Artículos SCI
2019
2019
Nanotecnología en Superficies y Plasma
Comparative studies on electrochemical energy storage of NiFe-S nanoflake and NiFe-OH towards aqueous supercapacitor
Naseri, M; Moradi, M; Hajati, S; Espinos, JP; Kiani, MAJournal of Materials Science-Materials in Electronics, 30 (2019) 4499-4510 DOI: 10.1007/s10854-019-00738-x
Abstract
In this study, electrochemical energy storage performances of an efficient Ni-Fe sulfide and hydroxide supported on porous nickel foam are compared. X-ray diffraction (XRD), X-rayphotoelectron spectroscopy (XPS) and energy-dispersive X-ray spectrometer (EDS) results confirmed the formation of Ni-Fe-S and Ni-Fe-OH electrodes. In addition, Brunauer-Emmett Teller (BET) was used to determine the specific surface area of the prepared materials. Moreover, the morphologies were observed by scanning electron microscopy (SEM). The brilliant characteristics of Ni-Fe-S could be attributed to transport acceleration in electrolyte ions and electrons, occurrence of redox reactions as well as the higher conductivity of the sample. From stand point of comparison, the capacitance of Ni-Fe-S is more than that of Ni-Fe-OH. Therefore, the exchange of O2- with S2- in Ni-Fe-OH lattice obviously improves the electrochemical performance. The as-fabricated Ni-Fe sulfide electrode exhibits a tremendous specific capacitance of 884.9Fg(-1) at 1A g(-1). Furthermore, an assembled asymmetric supercapacitor device using the activated carbon as negative electrode and this smart configuration (Ni-Fe-S) as positive electrode also provided a maximum specific power and specific energy of 8000Wkg(-1), 37.9 Whkg(-1), respectively. Also, it shows cycling stability with 88.8% capacitance retention after 1700 cycles in aqueous electrolyte, demonstrating its potential application in the next-generation high-performance supercapacitors used for energy storage.
Marzo, 2019 · DOI: 10.1007/s10854-019-00738-x
Nanotecnología en Superficies y Plasma
XPS primary excitation spectra of Zn 2p, Fe 2p, and Ce 3d from ZnO, α‐Fe2O3, and CeO2
Pauly, N.; Yubero, F.; Espinós, J.P.; Tougaard, S.Surface and Interface Analysis, 51 (2019) 353-360 DOI: 10.1002/sia.6587
Abstract
Metal oxides are important for current development in nanotechnology. X‐ray photoelectron spectroscopy(XPS) is a widely used technique to study the oxidation states of metals, and a basic understanding of the photoexcitation process is important to obtain the full information from XPS. We have studied core level excitations of Zn 2p, Fe 2p, and Ce 3d photoelectron emissions from ZnO, α‐Fe2O3, and CeO2. Using an effective energy‐differential XPS inelastic‐scattering cross section evaluated within the semiclassical dielectric response model for XPS, we analysed the experimental spectra to determine the corresponding primary excitation spectra, ie, the initial excitation processes. We find that simple emission (Zn 2p) as well as complex multiplet photoemission spectra (Fe 2p and Ce 3d) can be quantitatively analysed with our procedure. Moreover, for α‐Fe2O3, it is possible to use the software package CTM4XAS (Charge Transfer Multiplet program for X‐ray Absorption Spectroscopy) to calculate its primary excitation spectrum within a quantum mechanical model, and it was found to be in good agreement with the spectrum determined by analysis of the experiment.
Marzo, 2019 · DOI: 10.1002/sia.6587
Materiales de Diseño para la Energía y Medioambiente
Sustainable polycondensation of multifunctional fatty acids from tomato pomace agro-waste catalyzed by tin (II) 2-ethylhexanoate
J.A. Heredia-Guerrero, G. Caputo, S. Guzmán-Puyol, G. Tedeschi, A. Heredia, L. Ceseracciu, J.J. Benítez, A. AthanassiouMaterials Today Sustainability, 3-4 (2019) 100004 DOI: 10.1016/j.mtsust.2018.12.001
Abstract
Bioplastics were prepared from the fatty fraction (i.e., unsaturated and polyhydroxylated fatty acids) of tomato pomace agro-wastes. Aliphatic polyesters were synthesized at different temperatures (125, 150, and 175 °C), reaction times (0.25, 0.5, 0.75, 1, 3, 5, and 7 h), and amounts of tin (II) 2-ethylhexanoate (0, 0.02, 0.05, and 0.10 mmol) used as a catalyst. The rate constants and activation energies were calculated from infrared spectra. The right combination of reaction temperature and amount of catalyst improved the reaction kinetics (apparent k from ∼1 to ∼8.5 h−1), whereas the activation energy was reduced from ∼39 without catalyst to ∼28 kJ/mol when tin (II) 2-ethylhexanoate was present. Glass transitions between ca. −25 and ∼0 °C were measured by differential scanning calorimetry, strictly depending on the degree of polymerization. The amorphous character of the samples was confirmed by X-ray diffraction. Young's modulus and hardness were calculated from indentation tests and were typical of soft materials, although increased as the polycondensation reaction progressed. High water-contact angles (maximum value ∼109°) and low water uptakes (minimum value ∼2.1%) were determined. Physical properties were compared with those of common man-made plastics and polymers, finding that these tomato pomace bioplastics could be their realistic alternatives.
Marzo, 2019 · DOI: 10.1016/j.mtsust.2018.12.001
Reactividad de Sólidos - Tribología y Protección de Superficies
Microstructure, interfaces and properties of 3YTZP ceramic composites with 10 and 20 vol% different graphene-based nanostructures as fillers
Munoz-Ferreiro, C; Morales-Rodriguez, A; Rojas, TC; Jimenez-Pique, E; Lopez-Pernia, C; Poyato, R; Gallardo-Lopez, AJournal of Alloys and Compounds, 777 (2019) 213-224 DOI: 10.1016/j.jallcom.2018.10.336
Abstract
The graphene family comprises not only single layer graphene but also graphene-based nanomaterials (GBN), with remarkably different number of layers, lateral dimension and price. In this work, two of these GBN, namely graphene nanoplatelets (GNP) with n similar to 15-30 layers and few-layer graphene (FLG) with n < 3 layers have been evaluated as fillers in 3 mol% yttria stabilized tetragonal zirconia (3YTZP) ceramic composites. Composites with 10 and 20 vol% GNP or FLG have been fabricated by wet powder processing and spark plasma sintering (SPS) and the influence of the content and number of layers of the graphene-based filler has been assessed. For both graphene-based fillers, an intermediate zirconia oxycarbide has been detected in the grain boundaries. The lower stacking degree and much more homogeneous distribution of the FLG, revealed by transmission electron microscopy (TEM), can improve load transfer between the GBNs and the ceramic matrix. However, high FLG contents lower densification of the composites, due partly to the larger FLG interplanar spacing also estimated by TEM. The hardness (both Vickers and nanoindentation) and the elastic modulus decrease with increased GBN content and with improved graphene dispersion. The FLG greatly inhibit the crack propagation that occur perpendicular to their preferential orientation plane. The composites with thinner FLG have higher electrical conductivity than those with GNP. The highest electrical conductivity is achieved by composites with 20 vol% FLG in the direction perpendicular to the compression axis during sintering, sigma(perpendicular to) = 3400 +/- 500 Sm-1.
Marzo, 2019 · DOI: 10.1016/j.jallcom.2018.10.336
Degradation processes of historic metal threads used in some Spanish and Portuguese ornamentation pieces
Duran, A; Perez-Maqueda, R; Perez-Rodriguez, JLJournal of Cultural Heritage, 36 (2019) 135-142 DOI: 10.1016/j.culher.2018.09.006
Abstract
The degradation processes that occurred on metal threads applied in the embroidery used for clothing and in the ornamentation of sculptures, the Sevillian Holy Week processions, and Portuguese and Spanish palace and museum are thoroughly analyzed. Some threads from the 14th and 18–19th centuries were considered. In the metal threads, sulphur- and chlorine-based compounds were detected either individually or together, depending on the degradation process. Basic silver carbonate, sodium bicarbonate and copper-based compounds were also observed. The different degradation processes were attributed to different factors, such as environmental contamination, degradation of the fibrous cores, and inadequate cleaning and/or mechanical treatments.
Marzo, 2019 · DOI: 10.1016/j.culher.2018.09.006
Fotocatálisis Heterogénea: Aplicaciones
Synthesis of sol-gel pyrophyllite/TiO2 heterostructures: Effect of calcination temperature and methanol washing on photocatalytic activity
El Gaidoumi, A.; Doña Rodríguez, J.M.; Pulido Melián, E.; González-Díaz, O.M.; Navío Santos, J.M.; El Bali, B.; Kherbeche, A.Surfaces and Interfaces, 14 (2019) 19-25 DOI: 10.1016/j.surfin.2018.10.003
Abstract
We successfully synthesized an efficient photoactive pyrophyllite/TiO2 heterostructures using a sol-gel route at ambient temperature. The samples were prepared by exfoliation of a pyrophyllite layered-type clay by TiO2. The prepared samples exhibited strong photocatalytic activity for the degradation of phenol. The heterostructure PTi750 (SBET = 16.58 m2/g) calcined at 750 °C, in which the mixed phases of anatase and rutile exist (52.2% anatase/10.7% rutile), showed the highest photocatalytic activity against commercial TiO2Aeroxide P25. The methanol washed PTi750 was 5 times faster than the corresponding unwashed sample; phenol was totally degraded with a TOC reduction of 89.2%. The materials have been characterized by: X-ray diffraction (XRD), Diffuse reflectance UV–vis spectrophotometry (UV–Vis DRS), scanning electron microscopy (SEM) and BET specific surface area.
Marzo, 2019 · DOI: 10.1016/j.surfin.2018.10.003
Reactividad de Sólidos
Sample-Controlled analysis under high pressure for accelerated process studies
Perejon, A; Sanchez-Jimenez, PE; Soria-Hoyo, C; Valverde, JM; Criado, JM; Perez-Maqueda, LAJournal of the American Ceramic Society, 102 (2019) 1338-1346 DOI: 10.1111/jace.15960
Abstract
The potential of controlled rate thermal analysis (CRTA) for studying high-pressure gas-solid processes has been evaluated. CRTA is a type of smart temperature program based on a feedback system that uses any experimental signal related to the process evolution for commanding the temperature evolution. In this work, an instrument that uses the gravimetric signal for CRTA control has been designed and used for the study of two high-pressure gas-solid reactions: the highly exothermic thermal oxidation of TiC under high pressure of oxygen and the reduction in Fe2O3 under high pressure of hydrogen. Advantages of CRTA for discriminating overlapping processes and appraising kinetic reaction mechanisms are shown.
