of the Eu (III)-solvate species formed in a complexation process. [31][32][33][34][35][36][37][38][39][40][41] In the lanthanide series, the Eu(III) ion is most often being used as a fluorescent probe to understand the coordination behavior of the trivalent Ln(III)/An(III) complex with various ligands. [32][33][34][35][36][37][38][39][40][41][42] Among 5 D 0 → 7 F J transitions ( J = 0-6) observed in Eu(III) transition, 5 D 0 → 7 F 1 and 5 D 0 → 7 F 2 are the magnetic dipole (592 nm) and electric dipole (615 nm) transitions respectively and these transitions are usually inspected in identifying the chemical status and coordination mode of the metal ion in the ligand phase.…”

“…[31][32][33][34][35][36][37][38][39][40][41] In the lanthanide series, the Eu(III) ion is most often being used as a fluorescent probe to understand the coordination behavior of the trivalent Ln(III)/An(III) complex with various ligands. [32][33][34][35][36][37][38][39][40][41][42] Among 5 D 0 → 7 F J transitions ( J = 0-6) observed in Eu(III) transition, 5 D 0 → 7 F 1 and 5 D 0 → 7 F 2 are the magnetic dipole (592 nm) and electric dipole (615 nm) transitions respectively and these transitions are usually inspected in identifying the chemical status and coordination mode of the metal ion in the ligand phase. 33 In this context, the present paper emphasizes the coordination behavior of Eu(III) in [P 66614 ][NO 3 ] in its undiluted form exclusively by luminescence spectroscopy (more specifically time resolved fluorescence spectroscopy (TRFS)).…”