RESUMEN
Na3V2(PO4)2F3 (NVPF), a typical sodium superionic conductor (NASICON) type structure, has attracted much interest as a potential positive electrode in sodium-ion battery. However, the inherently poor electronic conductivity of phosphates compromises the electrochemical properties of this material. Here, we develop a general strategy to improve the electrochemical performance by preparing a new composite material "polyaniline (PANI)@NVPF" using a Pickering emulsion method. The X-ray diffraction and Raman results indicated a successful PANI coating without affecting the NASICON-type structure of NVPF, and they enhanced the interfacial bonding between the two components. Also, thermogravimetric analysis and scanning electron microscopy analyses revealed that the PANI content influenced the thermal stability and morphology of the nanocomposites. As a result, the sodium test cells exhibited multielectron reactions and a better rate performance for PANI@NVPF nanocomposites as compared to NVPF. Specifically, 2%PANI@NVPF maintained 70% of its initial capacity at 5C. Ex-situ electron paramagnetic resonance revealed the existence of mixed valence states of vanadium (V4+/V3+) in both discharge and charge processes. Consequently, the successful PANI coating into the sodium superionic conductor framework improved the sodium diffusion channels with a measurable increase of diffusion coefficients with cycling (ca. 3.25 × 10-11 cm2 s-1). Therefore, PANI@NVPF nanocomposites are promising cathode candidates for high-rate sodium-ion battery applications.
RESUMEN
The direct conversion of solar energy into chemical energy represents an enormous challenge for current science. One of the commonly proposed photocatalytic systems is composed of a photosensitizer (PS) and a catalyst, together with a sacrificial electron donor (ED) when only the reduction of protons to H2 is addressed. Layered double hydroxides (LDH) have emerged as effective catalysts. Herein, two Co-Al LDH and their composites with graphene oxide (GO) or graphene quantum dots (GQD) have been prepared by coprecipitation and urea hydrolysis, which determined their structure and so their catalytic performance, giving H2 productions between 1409 and 8643 µmol g-1 using a ruthenium complex as PS and triethanolamine as ED at 450 nm. The influence of different factors, including the integration of both components, on their catalytic behavior, has been studied. The proper arrangement between the particles of both components seems to be the determining factor for achieving a synergistic interaction between LDH and GO or GQD. The novel Co-Al LDH composite with intercalated GQD achieved an outstanding catalytic efficiency (8643 µmol H2 g-1) and exhibited excellent reusability after 3 reaction cycles, thus representing an optimal integration between graphene materials and Co-Al LDH for visible light driven H2 photocatalytic production.
RESUMEN
In this work, we synthesized several bionanocomposites of hydrotalcites containing carboxymethylcellulose as interlayer anion (HT-CMC) to be used as sorbents for parabens, a family of emergent pollutants (specifically, for 4-methyl-, 4-propyl- and 4-benzylparaben). Bionanocomposites were obtained by ultrasound-assisted coprecipitation and characterized by X-ray diffraction analysis, fourier transform infrared and raman spectroscopies, elemental and thermogravimetric analysis, scanning and transmission electron microscopies and X-ray fluorescence. All materials proved to be efficient sorbents for parabens through a process conforming to a pseudo second-order kinetics. The experimental adsorption data fitted the Freundlich model very closely and were also highly correlated with the Temkin model. The effects of pH, adsorbate concentration, amount of sorbent and temperature on the adsorption process was evaluated, obtaining the best results for methylparaben adsorption at pH 7, 25 mg of adsorbent and 348 K. The sorbent, HT-CMC-3, showed the highest adsorption capacity (>70%) for methylparaben. Furthermore, a reusability study showed that the bionanocomposite is reusable after its regeneration with methanol. The sorbent still retained its adsorption capacity for up to 5 times with a little loss of efficiency (<5%).
