Showing papers by "Centro de Investigación y Desarrollo Tecnológico en Electroquímica published in 2017"

Silver Clusters in Zeolites: From Self-Assembly to Ground-Breaking Luminescent Properties

Abstract: ConspectusInterest for functional silver clusters (Ag-CLs) has rapidly grown over years due to large advances in the field of nanoscale fabrication and materials science. The continuous development of strategies to fabricate small-scale silver clusters, together with their interesting physicochemical properties (molecule-like discrete energy levels, for example), make them very attractive for a wide variety of applied research fields, from biotechnology and the environmental sciences to fundamental chemistry and physics. Apart from useful catalytic properties, silver clusters (Agn, n < 10) were recently shown to also exhibit exceptional optical properties. The optical properties and performance of Ag-CLs offer strong potential for their integration into appealing micro(nano)-optoelectronic devices. To date, however, the rational design and directed synthesis of Ag-CLs with specific functionalities has remained elusive.The inability for rational design stems mainly from a lack of understanding of their nov...

Glycerol electro-oxidation in alkaline media using Pt and Pd catalysts electrodeposited on three-dimensional porous carbon electrodes

Abstract: In this work, Pd and Pt electrocatalysts were electrodeposited on three-dimensional carbon paper and carbon nanofoam with the purpose of increasing the catalytic area to improve the glycerol electro-oxidation. SEM and cross-sectional SEM micrographs showed that Pd and Pt particles were well-distributed over the entire three-dimensional electrode surfaces. Commercial Pd/C and Pt/C catalysts deposited by the spray method were used for comparison, showing lower surface area (SA) utilization than those electrodeposited. The electrodeposition effectiveness to cover the electrode surfaces was evaluated by changes in overall SA and through the calculation of electrochemically active surface area (EASA) and specific surface area (SSA). Despite the larger EASA values found for Pd and Pt on nanofoam, Pt on paper showed the highest utilization of the surface area, obtaining an SSA of 58.1 m2 g−1. Moreover, the electrodeposition of Pd and Pt dramatically increased the EASA versus the geometrical area, improving this ratio 16 (Pd on paper), 151 (Pt on paper), 158 (Pd on nanofoam) and 277-fold (Pt on nanofoam). The electrodeposited porous Pt electrodes showed good activity for glycerol oxidation, exhibiting a more negative potential than Pd-based materials. However, for fuel cell applications operated at intermediate temperatures, Pd on carbon paper is the optimal candidate to be used as an anode because of its high current density and excellent poisoning tolerance.

Grapefruit peels as biosorbent: characterization and use in batch and fixed bed column for Cu(II) uptake from wastewater

Abstract: BACKGROUND A study of copper adsorption onto biosorbents prepared from grapefruit peels (GP) is presented. The objectives of the present analysis were 1) to evaluate the use of Instant Controlled Pressure Drop (DIC) as a treatment of biosorbents preparation, 2) to assay the modified biosorbents in fixed-bed columns, and 3) to elucidate an adsorption mechanism of the metal on the modified biosorbents. RESULTS Mercury intrusion porosimetry studies showed that the use of DIC increases the porosity of material 11.3. Adsorption capacity of GP biosorbents, indicate that those prepared using DIC process had an increase of 32% and by using a subsequent chemical treatment, an enhancement of 69%, compared with simple dried GP peel. In fixed bed adsorption studies, the maximum adsorption capacity of the bed and the minimum adsorbent rate were 52.48 mg g−1 and 24 g L−1, respectively. CONCLUSION According to the results from the adsorption and characterization studies performed by SEM-EDS, FTIR and XPS, it is proposed that the adsorption mechanism was a physisorption phenomenon, between oxygen-containing groups and Cu(II) from water. High adsorption capacity can be achieved in using modified GP peels in fixed-bed columns; therefore, it is feasible to use it as a non-conventional adsorbent.

