Guy Campet

CdS-sensitized TiO2 in phenazopyridine photo-degradation: Catalyst efficiency, stability and feasibility assessment

Mineralization of phenazopyridine, 1, in water, under solar-simulator radiation was efficiently achieved using nanoparticle CdS-sensitized rutile TiO(2), TiO(2)/CdS, 2, as photo-catalysts. Despite that, 2 showed two main drawbacks. Firstly, the system was difficult to recover by simple filtration, and demanded centrifugation. Secondly, the sensitizer CdS showed relatively high tendency to leach out hazardous Cd(2+) ions under photo-degradation reaction conditions. In an attempt to solve out such difficulties, 2 was supported onto sand surface. The sand/TiO(2)/CdS system, 3, was easier to recover but showed slightly lower catalytic activity compared to 2. On the other hand, the support failed to prevent leaching of Cd(2+). This indicates limited future applicability of CdS-sensitized TiO(2) photo-catalyst systems, in solar-based water purification strategies, unless leaching out tendency is completely prevented.

Sur de nouveaux conducteurs anioniques de hautes performances

The study of ionic conduction in fluorides with fluorite type structure leads to new anionic superconductors of formulation Pb1−xBixF2+x (0 ⩽ x ⩽ 0.50). The strong polarizability of the Pb2+ and Bi3+ cations gives a highly conducting material. In particular Pb0.75Bi0.25F2.25 has a conductivity close to that of β-alumina.

Tin dioxide thin films prepared from a new alkoxyfluorotin complex including a covalent SnF bond

Abstract Fluorine-doped tin dioxide (FTO) films were elaborated from a new Sn(IV) molecular precursor, the tert amyloxyfluorodipentan-2,4-dionatotin(IV) complex, to be used via the sol–gel route. Upon controlled hydrolysis in acetonitrile, a fluorinated polystannoxane was formed as a stable xerosol, which was characterized by multinuclear magnetic resonance and Mossbauer spectroscopies, elemental analysis, and thermogravimetry coupled to mass spectrometry. This xerosol was further dissolved in acetonitrile for depositing highly transparent films by the spin-coating and spray pyrolysis techniques. Film composition was determined by X-ray photoelectron spectroscopy, electron probe microanalysis and energy dispersive X-ray analysis. The F/Sn atomic ratio was 3% for spin-coated films and 10% for the sprayed films. A noticeable amount of carbon (C/Sn #10 at.%) was detected in the films whatever the deposition technique. In every case, the film resistivity was found to be larger than the one obtained from separate tin and fluorine precursors. This result was attributed to the excess of carbon and fluorine content in the oxide layers relieved from the xerosol.

Roll-to-roll pulsed dc magnetron sputtering deposition of WO3 for electrochromic windows

Abstract This paper reports on the deposition conditions and properties of WO 3 films used as electrochromic layer in a monolithic device on a plastic substrate. The deposition technique employed was roll-to-roll pulsed dc magnetron sputtering. The oxide was deposited at room temperature in an argon and oxygen plasma on a transparent conducting ITO layer previously coated on a PET film. The influence of deposition parameters such as pulse mode, total pressure and oxygen partial pressure has been investigated, in order to obtain the best compromise between a high deposition rate and adequate electro-optical properties. As expected, the deposition rate increases with decreasing total pressure and oxygen partial pressure. To control the coloring/bleaching behavior, lithium ions from an aprotic electrolyte have been intercalated in films. Films with thickness around 400 nm exhibit a contrast ratio of 9:1. The optical efficiency increases slightly with increasing total pressure and lies between 30–40 cm 2 C −1 . Further, the coloring and bleaching time decreases with increasing total pressure, coloring being faster than bleaching. This is consistent with UV–Vis ellipsometric measurements which reveal that the refractive index decreases with increasing total pressure. TEM investigations also confirm that films deposited at low total pressure exhibit a dense structure whereas those deposited at high-pressure exhibit a columnar structure.