Marzo, 2019 · DOI: 10.1111/jace.15960
Reactividad de Sólidos
Anisotropic lattice expansion determined during flash sintering of BiFeO3 by in-situ energy-dispersive X-ray diffraction
Wassel, MAB; Perez-Maqueda, LA; Gil-Gonzalez, E; Charalambous, H; Perejon, A; Jha, SK; Okasinski, J; Tsakalakos, TScripta Materialia, 162 (2019) 286-291 DOI: 10.1016/j.scriptamat.2018.11.028
Abstract
BiFeO3 has a Curie temperature (T-c) of 825 degrees C, making it difficult to sinter using conventional methods while maintaining the purity of the material, as unavoidably secondary phases appear at temperatures above T-c Flash sintering is a relatively new technique that saves time and energy compared to other sintering methods. BiFeO3 was flash sintered at 500 degrees C to achieve 90% densification. In-situ energy dispersive X-ray diffraction (EDXRD) revealed that the material did not undergo any phase transformation, having been sintered well below the Tc. Interestingly, anisotropic lattice expansion in the material was observed when the sample was exposed to the electric field.
Marzo, 2019 · DOI: 10.1016/j.scriptamat.2018.11.028
Materiales Ópticos Multifuncionales
Tamm Plasmons Directionally Enhance Rare-Earth Nanophosphor Emission
Geng, DL; Cabello-Olmo, E; Lozano, G; Miguez, HACS Photonics, 6 (2019) 634-641 DOI: 10.1021/acsphotonics.8b01407
Abstract
Rare-earth-based phosphors are the materials on which current solid-state lighting technology is built. However, their large crystal size impedes the tuning, optimization, or manipulation of emitted light that can be achieved by their integration in nanophotonic architectures. Herein we demonstrate a hybrid plasmonic-photonic architecture capable of both channeling in a specific direction and enhancing by eight times the emission radiated by a macroscopically wide layer of nanophosphors. In order to do so, a slab of rare-earth-based nanocrystals is inserted between a dielectric multilayer and a metal film, following a rational design that optimizes the coupling of nanophosphor emission to collective modes sustained by the metal-dielectric system. Our approach is advantageous for the optimization of solid-state lighting systems.
Marzo, 2019 · DOI: 10.1021/acsphotonics.8b01407
Nanotecnología en Superficies y Plasma - Materiales Nanoestructurados y Microestructura
Test of a He-3 target for transfer reactions in inverse kinematics
Carozzi, G; Valiente-Dobon, JJ; Gadea, A; Siciliano, M; Mengoni, D; Fernandez, A; Godinho, V; Hufschmidt, D; Di Nitto, ANuovo cimento c-colloquia and communications in physics, 42 (2019) 94 DOI: 10.1393/ncc/i2019-19094-9
Abstract
With the aim of studying exotic nuclei close to the proton dripline, an innovative He-3 target was produced and tested in a collaboration between the Materials Science Institute of Seville (Spain) and the Legnaro National Laboratories (Italy). The target was manufactured with a new technique that aims to reduce the costs while providing high quality targets. The target was tested at the Legnaro National Laboratories. The results of this test are presented in this contribution.
Marzo, 2019 · DOI: 10.1393/ncc/i2019-19094-9
Nanotecnología en Superficies y Plasma
Growth of nanocolumnar thin films on patterned substrates at oblique angles
Garcia-Valenzuela, A; Munoz-Pina, S; Alcala, G; Alvarez, R; Lacroix, B; Santos, AJ; Cuevas-Maraver, J; Rico, V; Gago, R; Vazquez, L; Cotrino, J; Gonzalez-Elipe, AR; Palmero, APlasma Processes and Polymers, 16 (2019) e1800135 DOI: 10.1002/ppap.201800135
Abstract
The influence of one dimensional substrate patterns on the nanocolumnar growth of thin films deposited by magnetron sputtering at oblique angles is theoretically and experimentally studied. A well-established growth model has been used to study the interplay between the substrate topography and the thin film morphology. A critical thickness has been defined, below which the columnar growth is modulated by the substrate topography, while for thicknesses above, the impact of substrate features is progressively lost in two stages; first columns grown on taller features take over neighboring ones, and later the film morphology evolves independently of substrate features. These results have been experimentally tested by analyzing the nanocolumnar growth of SiO2 thin films on ion-induced patterned substrates.
Febrero, 2019 · DOI: 10.1002/ppap.201800135
Reactividad de Sólidos
Electrical properties of bismuth ferrites: Bi2Fe4O9 and Bi25FeO39
Perejon, A; Gil-Gonzalez, E; Sanchez-Jimenez, PE; West, AR; Perez-Maqueda, LAJournal of the European Ceramic Society, 39 (2019) 330-339 DOI: 10.1016/j.jeurceramsoc.2018.09.008
Abstract
Bi2Fe4O9 was prepared by solid-state reaction and the electrical properties measured by impedance spectroscopy. After annealing in O-2 at 900 degrees C, Bi2Fe4O9 is an electrically-homogeneous insulator. Its high frequency permittivity is constant (similar to 14.1) over the temperature range 300-400 degrees C and shows no evidence of incipient ferroelectricity at lower temperatures. On annealing in N-2 at 900 degrees C, the pellets gradually decompose.
Bi25FeO39 was prepared by both solid-state reaction and mechanosynthesis. It showed a modest amount of mixed conduction of both oxide ions and holes. Impedance analysis showed a complex response that best fitted an equivalent circuit consisting of a parallel combination of long-range conduction and short range dielectric relaxation elements.
The electrical conductivity of both Bi-2 Fe4O9 and Bi25FeO39 is less than that of BiFeO3 prepared by solid-state reaction, which indicates that any leakage conductivity of BiFeO3 is not due to the possible presence of small amounts of these secondary phases.
Febrero, 2019 · DOI: 10.1016/j.jeurceramsoc.2018.09.008
Reactividad de Sólidos
Synthesis of a cubic Ti(BCN) advanced ceramic by a solid-gas mechanochemical reaction
Chicardi, E; Garcia-Garrido, C; Beltran, AM; Sayagues, MJ; Gotor, FJCeramics International, 45 (2019) 3878-3885 DOI: 10.1016/j.ceramint.2018.11.060
Abstract
In this work, a titanium boron carbonitride advanced ceramic was successfully synthesised by a solid-gas mechanochemical reaction in a planetary ball mill from a mixture of elemental Ti, B, and C under nitrogen atmosphere. This material, with a general formula of Ti(BCN), exhibits a face-centred cubic structure (NaCl type) that is analogous to Ti(CN). This phase was gradually formed with sufficient milling time as a result of diffusional processes, which were permitted by the reduction of the energy in the system caused by the decrease in the spinning rate of the planetary ball mill. In contrast, under more energetic milling conditions, a mechanically induced self-sustaining reaction (MSR) took place, leading to the formation of a TiB2-Ti(CN) ceramic composite. The microstructural characterisation revealed that Ti(BCN) was composed of ceramic particles constituted of misoriented nanocrystalline domains. B, C and N were optimally distributed in the Ti(BCN) phase. The TiB2-Ti (CN) ceramic composite was composed of micrometric and nanometric particles homogeneously distributed. Additionally, the nitrogen content obtained for Ti(BCN) was higher than for the Ti(CN) phase in the composite material.
Febrero, 2019 · DOI: 10.1016/j.ceramint.2018.11.060
Materiales de Diseño para la Energía y Medioambiente
Eu3+ Luminescence in High Charge Mica: An In Situ Probe for the Encapsulation of Radioactive Waste in Geological Repositories
Martin-Rodriguez, R; Aguado, F; Alba, MD; Valiente, R; Perdigon, ACACS Applied Materials & Interfaces, 11 (4) (2019) 7559-7565 DOI: 10.1021/acsami.8b20030
Abstract
Isolation of high-level radioactive waste (HLW) in deep geological repositories (DGR) through a multibarrier concept is the most accepted approach to ensure long-term safety. Clay minerals are one of the most promising materials to be used as engineered barriers. In particular, high charge micas, as components of the engineered barrier, show superselectivity for some radioactive isotopes and a large adsorption capacity, which is almost twice that of the other low charge aluminosilicates. In addition, high charge micas are optimum candidates for decontamination of nuclear waste through two different mechanisms; namely an ion exchange reaction and a nonreversible mechanism involving the formation of new stable crystalline phases under hydrothermal conditions. In this work, we report a new in situ optical sensor based on the incorporation of Eu3+ in these high charge micas for tracking the long-term physical-chemical behavior of HLW contaminants in DRG under mild hydrothermal conditions. The incorporation of Eu3+ into the interlayer space of the mica originates a well resolved green and red luminescence, from both the 5D1 and 5D0 excited states, respectively. The formation of new crystalline phases under hydrothermal conditions involves important changes in the Eu3+ emission spectra and lifetime. The most interesting features of Eu3+ luminescence to be used as an optical sensor are (1) the presence or absence of the Eu3+ green emission from the 5D1 excited state, (2) the energy shift of the 5D0 → 7F0 transition, (3) the crystal-field splitting of the 7F1 Eu3+ level, and (4) the observed luminescence lifetimes, which are directly related to the interaction mechanisms between the lanthanide ions and the silicate network.
Febrero, 2019 · DOI: 10.1021/acsami.8b20030
Fotocatálisis Heterogénea: Aplicaciones
Mesoporous pyrophyllite–titania nanocomposites: synthesis and activity in phenol photocatalytic degradation
A. El Gaidoumi; J.M. Doña-Rodríguez; E. Pulido Melián; O.M. González-Díaz; B. El Bali; J.A. Navío; A. KherbecheResearch on Chemical Intermediates, 45 (2019) 333-353 DOI: 10.1007/s11164-018-3605-8
Abstract
Pyrophyllite–TiO2 nanocomposite PTi750 was successfully synthesized using a sol–gel method at ambient temperature based on exfoliation of the pyrophyllite layered clay by incorporation of the TiO2 precursor titanium(IV) t-butoxide. PTi750 exhibited higher photocatalytic activity in phenol degradation compared with commercial TiO2 Aeroxide P25. Ag-photodeposited PTi750 was more photoactive than PTi750, exhibiting detoxification, total degradation, and good mineralization of polluted solution and excellent stability after five reuses at optimal conditions in terms of the parameters pH, H2O2 concentration, and photocatalyst amount. The nanocomposites were investigated using several techniques, viz. diffuse-reflectance ultraviolet–visible (UV–Vis) spectrophotometry, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction analysis, X-ray fluorescence spectroscopy, Fourier-transform infrared spectroscopy, and Brunauer–Emmett–Teller (BET) specific surface area measurements.
Febrero, 2019 · DOI: 10.1007/s11164-018-3605-8
Reactividad de Sólidos
Tailoring the Band Gap in the ZnS/ZnSe System: Solid Solutions by a Mechanically Induced Self-Sustaining Reaction
Aviles, MA; Cordoba, JM; Sayagues, MJ; Gotor, FJInorganic Chemistry, 58 (2019) 2565-2575 DOI: 10.1021/acs.inorgchem.8b03183
Abstract
The complete ZnSxSe1-x solid solution was successfully obtained by the mechanochemical process denoted as a mechanically induced self-sustaining reaction. Excellent control of the chemical stoichiometry of the solid solution was possible by adjusting the atomic ratio of the starting Zn/S/Se elemental mixture subjected to milling. A mixture of both wurtzite-2H (hexagonal) and zinc blende (cubic) structures was always obtained, although for a similar milling time the proportion of the zinc blende structure increased with the Se content in the solid solution. However, wurtzite was the major phase for S-rich compositions when milling was stopped just after ignition. It was demonstrated that milling induces the wurtzite-to-zinc blende phase transition. The 8H hexagonal polytype was also observed in samples subjected to long milling times. Variation of the lattice parameters for both structures with the x value in the solid solution presented an excellent linearity, confirming the validity of Vegard's law. However, variation of the band-gap energy (E-g) with x was not perfectly linear, and a small bowing parameter of 0.34 was obtained. It was possible to tune the E-g value between those of the end members of the solid solution in a continuous manner by adjusting the stoichiometry of the solid solution. The morphology and crystalline domain size can also be controlled by adjusting, in this case, the postignition milling time of the mechanochemical process.
