Películas delgadas de V2O5 modificado con Ag depositadas utilizando configuraciones alternativas basadas en plasmas de ablación láser para su aplicación en sistemas fotocatalíticos

En este trabajo de investigación doctoral, se proponen tres configuraciones no convencionales de la técnica de ablación láser para preparar películas delgadas basadas en oxido de vanadio modificadas con diferentes cantidades de plata de manera controlada. A pesar de que la técnica de ablación láser ha sido ampliamente utilizada para preparar películas delgadas de una amplia gama de materiales, es una técnica poco adecuada para preparar películas delgadas formadas por materiales de diferente naturaleza, como es el caso de los denominados compositos. Con el propósito de contribuir a resolver este problema, se ha propuesto utilizar tres configuraciones alternativas basadas en ablación láser; en dos de las configuraciones propuestas se hacen interaccionar dos plasmas producidos simultáneamente a partir de materiales diferentes, en un caso, los plasmas se propagan en direcciones paralelas, en el otro, se utiliza una configuración de blancos múltiples, mientras que en el tercero se combina el plasma de ablación con un vapor producido por evaporación térmica. Con estas configuraciones se han preparado películas delgadas de óxido de vanadio con diferentes contenidos de plata que dan lugar a oxido de vanadio, así como diferentes vanadatos de plata en algunos casos decorados con nanopartículas de plata. Se evaluó la actividad fotocatalítica de las películas delgadas obtenidas con las diferentes configuraciones en la degradación de una solución de verde de malaquita empleando luz solar simulada con buenos resultados. Es importante mencionar que, hasta donde sabemos, los materiales obtenidos no han sido preparados utilizando estas configuraciones experimentales, lo que le confiere a este trabajo de tesis originalidad.A la Universidad Autónoma del Estado de México (UAEM), al Instituto Nacional de Investigaciones Nucleares (ININ) y a la Universidad Autónoma Metropolitana campus Iztapalapa (UAM-I) por las facilidades otorgadas para los estudios de doctorado. Al Centro Conjunto de Investigación en Química Sustentable UAEM-UNAM (CCIQS). Al Consejo Nacional de Ciencia y Tecnología (CONACyT) por la beca otorgada para los estudios de Doctorado y Beca Mixta con numero de becario CVU 325795 y al financiamiento a través de los proyectos CB-168827 y CB-240998 A la SIEA por la beca otorgada Movilidad Estudiantil de Estudios Avanzados 201

Synthesis and characterization of silver vanadates thin films for photocatalytic applications

Silver vanadates thin films were deposited by a hybrid deposition system combining laser ablation and thermal evaporation. A high purity vanadium target was ablated using the third harmonic of a Nd:YAG laser whereas high purity silver pellets were evaporated. The as-deposited thin films were subjected to thermal treatments at 400 °C to obtain crystalline films. For films without Ag amorphous V2O5 thin films were deposited and as the Ag is incorporated in the material different silver vanadates were obtained. The effect of the silver load on the composition, structure, optical properties, surface morphology and photocatalytic response of the deposited films was studied. The film composition, determined by X-ray photoelectron spectroscopy, reveals Ag contents from 5.5 to 18.9 at.%. The crystalline phases formed were identified by micro-Raman Spectroscopy; the results indicate the formation of three silver vanadates depending on the silver content. The morphology was observed using scanning electron microscopy, the filmś surface changes from a smooth surface to belts covering the surface and finally Ag nanoparticles are observed at the higher Ag contens. Optical properties determined from UV–vis reveal the presence of the surface plasmon signal in films containing silver. The films were tested in the photocatalytic degradation of Malachite Green dye reaching maximum degradations degrees close to 53% under solar irradiation. Reactive species trapping experiments suggest that O2 − produced by the O2 reduction via the photogenerated electrons drives the photodegradation mechanismCB-168827 CB-240998 F. Gonzalez-Zavala thanks to CONACyT for the PhD and Beca Mixta grants, and also to the SIEA-UAEM for the beca movilidad para estudios avanzados 2016. E. Rodríguez-Castellón thanks to project CTQ2015-68951-C3-3-R of Ministerio de Economía y Competitividad (Spain) and FEDER funds

