Insight into Speciation and Electrochemistry of Uranyl Ions in Deep Eutectic Solvents

Abstract

Understanding the speciation of metal ions in heterogeneous hydrogen-bonded deep eutectic solvents (DES) has immense importance for their wide range of applications in green technology, environmental remediation, and nuclear industry. Unfortunately, the fundamental nature of the interaction between DES and actinide ions is almost completely unknown. In the present work, we outline the speciation, solvation mechanism, and redox chemistry of uranyl ion (UO2 2+) in DES consisting of choline chloride (ChCl) and urea as the hydrogen-bond donor. Electrochemical and spectroscopic techniques along with molecular dynamics (MD) simulations have provided a microscopic insight into the solvation and speciation of the UO2 2+ ion in DES and also on associated changes in physical composition of the DES. The hydrogen-bonded structure of DES plays an important role in the redox behavior of the UO2 2+ ion because of its strong complexation with DES components. X-ray absorption spectroscopy and MD simulations showed strong covalent interactions of uranyl ions with the constituents of DES, which led to rearrangement of the hydrogen-bonding network in it without formation of any clusters or aggregations. This, in turn, stabilizes the most unstable pentavalent uranium (UO2 +) in the DES. MD analysis also highlights the fact that the number of H-bonds is reduced in the presence of uranyl nitrate irrespective of the presence of water with respect to pristine reline, which suggests high stability of the formed complexed species. The effect of added water up to 20 v/v % on speciation is insignificant for DES, but the presence of water influences the redox chemistry of UO2 2+ ions considerably. The fundamental findings of the present work would have far reaching consequences on understanding DES, particularly for application in the field of nuclear fuel reprocessing.

New Greener and Sustainable Methodology for Direct Sequestering and Analysis of Uranium Using a Maline Supramolecular Scaffold and Mechanistic Understanding through Speciation and Interaction Studies

“…Abbott et al. , reported that Maline has a higher solvation potential for hardly soluble metal oxides than the reline and ethaline. Gupta et al have described the dissolution of uranyl nitrate and uranium oxides with higher stoichiometric DESs urea/ChCl (2:1) (reline) and PTSA/ChCl (1:2), respectively . Moreover, the dissolution of other uranium matrices such as Rb 2 (U­(SO 4 ) 3 ), uranium metal powder, U 3 Si 2 , (U, Pu)­O 2 , and PuO 2 has not been explored in their studies. , Previous literature reports , imply that the urea (reline) and para-toluene sulphonic acid (PTSA) act as monodentate ligands via the oxygen atom.…”

“…Gupta et al have described the dissolution of uranyl nitrate and uranium oxides with higher stoichiometric DESs urea/ChCl (2:1) (reline) and PTSA/ChCl (1:2), respectively . Moreover, the dissolution of other uranium matrices such as Rb 2 (U­(SO 4 ) 3 ), uranium metal powder, U 3 Si 2 , (U, Pu)­O 2 , and PuO 2 has not been explored in their studies. , Previous literature reports , imply that the urea (reline) and para-toluene sulphonic acid (PTSA) act as monodentate ligands via the oxygen atom. Hence, it was anticipated that these ligands are unable to offer very strong interactions for the U metal ion.…”

“…It implies that increasing the concentration of PTSA lowers the solvating potential while increasing the concentration of the chloride ion (Cl – ) provides a higher solvating potential of DESs toward metal oxides. Based on the previous studies, , it was anticipated that in the dissolution of metal oxides with PTSA/ChCl DESs, the chloride ion (Cl – ) also participates in the coordination of metal ions, and hence, when the ChCl component is higher in PTSA/ChCl (1:2), the metal oxides show higher solubility. This suggests that the chelating ability of PTSA toward metal ions in DESs is lower than MA and in PTSA/ChCl DES, it is the chloride ion (Cl − ) that controls the solvating potential of DESs.…”

Computer Simulations of Deep Eutectic Solvents: Challenges, Solutions, and Perspectives

“…Parameters are given DES at 2D nanomaterial interfaces [ 313 ] 78 ChCl:Urea (1:2) No name of FF. Parameters are given DES with different nanotubes [ 324 ] 79 ChCl:Urea (1:2) Combine force field based on CGenFF and CHARMM 36 DES nanodroplet at carbon material [ 323 ] 80 ChCl:Urea (1:2) GAFF/ charges scaling is 0.9 for the ions DES droplets on ionic substrates [ 320 ] 81 ChCl:Urea (1:2) OPLS-AA/no corrections Dissolution of cellulose in DES [ 21 ] 82 ChCl:Urea (1:2) q4-MD force field/no corrections Molecular encapsulation [ 386 ] 83 ChCl:Urea (1:2) Monte Carlo/Empirical potential structure refinement (EPSR) Investigation of DES structure [ 387 ] 84 ChCl:Urea (1:2) OPLS-AA/no corrections Separation of uranyl Ions [ 388 ...…”

Review on Hydrometallurgical Recovery of Metals with Deep Eutectic Solvents

“…The study of Gupta et al ( [60]) investigated the behavior of uranyl ions (UO2 2+ ) dissolved in a DES made of ChCl and urea. The interaction between uranium and the DES was found to modify its redox behavior, which was studied by electrochemical techniques such as voltammetry.…”