Silver Zeolite Composites‐Based LEDs: A Novel Solid‐State Lighting Approach

Abstract: Silver clusters incorporated in a zeolite matrix represent a promising alternative for rare earth phosphors, organic dyes, and quantum dots as emitters in organic and hybrid organic/inorganic light-emitting diodes (OLEDs). Compared to other existing types of emitters, they combine an excellent stability to oxygen and humidity with a high luminescence quantum yield and color tunability. This study reports on the first use of these silver exchanged zeolites embedded in polyvinyl carbazole (PVK), which is expected to act as a conducting matrix, as emitters in a single-layer OLED. It is demonstrated that the introduction of these Ag zeolites leads to electroluminescence bands that clearly differ from pristine PVK OLEDs as well as from the photoluminescence spectra of the Ag zeolites. The current density and the spectral properties observed in these devices are strongly influenced by the zeolite silver loading, paving the way for a new type of easily tunable hybrid and cost-effective OLEDs.

Form Follows Function: Warming White LEDs Using Metal Cluster-Loaded Zeolites as Phosphors

Abstract: The recent development of light-emitting diodes (LEDs) using remote phosphors to generate white light has seen this family of devices become well-positioned to replace conventional lighting They offer higher efficiencies compared to traditional bulbs and do not contain toxic mercury, as with fluorescent lamps However, the color quality of the light emitted from commercial white LEDs, which is typically bluish, is not yet comparable to that of incandescent lamps In this Perspective, we discuss the potential application of luminescent metal clusters confined inside of zeolites as remote phosphors for designing warm white LEDs Such materials may not only improve the LEDs’ light quality but also help maintain device stability and efficiency, compared to other LED phosphors Moreover, in terms of optical properties and stability of metal-loaded zeolites, the necessary improvements and drawbacks are identified, and viable solutions—through rational design protocols—are outlined

Electrochemical Hydrogen Peroxide Production in Acidic Medium Using a Tubular Photo-reactor: Application in Advanced Oxidation Processes

Abstract: This paper describes the results obtained in the design and characterization of a tubular electrochemical reactor. The set-up was employed for on-site hydrogen peroxide (H2O2) production in an acidic medium (pH 3) to promote three electrochemical advanced oxi- dation processes (EAOP): electro-Fenton (EF), photoelectro-Fenton (PEF) and photocatalysis treatment (PT). These processes were evalu- ated by their abilities to degrade a commercial dye, Orange-II (OG- II), in solution using total organic carbon (TOC) removal and high performance liquid chromatography (HPLC). To have free solutions of iron in the EF and PEF systems, a Nafion membrane with dispersed iron was prepared. For use in photocatalysis, electrodes with a large superficial area were prepared by coating carbon cloth fiber supports with titanium dioxide (TiO2) using the electrophoretic (EP) method. In this work, wastewater samples with a large number of microorganisms (coliform bacteria) were treated with this new reactor design.

Water-Soluble Ruthenium (II) Chiral Heteroleptic Complexes with Amoebicidal in Vitro and in Vivo Activity.

Abstract: Three water-soluble Ru(II) chiral heteroleptic coordination compounds [Ru(en)(pdto)]Cl2 (1), [Ru(gly)(pdto)]Cl (2), and [Ru(acac)(pdto)]Cl (3), where pdto = 2,2′-[1,2-ethanediylbis-(sulfanediyl-2,1-ethanediyl)]dipyridine, en = ethylendiamine, gly = glycinate, and acac = acetylacetonate, have been synthezised and fully characterized. The crystal structures of compounds 1–3 are described. The IC50 values for compounds 1–3 are within nanomolar range (14, 12, and 6 nM, respectively). The cytotoxicity for human peripheral blood lymphocytes is extremely low (>100 μM). Selectivity indexes for Ru(II) compounds are in the range 700–1300. Trophozoites exposed to Ru(II) compounds die through an apoptotic pathway triggered by ROS production. The orally administration to infected mice induces a total elimination of the parasite charge in mice faeces 1–2-fold faster than metronidazole. Besides, all compounds inhibit the trophozoite proliferation in amoebic liver abscess induced in hamster. All our results lead us to pr...

