Thermal analysis and structural characterization of Bi<Subscript>4</Subscript>V<Subscript>2–x</Subscript>Ba<Subscript>x</Subscript>O<Subscript>11–1.5x</Subscript> (0.02≤<Emphasis Type="Italic">x</Emphasis>≤0.50)

This work reports the study of Bi₄V_2–xBa_xO_11–1.5x (0.02≤x≤0.50) series, which is a potential source of solid electrolytes to apply in oxygen sensors. X-ray powder diffraction was used to point out the formation of major ionic conductive phases and minor ones. The modifications of vanadate substructure were probed, at short range, by Fourier-transform infrared spectroscopy. Differential scanning calorimetry evidenced the formation of tetragonal γ phase, which can be ionic conductive, for x=0.14.     

Synthesis and characterization of Ti1−2xNbxNixO2−x/2 solid solutions

Doped-rutile has been traditionally used in ceramic pigments for its intense optical properties. In this paper, we compare the classical ceramic synthesis of Ti_1−2xNb_xNi_xO_2−x/2 system with the sol-gel methodology, which allows a reduction of the anatase-rutile transformation temperature. The composition was optimised in order to obtain a unique rutile phase with the minimum amount of pollutant Ni(II) and enhanced chromatic coordinates. Incorporation of the doping ions in the rutile structure was corroborated by XRD and Rietveld refinements. The species responsible for the colour mechanism were studied by different techniques. UV-VIS spectroscopy showed the characteristic features of Ni²⁺ ions, whose existence was corroborated by EPR and magnetic measurements. From these results, (Ni,Nb)doped-TiO₂ powder samples can be now shaped as thin films, monoliths, etc. by using sol-gel methodology without modifying their properties. This study introduces new possibilities of coloured TiO₂-based solid solutions in new combined advanced applications (colouring agent and photocatalyst, etc.).     

Hydrotalcite-quinolinate composites as catalysts in a coupling reaction

Samples of layered double hydroxides were prepared by a sol–gel procedure. Quinolinate Al(C₉H₆NO)₃ units were added during the synthesis, leading to composite quinolinate hydrotalcite-like compounds. The amount of quinolinate was varied, showing that the number of organic building blocks determines the physicochemical properties of materials, which differ significantly from those commonly reported for hydrotalcites without any quinolinate. The order of layers, specific surface area and coordination of aluminium were the parameters most significantly influenced by the presence of the quinolinate as a part of the brucite-like layers. The composite quinolinate-hydrotalcite materials were tested to catalyse the Kabachnik–Fields reaction.

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Graphical abstract Adding of quinolinate Al(C₉H₆NO)₃ to hydrotalcite-like compounds creates disorder in the stack of brucite-like layers, leading to a significant modification of structural, textural and catalytic properties. The presence of quinolinate inhibits the enchainment of octahedral blocks in hydrotalcite but develop specific surface areas as high as 600 m²g^?1.

     

Structural and spectroscopic study of a novel erbium titanate pink pigment prepared by sol-gel methodology

Pyrochlore oxides show a large variety of physical and chemical properties depending on the ordering/disordering of the cations and oxygen vacancies. Taking account of these structural features and the luminescent properties of lanthanides, a new family of colored materials is investigated. This paper studies the structural evolution of the erbium titanate system with temperature to establish its influence on the color properties. The success on the development of color is completely related to the sol-gel preparation method, underlining its higher reactivity compared to classical solid-state synthesis. After firing at 700 degrees C, the sol-gel material develops an intense pink coloration whose intensity significantly diminishes at 800 degrees C. X-ray diffraction and Rietveld refinements indicated the presence of nanocrystals with a fluorite-like structure at 700 degrees C, responsible for the intense coloration, which suffers a gradual atomic rearrangement toward an "ideal" pyrochlore phase. These results were corroborated by infrared and Raman measurements. UV-vis spectroscopy showed the influence of the Er(3+)-O bond covalence on the spectral properties. This study opens new perspectives to the development of more ecological colored sol-gel materials based on rare earth elements. Furthermore, the combination of the optical aspects with the classical pyrochlore properties (magnetization, heat capacity, conductivity, etc.) would provide new multifunctional materials for advanced applications.     

Influence of the Matrix in the Optical Response of Organic-Inorganic Hybrid Materials Doped with Europium(III)

Eu³⁺-doped siloxane-oxide hybrid nanocomposites have been prepared by hydrolysis and condensation of diethoxydimethylsilane (DEDMS) and different metallic alkoxides, M(OR) _n with M = Ti, Zr, Al and Ta. The luminescent properties of Eu³⁺ have been used to study the environment of the rare earth ion within the matrices. Emission spectra shows that the surrounding of the Eu³⁺ varies with the matrix composition and depends on the nature of the metal introduced as cross-linking agent. In addition, decay curves have been performed and they show different lifetime values for each system. Among the systems under investigation, the one with tantalum presents the most anisotropic surrounding and the lowest coordination number for the rare earth ion, and the one with aluminium, which shows the most symmetrical surrounding, presents a small lifetime value, probably due to the tendency of Al³⁺cation to attract and retain hydroxyl groups, responsible for luminescence quenching.     

Recognizing Soluble Groups from their Probabilistic Zeta Functions

It is proved that if P_G(s) has an Euler product expansion withall factors of the form where each q_i is a prime power, then G is soluble. 2000 MathematicsSubject Classification 20P05, 20F05, 11M41.     

Flavanone Glycosides,Triterpenes, Volatile Compounds and Antimicrobial Activity of Miconia minutiflora (Bonpl.) DC. (Melastomataceae)

Chemical composition of the essential oils and extracts and the antimicrobial activity of Miconia minutiflora were investigated. The flavanone glycosides, pinocembroside and pinocembrin-7-O-[4″,6″-HHDP]-β-D-glucose, were identified, along with other compounds that belong mainly to the triterpene class, besides the phenolics, gallic acid and methyl gallate. Sesquiterpenes and monoterpenes were the major compounds identified from the essential oils. Screening for antimicrobial activity from the methanolic extract of the leaves showed that the MIC and MMC values against the tested microorganisms ranged from 0.625 to 5 mg·mL⁻¹ and that the extract was active against microorganisms, Staphyloccocus aureus, Escherichia coli, and Bacillus cereus.     

A nickel(II) coordination polymer derived from a tridentate Schiff base ligand with N,O-donor groups: synthesis,crystal structure,spectroscopy, electrochemical behavior and electrocatalytic activity for H<Subscript>2</Subscript>O<Subscript>2</Subscript> electroreduction in alkaline medium

A Ni(II) coordination polymer [C₄₂H₄₂K₂N₄Ni₄O₂₇] has been synthesized under open-air mild reaction conditions and characterized by physicochemical and spectroscopic methods. The X-ray crystal structure of the complex has been obtained. The crystallographic data revealed that each metal center is in a distorted octahedral geometry where the ligand coordinates to the metal centers by a nitrogen from the imine group, an oxygen from the carboxylic acid and a phenoxide group as an endogenous bridge to the metal centers. The coordination sphere is completed by an acetate, coordinated as an exogenous bridging ligand to both nickel centers, plus one terminal water ligand on each nickel. The polymeric structure is an infinite chain involving the binuclear nickel structure and K⁺ ions. Carbon paste electrodes modified with the Ni(II) coordination polymer were prepared, and the electrochemical behavior and electrocatalytic activity toward H₂O₂ reduction were investigated. The electrochemical results suggest that this Ni(II) coordination polymer has good catalytic activity with respect to H₂O₂ reduction.