Febrero, 2019 · DOI: 10.1021/acs.inorgchem.8b03183
Fotocatálisis Heterogénea: Aplicaciones
Photodegradation of 2,4-dichlorophenoxyacetic acid over TiO2(B)/anatase nanobelts and Au-TiO2(B)/anatase nanobelts
Chenchana, A.; Nemamcha, A.; Moumeni, H.; Doña Rodríguez, J.M.; Araña, J.; Navío, J.A.; González Díaz, O.; Pulido Melián, E.Applied Surface Science, 467-468 (2019) 1076-1087 DOI: 10.1016/j.apsusc.2018.10.175
Abstract
In this work, novel TiO2-based nanobelts with various phases were synthesized: biphasic TiO2(B)/anatase, pure TiO2(B) and pure anatase. These catalysts were obtained via hydrothermal reaction using two nanoparticulated TiO2 photocatalysts as precursors: Aeroxide TiO2 P25 (P25) and TiO2 synthesized via a sol-gel process (SG). In addition, the surface of the photocatalysts was modified with gold using a photodeposition method. A characterization study of the different photocatalysts was performed with X-ray diffraction analysis (XRD), UV–Vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), X-ray photoelectron spectrum analysis (XPS) and Brunauer-Emmett-Teller measurements (BET). The photocatalytic reaction of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated under UVA irradiation. A toxicity analysis was performed with the marine bioluminescent bacteria Vibrio fischeri. The highest 2,4-D removal efficiency of 99.2% was obtained with the biphasic Au-TiO2(TiO2(B)/anatase) nanobelts with anatase as predominant phase. Toxicity was mainly due to the intermediate 2,4-dichlorophenol (2,4-DCP) which was eliminated in 4 h. The TiO2 nanobelt phase structure is shown to have a significant effect on photocatalytic activity.
Febrero, 2019 · DOI: 10.1016/j.apsusc.2018.10.175
Nanotecnología en Superficies y Plasma
Study of the Interface of the Early Stages of Growth under Quasi-Equilibrium Conditions of ZnO on Graphene/Cu and Graphite
Morales, C; Black, A; Urbanos, FJ; Granados, D; Mendez, J; del Campo, A; Yubero, F; Soriano, LAdvanced Materials Interfaces, 6 (2019) art. 1801689 DOI: 10.1002/admi.201801689
Abstract
The study of the early stages of growth of ZnO on graphene supported on Cu and on highly oriented pyrolytic graphite by means of reactive thermal evaporation of metallic Zn at room temperature is presented. This growth method allows to go in depth in the study of the fundamental interaction between ZnO and graphene at the interface in quasi-equilibrium conditions. Quantitative, chemical, and morphological analysis is performed using photoemission spectroscopy, atomic force, and scanning microscopies as experimental characterization techniques and factor analysis and inelastic peak shape analysis as modeling techniques. The growth of ZnO on a highly oriented pyrolytic graphite substrate is also studied using the same growth method for comparison. The results show that, in spite that the first atomic layer of both substrates is identical, the growth kinetics and morphology of the deposits are completely different. A model for the kinetics of the growth of ZnO on both substrates is proposed.
Febrero, 2019 · DOI: 10.1002/admi.201801689
Reactividad de Sólidos
Mechanochemical combustion synthesis of vanadium carbide (VC), niobium carbide (NbC) and tantalum carbide (TaC) nanoparticles
Jalaly, M; Gotor, FJ; Sayagues, MJInternational Journal of Refractory Metals & Hard Materials, 79 (2019) 177-184 DOI: 10.1016/j.ijrmhm.2018.12.011
Abstract
The nanoparticles of vanadium, niobium, and tantalum carbides were synthesized by a mechanically induced magnesiothermic combustion in the separate Mg/V2O5/C, Mg/Nb2O5/C, and Mg/Ta2O5/C systems. Initial materials in these systems ignited after short milling times of 10, 10, and 23 min, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM) and elemental mapping techniques were employed to characterize the combustion products. In this process, magnesium reduces initial oxides to generate elemental V/Nb/Ta to react with carbon, forming the carbide phases.
Febrero, 2019 · DOI: 10.1016/j.ijrmhm.2018.12.011
Reactividad de Sólidos
Multicycle CO2 capture activity and fluidizability of Al-based synthesized CaO sorbents
Azimi, B; Tahmasebpoor, M; Sanchez-Jimenez, PE; Perejon, A; Valverde, JMChemical Engineering Journal, 358 (2019) 679-690 DOI: 10.1016/j.cej.2018.10.061
Abstract
CaO-based materials have been identified as promising sorbents for highly efficient pre-combustion and post-combustion CO2 capture in fluidized beds operated at high temperatures by means of the Calcium Looping (CaL) process. However, Ca-based sorbents suffer from a decline of the capture capacity over multiple sorption/desorption cycles, mainly due to sintering, and from a markedly heterogeneous fluidization behavior due to the strength of interparticle attractive forces as compared to particle weight. The present study is focused on the development of novel synthetic CaO/Al2O3 sorbents for CO2capture with enhanced CaL performance and fluidizability by dry mixing with flow conditioner nanopowders. The influence of initial precursors on the sorbents multicycle activity at realistic CaL conditions has been investigated. The formation of a stable Ca9Al6O18 mixed-phase during the preparation of the sorbents promotes the multicycle capture capacity. The type of Ca and Al precursors, either soluble or insoluble, can significantly affect the dispersion of this stabilizer (Ca9Al6O18) in the sorbent matrix and, consequently, may affect the carbonation activity of the materials. The sorbent prepared from soluble aluminum nitrate and calcium nitrate precursors by sol-gel method exhibits a very stable multicycle capture capacity with a capture capacity around 0.2 g of CO2/g of sorbent after 21 cycles keeping a 72% of its initial capture capacity. The fluidizability of this promising sorbent was also investigated as affected by the addition of three different flow conditioners. Fluidization experiments confirmed the positive effect of using hydrophilic alumina and hydrophobic silica nanoparticles on improving the fluidizability of the synthesized sorbents.
Febrero, 2019 · DOI: 10.1016/j.cej.2018.10.061
Química de Superficies y Catálisis
Immobilization of Stabilized Gold Nanoparticles on Various Ceria-Based Oxides: Influence of the Protecting Agent on the Glucose Oxidation Reaction
Chenouf, M; Megias-Sayago, C; Ammari, F; Ivanova, S; Centeno, MA; Odriozola, JACatalysts, 9 (2019) 125 DOI: 10.3390/catal9020125
Abstract
The influence of the protecting agent's nature on gold particle size and dispersion was studied in this work over a series of gold-based catalysts. CO and glucose oxidation were chosen as catalytic reactions to determine the catalyst's structure-activity relationship. The nature of the support appeared to be the predominant factor for the increase in activity, as the oxygen mobility was decisive for the CO oxidation in the same way that the Lewis acidity was decisive for the glucose oxidation. For the same catalyst composition, the use of montmorillonite as the stabilizing agent resulted in better catalytic performance.
Febrero, 2019 · DOI: 10.3390/catal9020125
Fotocatálisis Heterogénea: Aplicaciones
Catalytic Efficiency of Cu-Supported Pyrophyllite in Heterogeneous Catalytic Oxidation of Phenol
El Gaidoumi, A.; Doña-Rodríguez, J.M.; Pulido Melián, E.; González-Díaz, O.M.; Navío, J.A.; El Bali, B.; Kherbeche, A.Arabian Journal for Science and Engineering, (2019) 1-13 DOI: 10.1007/s13369-019-03757-2
Abstract
The copper-impregnated pyrophyllite (Cu/RC) was prepared and used as catalyst in catalytic wet peroxide oxidation (CWPO) of phenol. The catalyst was prepared by impregnation of copper (2.5 wt%) into pyrophyllite-type clay and characterized by X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. The optimum operation conditions for CWPO of phenol over Cu/RC were determined by investigating the effects of pH, temperature, catalyst amount, and hydrogen peroxide concentration. Stability of the Cu/RC catalyst and toxicity of treated solution were studied, by measuring the copper concentration leached out from the catalyst and the inhibition of Vibrio fischeri bacteria bioluminescence, respectively. The probable degradation mechanism of phenol over Cu/RC was considered by HPLC analysis. The obtained results showed that Cu/RC achieved highest activity (total phenol degradation and 80% TOC reduction) and detoxification with remarkable low copper leaching concentration (0.006 mg\,L−1)mg\,L−1) at optimized conditions (pH == 3, T=50∘T=50∘C, 2 g\,L−1g\,L−1 catalyst amount, 50 mg L−1L−1phenol concentration and 7.45 mmol\,L−1mmol\,L−1 hydrogen peroxide concentration during 4 h). Meanwhile, few intermediates with low concentration were observed by the HPLC analysis for the CWPO of phenol. The Cu/RC catalyst showed a good activity after five successive runs (88% of degradation and 73% mineralization) at optimized conditions.
Febrero, 2019 · DOI: 10.1007/s13369-019-03757-2
Nanotecnología en Superficies y Plasma
Environmentally Tight TiO2-SiO2 Porous 1D-Photonic Structures
Garcia-Valenzuela, A; Lopez-Santos, C; Rico, V; Alvarez, R; Palmero, A; Gonzalez-Elipe, ARAdvanced Materials Interfaces, 6 (2019) art. 1801212 DOI: 10.1002/admi.201801212
Abstract
Although thin film porosity is the basis of many optical sensors, it can be deleterious for a stable optical behavior of passive optical elements due to the condensation of water and other vapors in their pores. This paper proposes a new strategy for the magnetron sputtering (MS) fabrication of environmentally tight SiO2-TiO2 porous multilayers. Thin films of these two oxides deposited in an oblique angle configuration (MS-OAD) present a nanocolumnar and highly porous nanostructure and, as a consequence, experience significant changes in their optical properties when exposed to water vapor. Similarly, the optical properties of Bragg reflectors and Bragg microcavities made of the stacking of porous and compact SiO2 and TiO2 thin films experience reversible changes when these 1D-photonic structures are exposed to water pressure. A key finding of this work is that a very thin capping layer of SiO2 deposited on the surface of porous SiO2 films in the stack, at the interlayer between the two oxides, efficiently seals the pores making the photonic structures environmentally tight. This capping layer approach is a useful strategy to incorporate porosity as an additional parameter to design the optical behavior of planar photonic structures while preserving optical and environmental stability.