Ag-modified vanadium oxide photocatalytic thin films deposited by a two parallel ablation plasmas configuration

Articulo de colaboracionThe application of a two ablation plasmas configuration to deposit vanadium oxide thin films modified with different amounts of silver is reported. In this configuration, two parallel plasmas are produced ablating simultaneously two different targets, V and Ag, to form the Ag-modified vanadium oxide thin films. The ablation of the vanadium target is performed under constant conditions in all deposits, while the silver produced plasma is varied. The effect of the amount of Ag incorporated in the films on their compositional, morphological, structural, and photocatalytic properties is studied. The results reveal that films with variable Ag content from 0.6 to 17.2 at. % are obtained. Depending on the silver content, the samples show very different surface morphologies from smooth surfaces to acicular structures in films containing Ag. Raman spectra reveal that as the silver content is increased different vanadium oxides coexist and at the highest Ag content a silver vanadate is formed. The photocatalytic activity for the degradation of the Malachite Green dye under simulated solar light is determined. It is found that in general terms, films containing silver show a higher photocatalytic response than V2O5 films aloneCONACYT project CB-24099

Deposition and Photocatalytic Activity of Ag:V2O5 Thin Films

In this work, the deposition and photocatalytic response of V2O5 thin films modified with different amounts of Ag (Ag:V2O5) is reported. Films were deposited on glass and silicon substrates (100), using the pulsed laser deposition (PLD) technique. A high purity vanadium target, with a different number of silver pellets attached on it were used. Thin films were characterized by energy dispersive spectroscopy (EDS) to determine the elemental chemical composition; structural changes due to the addition of Ag were monitored by Raman spectroscopy; Optical microscopy was used to observe the surface morphology and UV-Vis spectroscopy was employed to determine optical properties. Photocatalytic response of the prepared films was studied through the degradation of a malachite green solution using a solar irradiation source.Authors thank to the CONACyT project CB-168827

Thermoluminescent response of C-modified Al2O3 thin films deposited by parallel laser ablation plasmas

Aluminium oxide thin films modified with different amounts of carbon were prepared using a parallel laser ablation plasmas configuration. The effect of the amount of carbon incorporated in the films on their compositional, morphological, structural, and thermoluminescent properties was studied. The results showed that films with different C content, from 11 to 33 at. %, were obtained. The structural characterization revealed the growth of an amorphous material. Surface morphology of the obtained thin films showed smooth surfaces. The films were exposed to UV and gamma radiation (Co-60) in order to study their thermoluminescence response. The results tend to indicate that carbon incorporation into the alumina favours the increase of a high temperature TL peak.CONACyT CB 24099

Hydrogen production by laser irradiation of metals in water under an ultrasonic field: A novel approach

An alternative method for hydrogen production by laser irradiation of metals in water is proposed. Metals such as Ti, Al, Mg an Al–Mg alloy and Si, were laser ablated and subjected to an ultrasonic field simultaneously to promote a displacement chemical reaction of hydrogen from water. The produced gas was characterized by gas chromatography and mass spectrometry. Molecular hydrogen was found suggesting that this procedure allows the production of H 2 of high purity. All the studied metals under laser irradiation produced H 2 and the volume rise as the laser fluence was increased following a no-linear monotonic behavior with a similar tendency. Without ultrasound the amount of hydrogen was significantly reduced. An important advantage of the proposed H 2 production method is the low amount of mass consumed which lead to maximum hydrogen production rates close to 1300 ml/min per gr of aluminumThis work was partially supported by the CONACYT (Mexico) Projects CB-240998 and SENER-CONACYT 226151. The authors thank Arturo Olalde and Albina Gutierrez for their technical assistance

