Laura Mais

TiO2–WO3 nanostructured systems for photoelectrochemical applications

TiO2/WO3 mixed metal oxide is used in the present work as an anode for the photoelectrosplitting of water. TiO2 is used as the support under-layer in the form of either a compact or nanotubular structure. The over-layer of WO3 is obtained via cathodic electrodeposition, by means of pulse potential technique (PPT). The performances of the samples in neutral supporting electrolyte are compared when the samples are irradiated with light at two wavelengths, 365 nm and 400 nm. The effect of the WO3 loading on the performance is also investigated, as well as the charge transfer mechanism. The results from runs carried out in solutions containing glycerol are used to study the possible role of the WO3 over-layer in the whole working mechanism of the combined structure.

Electrodeposition of Zirconium from 1-Butyl-1-Methylpyrrolidinium-Bis(Trifluoromethylsulfonyl)imide: Electrochemical Behavior and Reduction Pathway

A study on the electrochemical deposition of Zr on platinum, gold, and boron doped diamond (BDD) from 1-butyl-1-methylpyrrolidinium-bis(trifuoromethylsulphonyl) imide is presented in this work. The electrochemical behavior of zirconium ions was investigated by cyclic voltammetries and chronopotentiometries, allowing establishing the mechanism of deposition. Deposition tests were carried out at different potentials and the related samples were analyzed by SEM and EDX. Structural and chemical analyses indicate that the obtained deposits are constituted by metallic zirconium. According to the electrochemistry of zirconium and based on the experimental results, the mechanism is Zr(IV) ⇒ Zr(II) ⇒ Zr.

Voltammetric Study on the Behaviour of Refractory Metals in ((BMP)(TFSA)) Ionic Liquid.

Electrochemical studies of tantalum fluoride and zirconium fluoride in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([BMP][TFSA]) ionic liquid were carried out in presence of lithium fluoride using cyclic voltammetry technique. The electrochemical behaviour of Ta(V) and Zr(IV) on gold and platinum substrates was investigated in the temperature range from R.T. to 200 °C at different values of scan rate and different potential windows. Special attention was paid to the mechanism of cathodic reduction. Cyclic voltammetries exhibit well-defined peaks attributed to the formation of metallic deposits on the substrates. The knowledge of electrode and chemical reactions based on the experimental results of the refractory metals considered allow us to propose a possible reaction path for the oxidation/reduction processes. The mechanisms of electrochemical reduction of Tantalum(V) depends strongly on the composition of the bath; using TaF5 as metal salt, two cathodic peaks due to Ta(V)/Ta(III) and Ta(III)/Ta reduction were observed. The cyclic voltammograms recorded at different values of scan rate have shown that the Ta(III)/Ta reduction process is mainly controlled by diffusion of the electroactive species to the electrode surface. It has been proposed that the mechanism for reduction of zirconium ions occurs in a one step process exchanging four electrons and controlled by the zirconium ions diffusion in the ionic liquid. The electrochemistry of refractory metals (IVB, VB and VIB groups) has been widely studied in molten salts to optimize the cathodic deposition process of these metals. Due to their properties, such as high strength and high corrosion resistance, refractory metals are widely used in electronics, optics, sensors, automotive, nuclear and aerospace industries. Conventional aqueous media cannot be always used as electrolytes due to the narrow electrochemical windows, low thermal stability and evaporation (Simka et al., 2009). The mechanism of the electrodeposition of refractory metals is not yet fully elucidated. Senderoff and Mellors (1966) developed a general process for the electrodeposition of eight of the nine refractory metals of groups IVB, VB and VIB as dense coherent deposits by using a solution of the refractory metal in a molten alkali-fluoride eutectic mixture from 680 °C to 800 °C. They concluded that an irreversible metal-producing step is a necessary (though not sufficient) condition for the deposition of coherent deposits from molten salts. The mechanical properties of refractory metals, such as the excellent corrosion resistance and the nuclear properties of some, make them particular interesting as coatings. Inman and White (1978) have summarized in a review the electrochemistry of refractory metals in molten salts electrolytes. The authors have reported that the recovery of a primary metal is ensured by using, as solvent, a melt having a much larger decomposition voltage than that of the solute and an inert cathode; controlling the electrodeposition of metal by rate processes other than mass transfer, will lead to coherent deposits. Few years later, Girginov et al. (1995) have presented a selective review of the anodic and cathodic processes of Ti, Zr, Nb and Ta from molten salts-based electrolytes in order to investigate the optimization of cathodic deposition of these metals highlighting that the two main types of electrolyte employed in the electrodeposition of refractory metals were chloride and fluoride based. The Ta(V) reduction has been studied in a wide range of melts, such as chlorine or fluorine melts. In FLINAK-K2TaF7 DOI: 10.3303/CET1441017

Practical Aspects on Electrochemical Disinfection of Urban and Domestic Wastewater

Abstract Electrochemical techniques are suitable for disinfection and purification of civil and domestic wastewaters. The tertiary treatment processes such as advanced oxidation processes and disinfection have been presented at active and nonactive electrode materials. Problems connected to mass transfer limitation in the reactor and possible formation of by-products are discussed. The main issues related to the modeling of the fluid dynamics of the reactor and the kinetics of the reactions involved are examined in order to describe the whole process of pollutant removal and bacteria inactivation during electrochemical disinfection of diluted solutions.

Highly ordered TiO2-WO3modified nanotubes array for photoelectrocatalytic oxidation of methyl orange

Coupled titanium dioxide-tungsten oxide array surface was used to remove methyl orange from water by photocatalytic anodic oxidation. The coating was prepared by anodizing a titanium foil in a glycerol/water electrolyte-containing NH4F followed by thermal treatment. Moreover, subsequent WO3 electrodeposition was realized on the previously obtained TiO2 nanotubular structure. As comparison, TiO2-WO3 structures were obtained by adding a tungstate salt in the glycerol/water electrolyte during the anodization step of Ti foil. Scanning electron microscopy imaging showed that the array coating consisted of closely spaced nanotubes perpendicular to the titanium plate. Moreover, subsequent electrodeposition of WO3 occurred on the wall of the nanotubes; when a tungstate salt was used during Ti anodization, the formation of nanotubes with different dimensions was observed. The synthesized materials were studied for the photoelectrocatalytic oxidation of methyl orange under applied bias potential. The degradation efficiency obtained using TiO2 nanotubes was higher than that obtained in presence of the coupled structure.

Synthesis of nanostructured materials for photoelectrochemical oxidation of organic compounds

Synthesis of Nanostructured Materials for Photoelectrochemical Oxidation of Organic Compounds Laura Mais*, Pablo Ampudia, Simonetta Palmas, Annalisa Vacca, Michele Mascia, Francesca Ferrara a Dipartimento di Ingegneria Meccanica, Chimica e dei Materiali, Università degli Studi di Cagliari, via Marengo 2, 09123 Cagliari, Italy b Sotacarbo S.p.A., c/o Grande Miniera di Serbariu, 09013 Carbonia, Italy l.mais@dimcm.unica.it