Scientific Papers in SCI
2015
2015
Materiales Ópticos Multifuncionales
Environmental Effects on the Photophysics of Organic-Inorganic Halide Perovskites
Galisteo-Lopez, JF; Anaya, M; Calvo, ME; Miguez, HJournal of Physical Chemistry Letters, 6 (2015) 2200-2205 DOI: 10.1021/acs.jpclett.5b00785
Abstract
The photophysical properties of films of organic-inorganic lead halide perovskites under different ambient conditions are herein reported. We demonstrate that their luminescent properties are determined by the interplay between photoinduced activation and darkening processes, which strongly depend on the atmosphere surrounding the samples. We have isolated oxygen and moisture as the key elements in each process, activation and darkening, both of which involve the interaction with photogenerated carriers. These findings show that environmental factors play a key role in the performance of lead halide perovskites as efficient luminescent materials.
June, 2015 · DOI: 10.1021/acs.jpclett.5b00785
Nanotecnología en Superficies y Plasma
Core-shell polydopamine magnetic nanoparticles as sorbent in micro-dispersive solid-phase extraction for the determination of estrogenic compounds in water samples prior to high-performance liquid chromatography-mass spectrometry analysis
Socas-Rodriguez, B; Hernandez-Borges, J; Salazar, P; Martin, M; Rodriguez-Delgado, MAJournal of Chromatography A, 1397 (2015) 1-10 DOI: 10.1016/j.chroma.2015.04.010
Abstract
In this work, core-shell Fe3O4@poly(dopamine) magnetic nanoparticles (m-NPs) were prepared and characterized in our laboratory and applied as sorbents for the magnetic-micro solid phase extraction (m-mu SPE) of twelve estrogenic compounds of interest (i.e. 17 alpha-estradiol, 17 beta-estradiol, estrone, hexestrol, 17 alpha-ethynylestradiol, diethylstibestrol, dienestrol, zearalenone, alpha-zearalanol,beta-zearalanol, alpha-zearalenol and beta-zearalenol) from different water samples. Separation, determination and quantification were achieved by high-performance liquid chromatography coupled to ion trap mass spectrometry with electrospray ionization. NPs@poly(dopamine) were synthesized by a chemical coprecipitation procedure and characterized by different surface characterization techniques (X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission and scanning electron microscopy, infrared and Raman spectroscopy, vibrating sample magnetometry, microelectrophoresis and adsorption/desorption isotherms). Parameters affecting the extraction efficiency of m-mu SPE (i.e. polymerization time, pH of the sample, extraction and elution conditions) were studied and optimized. The methodology was validated for Milli-Q, mineral, tap and wastewater using 2-methoxyestradiol as internal standard, obtaining recoveries ranging from 70 to 119% with relative standard deviation values lower than 20% and limits of quantification in the range 0.02-1.1 mu g/L.
June, 2015 · DOI: 10.1016/j.chroma.2015.04.010
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
A novel two-steps solvothermal synthesis of nanosized BiPO4 with enhanced photocatalytic activity
Zhang, YF; Sillanpaa, M; Obregon, S; Colon, GJournal of Molecular Catalysis A-Chemical, 402 (2015) 92-99 DOI: 10.1016/j.molcata.2015.03.011
Abstract
Nano-sized BiPO4 has been successfully synthesized via a novel designed two-steps solvothermal route using ethylene glycol as solvent. Comparing with traditional hydrothermal method, the novel approach could readily prepare BiPO4 with shorter time. The photocatalytic activity of prepared BiPO4 has been tested via degradation of methylene blue (MB) under light irradiation. The experimental results show that the BiPO4 prepared by novel route had enhanced photocatalytic activity and the synthetic parameters also impact the reaction rate meaningfully. Finally, the obtained samples have been widely characterized by means of powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), UV–vis diffuse reflectance spectra (DRS) and Fourier transformed infrared (FTIR) spectra. BiPO4 prepared by this novel approach have a particles size below 100 nm, which is a big improvement by comparing with previous works (few micrometer). The effect of EG during the formation of BiPO4 has been discussed and a possible formation mechanism is proposed.
June, 2015 · DOI: 10.1016/j.molcata.2015.03.011
Materiales Nanoestructurados y Microestructura
Island-type growth of Au–Pt heterodimers: direct visualization of misfit dislocations and strain-relief mechanisms
Garcia-Negrete, CA; Knappett, BR; Schmidt, FP; Rojas, TC; Wheatley, AEH; Hofer, F; Fernandez, ARSC Advances, 5 (2015) 55262-55268 DOI: 10.1039/C5RA09808D
Abstract
Structural and analytical characterization related to the formation mechanism of Au–Pt heterodimers from polyhedral Pt nanocrystals is reported. The observation of specific lattice strain effects and the emergence of misfit dislocations point to the relevance of the Stranski–Krastanov growth mode as a means of explaining the previously reported dimerisation reaction between Au and Pt. Two size-dependent strain relief mechanisms were identified. For dimers grown from 4.7 nm seeds, the mechanism is related to bulk lattice strain accumulation at {111} planes along with lattice relaxation effects on other crystalline planes. However, for dimers grown from 11.2 nm seed sizes, the formation of misfit dislocations proved to be a highly efficient mechanism by which to release interface mismatch strain. Nanoscale chemical mapping at Au–Pt interfaces also revealed Au–Pt alloying to be unlikely under the mild temperature conditions employed in this work for Au–Pt heterodimer synthesis.
June, 2015 · DOI: 10.1039/C5RA09808D
Química de Superficies y Catálisis
H-2 oxidation as criterion for PrOx catalyst selection: Examples based on Au-Co-O-x-supported systems
Reina, TR; Megias-Sayago, C; Florez, AP; Ivanova, S; Centeno, MA; Odriozola, JAJournal of Catalysis, 326 (2015) 161-171 DOI: 10.1016/j.jcat.2015.03.015
Abstract
A new approach for understanding PrOx reaction over gold catalysts is proposed in this work. The competition between H-2 and CO oxidation has been studied over a series of Au/MOx/Al2O3 (M = Ce and Co) catalysts in simulated post-reforming gas stream, containing H2O and CO2 for H-2 cleanup goals. The catalysts' behavior is correlated to their oxygen storage capacity, redox behavior, and oxidation ability. The estimation of the reaction rates reveals that in these solids the H-2 combustion, the selectivity limiting factor in the PrOx process, is mainly controlled by the support and not by the gold presence. The possible use of the hydrogen oxidation reaction as a catalyst selection criterion is discussed.
June, 2015 · DOI: 10.1016/j.jcat.2015.03.015
Nanotecnología en Superficies y Plasma
Porous, robust highly conducting Ni-YSZ thin film anodes prepared by magnetron sputtering at oblique angles for application as anodes and buffer layers in solid oxide fuel cells
Garcia-Garcia, Francisco J.; Yubero, Francisco; Gonzalez-Elipe, Agustin R.; Balomenou, Stella P.; Tsiplakides, Dimitris; Petrakopoulou, Ioanna; Lambert, Richard M.Inernational Journal of Hydrogen Energy, 40 (2015) 7382-7387 DOI: 10.1016/j.ijhydene.2015.04.001
Abstract
Uniform, highly porous, columnar thin films incorporating YSZ and NiO prepared by magnetron sputtering with deposition at glancing incidence exhibited stoichiometries close to that of the Y-Zr-Ni sputter target. Characterization by means of SEM, XRD, XPS and RBS revealed that the uniformly distributed nickel component in the as-deposited films consisted of NiO, and that the YSZ component was essentially amorphous. Annealing such films at 850 degrees C in hydrogen resulted in crystallization of the YSZ phase with preservation of the columnar morphology, while the NiO underwent reduction to metallic Ni, which partially segregated to the film surface. The hydrogen-annealed thin film anodes exhibited high conductivity, comparable to that of conventionally-prepared anodes, in both hydrogen and hydrogen/water mixtures at temperatures relevant to SOFC operation. They were also robust against strain-induced separation from the substrate under limited thermal cycling in both oxidizing and reducing atmospheres and are promising candidates for use as anodes in their own right and as strain-accommodating buffer layers between conventional anodes and the electrolyte for use in SOFC applications.