Photoelectrochemical properties of zinc oxide doped with 3d elements

Abstract The properties of ZnO photoanodes doped with transition elements (Cr, Mn, Fe, Co, Ni) have been investigated for photodecomposition of aqueous solutions. A large extension of the photoresponse occurs in the visible region, particularly with Co2+- and Mn2+-doped samples. The doping-ion coordination, the energy levels, and the mechanism of the charge transfer are discussed

Photoelectronic processes in transition-element doped n-type TiO2 electrodes

Abstract Photoelectronic properties of n-TiO2 anodes doped with first row transition elements and giving an absorption in the visible region, have been investigated. The photocurrent has been measured vs wavelength for a given electrode potential and vs time at different anode potentials. Significant photocurrents resulting from visible light excitation are observed for n-type TiO2 anodes doped with large amounts of trivalent chromium. When other transition elements (V3+ or Mn2+) are considered, such a long wavelength photoresponse was not observed. Co2+ and Ni2+ ions could not be introduced into n-TiO2 anodes because of the reduction into Co or Ni metal. The experimental data have been discussed on the basis of a model involving hole tunneling from Cr4+ ions to the valence band.

Enhancement of double-layer capacitance behavior and its electrical conductivity in layered poly (3, 4-ethylenedioxythiophene)-based nanocomposites

In this letter, we report on the enhanced double-layer capacitance of a layered poly (3, 4-ethylene dioxythiophene) PEDOT-MoO3 nanocomposite, which has been synthesized by a novel microwave irradiation method. The x-ray photoelectron spectroscopy analysis shows the changes in electron density and the shift in binding energy suggesting charge transfer from sulfur atoms upon PEDOT intercalation between MoO3 layers. The room-temperature conductivity for the PEDOT-MoO3 composite is found to be 1.82×10−1Scm−1, which is four orders of magnitude higher than that of the pristine oxide (3.78×10−5Scm−1). The enhanced double-layer capacitance of the PEDOT-MoO3 nanocomposite (∼300Fg−1) compared to that (∼40mFg−1) of pristine MoO3 is attributed to higher electronic conductivity, enhanced bidimensionality, and increase in surface area of the nanocomposite.

Entrapment of poly(3,4-ethylenedioxythiophene) between VS2 layers to form a new organic–inorganic intercalative nanocomposite

Here we report the synthesis and characterization of a new class of nanocomposite by direct in situ oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) with VS2 as a host material in the presence of an external oxidizing agent. Upon intercalation, the interlayer spacing of VS2 expands from 5.71 A to 14.01 A, followed by exfoliation and a restacking process facilitating expansion of the lattice in a direction perpendicular to the dichalcogenide layers. This change in interlayer separation is consistent with the existence of two phases of organic and inorganic species in the nanocomposites corresponding to the intercalation of PEDOT in the VS2 framework. The resulting nanocomposite is characterized by thermal analysis (TGA), X-ray diffraction, FTIR, SEM, TEM, and four-probe electrical conductivity measurements. The application potential of the nanocomposite as a cathode material for rechargeable lithium batteries is also demonstrated by the electrochemical intercalation of lithium into the PEDOT–VS2 nanocomposite, where a significant enhancement in the discharge capacity is observed (∼130 mA h g−1) compared to that (80 mA h g−1) for pristine VS2.

Extension of the photoresponse of semiconducting zinc oxide electrodes by 3d-impurities absorbing in the visible region of the solar spectrum

Abstract The photoelectrochemical behavior of polycrystalline ZnO: Mn+ anodes (Mn+= Cr3+, Mn2+, Fe3+, Co2+ and Ni2+) in an aqueous electrolyte has been investigated. An important extension of the photocurrent in the visible region is observed with 1.0 at.% Mn2+, Co2+ and Ni2+. The well-structured action spectra of the Co- and Ni-doped ZnO electrodes and their similarities with the absorption spectra allow the energy levels of the 3dn impurities to be located and enables the mechanism of the charge transfer at the semiconductor/electrolyte interface to be understood under visible irradiation.

A new polypyrrole/maghemite hybrid as a lithium insertion electrode

A new polypyrrole (PPY)/maghemite (γ-Fe2O3) hybrid was prepared by modification of the surface of maghemite nanoparticles using polymerization of pyrrole on the surface. Fourier Transform infrared (FTIR), X-ray diffraction and electron microscopy studies have proven that it was only a surface modification, keeping the core structure unchanged. Transmission electron micrographs have shown the presence of PPY on the intergrain surface between maghemite particles, leading to reduction of particle aggregation. The electrochemical lithium capacity has increased up to 270 mAh/g in the potential range between 1.3 and 4.3 V vs. Li at 8 mA/g. The modified samples showed an enhanced cyclability compared to the pristine one.