Febrero, 2019 · DOI: 10.1002/admi.201801212
Amber, beads and social interaction in the Late Prehistory of the Iberian Peninsula: an update
Odriozola, CP; Sousa, AC; Mataloto, R; Boaventura, R; Andrade, M; Garcia, RV; Garrido-Cordero, JA; Rodriguez, E; Martinez-Blanes, JM; Aviles, MA; Daura, J; Sanz, M; Riquelme, JAArchaeological and Anthropological Sciences, 11 (2019) 567-595 DOI: 10.1007/s12520-017-0549-7
Abstract
The identification of archaeological amber has been used in Iberian prehistory to evidence long-distance exchanges and engage Iberia in networks that connect western Europe with central and northern Europe, the emergence of social complexity, and the consolidation of trade networks. However, until now, no comprehensive analytical study of the Iberian amber has been produced to support any of the interpretive models currently in use. This paper approaches the analysis of Iberian Peninsula amber artefacts by considering their provenance (based on FTIR characterization), chronology, and spatial relationship with other exotica. Our work increases the number of analyzed artefacts to 156 (24%), out of the c. 647 currently known for the Iberian Peninsula. Based on these new data and a review of Murillo-Barroso and Martinon-Torres (2012), this overview outlines amber consumption patterns from the 6th to 2nd millennia BCE and demonstrates long-distance amber exchange connecting Iberia with the Mediterranean region from the Neolithic period onwards.
Febrero, 2019 · DOI: 10.1007/s12520-017-0549-7
Reactividad de Sólidos
Insight into the BiFeO3 flash sintering process by in-situ energy dispersive X-ray diffraction (ED-XRD)
Perez-Maqueda, LA; Gil-Gonzalez, E; Wassel, MA; Jha, SK; Perejon, A; Charalambous, H; Okasinski, J; Sanchez-Jimenez, PE; Tsakalakos, TCeramics International, 45 (2019) 2828-2834 DOI: 10.1016/j.ceramint.2018.07.293
Abstract
The sintering mechanism of BiFeO3 has been investigated in-situ by energy dispersive X-ray diffraction (ED-XRD) using a high-energy white collimated X-ray beam from the Advanced Photon Source (Argonne National Laboratories). Such radiation is very penetrating thereby allowing measurements of the sample even when placed inside the flash sintering set up. Additionally, the fast ED-XRD measurements permit monitoring the flash sintering process by providing information about phase composition and sample temperature in real time. Moreover, profile scans, obtained by moving the stage vertically while recording the ED-XRD spectra, permit investigating the homogeneity of the flash for the entire length of the sample. All experiments have been complemented by ex-situ studies. It has been concluded that flash sintering of BiFeO3 is a homogeneous process without any directionality effects. Furthermore, flash sintering takes place at quite low temperatures (below the Tc ≈ 830 °C), which may be related to the high quality of the samples, as pure, highly insulating ceramics without evidence of secondary phases with a homogenous nanostructured grain size distribution are obtained by this technique. Moreover, it is also evidenced that the rapid heating of the sample does not seem to justify, at least by itself, the densification process. Therefore, it appears that the electric current should play a role in the enhanced mobility during the sintering process.
Febrero, 2019 · DOI: 10.1016/j.ceramint.2018.07.293
Reactividad de Sólidos
Production of Ag-ZnO powders by hot mechanochemical processing
Guzman, D; Aguilar, C; Rojas, P; Criado, JM; Dianez, MJ; Espinoza, R; Guzman, A; Martinez, CTransactions of nonferrous metals society of China, 29 (2019) 365-373 DOI: 10.1016/S1003-6326(19)64946-0
Abstract
Ag-CdO composites are still one of the most commonly used electrical contact materials in low-voltage applications owing to their excellent electrical and mechanical properties. Nevertheless, considering the restriction on using Cd due to its toxicity, it is necessary to find alternative materials that can replace these composites. In this study, the synthesis of Ag-ZnO alloys from Ag-Zn solid solutions was investigated by hot mechanochemical processing. The hot mechanochemical processing was conducted in a modified attritor mill at 138 degrees C under flowing O-2 at 1200 cm(3)/min for 3.0 h. The microstructure and phase evolution were investigated using X-ray diffractometry, field emission gun scanning electron microscopy and transmission electron microscopy. The results suggest that it is possible to complete the oxidation of Ag-Zn solid solution by hot mechanochemical processing at a low temperature and short time. This novel synthesis route can produce Ag-ZnO composites with a homogeneous distribution of nanoscale ZnO precipitates, which is impossible to achieve using the conventional material processing methods. Considering the fact that the fundamental approach to improving electric contact material performance resides in obtaining uniform dispersion of the second-phase in the Ag matrix, this new processing route could open the possibility for Ag-ZnO composites to replace non-environmentally friendly Ag-CdO.
Febrero, 2019 · DOI: 10.1016/S1003-6326(19)64946-0
Fotocatálisis Heterogénea: Aplicaciones
Fluorinated and Platinized Titania as Effective Materials in the Photocatalytic Treatment of Dyestuffs and Stained Wastewater Coming from Handicrafts Factories
Murcia, J.J.; Cely, A.C.; Rojas, H.A.; Hidalgo, M.C.; Navío, J.A.Catalysts, 9 (2019) 179 DOI: 10.3390/catal9020179
Abstract
In this study, commercial and lab-prepared TiO2 were modified by fluorination and platinum photodeposition; and the effect of these modifications over the physicochemical and photocatalytic properties of TiO2 was evaluated. It was found that F and Pt addition leads to the modification of the optical and textural properties of TiO2. The materials prepared were tested in the photocatalytic degradation of different organic dyestuffs such as methylene blue (MB) and methyl orange (MO); the degradation of commercial anilines employed in the staining of natural fibers was also evaluated. Photocatalysis was also studied in this work as an eco-friendly treatment of wastewater coming from handicrafts factories. In general it was observed that the effectiveness of the photocatalytic treatment strongly depends on the substrate to be degraded, thus, fluorinated and platinized commercial Titania (Pt-F-P25) showed the best photocatalytic performance in the MB and MO photodegradation and in contrast, in the case of the anilines the highest degradation was obtained over commercial TiO2 fluorinated (F-P25). These results can be explained by differences observed in the structure and in the adsorption of these dyestuffs over the photocatalysts surfaces. F-P25 photocatalyst also demonstrated to be the best material for the treatment of real wastewater coming from handicrafts factories.
Febrero, 2019 · DOI: 10.3390/catal9020179
Materiales Ópticos Multifuncionales
Mechanism of Photoluminescence Intermittency in Organic-Inorganic Perovskite Nanocrystals
Galisteo-Lopez, JF; Calvo, ME; Rojas, TC; Miguez, HACS Applied Materials & Interfaces, 11 (4) (2019) 6344-6349 DOI: 10.1021/acsami.8b17122
Abstract
Lead halide perovskite nanocrystals have demonstrated their potential as active materials for optoelectronic applications over the past few years. Nevertheless, one issue that hampers their applicability has to do with the observation of photoluminescence intermittency, commonly referred to as "blinking", as in their inorganic counterparts. Such behavior, reported for structures well above the quantum confinement regime, has been discussed to be strongly related to the presence of charge carrier traps. In this work, we analyze the characteristics of this intermittency and explore the dependence on the surrounding atmosphere, showing evidence for the critical role played by the presence of oxygen. We discuss a possible mechanism in which a constant creation/annihilation of halide-related carrier traps takes place under light irradiation, with the dominant rate being determined by the atmosphere.
Febrero, 2019 · DOI: 10.1021/acsami.8b17122
Nanotecnología en Superficies y Plasma
An innovative approach for micro/nano structuring plasma polymer films
Thiry, D; Vinx, N; Aparicio, FJ; Moerman, D; Lazzaroni, R; Cossement, D; Snyders, RThin Solid Films, 672 (2019) 26-32 DOI: 10.1016/j.tsf.2018.12.050
Abstract
This work aims at presenting an innovative method for tailoring the morphology of functionalized plasma polymer films (PPF). The approach is based on the formation of a plasma polymer bilayer system in which the two layers differ by their chemical composition and cross-linking degree. As a case study, propanethiol-based plasma polymer films have been investigated. As revealed by a much higher S/C ratio than in the propanethiol precursor (i.e. 0.83 vs 0.33), it has been demonstrated that the bottom layer contains a large fraction of trapped sulfur-based molecules (e.g. H2S). When further covered by a denser PPF formed at higher energetic conditions, a three-dimensional morphological reorganization takes place giving rise to the micro/nano structuration of the organic material. The shape, the dimensions as well as the density of the generated structures are found to depend on the thickness of both coatings involved in the bilayer structure, offering a great flexibility for surface engineering. Annealing experiments unambiguously confirm the major role played by the sulfur-based trapped molecules for inducing the reshaping process. The whole set of data clearly paves the way for the development of an innovative approach for finely tailoring the morphology of functionalized PPF at the micro/nano scale.
Febrero, 2019 · DOI: 10.1016/j.tsf.2018.12.050
Nanotecnología en Superficies y Plasma
Holmium doped fiber thermal sensing based on an optofluidic Fabry-Perot microresonator
Lahoz, F; Martin, IR; Soler-Carracedo, K; Caceres, JM; Gil-Rostra, J; Yubero, FJournal of Luminescence, 206 (2019) 492-497 DOI: 10.1016/j.jlumin.2018.10.103
Abstract
An optical temperature sensor suitable for label free liquid sensing has been designed and characterized. The sensor combines the photochemical stability of rare earth doped glasses and the high sensitivity of interferometric resonators. It is formed by a planar Eabry-Perot (FP) microcavity filled with the liquid to be monitored. A Ho3+ doped tapered optical fiber has been placed inside the microcavity surrounded by the fluid medium. An external laser is focused on the optical fiber inside the cavity to induce the luminescence of the Ho3+ ions, which couples to the FP optical resonances. The spectral position of the FP resonances is highly sensitive to the refractive index of the cavity medium. A second laser is co-aligned with the first one to locally heat the liquid medium around the optical fiber. An average blue shift of the FP resonances around 32 pm/degrees C is measured. The limit of detection of the laser induced heating of the liquid medium is about 0.3 degrees C in the biological temperature range. Alternatively, a hot-plate is used to heat the system. Interestingly, a red shift of the FP modes is observed with 75 pm/degrees C dependence and 0.12 degrees C limit of detection features.
