Electrochemical Eu(III)/Eu(II) behaviors and recovery over terpyridyl-derivatized modified indium tin oxide electrode surfaces

Abstract

Understanding the electrochemical behaviors of lanthanide (Ln) ions is essential for the treatment, separation, and recovery of radioactive materials and Ln-containing industry waste. Herein, the electrochemical behavior of Eu(III)/Eu(II) ions and their recovery were studied over terpyridine-functionalized indium tin oxide (ITO) electrodes. Two different functionalization processes were performed via Au-S bonding on Au nanoparticle-loaded ITO and amide bonding on an amino alkoxysilane-functionalized ITO. Cyclic voltammetry was performed for the electrodes, with and without surface functionalization, in electrolytes containing NaClO4 and H2SO4. Electrodeposition by amperometry was performed to recover Eu ions as EuSO4 on the developed electrodes at a reduction potential of ~1.0 V (vs. Ag/AgCl), which is an irreversible reduction potential in NaClO4 electrolyte. The electrodes were fully characterized by scanning electron microscopy, X-ray diffraction crystallography, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and fluorescence lifetime measurements. Density functional theory calculations at the B3LYP/GENECP level of theory were employed for geometry optimization and the electronic energy state calculation for the complexation of Eu(III) and Eu(II) ions with the functionalized groups. The results obtained herein provide valuable information on the development of electrodes for the treatment of Ln and other related elements.