June, 2015 · DOI: 10.1016/j.ijhydene.2015.04.001
Materiales de Diseño para la Energía y Medioambiente
Uranium immobilization by FEBEX bentonite and steel barriers in hydrothermal conditions
Villa-Alfageme, M; Hurtado, S; El Mrabet, S; Pazos, MC; Castro, MA; Alba, MDChemical Engineering Journal, 269 (2015) 279-287 DOI: 10.1016/j.cej.2015.01.134
Abstract
FEBEX clay is considered a reference material in engineered barriers for safe storage of nuclear waste and uranium is a minor component of high-level radioactive waste (HLRW) and a main component of the spent nuclear fuel (SNF). Here, the kinetics of reaction of uranium with FEBEX was investigated in addition to the uranium immobilisation ability and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with UO22+ and tetravalent actinide simulator ZrO2+, also present in HLRW. The quantification of the reaction was performed through gamma spectrometry of uranium. Two mechanisms for UO22+ retention by FEBEX were detected: adsorption and formation of stable and insoluble new phases. The structural analyses performed using ZrO2+, confirmed the uranium adsorption and the presence of new phases, ZrO2 and Zr(SiO4), that emphasise the existence of a chemical reaction with the bentonite. The analysis of the velocity of reaction uranium-clay minerals revealed temperature dependence. An exponential fitting suggested that the removal of uranium from solution at temperatures over 200 °C could be completed in less than a year. For lower temperatures, several years are needed. Milliequivalents of UO22+ immobilised by the clay depended on temperature and time and were over cation exchange capacity (CEC) of FEBEX even at 100 °C (reaching 600% of CEC). The reaction with steel, also temperature dependent, was finally analysed. At 200 °C 40–70% of uranium reacted with steel. But only 30–15% reacted at 300 °C and 100 °C. The reactions provide a stable immobilisation mechanism for uranium even when its sorption and swelling capacities fail. Our experiments will be of particular interest for very deep borehole disposals were higher temperatures and pressures are expected.
June, 2015 · DOI: 10.1016/j.cej.2015.01.134
Materiales Ópticos Multifuncionales
Fine Tuning the Emission Properties of Nanoemitters in Multilayered Structures by Deterministic Control of their Local Photonic Environment
Alberto Jiménez-Solano, Juan Francisco Galisteo-López and Hernán MíguezSmall, 11 (2015) 2727-2732 DOI: 10.1002/smll.201402898
Abstract
Deterministic control on the dynamics of organic nanoemitters is achieved through precise control of its photonic environment. Resonators are fabricated by a combination of spin- and dip-coating techniques, which allows placement of the emitters at different positions within the sample, thus acting as a probe of the local density of states.
June, 2015 · DOI: 10.1002/smll.201402898
Reactividad de Sólidos
In Situ Synthesis of a ZrB2-Based Composite Powder Using a Mechanochemical Reaction for the Zircon/Magnesium/Boron Oxide/Graphite System
Jalaly, M; Bafghi, MSS; Tamizifar, M; Gotor, FJInternational Journal of Applied Ceramic Technology, 12 (2015) 551-559 DOI: 10.1111/ijac.12202
Abstract
A ZrSiO4/B2O3/Mg/C system was used to synthesize a ZrB2-based composite through a high-energy ball milling process. As a result of the milling process, a mechanically induced self-sustaining reaction (MSR) was achieved in this system. A composite powder of ZrB2-SiC-ZrC was prepared in situ by a magnesiothermic reduction with an ignition time of approximately 6min. The mechanism for the formation of the product was investigated by studying the relevant subreactions, the stoichiometric amount of B2O3, and thermal analysis.
May, 2015 · DOI: 10.1111/ijac.12202
Nanotecnología en Superficies y Plasma
Free-Base Carboxyphenyl Porphyrin Films Using a TiO2 Columnar Matrix: Characterization and Application as NO2 Sensors
Roales, Javier; Pedrosa, Jose M.; Guillen, Maria G.; Lopes-Costa, Tania; Castillero, Pedro; Barranco, Angel; Gonzalez-Elipe, Agustin R.Sensors, 15 (2015) 11118-11132 DOI: 10.3390/s150511118
Abstract
The anchoring effect on free-base carboxyphenyl porphyrin films using TiO2 microstructured columns as a host matrix and its influence on NO2 sensing have been studied in this work. Three porphyrins have been used: 5-(4-carboxyphenyl)10,15,20-triphenyl-21H,23H-porphyrin (MCTPP); 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin (p-TCPP); and 5,10,15,20-tetrakis(3-carboxyphenyl)-21H,23H-porphyrin (m-TCPP). The analysis of UV-Vis spectra of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 composite films has revealed that m-TCPP/TiO2 films are the most stable, showing less aggregation than the other porphyrins. IR spectroscopy has shown that m-TCPP is bound to TiO2 through its four carboxylic acid groups, while p-TCPP is anchored by only one or two of these groups. MCTPP can only be bound by one carboxylic acid. Consequently, the binding of p-TCPP and MCTPP to the substrate allows them to form aggregates, whereas the more fixed anchoring of m-TCPP reduces this effect. The exposure of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 films to NO2 has resulted in important changes in their UV-Vis spectra, revealing good sensing capabilities in all cases. The improved stability of films made with m-TCPP suggests this molecule as the best candidate among our set of porphyrins for the fabrication of NO2 sensors. Moreover, their concentration-dependent responses upon exposure to low concentrations of NO2 confirm the potential of m-TCPP as a NO2 sensor.
May, 2015 · DOI: 10.3390/s150511118
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
The role of silver nanoparticles functionalized on TiO2 for photocatalytic disinfection of harmful algae
Lee, Soo-Wohn; Obregon, S.; Rodriguez-Gonzalez, V.RSC Advances, 5 (2015) 44470-44475 DOI: 10.1039/C5RA08313C
Abstract
Silver loaded TiO2 samples were prepared by photodeposition of different amounts of Ag+ ions over commercial titanium dioxide (Evonik TiO2 P25) in aqueous media without the presence of sacrificial agents. The obtained photocatalysts were characterized by several techniques such as X-ray powder diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) in order to correlate the effect of the silver amount on the photocatalytic properties of the final nanocomposite. The effect of the silver nanoparticles on the photocatalytic behaviour of TiO2 was evaluated by means of the photodegradation of methyl orange dye and the inactivation of noxious algae Tetraselmis suecicaand Amphidium carterae under continuous exposure of low power irradiation UV-light. The sample with 1.5% wt of silver nanoparticles showed the highest photocatalytic elimination of the azo dye and both algae types. According to the results, the cells were deformed during the photocatalytic process by the attack of highly reactive species such as hydroxyl radicals, H2O2 and superoxide ions generated on the TiO2 surface. The algae cells were not regenerated by themselves after the photocatalytic process due the high degree of fragmentation that they suffered during the light irradiation.