Febrero, 2019 · DOI: 10.1016/j.jlumin.2018.10.103
Química de Superficies y Catálisis
Does shaping catalysts modify active phase sites? A comprehensive in situ FTIR spectroscopic study on the performance of a model Ru/Al2O3 catalyst for the CO methanation
Bobadilla, LF; Munoz-Murillo, A; Laguna, OH; Centeno, MA; Odriozola, JAChemical Engineering Journal, 357 (2019) 248-257 DOI: 10.1016/j.cej.2018.09.166
Abstract
Routinely, it seems assumed that the catalytic layer coated on monoliths and microchannel reactors preserve the properties of the initial powder catalyst. However, this assumption should be reasonably demonstrated since the set of chemical and physical manipulations involved in the preparation of these catalytic devices hardly does not alter the surface of the starting catalyst powders. This work aims to evaluate the transformations that takes place in a model Ru/Al2O3 catalyst during a typical slurry preparation procedure and their impact on the catalytic performance for the CO methanation reaction and the selective methanation of CO in CO2-rich reformate gases. For this purpose, we have conducted an in situ comprehensive study by means of Fourier Transform Infrared Spectroscopy (FTIR) in which the nature of the species present on the surface of the catalyst during CO hydrogenation was analyzed. This study reveals that during the preparation of the slurry the starting Ru/Al2O3 catalyst suffers a redispersion of metallic Ru particles and more surface hydroxyls are created by the incorporation of additional alumina. These modifications have a noticeable influence in the catalytic performance and despite their importance, these aspects have been poorly considered in other studies.
Febrero, 2019 · DOI: 10.1016/j.cej.2018.09.166
Fotocatálisis Heterogénea: Aplicaciones
Urban wastewater treatment by using Ag/ZnO and Pt/TiO2 photocatalysts
J.J. Murcia, L.G. Arias Bolivar, H.A. Rojas Sarmiento, E.G. Ávila Martínez, C. Jaramillo Páez, M.A. Lara, J.A. Navío Santos, M.C. Hidalgo LópezEnvironmental Science and Pollution Research (2018) 1-9 DOI: 10.1007/s11356-018-1592-3
Abstract
In this study, the treatment of wastewater coming from a river highly polluted with domestic and industrial effluents was evaluated. For this purpose, series of photocatalysts obtained by ZnO and TiO2 modification were evaluated. The effect of metal addition and Ti precursor (in the case of the titania series) over the physicochemical and photocatalytic properties of the materials obtained was also analyzed. The evaluation of the photocatalytic activity showed that semiconductor modification and precursor used in the materials synthesis are important factors influencing the physicochemical and therefore the photocatalytic properties of the materials obtained. The water samples analyzed in the present work were taken from a highly polluted river, and it was found that the effectiveness of the photocatalytic treatment increases when the reaction time increases and for both, wastewater samples and isolated Escherichia coli strain follow the next order Pt/TiO2 << ZnO. It was also observed that biochemical and chemical demand oxygen and turbidity significantly decrease after treatment, thus indicating that photocatalysis is a non-selective technology, which can lead to recover wastewater containing different pollutants.
Febrero, 2019 · DOI: 10.1007/s11356-018-1592-3
Reactividad de Sólidos
High-performance and low-cost macroporous calcium oxide based materials for thermochemical energy storage in concentrated solar power plants
Jimenez, PES; Perejon, A; Guerrero, MB; Valverde, JM; Ortiz, C; Maqueda, LAPApplied Energy, 235 (2019) 543-552 DOI: 10.1016/j.apenergy.2018.10.131
Abstract
High energy density, cycling stability, low cost and scalability are the main features required for thermochemical energy storage systems to achieve a feasible integration in Concentrating Solar Power plants (CSP). While no system has been found to fully satisfy all these requirements, the reversible CaO/CaCO3 carbonation reaction (CaL) is one of the most promising since CaO natural precursors are affordable and earth-abundant. However, CaO particles progressively deactivate due to sintering-induced morphological changes during repeated carbonation and calcinations cycles. In this work, we have prepared acicular calcium and magnesium acetate precursors using a simple, cost-effective and easily scalable technique that requires just the natural minerals and acetic acid, thereby avoiding expensive reactants and environmentally unfriendly solvents. Upon thermal decomposition, these precursors yield a stable porous structure comprised of well dispersed MgO nanoparticles coating the CaO/CaCO3 grains that is resistant to pore-plugging and sintering while at the same time exhibits high long term effective conversion. Process simulations show that the employment of these materials could significantly improve the overall CSP-CaL efficiency at the industrial level.
Febrero, 2019 · DOI: 10.1016/j.apenergy.2018.10.131
Reactividad de Sólidos
Effects of the speed ratio on the efficiency of planetary mills
Real, C; Gotor FJHeliyon, 5 (2019) e01227 DOI: 10.1016/j.heliyon.2019.e01227
Abstract
The ignition time (tig) of the mechanically induced self-sustaining reaction (MSR) process involving the formation of TiB2 from Ti/2B elemental mixtures was used to study the influence of the ratio (k = -ωv/ωd) between the rotational speed of the supporting disc (ωd) and vials (ωv) on the milling efficiency of a Pulverisette 4 planetary mill. The variation of the inverse of the ignition time (1/tig), which is directly related to the milling power provided by the planetary mill, with the process conditions has shown that it is not possible to find a single k value as optimal independently of the experimental conditions used (ωd and the ball-to-powder ratio, BPR). Moreover, it was observed that the lowest milling efficiency (longer tig values) was found for k = 1, which is the usual value employed in routine laboratory works. The best efficiencies were found for the larger k values (2.5 or 3). At lower ωd, the shortest tig was obtained for k = 2.5 and at higher ωd for k = 3, independently of BPR.
Febrero, 2019 · DOI: 10.1016/j.heliyon.2019.e01227
Fotocatálisis Heterogénea: Aplicaciones
Coupling of Ag2CO3 to an optimized ZnO photocatalyst: Advantages vs. disadvantages
P. Sánchez-Cid; C. Jaramillo-Páez; J.A. Navío; A.N. Martín-Gómez; M.C. HidalgoJournal of Photochemistry and Photobiology A: Chemistry, 369 (2019) 119-132 DOI: 10.1016/j.jphotochem.2018.10.024
Abstract
With the aim of improving the photocatalytic properties of a previously optimized zinc oxide photocatalyst, the effect of the incorporation of different amounts of Ag2CO3 on the aforementioned ZnO has been studied. For this purpose we report the synthesis, by means of simple precipitation procedures, of bare ZnO and Ag2CO3 samples as well as the coupled materials ZnO/Ag2CO3 (X) (where X = 1%, 2%, 4% and 5% in molar percentages). Both, single and coupled materials have been characterized by different techniques (XRD, XRF, N2-absorption, SEM, TEM, UV–vis/DRS and XPS). To assess the advantages or disadvantages that Ag2CO3 addition could have over the optimized ZnO, the photocatalytic properties have been established by following the photo-degradation of selected toxic molecules, both in the UV and in the visible, as well as using complementary techniques of liquid medium analyses (TOC and Atomic Emission Spectrometry with plasma ICP). Three selected substrates were chosen: Rhodamine B (RhB) as a dye, and phenol and caffeine as colourless recalcitrant toxic molecules.
Our results suggest that although the use of Ag2CO3 could be beneficial to implement the optical absorption towards the visible region, however, other effects have to be bore in mind, such as the photo-corrosion of Ag2CO3 and the chemical structure of the chosen substrate, to elucidate whether the addition of Ag2CO3 has beneficial or detrimental effects on the photocatalytic properties of the coupled ZnO/Ag2CO3 materials.
Enero, 2019 · DOI: 10.1016/j.jphotochem.2018.10.024
Materiales de Diseño para la Energía y Medioambiente
Influence of framework and interlayer on the colloidal stability of design swelling high-charged micas
Osuna, FJ; Cota, A; Fernandez, MA; Pavon, E; Sanchez, RMT; Alba, MDColloids and Surfaces A: Physicochemical and Engineering Aspects, 561 (2019) 32-38 DOI: 10.1016/j.colsurfa.2018.09.086
Abstract
Stability of colloidal clay minerals dispersion of fundamental in many industrial processes. Therefore, surface charge of the synthetic swelling high-charged mica family, Na-Mica-n (n = 2 or 4, n is the total layer charge) were investigated to study its colloidal dispersion stability as a function of the framework and interlayer space composition. Na-Mica-n (n = 2 or 4) micas were synthesized and functionalized with ethylammonium, mercaptoethylammonium or octadecylammonium. Their zeta-potential evolutions as a function of solution pH were correlated with their structural, compositional and morphological characteristics. The results have shown that the total charge of swelling high charged micas, Mica-n, didn´t affect significantly their colloidal dispersion stability, the interlayer composition and interlayer cation arrangement were the main factors of colloidal behaviour. The synthesis and functionalization of those synthetic micas can be tuned for their optimal use.
Enero, 2019 · DOI: 10.1016/j.colsurfa.2018.09.086
Materiales Ópticos Multifuncionales
Flexible nanophosphor films doped with Mie resonators for enhanced out-coupling of the emission
Miranda-Munoz, JM; Geng, DL; Calvo, ME; Lozano, G; Miguez, HJournal of Materials Chemistry C, 7 (2019) 267-274 DOI:
Abstract
Herein, we present a general method to prepare self-standing flexible photoluminescent coatings of controlled opacity for integration into light-emitting diodes (LEDs) employing cost-effective solution-processing methods. From colloidal suspensions of nano-sized phosphors, we fabricate light-emitting transparent films that can be doped with spherical scatterers, which act as Mie resonators that trigger a controlled photoluminescence enhancement, evidenced by the reduction of the guided light along the layer. This results in an enhanced emission compared to that extracted from a bare phosphor layer. We show not only that emission is visible under ultraviolet-LED illumination for both rigid and flexible versions of the coatings, but we also prove the feasibility of the integration of these flexible conversion layers into such devices. We believe these results can contribute to develop more efficient and cost-effective illumination sources by providing efficient and easy-to-handle conversion layers susceptible to excitation by LEDs emitting at wavelengths in the near UV region.
Enero, 2019 · DOI:
Fotocatálisis Heterogénea: Aplicaciones
Synthesis and Characterization of ZnO-ZrO2 Nanocomposites for Photocatalytic Degradation and Mineralization of Phenol
Lopez, MCU; Lemus, MAA; Hidalgo, MC; Gonzalez, RL; Owen, PQ; Oros-Ruiz, S; Lopez, SAU; Acosta, JJournal of Nanomaterials (2019) art. 1015876, 12 pages DOI: 10.1155/2019/1015876
Abstract
ZnO-ZrO2 nanocomposites using zinc (II) acetylacetonate and different ZnO contents (13, 25, 50, and 75% mol) were synthesized through sol-gel method. The synthesis process was strongly related to nanocomposite properties especially on their structural composition. The obtained ZnO-ZrO2 nanomaterials presented tetragonal crystalline structure for zirconia whereas hexagonal one was formed in ZnO. Raman spectroscopy and XRD patterns confirmed the formation of tetragonal zirconia whereas inhibition of monoclinic structure was observed. Addition of ZnO affected the pore size distribution of the composite, and the measured specific surface areas were from 10 m2/g (for pure ZnO) to 46 m2/g (pristine ZrO2). Eg values of ZrO2 were modified by ZnO addition, since calculated values using Kubelka-Munk’s function varied from 4.73 to 3.76 eV. The morphology and size of the nanomaterials investigated by electron microscopy showed formation of nanorods for ZnO with sizes ranging from 50 nm to 300 nm while zirconia was formed by smaller particles (less than 50 nm). The main advantage of using the nanocomposite for photocatalytic degradation of phenol was the mineralization degree, since 75ZnO-ZrO2 nanocomposite surpassed mineralization reached by pure ZnO and also inhibited formation of undesirable intermediates.