RESUMEN
The fabrication of low-cost carbon materials and high-performance sodium- and magnesium-ion batteries comprising hierarchical porous electrodes and superior electrolytes is necessary for complementing Li-ion energy storage. In this work, nongraphitic high-surface porous carbons (NGHSPCs) exhibited an unprecedented formation of n-stages (stage-1 and stage-2) due to the co-intercalation of sodium (Na(dgm)2C20) with diglyme. X-ray diffraction patterns, Patterson diagram, Raman spectra, and IR spectra suggested the presence of n-stages. This phenomenon implies an increase of the initial capacity (â¼200 mAh g-1) and good Na-ion diffusion (2.97 × 10-13 cm2 s-1), employing diglyme as compared to standard electrolytes containing propylene carbonate and fluoroethylene carbonate. Additionally, the current approach is scalable to full Na- and Mg-ion cells by using t-Na5V(PO4)2F2 and MgMnSiO4 cathodes, respectively, reaching 250 and 110 W h kg-1 based on the anode mass. The simultaneous Mg (de)insertion from/into MgMnSiO4 and the adsorption/desorption of bistriflimide ions on the NGHSPC surface is responsible for capacity enhancement.
RESUMEN
The presence of potent organic endocrine-disrupting chemicals (EDCs) in natural aquifers can have adverse impacts on public health and the environment. 4-nonylphenol, one such EDC, can be efficiently removed from water by adsorption onto a clayey material. In this work, we created an effective sorbent for this purpose by using co-precipitation and subsequent ion-exchange to intercalate the organic anion deoxycholate into a Mg/Al hydrotalcite. Intercalating deoxycholate ions increased the organophilicity of the hydrotalcite surface. The solid was used to adsorb 4-nonylphenol at different pollutant concentrations and temperatures. The adsorption process was subjected to a kinetic study. Based on the results, the EDC was adsorbed by chemisorption. In addition, based on the equilibrium isotherms used for the process, the Freundlich model was the most accurate in reproducing the adsorption of 4-nonylphenol onto deoxycholate-intercalated hydrotalcite.
Asunto(s)
Contaminantes Químicos del Agua , Agua , Adsorción , Hidróxido de Aluminio , Ácido Desoxicólico , Cinética , Hidróxido de Magnesio , Fenoles , Contaminantes Químicos del Agua/análisisRESUMEN
This article explores the effect of the synthetic method of titanium dioxide (TiO2)/C composites (physical mixture and the water-assisted/unassisted sol-gel method) on their photocatalytic activity for hydrogen production through glycerol photoreforming. The article demonstrates that, apart from a high surface area of carbon and the previous activation of its surface to favor titania incorporation, the appropriate control of titania formation is crucial. In this sense, even though the amount of incorporated titania was limited by the saturation of carbon surface groups (in our case, ca. 10 wt.% TiO2), the sol-gel process without water addition seemed to be the best method, ensuring the formation of small homogeneously-distributed anatase crystals on mesoporous carbon. In this way, a ca. 110-fold increase in catalyst activity compared to Evonik P25 (expressed as hydrogen micromole per grams of titania) was achieved.
RESUMEN
In this work, we conducted a careful study of the mortar and paint in the Roman wall painting housed by the triclinium of the so-called Domus in the Road Safety Education Park of Córdoba, Spain. A combination of X-ray diffraction, Raman and X-ray fluorescence spectroscopies allowed the different substances used to obtain the pigments present in the painting to be identified. The painting was found to contain five different colours (red, yellow, blue, green and white) in various hues. The red pigment was obtained from hematite and the yellow pigment from goethite. The blue pigment, which was the least abundant, was prepared from Egyptian blue, and the green pigment from green earths. Finally, the white pigment came from lime. The binders used were identified by infrared spectroscopy and gas chromatography with mass spectrometry detection. The painting fragments studied contained vestiges of bee wax or its decomposition products, which suggests that the paint was applied encaustically.