May, 2015 · DOI: 10.1039/C5RA08313C
Nanotecnología en Superficies y Plasma
Electrochemical activation of an oblique angle deposited Cu catalyst film for H-2 production
Gonzalez-Cobos, J; Rico, VJ; Gonzalez-Elipe, AR; Valverde, JL; de Lucas-Consuegra, ACatalysis Science & Technology, 5 (2015) 2203-2214 DOI: 10.1039/c4cy01524j
Abstract
A novel Cu catalyst film was prepared by oblique angle physical vapour deposition (OAD) on a K-βAl2O3 solid electrolyte (alkaline ionic conductor) for catalytic/electrocatalytic purposes. This technique allowed us to obtain a highly porous and electrically conductive Cu catalyst electrode which was tested in the partial oxidation of methanol (POM) reaction for H2 production and its catalytic activity was in situ enhanced via electrochemical promotion of catalysis (EPOC). The electropromotional effect was reversible and reproducible, and allowed us to increase both hydrogen and methyl formate production rates by almost three times under optimal promotion conditions (320 °C, 2.2 × 10−7 mol of K+ transferred). The observed promotional effect was attributed to a decrease in the Cu catalyst work function as a consequence of the controlled migration of electropositive K+ ions which favoured the chemisorption of electron acceptor molecules (O2) at the expense of the electron donor ones (CH3OH). Under the reaction conditions these ions formed some kinds of potassium surface compounds as demonstrated by SEM, EDX and XPS post-reaction characterization analyses. The obtained results demonstrate the interest of the used catalyst-electrode preparation technique for the electrochemical activation of non-noble metal catalyst films.
May, 2015 · DOI: 10.1039/c4cy01524j
Materiales Nanoestructurados y Microestructura
STEM-in-SEM high resolution imaging of gold nanoparticles and bivalve tissues in bioaccumulation experiments
C.A. García-Negrete; M.C. Jiménez de Haro; J. Blasco; M. Soto; A. FernándezAnalyst, 140 (2015) 3082-3089 DOI: 10.1039/C4AN01643B
Abstract
The methodology termed scanning transmission electron microscopy in scanning electron microscopy (STEM-in-SEM) has been used in this work to study the uptake of citrate stabilized gold nanoparticles (AuNPs) (average particle sizes of 23.5 ± 4.0 nm) into tissue samples uponin vitro exposure of the dissected gills of the Ruditapes philippinarum marine bivalve to the nanoparticle suspensions. The STEM-in-SEM methodology has been optimized for achieving optimum resolution under SEM low voltage operating conditions (20–30 kV). Based on scanning microscope assessments and resolution testing (SMART), resolutions well below 10 nm were appropriately achieved by working at magnifications over 100k×, with experimental sample thickness between 300 and 200 nm. These relatively thick slices appear to be stable under the beam and help avoid NP displacement during cutting. We herein show that both localizing of the internalized nanoparticles and imaging of ultrastructural disturbances in gill tissues are strongly accessible due to the improved resolution, even at sample thicknesses higher than those normally employed in standard TEM techniques at higher voltages. Ultrastructural imaging of bio-nano features in bioaccumulation experiments have been demonstrated in this study.
May, 2015 · DOI: 10.1039/C4AN01643B
Química de Superficies y Catálisis
Mono and bimetallic Cu-Ni structured catalysts for the water gas shift reaction
O. Arbeláez, T.R. Reina, S. Ivanova, F. Bustamante, A.L. Villa, M.A. Centeno, J.A. OdriozolaApplied Catalysis A-General, 497 (2015) 1-9 DOI: 10.1016/j.apcata.2015.02.041
Abstract
The water-gas shift (WGS) reaction over structured Cu, Ni, and bimetallic Cu-Ni supported on active carbon (AC) catalysts was investigated. The structured catalysts were prepared in pellets form and applied in the medium range WGS reaction. A good activity in the 180–350 °C temperature range was registered being the bimetallic Cu-Ni:2-1/AC catalyst the best catalyst. The presence of Cu mitigates the methanation activity of Ni favoring the shift process. In addition the active carbon gasification reaction was not observed for the Cu-containing catalyst converting the active carbon in a very convenient support for the WGS reaction. The stability of the bimetallic Cu-Ni:2-1/AC catalyst under continuous operation conditions, as well as its tolerance towards start/stop cycles was also evaluated.
May, 2015 · DOI: 10.1016/j.apcata.2015.02.041
Nanotecnología en Superficies y Plasma
Anisotropic In-Plane Conductivity and Dichroic Gold Plasmon Resonance in Plasma-Assisted ITO Thin Films e-Beam-Evaporated at Oblique Angles
Parra-Barranco, Julian; Garcia-Garcia, Francisco J.; Rico, Victor; Borras, Ana; Lopez-Santos, Carmen; Frutos, Fabian; Barranco, Angel; Gonzalez-Elipe, Agustin R.ACS Applied Materials & Interfaces, 7 (2015) 10993-11001 DOI: 10.1021/acsami.5b02197
Abstract
ITO thin films have been prepared by electron beam evaporation at oblique angles (OA), directly and while assisting their growth with a downstream plasma. The films microstructure, characterized by scanning electron microscopy, atomic force microscopy, and glancing incidence small-angle X-ray scattering, consisted of tilted and separated nanostructures. In the plasma assisted films, the tilting angle decreased and the nanocolumns became associated in the form of bundles along the direction perpendicular to the flux of evaporated material. The annealed films presented different in-depth and sheet resistivity as confirmed by scanning conductivity measurements taken for the individual nanocolumns. In addition, for the plasma-assisted thin films, two different sheet resistance values were determined by measuring along the nanocolumn bundles or the perpendicular to it. This in-plane anisotropy induces the electrochemical deposition of elongated gold nanostructures. The obtained Au-ITO composite thin films were characterized by anisotropic plasmon resonance absorption and a dichroic behavior when examined with linearly polarized light.
May, 2015 · DOI: 10.1021/acsami.5b02197
Reactividad de Sólidos
Toughening of complete solid solution cermets by graphite addition
Chicardi, E; Torres, Y; Sayagues, MJ; Medri, V; Melandri, C; Cordoba, JM; Gotor, FJChemical Engineering Journal, 267 (2015) 297-305 DOI: 10.1016/j.cej.2015.01.022
Abstract
(Ti0.95Ta0.05)(C0.5N0.5)-Co complete solid solution cermets (CSCs) were developed by a mechanochemical synthesis process and a pressureless sintering method. The effect of different percentages of graphite used as a sintering additive on the nature of the binder phase and the mechanical properties of the cermets was investigated. Microstructural and mechanical characterisations were carried out by X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Vickers hardness, indentation fracture toughness and nanoindentation. The addition of graphite modified the carbon activity during sintering, reducing the dissolution of carbonitride ceramic particles into the molten binder. The amount of Ti and Ta remaining in the binder after sintering gradually decreased as the amount of graphite added increased, which induced a change in the nature of the binder phase. When no graphite was added, the binder consisted of the brittle TixTa1−xCo2 intermetallic phase. With the increase in the amount of graphite added, the formation of more ductile phases, such as TixTa1−xCo3 and α-Co, was observed, causing a significant improvement in the toughness of the cermets.
May, 2015 · DOI: 10.1016/j.cej.2015.01.022
Materiales y Procesos Catalíticos de Interés Ambiental y Energético - Nanotecnología en Superficies y Plasma
Theory and Practice: Bulk Synthesis of C3B and its H2- and Li-Storage Capacity
King, TC; Matthews, PD; Glass, H; Cormack, JA; Holgado, JP; Leskes, M; Griffin, JM; Scherman, OA; Barker, PD; Grey, CP; Dutton, SE; Lambert, RM; Tustin, G; Alavi, A; Wright, DSAngewandte Chemie International Edition, 54 (2015) 5919-5923 DOI: 10.1002/anie.201412200
Abstract
Previous theoretical studies of C3B have suggested that boron-doped graphite is a promising H2- and Li-storage material, with large maximum capacities. These characteristics could lead to exciting applications as a lightweight H2-storage material for automotive engines and as an anode in a new generation of batteries. However, for these applications to be realized a synthetic route to bulk C3B must be developed. Here we show the thermolysis of a single-source precursor (1,3-(BBr2)2C6H4) to produce graphitic C3B, thus allowing the characteristics of this elusive material to be tested for the first time. C3B was found to be compositionally uniform but turbostratically disordered. Contrary to theoretical expectations, the H2- and Li-storage capacities are lower than anticipated, results that can partially be explained by the disordered nature of the material. This work suggests that to model the properties of graphitic materials more realistically, the possibility of disorder must be considered.