Enero, 2019 · DOI: 10.1155/2019/1015876
Nanotecnología en Superficies y Plasma
Isotope Labelling for Reaction Mechanism Analysis in DBD Plasma Processes
Navascues, P; Obrero-Perez, JM; Cotrino, J; Gonzalez-Elipe, AR; Gomez-Ramirez, ACatalysts, 9(1) (2019) 45 DOI: 10.3390/catal9010045
Abstract
Dielectric barrier discharge (DBD) plasmas and plasma catalysis are becoming an alternative procedure to activate various gas phase reactions. A low-temperature and normal operating pressure are the main advantages of these processes, but a limited energy efficiency and little selectivity control hinder their practical implementation. In this work, we propose the use of isotope labelling to retrieve information about the intermediate reactions that may intervene during the DBD processes contributing to a decrease in their energy efficiency. The results are shown for the wet reforming reaction of methane, using D2O instead of H2O as reactant, and for the ammonia synthesis, using NH3/D-2/N-2 mixtures. In the two cases, it was found that a significant amount of outlet gas molecules, either reactants or products, have deuterium in their structure (e.g., HD for hydrogen, CDxHy for methane, or NDxHy for ammonia). From the analysis of the evolution of the labelled molecules as a function of power, useful information has been obtained about the exchange events of H by D atoms (or vice versa) between the plasma intermediate species. An evaluation of the number of these events revealed a significant progression with the plasma power, a tendency that is recognized to be detrimental for the energy efficiency of reactant to product transformation. The labelling technique is proposed as a useful approach for the analysis of plasma reaction mechanisms.
Enero, 2019 · DOI: 10.3390/catal9010045
Materiales Coloidales
Enhancing Luminescence and X-ray Absorption Capacity of Eu3+:LaF3 Nanoparticles by Bi3+ Codoping
Mancebo, DG; Becerro, AI; Corral, A; Moros, M; Balcerzyk, M; de la Fuente, JM; Ocana, MACS Omega, 4 (2019) 765-774 DOI: 10.1021/acsomega.8b03160
Abstract
Bi3+ codoping has been proposed in this work with a twofold objective, namely, enhancing the luminescence emission of Eu3+:LaF3 nanoparticles (NPs) and increasing their X-ray attenuation capacity, with the purpose of obtaining a bimodal bioprobe for luminescence bioimaging and X-ray computed tomography. The synthesis method, reported here for the first time for LaF3 particles, allowed obtaining uniform, nonaggregated NPs using a homogeneous precipitation in polyol medium at room temperature in just 2 h. The simplicity of the synthesis method allows the large-scale production of NPs. LaF3 NPs with different Eu3+ contents were first synthesized to find the critical Eu3+ concentration, producing the highest emission intensity. This concentration was subsequently used to fabricate Bi3+-Eu3+-codoped LaF3 NPs using the same method. The emission intensity of the codoped NPs increased in more than one order of magnitude, thanks to the possibility of excitation through the Bi3+. Eu3+ energy-transfer band. The luminescence properties of the codoped NPs were analyzed in detail to find the mechanism responsible for the emission enhancement. Finally, it was demonstrated that the high atomic number of Bi3+, higher than that of lanthanides, was an added value of the material because it increased its X-ray attenuation capacity. In summary, the LaF3 NPs codoped with Eu3+ and Bi3+ presented in this work are promising candidates as a bimodal bioprobe for luminescence bioimaging and X-ray computed tomography.
Enero, 2019 · DOI: 10.1021/acsomega.8b03160
Reactividad de Sólidos
La0.59Li0.24TiO3 ceramics obtained by spark plasma sintering: Electric behavior analysis
Pereira, JS; Guerrero, F; Romaguera-Barcelay, Y; Anglada-Rivera, J; Sales, JCC; Silva, RS; Zulueta, Y; Poyato, R; Gallardo, A; Almeida, A; Moreira, JA; Leyet, YMaterials Research Express, 6 (2019) art. 015504 DOI: 10.1088/2053-1591/aae496
Abstract
This work describes the electric study of Lithium lanthanum titanate (La0.59Li0.24TiO3) ceramics performed by Complex Impedance Spectroscopy. The nanoparticle powders have been synthesized through high energy ball milling and sintered via Spark Plasma Sintering technique. The experimental impedance data have been analyzed using the equivalent circuit model, the Extended Jonscher universal law and the derivative method. From these models, we have determined the dielectric response as well as the grain and grain boundary conductivity. The samples show ionic conductivity values between 10(-5) to 10(-4) S cm(-1) in the studied temperature range, and activation energy values 0.24 eV and 0.48 eV for grain and grain boundary, respectively. These results confirm the Li+ ions mobility through the crystalline structure of the material.
Enero, 2019 · DOI: 10.1088/2053-1591/aae496
Materiales Coloidales
Biocompatibility assessment of up-and down-converting nanoparticles: implications of interferences with in vitro assays
Pem, Barbara; Gonzalez-Mancebo, Daniel; Moros, Maria; Ocana, Manuel; Becerro, Ana Isabel; Pavicic, Ivan; Selmani, Atida; Babic, Michal; Horak, Daniel; Vinkovic Vrcek, IvanaMethods and Applications in Fluorescence, 7 (2019) 014001 DOI: 10.1088/2050-6120/aae9c8
Abstract
The safety assessment of nanoparticles (NPs) is crucial during their design and development for biomedicine. One of the prerequisite steps during this evaluation is in vitro testing that employs cell-based assays not always validated and well-adapted for NPs. Interferences with in vitro assays may arise due to the nano-related optical, oxidative, fluorescent, surface and catalytic properties of NPs. Thus, proper validation of each assay system has to be performed for each NP type. This study aimed to evaluate the applicability of the most common in vitro cytotoxicity assays for the safety assessment of up- and down-converting lanthanide-doped NPs. Conventional cell viability tests and fluorescence-based assays for oxidative stress response were selected to determine the biological effects of up- and down-converting NPs to human brain cells. Comparison with known silver and iron oxide NPs was made for verification purposes. Both the plate reader and flow cytometric measurements were examined. The obtained results indicated that both types of Ln-doped NPs interfered to a much lesser extent than metallic NPs. In addition, the great potential of both up- and down-converting NPs for biomedicine was manifested due to their biocompatibility and low toxicity.
Enero, 2019 · DOI: 10.1088/2050-6120/aae9c8
Materiales Ópticos Multifuncionales
Highly Efficient Transparent Nanophosphor Films for Tunable White-Light-Emitting Layered Coatings
Geng, DL; Lozano, G; Miguez, HACS Applied Materials & Interfaces, 11 (4) (2019) 4219-4225 DOI: 10.1021/acsami.8b17368
Abstract
Bright luminescence in rare-earth (RE) nanocrystals, the so-called nanophosphors, is generally achieved by choosing a host that enables an effective excitation of the RE activator through charge or energy transfer. Although tungstate, molybdate, or vanadate compounds provide the aforementioned transfer, a comparative analysis of the efficiency of such emitters remains elusive. Herein, we perform a combined structural and optical analysis, which reveals that the tetragonal GdVO4 matrix gives rise to the highest efficiency among the different transparent nanophosphor films compared. Then, we demonstrate that by a sequential stacking of optical quality layers made of Eu3+- and Dy3+-doped nanocrystals, it is possible to attain highly transparent white-light-emitting coatings of tunable shade with photoluminescence quantum yields above 35%. Layering provides a precise dynamic tuning of the chromaticity based on the photoexcitation wavelength dependence of the emission of the nanophosphor ensemble without altering the chemical composition of the emitters or degrading their efficiency. The total extinction of the incoming radiation along with the high quantum yields achieved makes these thin-layered phosphors one of the most efficient transparent white converter coatings ever developed.
Enero, 2019 · DOI: 10.1021/acsami.8b17368
Tribología y Protección de Superficies
Influence of Al and Y content on the oxidation resistance of CrAlYN protective coatings for high temperature applications: New insights about the Y role
Rojas, TC; Dominguez-Meister, S; Brizuela, M; Sanchez-Lopez, JCJournal of Alloys and Compounds, 777 (2019) 1172-1181 DOI: 10.1016/j.jallcom.2018.09.280
Abstract
CrAlYN hard coatings with two different average Al contents: similar to 16 at.% and similar to 25 at.%, and Y concentration varying between 1.2 and 5.7 at.% were deposited by direct current reactive magnetron co-sputtering of mixed Cr-Al and Y targets on commercial M2 steel substrates. The samples were heated to 1000 degrees C in air during 2 h to study their oxidation resistance and thermal stability. The Y content is critical and the coatings present different behaviour depending on the Al content. The best oxidation resistance and thermal stability are obtained for the coating with similar to 16 at.% Al and 3.4 at.% Y. The initial film microstructure and the cubic phase (fcc-CrAlN) were retained, and a thin (Cr,Al)(2)O-3 oxide protective scale was formed. At lower Y content (1.2 at.%) iron, from the substrate crosses the coating, while a higher content (4.6 at.%) avoided the iron diffusion at the expense of a thicker oxide scale with new oxide phases. The coatings with higher Al content (similar to 25 at. %) were not thermally stable at 1000 degrees C. A good oxidation resistance was obtained for 2.6 at.% of Y although new phases (hcp-AlN and Cr-Fe) were formed. Higher amount of yttrium (similar to 5.7 at. %) led to the complete oxidation of the coating.
Enero, 2019 · DOI: 10.1016/j.jallcom.2018.09.280
2018
2018
Materiales Coloidales - Materiales Ópticos Multifuncionales - Materiales y Procesos Catalíticos de Interés Ambiental y Energético
Revealing the substitution mechanism in Eu3+:CaMoO4 and Eu3+,Na+:CaMoO4 phosphors
Becerro, AI; Allix, M; Laguna, M; Gonzalez-Mancebo, D; Genevois, C; Caballero, A; Lozano, G; Nunez, NO; Ocana, MJournal of Materials Chemistry C, 6 (2018) 47 DOI: 10.1039/c8tc04595j
Abstract
Eu3+-Doped calcium molybdate is an excellent phosphor for lighting and display devices due to the very intense pure red emission after UV excitation. It has been reported in the literature that the CaMoO4 unit cell volume expands after Eu3+ doping, in spite of the smaller Eu3+ ionic radius compared with Ca2+. Likewise, several studies found that the emission intensity of the phosphor could be improved by codoping with alkaline ions like Li+, Na+ or K+. None of these studies correlated the apparent volume expansion and luminescence enhancement with the crystal structural details. This paper analyses the aliovalent substitution mechanism and crystal structure of Eu3+:CaMoO4 and Eu3+,Na+:CaMoO4 phosphors using complementary techniques like Raman spectroscopy, EXAFS and SPD. We found that the substitution mechanism was different for both systems, with Ca site vacancies forming in the Eu3+:CaMoO4 phosphors and leading to Ca1-3xEu2xxMoO4 compositions, while the Eu3+,Na+:CaMoO4 phosphors formed Ca1-2xEuxNaxMoO4. SPD showed that the cell volume expansion observed with increasing Eu3+ content is related to the increase of the Mo-O bond distance due to the higher electronegativity of Eu3+ compared with Ca2+. Finally, it was shown that the luminescence properties, i.e. lifetime values and quantum yields (the latter reported here for the first time), do not depend on the presence of monovalent ions in the crystal structure but, exclusively, on the Eu3+ content of the phosphor. The integral and detailed analysis of the materials presented in this paper, ranging from crystal structure to luminescent properties including elemental composition, allows a full picture of the structure-property relationships that had never been addressed before for CaMoO4-based phopshors.