RESUMEN
Oleate ion was intercalated into a hydrotalcite obtained using a conventional precipitation method and an alternative, novel method involving microwave-assisted ion exchange. The latter method gave a more crystalline hydrotalcite with better textural properties than the former. The spacing between layers in the hydrotalcites was used to epoxidize the double bond in oleate ion. X-ray diffraction patterns revealed that the layered structure of the hydrotalcites was not altered by the reaction. The epoxidation of oleate ion with m-chloroperbenzoic acid (mCPBA) was monitored using Raman spectroscopy. The results of this work testify to the high potential of hydrotalcites as molecular reactors for reactions in confined spaces.
RESUMEN
A highly flexible method based on micro-Raman spectroscopy was used to examine pigment traces on an Annunciation sculpture group dating from the late Middle Ages. The group comprises a statue of the Archangel Gabriel and another of the Virgin Mary. Both are currently housed in the Archaeological Museum of Cordoba, southern Spain. Information about the pigment palette used by the artists of the time to decorate religious limestone sculptures was for the first time obtained. The pigments found included vermilion (HgS), hematite (α-Fe2O3), azurite [Cu3(CO3)2(OH)2], cerussite (PbCO3) and anatase (TiO2). None was directly applied to the sculptures; rather, the limestone was coated with a primer containing calcium carbonate (possibly chalk or half-chalk). The polychromy on both sculptures, which was originally applied in the XV century and seriously damaged in the XVIII, had been treated with an ochre-coloured priming layer of gypsum to make it more uniform and optically similar to the underlying stone.
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Selected bronze fragments unearthed at Cerro de la Cruz (Almedinilla, southern Spain) were analyzed to determine the chemical composition of the corrosion products formed on their surface. The fragments came from a large bronze cauldron used in an Iberian village that was devastated in the mid II century BCE - possibly around 141â¯BCE. The fragments were analyzed by using various instrumental techniques including electron scanning microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence (XRF) spectroscopy, and also by X-ray diffraction (XRD) and micro-Raman spectroscopy. Based on the results, being buried for a long time caused the main elements in the alloy to mineralize and form stratified layers consisting of various mineral phases including cuprite (Cu2O), malachite [Cu2CO3(OH)2] and cassiterite (Sn2O). The fragments also contained chloride and trihydroxychloride compounds such as nantokite (CuCl) and atacamite [Cu2Cl(OH)3], respectively, which make conservation of archaeological objects troublesome. These results testify to a strong interaction of the alloy elements with soil components. Also, the results obtained suggest a Type I of corrosion structure. Using the SEM-EDS, XRD and XRF and micro-Raman spectroscopies allowed corrosion products in the fragments to be successfully characterized in microchemical and structural.
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In this work, we analysed the preparatory layer and paintings in the hypocaustum of the Roman villa of El Ruedo (Almedinilla, southern Spain). The specimens studied were from the III and IV centuries. Raman microscopy was for the first time used here to examine Roman pictures in the south of the Iberian peninsula. The results obtained allowed us to establish the chemical nature of the different pigments used by the Roman artists. All were applied over a preparatory layer consisting of limewash. The different colours used (black, white, red, yellow, green and blue) were obtained by using carbon, calcite, gypsum, hematite, goethite, green earth and Egyptian blue. Some exhibited various hues that were obtained by mixing the previous compounds. Worth special note is the incipient presence of blue pigments, which were rarely used in Roman Hispania owing to their scarcity and high price.
RESUMEN
Two hundred and five isolates of Klebsiella pneumoniae were collected from Nantes University Hospital in 2002. A new 30bp deletion was detected downstream of the -10 box of the SHV-1 promoter in a clinical K. pneumoniae isolate with a high amoxicillin/clavulanic acid minimum inhibitory concentration. Reverse transcription polymerase chain reaction revealed increased transcription of bla(SHV-1) mRNA. All conjugation mating assays failed. This new promoter was cloned upstream of the cat gene of the reporter plasmid pKK232-8 and compared with previously described bla(SHV-1) promoters. The deletion induced a 15-fold increase in promoter strength compared with the usual weak promoter. This study reports a new genetic event that increases bla(SHV-1) chromosomal gene expression, which may be of clinical relevance when associated with porin deficiency.