In order to examine the chemical form of uranyl species in 1-ethyl-3-methylimidazolium (EMI) based ionic liquids, UV-visible absorption spectra of solutions prepared by dissolving [EMI] 2[UO 2Cl 4] into a mixture of EMICl and EMIBF 4 (50:50 mol%) were measured. As a result, it was confirmed that uranyl species in the mixture of EMICl and EMIBF4 existed as [UO 2Cl 4] 2-. Cyclic voltammograms (CVs) of [UO 2Cl 4] 2- in the mixture were measured at 25 °C using a Pt working electrode, a Pt wire counter electrode, and an Ag/Ag + reference electrode (0.01 M AgNO 3, 0.1 M tetrabutylammonium perchlorate in acetonitrile) in a glove box under an Ar atmosphere. Peaks corresponding to one redox couple were observed around -1.05 V (E pc) and -0.92 V (E pa) vs. ferrocene/ferrocenium ion (Fc/Fc +). The potential differences between two peaks (ΔE p) increased from 101 to 152 mV with an increase in the scan rate from 50 to 300 mV s -1, while the (E pc + E pa)/2 value was constant, -0.989 V vs. Fc/Fc + regardless of the scan rate. Furthermore, the diffusion coefficient of [UO 2Cl 4] 2- and the standard rate constant were estimated to be 3.7 × 10 -8 cm 2 s -1 and (2.7-2.8) × 10 -4 cm s -1 at 25 °C. By using the diffusion coefficient and the standard rate constant, the simulation of CVs was performed based on the reaction, [UO 2Cl 4] 2- + e - = [UO 2Cl 4] 3-. The simulated CVs were found to be consistent with the experimental ones. From these results, it is concluded that [UO 2Cl 4] 2- in the mixture of EMICl and EMIBF 4 is reduced to [UO 2Cl 4] 3- quasi-reversibly at -0.989 V vs. Fc/Fc +.
ASJC Scopus subject areas
- 化学 (全般)