May, 2015 · DOI: 10.1002/anie.201412200
Materiales Ópticos Multifuncionales
An Optically Controlled Microscale Elevator Using Plasmonic Janus Particles
Nedev, S; Carretero-Palacios, S; Kuhler, P; Lohmuller, T; Urban, AS; Anderson, LJE; Feldmann, JACS Photonics, 2 (2015) 491-496 DOI: 10.1021/ph500371z
Abstract
In this article, we report how Janus particles, composed of a silica sphere with a gold half-shell, can be not only stably trapped by optical tweezers but also displaced controllably along the axis of the laser beam through a complex interplay between optical and thermal forces. Scattering forces orient the asymmetric particle, while strong absorption on the metal side induces a thermal gradient, resulting in particle motion. An increase in the laser power leads to an upward motion of the particle, while a decrease leads to a downward motion. We study this reversible axial displacement, including a hysteretic jump in the particle position that is a result of the complex pattern of a tightly focused laser beam structure above the focal plane. As a first application we simultaneously trap a spherical gold nanoparticle and show that we can control the distance between the two particles inside the trap. This photonic micron-scale “elevator” is a promising tool for thermal force studies, remote sensing, and optical and thermal micromanipulation experiments.
April, 2015 · DOI: 10.1021/ph500371z
Reactividad de Sólidos
Morphological changes on graphene nanoplatelets induced during dispersion into an epoxy resin by different methods
Moriche, R; Prolongo, SG; Sanchez, M; Jimenez-Suarez, A; Sayagues, MJ; Urena, AComposites Part B-Engineering, 72 (2015) 199-205 DOI: 10.1016/j.compositesb.2014.12.012
Abstract
A structural analysis demonstrating how the manufacturing method of graphene nanoplatelets (GNPs) into a polymer matrix can strongly modify the GNPs morphology and, consequently, their properties, was carried out. Three different methods based on sonication and high shear forces were used to elucidate defects induction and possible size diminution. Manufacturing methods including high shear forces caused the extension of the GNPs while sonication induces wrinkling of the sheets. Residual stresses are induced in the nanoplatelets structure showing an increase in the Raman intensities ratios I-D/I-G and I-D/I-G when a major cycles number of calendering are applied.
April, 2015 · DOI: 10.1016/j.compositesb.2014.12.012
Materiales Coloidales
Biosynthesis of silver fine particles and particles decorated with nanoparticles using the extract of Illicium verum (star anise) seeds
Luna, Carlos; Chavez, V. H. G.; Diaz Barriga-Castro, Enrique; Nunez, Nuria O.; Mendoza-Resendez, RaquelSpectrochimica Acta Part A-Molecular and Biomolecular Spectroscopy, 141 (2015) 43-50 DOI: 10.1016/j.saa.2014.12.076
Abstract
Given the upsurge of new technologies based on nanomaterials, the development of sustainable methods to obtain functional nanostructures has become an imperative task. In this matter, several recent researches have shown that the biodegradable natural antioxidants of several plant extracts can be used simultaneously as reducing and stabilizing agents in the wet chemical synthesis of metallic nanoparticles, opening new opportunities to design greener synthesis. However, the challenge of these new techniques is to produce stable colloidal nanoparticles with controlled particle uniformity, size, shape and aggregation state, in similar manner than the well-established synthetic methods. In the present work, colloidal metallic silver nanoparticles have been synthesized using silver nitrate and extracts of Illicium verum (star anise) seeds at room temperature in a facile one-step procedure. The resulting products were colloidal suspensions of two populations of silver nanoparticles, one of them with particle sizes of few nanometers and the other with particles of tens of nm. Strikingly, the variation of the AgNO3/extract weight ratio in the reaction medium yielded to the variation of the spatial distribution of the nanoparticles: high AgNO3/extract concentration ratios yielded to randomly dispersed particles, whereas for lower AgNO3/extract ratios, the biggest particles appeared coated with the finest nanoparticles.-This biosynthesized colloidal system, with controlled particle aggregation states, presents plasmonic and SERS properties with potential applications in molecular sensors and nanophotonic devices.
April, 2015 · DOI: 10.1016/j.saa.2014.12.076
Reactividad de Sólidos
Mechanically induced self-propagating reaction of vanadium carbonitride
Roldan, MA; Alcala, MD; Real, CCeramics International, 41 (2015) 4688-4695 DOI: 10.1016/j.ceramint.2014.12.016
Abstract
Vanadium carbonitrides (VCxN1-x) were prepared via mechanosynthesis from mixtures of elemental vanadium and carbon with different V/C atomic ratios under a nitrogen atmosphere using a high-energy ball mill. We obtained the full composition range of carbonitrides at room temperature. The products were characterized using X-ray diffraction, scanning electron microscopy and electron energy loss spectroscopy. The results showed particle-sized products with high sinterability and very high microhardness.
April, 2015 · DOI: 10.1016/j.ceramint.2014.12.016
Materiales de Diseño para la Energía y Medioambiente
Self-Assembling of Tetradecylammonium Chain on Swelling High Charge Micas (Na-Mica-3 and Na-Mica-2): Effect of Alkylammonium Concentration and Mica Layer Charge
Pazos, MC; Cota, A; Osuna, FJ; Pavon, E; Alba, MDLangmuir, 31 (2015) 4394-4401 DOI: 10.1021/acs.langmuir.5b00224
Abstract
A family of tetradecylammonium micas is synthesized using synthetic swelling micas with high layer charge (NanSi8-nAln,Mg6F4O20 center dot XH2O, where n = 2 and 3) exchanged with tetradecylammonium cations. The molecular arrangement of the surfactant is,elucidated on the basis of XRD patterns and DTA. The ordering conformation of the surfactant molecules into the interlayer space of Micas is investigated by IR/FT, C-13, Al-27, and Si-29 MAS NMR. The structural arrangement of the tetradecylammonium cation in the interlayer space of high-charge micas is more sensitive to the effect of the mica layer charge at high concentration. The surfactant arrangement is found to follow the bilayer-paraffin model for all values of layer charge and surfactant concentration. However, at initial concentration below the mica CEC, a lateral monolayer is also observed. The amount of ordered conformation all-trans is directly proportional to the layer charge and surfactant concentration.
April, 2015 · DOI: 10.1021/acs.langmuir.5b00224
Materiales Nanoestructurados y Microestructura
Self-lubricity of WSex nanocomposite coatings
S. Dominguez-Meister; M. Conte; A. Igartua; T.C. Rojas; J.C. Sánchez-LópezACS Applied Materials & Interfaces, 7 (2015) 7979-7986 DOI: 10.1021/am508939s
Abstract
Transition metal chalcogenides with lamellar structure are known for their use in tribological applications although limited to vacuum due to their easy degradation in the presence of oxygen and/or moisture. Here we present a tailored WSex coating with low friction (0.07) and low wear rates (3 × 10–7 mm3 Nm–1) even in ambient air. To understand the low friction behavior and lower chemical reactivity a tribological study is carried out in a high-vacuum tribometer under variable pressure (atmospheric pressure to 1 × 10–8 mbar). A detailed investigation of the film nanostructure and composition by advanced transmission electron microscopy techniques with nanoscale resolution determined that the topmost layer is formed by nanocrystals of WSe2 embedded in an amorphous matrix richer in W, a-W(Se). After the friction test, an increased crystalline order and orientation of WSe2 lamellas along the sliding direction were observed in the interfacial region. On the basis of high angle annular dark field, scanning transmission electron microscopy, and energy dispersive X-ray analysis, the release of W atoms from the interstitial basal planes of the a-W(Se) phase is proposed. These W atoms reaching the surface, play a sacrificial role preventing the lubricant WSe2 phase from oxidation. The increase of the WSe2 crystalline order and the buffer effect of W capturing oxygen atoms would explain the enhanced chemical and tribological response of this designed nanocomposite material.
