Sophie Peulon

Mechanistic Study of Cathodic Electrodeposition of Zinc Oxide and Zinc Hydroxychloride Films from Oxygenated Aqueous Zinc Chloride Solutions

Films of zinc oxide and related compounds [ZnO, ZnO x (OH) y , Zn(OH) x Cl y ] are electrodeposited cathodically in aqueous zinc chloride solutions using dissolved oxygen as a precursor. The influence of the precursor concentrations, pH, and deposition temperature on the growth, composition, and properties of the films are investigated by means of in situ techniques : voltammetry, electrochemical quartz-crystal microgravimetry, surface pH, and ex situ techniques: X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The deposition mechanism is analyzed in terms of electrochemically induced surface precipitation due to an increase of local pH resulting from the oxygen reduction reaction. This approach allows us to explain the formation of either zinc hydroxychloride compounds or zinc oxide from their calculated solubility diagrams. In conditions of the formation of ZnO, a dramatic effect of temperature is observed, with a transition between amorphous insulating zinc oxyhydroxide to well-crystallized and conducting zinc oxide when the temperature increases (T transition 50 °C).

Electrochemical deposition of thin films of green rusts 1 and 2 on inert gold substrate

Abstract Green rusts are layered Fe(II)–Fe(III) hydroxy-salts that play an important role in iron corrosion, soil chemistry, and environmental engineering. Successful electrochemical depositions of thin layers of green rusts incorporating anions such as carbonate or chloride (GRs1) or sulphate (GR2) on gold substrate are presented. As far as we know, it is the first time that such synthesis has been reported. The thin layers of green rusts were characterized by ex situ methods such as XRD, SEM, EDS and FTIR. This new way of synthesis allowed us to get green rust particles with sizes significantly larger than those obtained from the ways reported until now.

Interaction between uranium(VI) and siderite (FeCO3) surfaces in carbonate solutions

Abstract In order to assess the security of a long-term disposal of nuclear spent fuel, the prediction of radionuclide migration is needed. This paper presents the interaction between uranium(VI) and siderite surfaces, an iron carbonate present both in the near- and far-field of the storage, in carbonate solutions. The amount of uranium on the surface was determined after the interaction by alpha spectrometry. It appeared that the amount of uranium(VI) dropped with high pH and carbonate concentration, likely because of the predominance of UO2(CO3)22- and UO2(CO3)34- complexes in solution. The U4f X-ray photoelectron spectrum clearly highlighted that uranium present on the film has two different oxidation states and thus that uranium(VI) has been partially reduced by siderite.

Retention and redox behaviour of uranium(VI) by siderite (FeCO3)

Abstract In the context of long-term nuclear waste management, understanding the migration of a major component of spent fuel, uranium namely, in the environment is of major importance. This study presents the kinetics of uranium(VI) retention and reduction in carbonate solutions by siderite, an iron carbonate present both in the near- and far-field. At pH 9, uranium(VI) is retained at the surface, reduced and then precipitated into UO2.67. At pH 7, uranium(VI) seems, first, to be incorporated into iron precipitates at the solid/liquid interface and, subsequently, reduced by the Fe(II) contained in the thin layer.