Publicaciones: Nanocomposites Multifuncionales

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26

Apr 2018

Metastable phase in binary and ternary 12-carat gold alloys at low temperature

Posted by / in Publicaciones Destacadas, Publicaciones Materiales Multifuncionales 2018, Publicaciones: Nanocomposites Multifuncionales, Publications 2018, Últimas Publicaciones CINN / No comments yet

Low temperature phase transitions in 12-carat gold alloys have been investigated for binary Au-Cu and ternary Au-Cu-Ag compositions. The thermal analyses investigations using differential scanning calorimetry (DSC) and the dilatometry were performed in the 50–300 °C temperature range in order to detect the structural transformations. The thermal analyses were carried out on annealed samples at 700 °C for two hour followed by water quenching. They reveal an important new reaction for both used compositions and both thermal techniques confirm each other. This reaction has been assessed as pre-ordering reaction. SEM and STM imaging were performed on annealed samples at 700 °C for two hours and water quenched followed by a heating from room temperature up to the temperature of the new peaks obtained in the thermal study. The imaging reveals the relationship between the pre-ordering reaction and the surface aspect presented in the fact of dendrite precipitates. A series of SEM observation have been performed in order to follow the kinetic of the observed precipitates by the way of several series of heating up, from 140 to 220 °C for the binary composition and from 100 to 180 °C for the ternary composition. Furthermore, this study shows that the silver accelerates the ordering reaction.

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16

Apr 2018

Synthesis, crystal structure, photoluminescence and dielectric properties of a new organic–inorganic compound: tetrachlorocadmate (II) 2.2′-bipyridinium

Posted by / in Publicaciones Materiales Multifuncionales 2018, Publicaciones: Nanocomposites Multifuncionales, Publications 2018, Últimas Publicaciones CINN / No comments yet

Single crystals of a new organic–inorganic compound (C10H10N2) CdCl4 were grown by the slow evaporation technique and characterized by X-ray diffraction, Hirshfeld surface, Infrared absorption, Solid state 13C NMR, photoluminescence (PL) properties, differential scanning calorimetry (DSC) and dielectric measurements. The title compound belongs to the monoclinic space group P21/c with the following unit cell parameters: a = 7.29420(1), b = 13.9206(3), c = 14.3880(3) Å, β = 100.247(2)° and Z = 4. The structure can be described by the alternation of two different cationic-anionic layers. It consists of isolated [CdCl4]2− tetrahedral anions and 2.2′ bipyridinium (C10H10N2)2+ cations, which are connected via N–H⋯Cl hydrogen bonds. The Hirshfeld surface analysis was conducted to investigate intermolecular interactions and associated 2D fingerprint plots, revealing the relative contribution of these interactions in the crystal structure quantitatively. Furthermore, the room temperature infrared (IR) spectrum of the title compound was recorded and analyzed on the basis of detailed vibrational studies found in the literature; the detailed assignment confirms the presence of the organic groups. Solid state 13C NMR spectrum shows four signals, confirming the solid state structure determined by X-ray diffraction. Besides, photoluminescence measurements showed a strong emission line at 2.95 eV associated with radiative recombinations of excitons confined within the [CdCl4]2−which were investigated at room temperature. Finally, the thermal analysis studies were performed, and phase transition was found in the temperature range between 300 and 550 K, while the electrical measurements were performed to discuss the phase-transition mechanism.

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16

Apr 2018

Influence of iron doping on the photocatalytic activity of nanocrystalline TiO2 particles fabricated by ultrasound method for enhanced degradation of organic dye

Posted by / in Publicaciones Materiales Multifuncionales 2018, Publicaciones: Nanocomposites Multifuncionales, Publications 2018, Últimas Publicaciones CINN / No comments yet

Synthesis and characterization of Fe doped TiO2 composite with iron concentration varying from 0 to 7% as a photocatalyst in the photodegradation of methylene orange on UV–Vis light irradiation in a closed reactor has been carried out. Synthesis was conducted by the ultrasound method at room temperature using tetrabutyl titanate and iron(III)chloride 6-hydrate as a precursor, followed by thermal treatment at a temperature of 600 °C. The characterizations were performed using X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscopy (SEM), FT-IR spectrometry, thermal analysis, UV–Vis diffuse reflectance spectrophotometer, photoluminescence and Brunauer–Emmett–Teller (BET). XRD spectra revealed that samples crystallized in the anatase phase at 600 °C. The transmission and SEM were used to detect the morphology of synthesized nanoparticles, which sizes changed with the altitude in the doping concentration to 7%. FTIR spectra exhibit broad peaks where anatase phases of TiO2 demonstrate very sharp peaks. In accordance with UV–Vis absorption measurements, this diminution of nanoparticles sizes was followed by a decrease in the band gap value from 3.21 eV, for undoped TiO2, to 2.46 eV, for TiO2 doped at 7%. The TGA showed three mass losses, whereas DTA resulted in three endothermic peaks. The maximum photoconversion efficiency was 2.5%, which was six times the photoconversion efficiency of undoped TiO2. Finally, the prepared materials were used to photocatalyse the decolourization of methylene orange in aqueous medium as a model compound under the illumination of visible light (λ = 420 nm).

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