An electrochemical technique for sensing uranium adsorption and desorption.

Uranium is a toxic, heavy metal that can pose elevated health risks if leached into the environment. Uranium mobility is dependent on many factors, including speciation, solution pH, ligands in solution, and presence of surfaces. Surface adsorption is one phenomenon that inhibits uranium mobility in the environment and is studied as a naturally occurring phenomenon as well an intentional tool for environmental remediation. This work presents and validates a potentiometric, electrochemical technique for sensing uranium adsorption on and desorption from an electrochemically active surface solely through changes of the electrode potential. This novel electrochemical technique presents a new lens to study adsorption that complements external techniques (e.g., spectroscopy). Indication of adsorption and desorption via the electrochemical technique are gravimetrically validated using an electrochemical quartz crystal microbalance. This work contributes a unique, complementary technique that corroborates the adsorption of uranium on an electrode surface.

Solvation Structure, Dynamics, and Charge Transfer Kinetics of Cu2+ and Cu+ in Choline Chloride Ethylene Glycol Electrolytes.

Experimental measurements and classical molecular dynamics (MD) simulations were carried out to study electrolytes containing CuCl2 and CuCl salts in mixtures of choline chloride (ChCl) and ethylene glycol (EG). The study focused on the concentration of 100 mM of both CuCl2 and CuCl with the ratio of ChCl/EG varied from 1:2, 1:3, 1:4, to 1:5. It was found that the Cu2+ and Cu+ have different solvation environments in their first solvation shell. Cu2+ is coordinated by both Cl- anions and EG molecules, whereas Cu+ is only solvated by EG. However, both Cu2+ and Cu+ show strong interactions with their second solvation shells, which include both Cl- anions and EG molecules. Considering both the first and second solvation shells, the concentrations of Cu2+ and Cu+ that have various coordination numbers in each solution were calculated and were found to correlate qualitatively with the exchange current density trends reported in previous experiments of Cu2+ reduction to Cu+. This finding makes a connection between atomic solvation structure observed in MD simulations and redox reaction kinetics measured in electrochemical experiments, thus revealing the significance of the solvation environment of reduced and oxidized species for electrokinetics in deep eutectic solvents.

Copper Electrodeposition from Deep Eutectic Solvents-Voltammetric Studies Providing Insights into the Role of Substrate: Platinum vs Glassy Carbon.

We report on the effect of the substrate on electrochemical deposition of Cu from deep eutectic solvent ethaline. We investigated the polarization behavior during electrodeposition of Cu on Pt and glassy carbon (GC) from both Cu2+ and Cu+ containing ethaline using cyclic voltammetry (CV). Formation of bulk Cu deposits on both substrates underwent nucleation and growth processes; however, the nucleation was considerably sluggish on GC compared to Pt. While experiments in Cu+ solutions indicated that coalescence of Cu islands on Pt is a slow process and that its surface may not be fully covered by Cu, such determination of Cu coverage could not be made on GC. Cu dissolution is also slower from GC than from Pt. It was observed that CV of Cu deposition on GC is influenced by the surface preparation method. Since ethaline has high chloride concentration, a parallel study in aqueous 3 M NaCl solution was conducted in order to examine the influence of the chloride medium on the electrodeposition process. This revealed that electrodeposition in both media occurred in the same manner but with different charge and mass transfer rates caused by the differences in viscosity and chloride concentrations of the two solutions.