New insights on the doping of ZnO films with elements from group IIIA through electrochemical deposition

This study was focused in the electrodeposition of both compact and nanostructured extrinsic n-type doped ZnO films, which was achieved with aluminum, gallium, and indium. These elements were directly added into a Zn(II) rich electrolyte with molecular oxygen acting as an oxide precursor in aqueous perchlorate media. This way, the use of nitrate ions, whose by-products are accumulated in the aqueous electrolyte, and chloride ions, an electrically active element in ZnO, was therefore avoided. Speciation diagrams, conditional solubility diagrams and a potentiodynamic study were used to explain the way in which extrinsic n-type ZnO can be prepared by electrochemical deposition. Relatively compact films with a highly preferred orientation along the c-axis were suitable for impedance measurements, thus allowing the measurement of their doping levels. Al- and Ga-doped lamellar nanostructures were successfully prepared when the nature of the anion was changed from perchlorate to sulfate. Under specific conditions, the structure of these films changed from opened and isolated nanosheets to interconnected ones. Morphological, optical, and crystallographic properties of these films were also analyzed. Results and discussion presented here should provide a better understanding toward the study of alternative materials in fields such as photovoltaics and photocatalysis.     

New dicyclopentadiene-based scaffolds

New tricyclic and tetracyclic derivatives have been obtained from dicyclopentadiene as scaffolds for the preparation of diterpene analogues. Key functionalities with well defined spatial dispositions were placed on three different skeletons. The inaccessibility of external (and also internal) reagents to the concave face of these compounds rendered them resistant to several transformations.     

A functorial construction of moduli of sheaves

We show how natural functors from the category of coherent sheaves on a projective scheme to categories of Kronecker modules can be used to construct moduli spaces of semistable sheaves. This construction simplifies or clarifies technical aspects of existing constructions and yields new simpler definitions of theta functions, about which more complete results can be proved. Dedicated to the memory of Joseph Le Potier.     

Colloidal characterization of micron-sized rod-like magnetite particles

Rod-like magnetite particles have been prepared following a precipitation procedure in the presence of an external magnetic field. These particles have been characterized and results compared to those obtained for spheres which were synthesized following the same recipe but in the absence of a magnetic field. Both spheres and rod-like particles have a saturation magnetization of 475 kA/m, an isoelectric point at approximately pH 6.6, and a magnetite inverse spinel structure. DLVO theory qualitatively predicts the results obtained regarding the stability of the magnetite dispersions.     

Olefin epoxidations in the ionic liquid [C4mim][PF6] catalysed by oxodiperoxomolybdenum species in situ generated from molybdenum trioxide and urea–hydrogen peroxide: The synthesis and molecular structure of [Mo(O)(O2)2(4-MepyO)2]·H2O

Commercially available molybdenum(VI) compounds, including molybdenum trioxide, were successfully employed as catalyst precursors in the epoxidation of olefins with urea–hydrogen peroxide adduct (UHP) in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [C₄mim][PF₆]. After oxidation, the corresponding epoxides were isolated by extraction with diethyl ether. Additionally the ionic liquid–catalyst mixture was recycled and reused in further catalytic cycles. The catalytic species is assumed to be an oxodiperoxomolybdenum species which forms in situ. A representative complex of this type was thus isolated and characterised. Reaction of excess 4-methylpyridine-1-oxide (4-MepyO) with MoO₃ dissolved in aqueous hydrogen peroxide afforded [Mo(O)(O₂)₂(4-MepyO)₂]·H₂O (1) as yellow crystals. Compound 1, an active epoxidation catalyst, was subsequently characterised and its structure determined by X-ray crystallography.     

Morphisms between complete Riemannian pseudogroups

We introduce the concept of morphism of pseudogroups generalizing the étalé morphisms of Haefliger. With our definition, any continuous foliated map induces a morphism between the corresponding holonomy pseudogroups. The main theorem states that any morphism between complete Riemannian pseudogroups is complete, has a closure and its maps are C^∞ along the orbit closures. Here, completeness and closure are versions for morphisms of concepts introduced by Haefliger for pseudogroups. This result is applied to approximate foliated maps by smooth ones in the case of transversely complete Riemannian foliations, yielding the foliated homotopy invariance of their spectral sequence. This generalizes the topological invariance of their basic cohomology, shown by El Kacimi-Alaoui-Nicolau. A different proof of the spectral sequence invariance was also given by the second author.     

Amperometric PMMA-microchip with integrated gold working electrode for enzyme assays

The use of a gold film in-channel detector combined with a poly(methyl methacrylate) (PMMA) CE microchip has been tested for alkaline phosphatase (AP) enzymatic assays. Tris-borate or Tris-Gly (pH 9.0, 50 mmol L^–1) buffer solutions were appropriate as running buffer. Signals for three common AP products: -naphthol, p-nitrophenol, and ascorbic acid, were obtained. They were reproducible (RSD 4.4% for six successive electropherograms corresponding to 5 mmol L^–1 -naphthol solution) and the response was dependent on concentration (linear relationship for ascorbic acid solutions between 5 and 20 mmol L^–1 concentration). Use of an end-channel gold film electrode was also investigated. If one of the reagents (substrate or enzyme) is included in the running buffer, two different types of enzymatic assay are feasible in less than 3 min.     

Further research on the photo-SPME of triclosan

In this study the photoinduced degradation of triclosan has been investigated by photo-solid-phase microextraction (photo-SPME). In photo-SPME, photodegradation is carried out on the SPME fibre containing the target compound. Triclosan was extracted from aqueous solutions by use of polydimethylsiloxane SPME fibres and these were subsequently exposed to UV irradiation (power 8 W, wavelength 254 nm) for different times (from 2 to 60 min). The photodegradation kinetics of triclosan were investigated, the photoproducts generated were tentatively identified, and the photochemical behaviour of these products was studied by use of this on-fibre approach followed by gas chromatographic–mass spectrometric analysis. Eight photoproducts were tentatively identified, including chlorinated phenols, chlorohydroxydiphenyl ethers, 2,8-dichlorodibenzo-p-dioxin, and a possible dichlorodibenzodioxin isomer or dichlorohydroxydibenzofuran. The main photodegradation mechanisms were postulated and photodegradation pathways proposed. The effect of pH on triclosan degradation and on triclosan-to-dioxin conversion was also investigated. Triclosan degradation occurred, and generation of 2,8-dichlorodibenzo-p-dioxin was confirmed, throughout the pH range studied (from 3 to 9).