April, 2015 · DOI: 10.1021/am508939s
Fotocatálisis Heterogénea: Aplicaciones
Photocatalytic reduction of CO2 over platinised Bi2WO6-based materials
Murcia-Lopez, S; Vaiano, V; Hidalgo, MC; Navio, JA; Sannino, DPhotochemical & Photobiological Sciences, 14 (2015) 678-685 DOI: 10.1039/c4pp00407h
Abstract
The photocatalytic reduction of CO2 with H2O to produce CH4 in the gas phase was carried out in the presence of two Bi2WO6-based materials. For this purpose, single Bi2WO6 and a coupled Bi2WO6-TiO2 system were synthesised and metallised with Pt, through a Pt photodeposition method. Then, the samples were characterised and the photocatalytic activity was evaluated in a continuous fluidised-bed reactor irradiated with UV light. Single Bi2WO6 presents an interesting behaviour under H2O rich conditions. In particular, the metallisation improves the material's performance for CH4 formation, while the TiO2 addition to Bi2WO6 increases the CH4 yield only at low H2O/CO2 ratio. The Bi2WO6-TiO2 system metallised with a Pt photocatalyst displayed the highest CH4 yield among all the prepared photocatalysts. The stability of the system can be enhanced through the addition of a blue phosphor to the reactant mixture, especially under H2O rich conditions.
April, 2015 · DOI: 10.1039/c4pp00407h
Reactividad de Sólidos
Applications of sample-controlled thermal analysis (SCTA) to kinetic analysis and synthesis of materials
Perez-Maqueda, L. A.; Criado, J. M.; Sanchez-Jimenez, P. E.; Dianez, M. J.Journal of Thermal Analysis and Calorimetry, 120 (2015) 45-51 DOI: 10.1007/s10973-014-4176-6
Abstract
The advantages of the sample-controlled thermal analysis (SCTA) for both the kinetic analysis of solid-state reactions and the synthesis of materials are reviewed. This method implies an intelligent control of the temperature by the solid-state reaction under study in such a way that the reaction rate as a function of the time fits a profile previously defined by the user. It has been shown that SCTA has important advantages for discriminating the kinetic model of solid-state reactions as compared with conventional rising temperature methods. Moreover, the advantages of SCTA methods for synthesising materials with controlled texture and structure are analysed.
April, 2015 · DOI: 10.1007/s10973-014-4176-6
Materiales Nanoestructurados y Microestructura
Hydrogen production through sodium borohydride ethanolysis
Arzac, GM; Fernandez, AInternational Journal of Hydrogen Energy, 40 (2015) 5326-5332 DOI: 10.1016/j.ijhydene.2015.01.115
Abstract
In this work, sodium borohydride (SB) ethanolysis was explored for the first time as a method to generate hydrogen for Polymer Exchange Membrane Fuel Cells. Ethanolysis by-product was characterized by Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, and Nuclear Magnetic Resonance. Metal and acid catalysts were tested. RuCl3 center dot 3H(2)O was the best metal catalyst. Acetic acid was selected for the study because of its effectiveness, low cost and relative greenness. The maximum gravimetric hydrogen density obtained was 2.1% wt. The addition of water produces an increase in hydrogen generation rate and a decrease in conversion. The use of ethanol-methanol mixtures produces an increase in reaction rates in absence of catalyst. As a proof of concept the reaction was performed in a small reactor which operates by the addition of ethanolic acetic acid solutions to solid SB (in the form of granules). The reactor produces stable and constant hydrogen generation in the range of 20-80 ml min(-1) during 1 h at constant temperature (around 27-35 degrees.
April, 2015 · DOI: 10.1016/j.ijhydene.2015.01.115
Materiales de Diseño para la Energía y Medioambiente
Pectin-Lipid Self-Assembly: Influence on the Formation of Polyhydroxy Fatty Acids Nanoparticles
Guzman-Puyol, Susana; Jesus Benitez, Jose; Dominguez, Eva; Bayer, Ilker Sefik; Cingolani, Roberto; Athanassiou, Athanassia; Heredia, Antonio; Heredia-Guerrero, Jose AlejandroPLoS One, 10 (2015) e0124639 DOI: 10.1371/journal.pone.0124639
Abstract
Nanoparticles, named cutinsomes, have been prepared from aleuritic (9,10,16-trihidroxipalmitic) acid and tomato fruit cutin monomers (a mixture of mainly 9(10), 16-dihydroxypalmitic acid (85%, w/w) and 16-hydroxyhexadecanoic acid (7.5%, w/w)) with pectin in aqueous solution. The process of formation of the nanoparticles of aleuritic acid plus pectin has been monitored by UV-Vis spectrophotometry, while their chemical and morphological characterization was analyzed by ATR-FTIR, TEM, and non-contact AFM. The structure of these nanoparticles can be described as a lipid core with a pectin shell. Pectin facilitated the formation of nanoparticles, by inducing their aggregation in branched chains and favoring the condensation between lipid monomers. Also, pectin determined the self-assembly of cutinsomes on highly ordered pyrolytic graphite (HOPG) surfaces, causing their opening and forming interconnected structures. In the case of cutin monomers, the nanoparticles are fused, and the condensation of the hydroxy fatty acids is strongly affected by the presence of the polysaccharide. The interaction of pectin with polyhydroxylated fatty acids could be related to an initial step in the formation of the plant biopolyester cutin.
April, 2015 · DOI: 10.1371/journal.pone.0124639
Materiales Coloidales
Up-conversion in Er3+/Yb3+ co-doped LaPO4 submicron-sized spheres
Garcia-Sevillano, J.; Cantelar, E.; Cusso, F.; Ocana, M.Optical Materials, 41 (2015) 104-107 DOI: 10.1016/j.optmat.2014.10.022
Abstract
Er3+/Yb3+ co-doped materials have been extensively used for imaging in biomedical applications using either visible up-converted (UC) or near-infrared (NIR) emissions. The UC spectrum is composed mainly by two Erbium emissions in the green (2H11/2:4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) spectral range, while the NIR spectrum includes Er3+ (λ ∼ 1.5 μm, 4I13/2 → 4I15/2) and Er3+/Yb3+ (λ ∼ 980 nm, 2F5/2 → 2F7/2(Yb3+):4I11/2 → 4I15/2 (Er3+)) transitions; which relative intensities are dependent on several physical parameters. In the present work, we present the preparation and optical characterization of Er3+/Yb3+ co-doped LaPO4 submicron-sized spheres. The luminescence (CW and pulsed) characteristics, after different post-annealing treatments, are studied. It is found that such treatments strongly increment the emission efficiency, possibly due to the suppression of residual impurities. After calcination at 1100 °C the material behaves as an excellent UC and NIR–NIR wavelength converter.
March, 2015 · DOI: 10.1016/j.optmat.2014.10.022
Materiales Nanoestructurados y Microestructura
High N-content a-C:N films elaborated by femtosecond PLD with plasma assistance
Maddi, C; Donnet, C; Loir, AS; Tite, T; Barnier, V; Rojas, TC; Sanchez-Lopez, JC; Wolski, K; Garrelie, FApplied Surface Science, 332 (2015) 346-353 DOI: 10.1016/j.apsusc.2015.01.123
Abstract
Amorphous carbon nitride (a-C:N) thin films are a interesting class of carbon-based electrode materials. Therefore, synthesis and characterization of these materials have found lot of interest in environmental analytical microsystems. Herein, we report the nitrogen-doped amorphous carbon thin film elaboration by femtosecond pulsed laser deposition (fs-PLD) both with and without a plasma assistance. The chemical composition and atomic bonding configuration of the films were investigated by multi-wavelength (MW) Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). The highest nitrogen content, 28 at.%, was obtained with plasma assistance. The I(D)/I(G) ratio and the G peak position increased as a function of nitrogen concentration, whereas the dispersion and full width at half maximum (FWHM) of G peak decreased. This indicates more ordered graphitic like structures in the films both in terms of topological and structural, depending on the nitrogen content. EELS investigations were correlated with MW Raman results. The interpretation of XPS spectra of carbon nitride films remains a challenge. Plasma assisted PLD in the femtosecond regime led to a significant high nitrogen concentration, which is highlighted on the basis of collisional processes in the carbon plasma plume interacting with the nitrogen plasma.