Diciembre, 2018 · DOI: 10.1039/c8tc04595j
Materiales Ópticos Multifuncionales
Improving the Bulk Emission Properties of CH3NH3PbBr3 by Modifying the Halide-Related Defect Structure
Tiede, David O.; Calvo, Mauricio E.; Galisteo-Lopez, Juan F.; Miguez, HernanJournal of Physical Chemistry C, 122 (2018) 27250-27255 DOI: 10.1021/acs.jpcc.8b09315 DEC 6 2018
Abstract
The peculiar defect chemistry of hybrid organic–inorganic lead halide perovskites is believed to be partially responsible for the outstanding performance of this solution-processed material in optoelectronic devices. While most effort has been put on the management of halide defects (the ones presenting the highest mobility) for CH3NH3PbI3, its bromide counterpart has not been so widely studied. Although the former is the material of choice for photovoltaics, the latter is present in most light-emitting applications. Here, we report how the exposure of CH3NH3PbBr3 single crystals to a bromine atmosphere strongly affects its emission properties. Such improvement takes place in the absence of apparent signs of degradation and remains for tens of hours. We propose an explanation based on the defect structure for this material where bromine-related defects can act as deep or shallow traps. These results are of relevance for a material expected to be present in a new generation of solution-processed light-emitting devices.
Diciembre, 2018 · DOI: 10.1021/acs.jpcc.8b09315 DEC 6 2018
Química de Superficies y Catálisis
Understanding the Role of the Acid Sites in 5-Hydroxymethylfurfural Oxidation to 2,5-Furandicarboxylic Acid Reaction over Gold Catalysts: Surface Investigation on CexZr1-xO2 Compounds
Megias-Sayago, C; Chakarova, K; Penkova, A; Lolli, A; Ivanova, S; Albonetti, S; Cavani, F; Odriozola, JAACS Catalysis, 8 (2018) 11154-11164 DOI: 10.1021/acscatal.8b02522 DEC 2018
Abstract
A series of CexZr1-xO2 supports with different Ce/Zr molar ratios were utilized for the preparation of gold catalyst used in the selective oxidation of 5-hydroxymethyl-2-furfural to 2,5-furandicarboxylic acid. The used method of gold deposition allows the preparation of gold particles with homogeneous size and shape distribution, a formulation very useful for studies dedicated to revealing the support participation in the reaction. The supports are characterized by Fourier transform infrared spectroscopy using CO as probe molecule, and the sample catalytic activity is thereafter correlated to the support acid site distribution. The possible participation of its Lewis/Bronsted acidity in the reaction mechanism is also proposed.
Diciembre, 2018 · DOI: 10.1021/acscatal.8b02522 DEC 2018
Reactividad de Sólidos
Role of calcium looping conditions on the performance of natural and synthetic Ca-based materials for energy storage
Sarrion, B; Perejon, A; Sanchez-Jimenez, PE; Perez-Maqueda, LA; Valverde, JMJournal of CO2 utilization, 28 (2018) 374-384 DOI: 10.1016/j.jcou.2018.10.018
Abstract
In this work, the multicycle activity of natural CaO precursors (limestone and dolomite) and Ca-based composites (Ca3Al2O6/CaCO3 and ZrO2/CaCO3 mixtures) has been studied for Thermochemical Energy Storage (TCES) in Concentrated Solar Power (CSP) plants by means of the Calcium-Looping process (CaL), using two integration schemes proposed elsewhere that differ in the calcination stages. Under CSP-He conditions, calcination for CaO regeneration is performed under pure He at low temperatures (725 degrees C) while under CPS-CO2 conditions calcination is carried out under pure CO2 at high temperatures (950 degrees C). The latter avoids the use of selective membranes to separate He from CO2 even though it requires the use of more expensive materials for solar receptors. Carbonation/calcination conditions drastically affect the multicycle CO2 uptake of the materials tested. Effective multicycle conversion is higher in CSP-He tests due to the mild conditions employed for calcination, which mitigates CaO sintering. On the other hand, the harsh calcination conditions used in CSP-CO2 tests enhance sintering of CaO derived from limestone and the Ca3Al2O6/CaCO3 composite due to the low Tammann temperature of Ca3Al2O6. CaO sintering is hindered by the presence of inert oxides with high Tammann temperatures, such as ZrO2 in the ZrO2/CaCO3 composite and MgO in dolomite. Dolomite derived CaO shows high effective conversion values along the carbonation/calcination cycles when tested under both types of conditions, as compared to limestone and the composites, which suggests that the integration scheme based on CSP-CO2 conditions would be a feasible alternative to CSP-He if natural dolomite were used as CaO precursor.
Diciembre, 2018 · DOI: 10.1016/j.jcou.2018.10.018
Materiales Avanzados
Degradation of a LDPE film applied as a greenhouse cover design material: the effect of ageing and mechanical modelling
Garzon, Eduardo; Ortiz Rodriguez, Isabel Maria; Castillo, Jose; Jose Sanchez-Soto, PedroRevista de la Construcción, 17 (3) (2018) 457-464 DOI: 10.7764/RDLC.17.3.457 DEC 2018
Abstract
In this work, we studied the mechanical performance of an LDPE film (0.22 mm in thickness) used as a material in the design of greenhouse covers. We investigated the effects of ageing at different periods of its service life and applying chemical substance treatments used as pesticides on greenhouse crops and after breakage using mechanical traction. Numerical simulations were performed using the finite element method. For this purpose, one section of the complete geometry of the greenhouse cover and different load conditions (1-5 kPa) were considered for the modelling. The performance of the polymer was assumed to be linearly elastic to simplify the governing equations. The study demonstrated that the LDPE film used was no longer effective as a greenhouse cover film due to the degradation of its mechanical properties. It was shown that the general performance of this film was in the plastic zone and its performance was non-linear. The results deduced from the present study are of interest because they show the material failure process of greenhouse covers in relation to the degradation process.
Diciembre, 2018 · DOI: 10.7764/RDLC.17.3.457 DEC 2018
Química de Superficies y Catálisis
New concept for old reaction: Novel WGS catalyst design
Garcia-Moncada, N; Gonzalez-Castano, M; Ivanova, S; Centeno, MA; Romero-Sarria, F; Odriozola, JAApplied Catalysis B-Environmental, 238 (2018) 1-5 DOI: 10.1016/j.apcatb.2018.06.068
Abstract
The viability of water gas shift catalytic system for mobile application passes through obligatory reactor volume reduction, achieved normally by using less charge of more efficient catalyst. Completely new concept for catalyst design is proposed: a catalytic system including classically reported WGS catalysts of different nature or active phase (Cu, Pt or Au) mechanically mixed with an ionic conductor. The influence of the later on catalyst activity is studied and discussed, more precisely its effect on the rate of the reaction-limiting step and catalysts' efficiency. It is demonstrated with this study, that the presence of an ionic conductor in contact with a WGS catalyst is essential for the water supply (dissociation and transport), thereby potentiating the water activation step, whatever the mechanism and catalyst overall performance.
Diciembre, 2018 · DOI: 10.1016/j.apcatb.2018.06.068
Fotocatálisis Heterogénea: Aplicaciones
A comparative assessment of the UV-photocatalytic activities of ZnO synthesized by different routes
Jaramillo-Paez, C; Sanchez-Cid, P; Navio, JA; Hidalgo, MCJournal of Environmental Chemical Engineering, 6 (2018) 7161-7171 DOI: 10.1016/j.jece.2018.11.004
Abstract
ZnO was synthesized by a precipitation procedure, free of template agent, by mixing aqueous solutions of Zn (OAc)(2) and dissolved Na2CO3 at pH ca. 7. This material was calcined at different temperatures (200-600 degrees C for 2 h). In two other alternative procedures, after the precipitation, the suspension was taken to hydrothermal treatments or to microwave treatments, subjecting them to calcination treatments at the same temperatures as the previous material. All materials were characterized using various techniques. The photocatalytic activity was assessed in the degradation of methyl orange and phenol using UV-illumination and evaluating the corresponding percentages of conversion and mineralization. A minimal difference between the relative intensities of the exposed faces (I100I002) related to XRD for the synthesized samples seems to be an important factor in obtaining good photocatalytic properties. This minimum, was achieved with a calcination treatment at 400 degrees C for 2 h. With this calcination treatment, no significant variations were observed in the photocatalytic activities of ZnO obtained by the three procedures, although in all cases the zinc oxides obtained exhibited, for each substrate, higher UV-photocatalytic activities than those obtained with TiO2 (P25) used as a reference catalyst. In all cases, the samples showed no photocatalytic activity in the visible region of the spectrum.
Diciembre, 2018 · DOI: 10.1016/j.jece.2018.11.004
Química de Superficies y Catálisis
CO/H-2 adsorption on a Ru/Al2O3 model catalyst for Fischer Trospch: Effect of water concentration on the surface species
Jimenez-Barrera, E; Bazin, P; Lopez-Cartes, C; Romero-Sarria, F; Daturi, M; Odriozola, JAApplied Catalysis B-Environmental, 237 (2018) 986-995 DOI: 10.1016/j.apcatb.2018.06.053
Abstract
Water presence and concentration strongly influence CO conversion and CS+ selectivity in the Fischer Tropsch reaction. In this work, the influence of the water concentration was investigated using a model Ru/Al2O3 (5 wt. %) catalyst. The surface species formed after CO and H-2 adsorption in dry and wet (different water concentrations) conditions were analyzed by FTIR. Firstly, water adsorption was carried out up to complete filling of the pores and then CO was put in contact with the catalyst. The absence of adsorbed CO species in these conditions evidences that CO diffusion in water controls the access of the gas to the active sites and explains the negative effect of high water concentrations reported by some authors. Moreover, the adsorption of a mixture of CO + H-2 + H2O, being the water concentration close to that needed to have a monolayer, and a dry mixture of CO + H-2 were carried out and compared. Results evidence that water in this low concentration, is able to gasify the surface carbon species formed by CO dissociation on the metallic sites. This cleaning effect is related to the positive effect of water on CO conversion detected by some authors.
