Direct dissolution of uranium oxides in deep eutectic solvent: An insight using electrochemical and luminescence study

Abstract Nuclear energy is going to be the most potential option for solving the global energy crisis owing to its cost efficiency and environment friendliness. This work was carried with objective to propose a cheap, non-toxic and green solvent for dissolution of actinide oxide which is highly relevant from nuclear fuel reprocessing point of view. This prompted us to take the challenging research problem of investigating the dissolution behavior of different Uranium oxides (UO3, UO2 and U3O8) in p-Toluenesulfonic acid monohydrate (PTSA) based deep eutectic solvent (DES) and investigating its redox behavior and speciation using cyclic voltammetry (CV) and photoluminescence spectroscopy. We initiated with synthesis of relatively new class of DES consisting of Choline chloride (ChCl) and PTSA using mechanochemical route. The metal concentration dissolved was determined by EDXRF and it was found that PTSA: ChCl (1:2) was better in terms of solubility for uranium oxides as compared to PTSA: ChCl (1:1) and Malonic acid: ChCl (1:1). The formation of DES consisting of Hydrogen bonding network is confirmed using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. It could also be found that uranium oxide dissolution doesn’t distort the H-bonding network of DESs. Based on CV results it was proposed that U(VI)/U(V) reduction is controlled not only by diffusion of U(VI) ion in PTSA:ChCl (1:2), but also by the kinetics of the charge transfer reaction occurring at the electrode-electrolyte interphase. Luminescence spectroscopy suggested U(VI) in DES has U–O single bond moiety, having UO66− local coordination with excited state lifetime of 9.5 μs.