March, 2015 · DOI: 10.1016/j.apsusc.2015.01.123
Materiales de Diseño para la Energía y Medioambiente
Synthesis temperature effect on Na-Mica-4 crystallinity and heteroatom distribution
Naranjo, M; Castro, MA; Cota, A; Osuna, FJ; Pavon, E; Alba, MDMicroporous and Mesoporous Materials, 204 (2015) 282-288 DOI: 10.1016/j.micromeso.2014.11.026
Abstract
The discovery of swelling brittle mica, Na-Mica-4, has been one of the most significant advances in the pursuit for a material with high ion-exchange capacity. For technical applications, the control of the phase evolution during the synthesis is crucial. The main aim of this study was to investigate the effect of Na-Mica-4 synthesis temperature on the crystalline phase evolution, Si–Al distribution in the tetrahedral sheet, the Al occupancy between tetrahedral and octahedral sites and their effects on the interlayer space composition. The synthesis temperature range between 600 °C and 900 °C was explored. At low temperature (600 °C), the precursors were transformed in a low-charged swelling 2:1 phyllosilicate, saponite type, which was progressively aluminum enriched with temperature. The high-charged swelling mica was completely formed at 700 °C, although a minor anhydrous contribution remained up to 850 °C. Up to 800 °C, silicates and fluorides secondary phases were detected as a minor contribution.
March, 2015 · DOI: 10.1016/j.micromeso.2014.11.026
Materiales Nanoestructurados y Microestructura
Transmission electron microscopy of thiol-capped Au clusters on C: Structure and electron irradiation effects
Lionel C. Gontard, Rafal E. Dunin-BorkowskiMicron DOI: 10.1016/j.micron.2014.12.001
Abstract
High-resolution transmission electron microscopy is used to study interactions between thiol-capped Au clusters and amorphous C support films. The morphologies of the clusters are found to depend both on their size and on the local structure of the underlying C. When the C is amorphous, larger Au clusters are crystalline, while smaller clusters are typically disordered. When the C is graphitic, the Au particles adopt either elongated shapes that maximize their contact with the edge of the C film or planar arrays when they contain few Au atoms. We demonstrate the influence of electron beam irradiation on the structure, shape and stability of the Au clusters, as well as on the formation of holes bounded by terraces of graphitic lamellae in the underlying C.
March, 2015 · DOI: 10.1016/j.micron.2014.12.001
Materiales Ópticos Multifuncionales
Nanolevitation Phenomena in Real Plane-Parallel Systems Due to the Balance between Casimir and Gravity Forces
Esteso, V; Carretero-Palacios, S; Miguez, HJournal of Physical Chemistry C, 119 (2015) 5663-5670 DOI: 10.1021/jp511851z
Abstract
We report on the theoretical analysis of equilibrium distances in real plane-parallel systems under the influence of Casimir and gravity forces at thermal equilibrium. Due to the balance between these forces, thin films of Teflon, silica, or polystyrene in a single-layer configuration and immersed in glycerol stand over a silicon substrate at certain stable or unstable positions depending on the material and the slab thickness. Hybrid systems containing silica and polystyrene, materials which display Casimir forces and equilibrium distances of opposite nature when considered individually, are analyzed in either bilayer arrangements or as composite systems made of a homogeneous matrix with small inclusions inside. For each configuration, equilibrium distances and their stability can be adjusted by fine-tuning of the volume occupied by each material. We find the specific conditions under which nanolevitation of realistic films should be observed. Our results indicate that thin films of real materials in plane-parallel configurations can be used to control suspension or stiction phenomena at the nanoscale.
March, 2015 · DOI: 10.1021/jp511851z
Química de Superficies y Catálisis
Ni-CeO2/C Catalysts with Enhanced OSC for the WGS Reaction
Pastor-Perez, L; Ramirez Reina, T; Ivanova, S; Centeno, MA; Odriozola, JA; Sepulveda-Escribano, ACatalysts, 5 (2015) 298-309 DOI: 10.3390/catal5010298
Abstract
In this work, the WGS performance of a conventional Ni/CeO2 bulk catalyst is compared to that of a carbon-supported Ni-CeO2 catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO2/C catalyst is associated to its oxygen storage capacity, a parameter that strongly influences the WGS behavior. The stability of the carbon-supported catalyst under realistic operation conditions is also a subject of this paper. In summary, our study represents an approach towards a new generation of Ni-ceria based catalyst for the pure hydrogen production via WGS. The dispersion of ceria nanoparticles on an activated carbon support drives to improved catalytic skills with a considerable reduction of the amount of ceria in the catalyst formulation.
March, 2015 · DOI: 10.3390/catal5010298
Química de Superficies y Catálisis
Ionic liquid immobilization on carbon nanofibers and zeolites: Catalyst design for the liquid-phase toluene chlorination
Losch, Pit; Martinez Pascual, Antonio; Boltz, Marilyne; Ivanova, Svetlana; Louis, Benoit; Montilla, Francisco; Antonio Odriozola, JoseComptes Rendus Chimie, 18 (2015) 324-329 DOI: 10.1016/j.crci.2014.06.006
Abstract
The environmental-friendly chlorination reaction of toluene by trichloroisocyanuric acid (TCCA, C3N3O3Cl3) was investigated applying immobilized ionic liquids (ILs) on different supports. Ionic liquids were grafted either on carbon nanofibers (CNF) or encapsulated in zeolites. Their influence on the chlorination activity as well as on the selectivity in different chlorinated products was studied. An unusually high selectivity toward meta-chlorotoluene was achieved, up to 36%. Hence, the selectivity could be tuned to produce either expected ortho-/para-chlorotoluene or meta-chlorotoluene with a proper support choice.
March, 2015 · DOI: 10.1016/j.crci.2014.06.006
Nanotecnología en Superficies y Plasma
Nanocolumnar coatings with selective behavior towards osteoblast and Staphylococcus aureus proliferation
Izquierdo-Barba, Isabel; Miguel Garcia-Martin, Jose; Alvarez, Rafael; Palmero, Alberto; Esteban, Jaime; Perez-Jorge, Concepcion; Arcos, Daniel; Vallet-Regi, MariaActa Biomaterialia, 15 (2015) 20-28 DOI: 10.1016/j.actbio.2014.12.023
Abstract
Bacterial colonization and biofilm formation on orthopedic implants is one of the worst scenarios in orthopedic surgery, in terms of both patient prognosis and healthcare costs. Tailoring the surfaces of implants at the nanoscale to actively promote bone bonding while avoiding bacterial colonization represents an interesting challenge to achieving better clinical outcomes. Herein, a Ti6Al4V alloy of medical grade has been coated with Ti nanostructures employing the glancing angle deposition technique by magnetron sputtering. The resulting surfaces have a high density of nanocolumnar structures, which exhibit strongly impaired bacterial adhesion that inhibits biofilm formation, while osteoblasts exhibit good cell response with similar behavior to the initial substrates. These results are discussed on the basis of a "lotus leaf effect" induced by the surface nanostructures and the different sizes and biological characteristics of osteoblasts and Staphylococcus aureus.
