Abstract
In this study, phosphonium-based ionic liquids (IL), i.e., triethyl-n-pentyl, triethyl-n-octyl, and triethyl-n-dodecyl phosphonium bis(trifluoromethyl-sulfonyl)amide, [P222X][NTf2], (X = 5, 8, and 12) were investigated for Au(III) extraction. The IL–Au complex was identified as [P2225][AuCl4] using UV–Vis–NIR and Raman spectroscopic analyses. Slope analyses with the concentration dependence of [P222X
+] confirmed the anion-exchange mechanism of Au(III) extraction by [P222X
+] (X = 5, 8, and 12). The enthalpy, entropy, and Gibbs free energy for Au(III) extraction were determined using thermodynamic analysis, indicating that lower temperatures had a positive effect on the Au(III) extraction. Electrochemical analysis revealed that extracted Au(III) can be reduced in two steps: (i) Au(III) + 2e− → Au(I), (ii) Au(I) + e− → Au(0)]. The diffusion coefficients of the extracted Au(III) species in [P222X][NTf2] (X = 5, 8, and 12) were evaluated from 323 to 373 K using semi-integral and semi-differential analyses. Because of the viscosity of the IL medium, the diffusion coefficient of the extracted Au(III) increases with increasing alkyl chain length. The 4f
7/2 spectrum based on X-ray photoelectron spectroscopy revealed that the Au electrodeposits obtained after 10 cycles of continuous extraction and electrodeposition were in the metallic state.
Publisher
The Electrochemical Society
Subject
Materials Chemistry,Electrochemistry,Surfaces, Coatings and Films,Condensed Matter Physics,Renewable Energy, Sustainability and the Environment,Electronic, Optical and Magnetic Materials
Cited by
5 articles.
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