Diciembre, 2018 · DOI: 10.1016/j.apcatb.2018.06.053
Química de Superficies y Catálisis
Metal Micro-Monoliths for the Kinetic Study and the Intensification of the Water Gas Shift Reaction
Garcia-Moncada, N; Groppi, G; Beretta, A; Romero-Sarria, F; Odriozola, JACatalysts, 8 (2018) art. 594 DOI: 10.3390/catal8120594
Abstract
A kinetic study of the water gas shift (WGS) reaction has been carried out on a Pt-based catalyst promoted by a Zr-based proton conductor. The investigation was first performed on powders with diluted feed mixtures and then extended to more severe and representative conditions by using a catalyst coated metallic micromonolith. Temperature measurements reveal that isothermal conditions were obtained along the micromonolith during the tested conditions. In addition, the very thin catalytic layer allows for the discarding of intraporous resistances, providing excellent conditions to analyse the kinetics of the WGS reaction under the integral regime. The proposed rate expression accounts for independence on CO concentration, an inhibiting effect of H-2 and a promoting effect of H2O; kinetic orders on CO and H-2 are in line with those reported in the literature for the Pt-based catalyst. Instead, the obtained reaction order of water (0.36) is significantly lower than that reported for unpromoted catalysts (typically 0.77-1.10) in good agreement with the proposed water-enhancer effect of the proton conductor on the rate-limiting step. Metallic micromonoliths turn out to be a powerful tool for the kinetic investigation, due to the absence of mass and heat transport limitations and represent a strategy for the intensification of the WGS unit for future applications of fuel processors in small mobile devices.
Diciembre, 2018 · DOI: 10.3390/catal8120594
Reactividad de Sólidos
Molten carbonate salts for advanced solar thermal energy power plants: Cover gas effect on fluid thermal stability
Fereres, S; Prieto, C; Gimenez-Gavarrell, P; Rodriguez, A; Sanchez-Jimenez, PE; Perez-Maqueda, LASolar Energy Materials and Solar Cells, 188 (2018) 119-126 DOI: 10.1016/j.solmat.2018.08.028
Abstract
The eutectic mixture Li2CO3-Na2CO3-K2CO3 is investigated as a high temperature heat transfer fluid and storage medium alternative for molten salt solar thermal power plants. This salt has an operating temperature range of 400–700 °C, enabling the use of higher temperature/efficiency power cycles. However, this carbonate mixture is known to thermally decompose in air. This study evaluates the thermal stability of the salt mixture under different cover gases: air, nitrogen, carbon dioxide, and an 80/20 carbon dioxide/air mixture. Initial characterization is performed through thermogravimetric analysis (TGA), followed by larger scale testing in a custom-made reactor to simulate conditions closer to its practical use. The results show improved thermal stability with a CO2 atmosphere. The decomposition kinetics under different cover gases are estimated from TGA data. However, larger-scale, longer duration experiments show much slower decomposition rates compared to the classical TGA approach. These findings indicate that the main contribution to mass loss in TGA is due to vaporization rather than thermal decomposition. Thus, a proper evaluation of the molten salt´s thermal stability can only be obtained from reactor experiments where vaporization is inhibited. Very long induction periods (of the order of days) are observed, suggesting that the kinetic decomposition mechanism is a nucleation and growth type. Other considerations for future plants incorporating these high temperature salts are discussed.
Diciembre, 2018 · DOI: 10.1016/j.solmat.2018.08.028
Química de Superficies y Catálisis
Policies and Motivations for the CO2 Valorization through the Sabatier Reaction Using Structured Catalysts. A Review of the Most Recent Advances
Navarro, JC; Centeno, MA; Laguna, OH; Odriozola, JACatalysts, 8 (2018) art. 578 DOI: 10.3390/catal8120578
Abstract
The current scenario where the effects of global warming are more and more evident, has motivated different initiatives for facing this, such as the creation of global policies with a clear environmental guideline. Within these policies, the control of Greenhouse Gase (GHG) emissions has been defined as mandatory, but for carrying out this, a smart strategy is proposed. This is the application of a circular economy model, which seeks to minimize the generation of waste and maximize the efficient use of resources. From this point of view, CO2 recycling is an alternative to reduce emissions to the atmosphere, and we need to look for new business models which valorization this compound which now must be considered as a renewable carbon source. This has renewed the interest in known processes for the chemical transformation of CO2 but that have not been applied at industrial level because they do not offer evident profitability. For example, the methane produced in the Sabatier reaction has a great potential for application, but this depends on the existence of a sustainable supply of hydrogen and a greater efficiency during the process that allows maximizing energy efficiency and thermal control to maximize the methane yield. Regarding energy efficiency and thermal control of the process, the use of structured reactors is an appropriate strategy. The evolution of new technologies, such as 3D printing, and the consolidation of knowledge in the structing of catalysts has enabled the use of these reactors to develop a wide range of possibilities in the field. In this sense, the present review presents a brief description of the main policies that have motivated the transition to a circular economy model and within this, to CO2 recycling. This allows understanding, why efforts are being focused on the development of different reactions for CO2 valorization. Special attention to the case of the Sabatier reaction and in the application of structured reactors for such process is paid.
Diciembre, 2018 · DOI: 10.3390/catal8120578
Nanotecnología en Superficies y Plasma
Influence of irrigation conditions in the germination of plasma treated Nasturtium seeds
Molina, R; Lopez-Santos, C; Gomez-Ramirez, A; Vilchez, A; Espinos, JP; Gonzalez-Elipe, ARScientific Reports, 8 (2018) art. 16442 DOI: 10.1038/s41598-018-34801-0
Abstract
Plasma treatments had emerged as a useful technique to improve seed germination. In this work we investigate the influence of different irrigation conditions and plasma treatments on the germination of nasturtium seeds. During plasma treatment, seeds experience a progressive weight loss as a function of treatment time that has been associated to water release, a process that is more pronounced after longer plasma treatment times. Seeds treated for short times (<30 s) are able to germinate more efficiently than untreated specimen under hydric stress (drought conditions), while plasma treatments for longer times (up to 300 s) impaired germination independently on irrigation conditions. Characterization analysis of plasma treated seeds by FTIR-ATR, SEM/EDX and XPS showed that plasma treatment affected the chemical state of pericarp while, simultaneously, induced a considerable increase in the seeds water uptake capacity. The decrease in germination efficiency found after plasma treatment for long times, or for short times under optimum irrigation conditions, has been attributed to that the excess of water accumulated in the pericarp hampers the diffusion up to the embryo of other agents like oxygen which are deemed essential for germination.
Noviembre, 2018 · DOI: 10.1038/s41598-018-34801-0
Reactividad de Sólidos
Scalable synthesis of potential solar cell absorber Cu2SnS3 (CTS) from nanoprecursors
Hegedus, M; Balaz, M; Tesinsky, M; Sayagues, MJ; Siffalovic, P; Krulakova, M; Kanuchova, M; Briancin, J; Fabian, M; Balaz, PJournal of Alloys and Compounds, 768 (2018) 1006-1015 DOI: 10.1016/j.jallcom.2018.07.284
Abstract
The present paper demonstrates an easy and scalable mechanochemical synthesis of ternary sulfide Cu2SnS3 (CTS) as a promising solar cell absorber. For the synthesis, pre-milled nanoparticles of CuS and SnS were used. The pure CTS phase was readily obtained after 60 min of milling in a laboratory planetary ball mill and 240 min in an industrial eccentric vibration industrial mill, respectively. The reaction progress of laboratory scale synthesis was studied by the quantitative Rietveld analysis. The reaction speed reaches its maximum at 4.6 min and the reaction is completed at approximately 60 min, according to the fitted data. The products of the syntheses were further characterized by X-ray powder diffractometry, Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and UV-Vis spectroscopy. The results revealed formation of near-stoichiometric CTS nanoparticles with tetragonal I-42m symmetry. An average crystallites size of approximately 10-15 nm was determined for CTS phase. The SEM images support quintessential polydisperse character of the powders obtained by ball-milling approach. The materials seem to be suitable for photovoltaic applications with the band-gap energies of approximately 1.16-1.19 eV.
Noviembre, 2018 · DOI: 10.1016/j.jallcom.2018.07.284
Materiales Ópticos Multifuncionales
High voltage vacuum-deposited CH3NH3PbI3–CH3NH3PbI3 tandem solar cells
Avila, J; Momblona, C; Boix, P; Sessolo, M; Anaya, M; Lozano, G; Vandewal, K; Miguez, H; Bolink, HJEnergy & Environmental Science, 11 (2018) 3292-3297 DOI: 10.1039/c8ee01936c
Abstract
The recent success of perovskite solar cells is based on two solid pillars: the rapid progress of their power conversion efficiency and their flexibility in terms of optoelectrical properties and processing methods. That versatility makes these devices ideal candidates for multi-junction photovoltaics. We report an optically optimized double junction CH3NH3PbI3-CH3NH3PbI3 tandem solar cell where the matched short-circuit current is maximized while parasitic absorption is minimized. The use of an additive vacuum-deposition protocol allows us to reproduce calculated stack designs, which comprise several charge selective materials that ensure appropriate band alignment and charge recombination. This rationalized configuration yields an unprecedented open circuit voltage of 2.30 V. Furthermore, this tandem solar cell features efficiencies larger than 18%, higher than those of the individual sub-cells. Low photo-current values allow reducing the losses associated to the series resistance of transparent contacts, which opens the door to the realization of efficient large area modules.
Noviembre, 2018 · DOI: 10.1039/c8ee01936c
Reactividad de Sólidos
Mechanically induced combustion synthesis of niobium carbonitride nanoparticles
Jalaly, M; Gotor, FJ; Sayagues, MJJournal of Solid State Chemistry, 267 (2018) 106-112 DOI: 10.1016/j.jssc.2018.08.027
Abstract
Niobium carbonitride [Nb(C,N)] nanoparticles were synthesized by a combustive mechanochemical reaction in the Mg/Nb2O5/C3H6N6 system. High-energy ball milling was used to promote a mechanically induced self-sustaining reaction (MSR). Combustion occurred after a very short milling period of 5 min. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) analyses revealed that the nature of the product is an intermixed carbonitride material. The formation mechanism of Nb(C,N) resulted from the magnesiothermic reduction of niobium oxide to generate elemental Nb, which then reacted with the species generated from the melamine decomposition.
Noviembre, 2018 · DOI: 10.1016/j.jssc.2018.08.027
Química de Superficies y Catálisis
Analysis of the variables that modify the robustness of Ti-SiO2 catalysts for alkene epoxidation: Role of silylation, deactivation and potential solutions
Plata, JJ; Pacheco, LC; Remesal, ER; Masa, MO; Vega, L; Marquez, AM; Odriozola, JA; Sanz, JFMolecular Catalysis, 459 (2018) 55-60 DOI: 10.1016/j.mcat.2018.08.010
Abstract
Catalytic epoxidation of alkenes plays an essential role in the transformation and synthesis of many organic chemicals. Ti atoms grafted on mesoporous silica, silylated on the surface, is considered the most active and selective catalyst for these reactions. However, the durability and robustness of the active centers remain as the main drawback in industry. In this paper, the characterization of industrial samples is combined with DFT calculations to rationalize the deactivation process of the catalyst and improve its performance. Silylating agents are characterized by experimental and simulated 29Si-NMR and their role in the catalytic mechanism is analysed. Potential deactivation processes are identified before, during and after the reaction. Modifications of the silylating agents and of the active center are proposed to improve the durability of the catalyst.
Noviembre, 2018 · DOI: 10.1016/j.mcat.2018.08.010
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