March, 2015 · DOI: 10.1016/j.actbio.2014.12.023
Materiales de Diseño para la Energía y Medioambiente
Microstructure, elastic and inelastic properties of partially graphitized biomorphic carbons
Orlova, TS; Kardashev, BK; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J; Martinez-Fernandez, JPhysics of the Solid State, 57 (2015) 586-591 DOI: 10.1134/S106378341503018X
Abstract
The microstructural characteristics and amplitude dependences of the Young's modulus E and internal friction (logarithmic decrement delta) of biocarbon matrices prepared by beech wood carbonization at temperatures T (carb) = 850-1600A degrees C in the presence of a nickel-containing catalyst have been studied. Using X-ray diffraction and electron microscopy, it has been shown that the use of a nickel catalyst during carbonization results in a partial graphitization of biocarbons at T (carb) a parts per thousand yen 1000A degrees C: the graphite phase is formed as 50- to 100-nm globules at T (carb) = 1000A degrees C and as 0.5- to 3.0-mu m globules at T (carb) = 1600A degrees C. It has been found that the measured dependences E(T (carb)) and delta(T (carb)) contain three characteristic ranges of variations in the Young's modulus and logarithmic decrement with a change in the carbonization temperature: E increases and delta decreases in the ranges T (carb) < 1000A degrees C and T (carb) > 1300A degrees C; in the range 1000 < T (carb) < 1300A degrees C, E sharply decreases and delta increases. The observed behavior of E(T (carb)) and delta(T (carb)) for biocarbons carbonized in the presence of nickel correlates with the evolution of their microstructure. The largest values of E are obtained for samples with T (carb) = 1000 and 1600A degrees C. However, the samples with T (carb) = 1600A degrees C exhibit a higher susceptibility to microplasticity due to the presence of a globular graphite phase that is significantly larger in size and total volume.
March, 2015 · DOI: 10.1134/S106378341503018X
Materiales Ópticos Multifuncionales
Sunlight Absorption Engineering for Thermophotovoltaics: Contributions from the Optical Design
Miguez, HChemSusChem, 8 (2015) 786-788 DOI: 10.1002/cssc.201403361
Abstract
Nowadays, solar thermophotovoltaic systems constitute a platform in which sophisticated optical material designs are put into practice with the aim of achieving the long sought after dream of developing an efficient energy conversion device based on this concept. Recent advances demonstrate that higher efficiencies are at reach using photonic nanostructures amenable to mass production and scale-up.
March, 2015 · DOI: 10.1002/cssc.201403361
Materiales de Diseño para la Energía y Medioambiente
Effect of catalytic graphitization on the electrochemical behavior of wood derived carbons for use in supercapacitors
Gutierrez-Pardo, A; Ramirez-Rico, J; Cabezas-Rodriguez, R; Martinez-Fernandez, JJournal of Power Sources, 278 (2015) 18-26 DOI: 10.1016/j.jpowsour.2014.12.030
Abstract
Porous graphitic carbons were successfully obtained from wood precursors through pyrolysis using a transition metal as catalyst. Once the catalyst is removed, the resulting material mimics the microstructure of the wood and presents high surface area, open and interconnected porosity and large pore volume, high crystallinity and good electrical conductivity, making these carbons interesting for electrochemical devices. Carbons obtained were studied as electrodes for supercapacitors in half cell experiments, obtaining high capacitance values in a basic media (up to 133 F g−1 at current densities of 20 mA g−1 and 35 F g−1 at current densities of 1 A g−1). Long-cycling experiments showed excellent stability of the electrodes with no reduction of the initial capacitance values after 1000 cycles in voltammetry.
March, 2015 · DOI: 10.1016/j.jpowsour.2014.12.030
Materiales Avanzados
Valorization and inertization of galvanic sludge waste in clay bricks
Perez-Villarejo, L; Martinez-Martinez, S; Carrasco-Hurtado, B; Eliche-Quesada, D; Urena-Nieto, C; Sanchez-Soto, PJApplied Clay Science, 105-106 (2015) 89-99 DOI: 10.1016/j.clay.2014.12.022
Abstract
Galvanic sludge wastes (GSW) are produced by the physico-chemical treatments of wastewater generated by electroplating plants. These materials have a significant potential for the production of clay ceramic bricks. This paper focuses on the viability of the inertization of heavy metals from GSW mixed with clays. The original materials were obtained by mixing three types of raw clay (red, yellow and black) in equal parts with GSW. These mixtures were characterized by XRD, XRF, and chemical elemental analysis CHNS. The dosage of GSW in the clay–GSW bricks was up to 5 wt.%. The bricks were then manufactured using conventional processes. The influence of the amount of GSW was evaluated after firing the clay–GSW composites at 950 °C for 1 h. The engineering properties of the fired samples, such as density, water absorption, open porosity, water suction and compressive strength, with and without the GSW, were determined. The incorporation of GSW into the clay mix clearly decreased the linear shrinkage and bulk density of the bricks in comparison with the fired clay used as a control. These GSW–clay composites also showed lower open porosity. According to the results obtained for the bulk density of the bricks, samples with GSW addition showed slightly lower values of open porosity than clay bodies, indicating that the GSW–clay samples had slightly higher closed porosity values. This was also shown by SEM. The open porosity, SEM and pore size distribution tests indicated that the porosity generated by the addition of GSW was mainly closed and, therefore, GSW bricks had excellent mechanical properties. The environmental risks of the incorporation of GSW, rich in heavy metals (Cr, Zn, Ni and others), to a clay matrix were evaluated by leaching tests of the fired products. The results indicated a successful inertization of the pollutants.
March, 2015 · DOI: 10.1016/j.clay.2014.12.022
Reactividad de Sólidos
Nanoindentation of (Ti,Ta)(C,N)-Co cermets prepared by methods of mechanochemistry
Hvizdos, Pavol; Balko, Jan; Manuel Cordoba, Jose; Chicardi, ErnestoInternational Journal of Refractory Metals & Hard Materials, 49 (2015) 219-224 DOI: 10.1016/j.ijrmhm.2014.07.038
Abstract
Four materials TixTa(1 - x)C(0.5)N(0.5)-20%Co of two chemical compositions (x = 0.9 and 0.95) and two high energy milling methods (one stage and two stage milling) have been prepared. Nano-hardness and elastic modulus for microstructure as a whole and for individual constituent phases (matrix and carbide grains) were obtained by instrumented indentation. Individual targeted indentations as well as grid nanoindentation technique were used to discern the individual constituents' properties. Maximum loads of 20 mN for individual phases and 300 mN for composite microstructure were applied. Materials with higher amount of Ti had larger grains but the milling procedure had stronger influence on the grain size. The two step milling resulted in finer microstructures but with a much wider grain size distribution. Final composite mechanical properties, however, were very similar. Hardness and indentation elasticity modulus of all materials were comparable within the errors of measurement.
March, 2015 · DOI: 10.1016/j.ijrmhm.2014.07.038
Materiales Ópticos Multifuncionales
Highly Efficient Perovskite Solar Cells with Tunable Structural Color
W. Zhang, M. Anaya, G. Lozano, M.E. Calvo, M.B. Johnston, H. Míguez, H.J. SnaithNano Letters, 15 (2015) 1698-1702 DOI: 10.1021/nl504349z
Abstract
The performance of perovskite solar cells has been progressing over the past few years and efficiency is likely to continue to increase. However, a negative aspect for the integration of perovskite solar cells in the built environment is that the color gamut available in these materials is very limited and does not cover the green-to-blue region of the visible spectrum, which has been a big selling point for organic photovoltaics. Here, we integrate a porous photonic crystal (PC) scaffold within the photoactive layer of an opaque perovskite solar cell following a bottom-up approach employing inexpensive and scalable liquid processing techniques. The photovoltaic devices presented herein show high efficiency with tunable color across the visible spectrum. This now imbues the perovskite solar cells with highly desirable properties for cladding in the built environment and encourages design of sustainable colorful buildings and iridescent electric vehicles as future power generation sources.