Antimicrobial and antioxidant properties of byproduct extracts of mango fruit

Byproducts of fruit processing could have higher content of phenolic compounds that can act as antimicrobial and antioxidant agents. In this context, the main objective of this study was to obtain extracts from peel, seed, and unused flesh of Haden, Ataulfo and Tommy Atkins mango varieties, in order to measure their antioxidant and antimicrobial properties. The extraction was performed using different methods, such as methanolic-polar, methanolic-non-polar, ethanolic-polar, ethanolic-non-polar and water infusion. The total phenolic content of the ethanolic-non-polar extract from seed of mango Haden showed 875.06 mg/g, DPPH EC50: 0.04 mg/mL, cau-sing a 100 % inhibition of bacteria pathogens applying 25 mg/mL and inhibition of 89.78 % against Alternaria applying 6.25 mg/mL. The flesh always showed the lowest content and bioactivity of the tested parameters. These results demonstrate the antimicrobial and antioxidant potential uses of fruit byproducts as sources of bioactive compounds

Antioxidant and Antimicrobial Capacity of Phenolic Compounds of Mango (Mangifera indica L.) Seed depending upon the Extraction Process

The extraction method is critical for the recovery of phenolic compounds. The main goal was to evaluate the effect of an extraction process from mango seed on their phenolic profile, antioxidant and antimicrobial capacities. Phenolic extraction was performed in different steps: maceration, alkaline hydrolysis, acid/alkaline hydrolysis, polar and non-polar fraction of an ethyl acetate separation.The macerated extract showed a higher variety of polyphenols from mango seed:gallic (138.36 µg/g dry weight), coumaric (65.36 µg/g), ferulic (1376.67 µg/g) , chlorogenic (57.75 µg/g) anddicaffeoylquinic (219.29 µg/g) acids, catechin (16.78 µg/g) and rutin (6678.62µg/g). In alkaline hydrolyzed extract most of these compounds were lost, ferulic acid decreased 1356.77 µg/g dw and gallic acid increased 1383.89 µg/g dw. Gallic and chlorogenic acids increased 165 and 969. 45 µg/g dw respectively in acid/alkaline hydrolyzed, 109.57 and 841.38 µg/g dw respectively in non-polar and 277.15 and 77.88 µg/g dw respectively in polar extracts related to the macerated extract. Rutin was found only in acid/hydrolyzed and non-polar extract in lesser amount (87.62 and 78.51 µg/g dw) compared to macerated extract. The content of phenolic compounds was higher for the macerated extract (phenols=484.42 mg GAE/g and flavonoids=86.59 mg QE/g) than for the other steps. Acid/alkaline hydrolysis increased the antioxidant activity (1787.67 μmol TE/g for DPPH and 3692.86 μmol TE/g for TEAC); while the alkaline hydrolysis increased the antimicrobial effectivity (MIC=2.5 mg/mL for bacteria and 0.5 mg/mL for yeast). Results indicate that the acid or alkaline hydrolysis yields a stronger antioxidant and antimicrobial extract

Improved functionalization of oleic acid-coated iron oxide nanoparticles for biomedical applications

Superparamagnetic iron oxide nanoparticles can providemultiple benefits for biomedical applications in aqueous environments such asmagnetic separation or magnetic resonance imaging. To increase the colloidal stability and allow subsequent reactions, the introduction of hydrophilic functional groups onto the particles’ surface is essential. During this process, the original coating is exchanged by preferably covalently bonded ligands such as trialkoxysilanes. The duration of the silane exchange reaction, which commonly takes more than 24 h, is an important drawback for this approach. In this paper, we present a novel method, which introduces ultrasonication as an energy source to dramatically accelerate this process, resulting in high-quality waterdispersible nanoparticles around 10 nmin size. To prove the generic character, different functional groups were introduced on the surface including polyethylene glycol chains, carboxylic acid, amine, and thiol groups. Their colloidal stability in various aqueous buffer solutions as well as human plasma and serum was investigated to allow implementation in biomedical and sensing applications.status: publishe