Electrochemical and Spectroscopic Study of EuIII and EuII Coordination in the 1‐Ethyl‐3‐methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid. Issue 63 (14th October 2020)

• Record Type: Journal Article
• Authors: Bengio, David; Dumas, Thomas; Arpigny, Sylvie; Husar, Richard; Mendes, Eric; Solari, Pier Lorenzo; Schlegel, Michel L.; Schlegel, Daniel; Pellet‐Rostaing, Stéphane; Moisy, Philippe
• Is Part Of: Chemistry. Volume 26:Issue 63(2020)
• Page Start: 14385
• Page End: 14396
• Publication Date: 2020-10-14
• Subjects: electrochemistry -- europium -- ionic liquids -- rare earths -- UV/Vis spectroscopy; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202001469
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Separation processes based on room temperature ionic liquids (RTIL) and electrochemical refining are promising strategies for the recovery of lanthanides from primary ores and electronic waste. However, they require the speciation of dissolved elements to be known with accuracy. In the present study, Eu coordination and Eu III /Eu II electrochemical behavior as a function of water content in 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf2 ]) was investigated using UV–visible spectrophotometry, time‐resolved laser fluorescence spectroscopy, electrochemistry, and X‐ray absorption spectroscopy. In situ measurements were performed in spectroelectrochemical cells. Under anhydrous conditions, Eu III and Eu II were complexed by NTf2, forming Eu−O and Eu−(N, O) bonds with the anion sulfoxide function and N atoms, respectively. This complexation resulted in a greater stability of Eu II, and in quasi‐reversible oxidation–reduction with an E0 ' potential of 0.18 V versus the ferrocenium/ferrocene (Fc + /Fc) couple. Upon increasing water content, progressive incorporation of water in the Eu III coordination sphere occurred. This led to reversible oxidation–reduction reactions, but also to a decrease in stability of the +II oxidation state ( E 0 '=−0.45 V vs. Fc + /Fc in RTIL containing 1300 mm water). Abstract : The electrochemical behavior and speciation of Eu in the 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid are described in this work. In particular the coordination changes upon hydration or reduction of Eu III to Eu II were investigated by coupling spectroscopic and electrochemical techniques.