Synthesis of a Small Amorphous PdMo/C Nanocatalyst and Pd Nanocubes Enclosed within (100) Planes and Their Use for Ethylene Glycol Electro–oxidation

Abstract: In this work, PdMo/C and Pd/C nanocubes were synthesized and used for the electro-oxidation of ethylene glycol. XRD patterns revealed that the Pd/C nanocubes had an average crystallite size of 10.9 nm, while the PdMo/C nanoparticles were amorphous. HRTEM images indicated the presence of only cubic-shaped nanoparticles for Pd/C nanocubes and semispherical nanoparticles for PdMo/C with sizes of 9 and 2 nm, respectively. XPS and line-scan EDX spectroscopy confirmed the presence of Pd and Mo in the PdMo/C nanocatalyst, and the Mo was determined to be incorporated with Pd in the form MoO3. The Pd/C nanocubes exhibited 9.3-fold higher current density than commercial Pd/C, demonstrating the superior activity of the (100) facet. The combined effects of the amorphous structure and the presence of molybdenum oxides enhanced the activity of PdMo/C, which demonstrated a 1.5-fold higher current density than the Pd/C nanocubes and a 12-fold higher density than commercial Pd/C.

Characterization and corrosion resistance of electroless black Ni-P coatings of double black layer on carbon steel

Abstract: In this work, the corrosion evaluation of a double black layer, by an acidic bath of double electroless Ni-P coatings, were conducted. A double black layer and a coarse sandblast finishing were intended for increasing the sunlight absorption and its anchoring. The surface preparation process comprises four stages: A) a Ni-P electroless coating, B) an acidic attack for a black layer formation, C) a second Ni-P electroless coating, and D) an acidic attack for a second black layer. The properties of the coating were investigated by X-ray diffraction, scanning electron microscopy, mechanical profilometry, confocal laser scanning microscopy and low-discharge optical emission spectroscopy. The results of these studies indicate that a double layer Ni-P coating with Rp and corrosion rate values of 1170 Ω cm2 and 0.4 mm/year were obtained, thereby exhibiting an increase in corrosion resistance compared to a one layer Ni-P coating. The GDOES profiles show two Ni-P coatings and two black layers intercalated through small variations of the percentage of nickel and phosphorus, which was associated with the interface between both layers.

Samarium Additive Effect onto the Nickel Electrodeposition Process

Abstract: In the present work, nickel-samarium coatings (Ni-Sm) with 1.88% of samarium were obtained by electrodeposition from a nickel electrolyte composed of (NH2HSO3, Ni(CO3)2 and H3BO3) and containing Sm2(SO4)3. The electroactivity intervals of each component of the electrolytic bath and the effect of samarium (III) on the nickel electroplating process were studied by cyclic voltammetry and by electrochemical impedance spectroscopy (EIS). The results indicate that H3BO3 and Sm2(SO4)3 added to the electrolytic bath are both reduced during the nickel electroplating. The Ni-Sm coatings were characterized using scanning electron microscopy (SEM), X-ray Diffraction (XRD), X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS). The results indicate that the samarium species incorporated in the nickel coatings are found as Sm(III) and Sm(II) hydroxides or oxides.

Reversible photochromic effect in the TiO2—polymer hybrid system

Abstract: The photochromism of poly methyl methacrylate–TiO2 composites have been investigated in this research. Amorphous titanium oxide was synthesized by sol–gel using titanium isopropoxide. The titanium solution was mixed with a dissolved polymer. The composite shows photo-response under UV radiation by changing, generally, to a dark brown tonality. This effect was reversible in different time ranges according to the intensity and exposure time. The mechanism for this photochromic change was proposed as a reduction of TiOOH domains to Ti3+ and not directly from amorphous TiO2, which provide electron-hole pairs after absorbing UV. The backscattered electrons image shows the clusters or domains of titanium compounds as white dots, ranging from 0.1 to 1 μm. The electron spin resonance spectroscopy signals indicated a titanium valence change from Ti(IV) to Ti(III). The X-ray photoelectron spectroscopy peaks positions for Ti 2p1/2 and Ti 2p3/2 were assigned as Ti4+. The values were obtained for Ti 2p3/2 and the identified species were Ti4+ and Ti3+, that correspond to TiO2, Ti2O3, and Ti(OOH). Few and small crystalline domains were identified by Transmission Electron Microscope as orthorhombic TiO2.’