March, 2015 · DOI: 10.1021/nl504349z
Materiales de Diseño para la Energía y Medioambiente
Sliding wear resistance of sintered SiC-fiber bonded ceramics
Vera, MC; Ramirez-Rico, J; Martinez-Fernandez, J; Singh, MInternational Journal of Refractory Metals & Hard Materials, 49 (2015) 232-239 DOI: 10.1016/j.ijrmhm.2014.06.020
Abstract
Advanced SiC-based ceramics and fiber reinforced composites are interesting materials for a wide variety of applications involving sliding wear conditions because of their excellent thermomechanical properties. The microstructure and wear resistance of sintered SiC fiber bonded ceramics (SA Tyrannohex) were studied. The material is composed of SiC-fibers in two orientations, with polygonal cross sections and cores having higher carbon content than their surroundings, as observed with SEM. A thin layer of C exists between the fibers. This layer has been found to be a turbostratic-layered structure oriented parallel to the fiber surface. XRD shows that the material is highly crystalline and composed mostly of β-SiC. Unlubricated wear behavior of the SA-Tyrannohex material when sliding against a Si3N4 ball in air at room temperature was evaluated. Experiments were performed using a pin on disk apparatus, under different normal loads of 2, 5 and 10 N at sliding speeds of 25, 50, 100 mm/s. A decrease of the friction coefficient with load was found due to the presence of the turbostratic carbon layer between the fibers. Wear rates of the order of 100 mm3/MJ were obtained, independently of sliding speed. Microfracture of the fibers is the main wear mechanism.
March, 2015 · DOI: 10.1016/j.ijrmhm.2014.06.020
Materiales de Diseño para la Energía y Medioambiente
Sliding wear resistance of biomorphic SiC ceramics
Vera, MC; Ramirez-Rico, J; Martinez-Fernandez, J; Singh, MInternational Journal of Refractory Metals & Hard Materials, 49 (2015) 327-333 DOI: 10.1016/j.ijrmhm.2014.07.004
Abstract
Biomorphic SiC ceramics were fabricated from four different wood precursors and their Knoop hardness and sliding wear resistance when sliding against a Si3N4 ball in air were studied. Tribological experiments were performed using a pin on disk apparatus, under normal loads of 2 and 5 N, at a sliding speed of 100 mm/s. The effects of specimen porosity and microstructure on measured wear were evaluated. A commercial sintered silicon carbide ceramic was also tested for comparison. Small differences in friction coefficient comparable to monolithic SiC ceramics were obtained. Several concurrent wear mechanisms are taking place: microfracture, plastic deformation in the Si phase and oxidation of the Si and/or SiC phase. The presence of an oxide tribolayer was assessed using fluorescence microscopy. Wear rates were found to scale with SiC content and depend on residual porosity in the composite.
March, 2015 · DOI: 10.1016/j.ijrmhm.2014.07.004
Química de Superficies y Catálisis
Role of ruthenium on the catalytic properties of CeZr and CeZrCo mixed oxides for glycerol steam reforming reaction toward H2 production
Martinez, LM; Araque, M; Centeno, MA; Roger, ACCatalysis Today, 242 (2015) 80-90 DOI: 10.1016/j.cattod.2014.07.034
Abstract
The effect of ruthenium on the physico-chemical properties of CeZr and CeZrCo mixed oxides for H2production by glycerol steam reforming reaction has been studied. The combination of in situ Raman spectroscopy under both reductive and oxidative conditions, H2/O2 pulses and XRD, Raman, BET analysis, H2-TPR and TPD-TPO analyses contributed to the determination of the structural and textural properties, redox behavior, re-oxidation capacity and resistance to carbon deposition of the synthesized catalysts. The results show that the catalytic activity is improved by the (positive) cooperative and complementary effect between cobalt and ruthenium that favors the selectivity toward the steam reforming, selective to H2, with respect to the unselective thermal decomposition of glycerol. Ruthenium stabilizes the cobalt cations inserted in the fluorite structure preventing its rejection as Co3O4; and provides the necessary hydrogen to reduce Ce4+. The combination cobalt–ruthenium modifies positively the redoxproperties of the catalysts, increases the re-oxidation capacity (OSC) and promotes the gasification of the carbon deposits. Under the reaction conditions, the decrease in glycerol conversion came along with a change of selectivity. The formation of H2 and CO2 were strongly decreased, while the formation of CO, C2H4 and condensable products (mainly hydroxyacetone) increase. The differences in the catalytic stability and activity of the catalysts are related to the capability of the catalysts to activate H2O under the reaction conditions, favoring the steam reforming reaction over the thermal decomposition.
March, 2015 · DOI: 10.1016/j.cattod.2014.07.034
Materiales de Diseño para la Energía y Medioambiente
Polyester Films Obtained by Noncatalyzed Melt-Condensation Polymerization of Aleuritic (9,10,16-Trihydroxyhexadecanoic) Acid in Air
Benitez, JJ; Heredia-Guerrero, JA; Guzman-Puyol, S; Dominguez, E; Heredia, AJournal of Applied Polymer, 132 (2015) Art. 41328 DOI: 10.1002/app.41328
Abstract
To mimic nontoxic and fully biodegradable biopolymers like the plant cutin, polyester films from a natural occurring fatty polyhydroxyacid like aleuritic (9,10,16-trihydroxyhexadecanoic) acid have been prepared by noncatalyzed melt-polycondensation at moderate temperature (150 degrees C) directly in air. The course of the reaction has been followed by infrared spectroscopy, C-13 magic angle spinning nuclear magnetic resonance spectroscopy, differential scanning calorimetry and X-ray diffraction and well differentiated stages are observed. First, a high conversion esterification reaction leads to an amorphous rubbery, infusible, and insoluble material whose structure is made out of ester linkages mostly involving primary hydroxyls and partially branched by minor esterification with secondary ones. Following the esterification stage, the cleavage of vicinal secondary hydroxyls and further oxidation to carboxylic acid is observed at the near surface region of films. New carboxylic groups created also undergo esterification and generate cross-linking points within the polymer structure. Additionally, and despite the harsh preparation conditions used, very little additional side reaction like peroxidation and dehydration are observed. Results demonstrate the feasibility of polyester films fabrication from a reference fatty polyhydroxyacid like aleuritic acid by noncatalyzed melt-polycondensation directly in air. The methodology can potentially be extended to similar natural occurring hydroxyacids to obtain films and coatings to be used, for instance, as nontoxic and biodegradable food packaging material.
February, 2015 · DOI: 10.1002/app.41328
Materiales Nanoestructurados y Microestructura
Tribocorrosion behavior of TiBxCy/a-C nanocomposite coating in strong oxidant disinfectant solutions
Gracia-Escosa, E; Garcia, I; Sanchez-Lopez, JC; Abad, MD; Mariscal, A; Arenas, MA; de Damborenea, J; Conde, ASurface & Coatings Technology, 263 (2015) 78-85 DOI: 10.1016/j.surfcoat.2014.12.047
Abstract
Corrosion and tribocorrosion studies of a TiBxCy/a-C coating deposited on AISI 316L steel have been performed in an aqueous solution of 026 vol.% acetic, 0.16 vol.% peracetic and 0.18 vol.% hydrogen peroxide (commercial product Oxonia I vol.%). The corrosion current density of the TiBxCy/a-C coating ranges on the same order as bare steel but with a significantly decreasing friction (0.1 vs. 0.6) and wear rate (similar to 10 times lower). The compact microstructure of the coating hinders the access of the aggressive electrolyte to the substrate, preventing the onset of the corrosion attack, while maintaining an excellent tribological behavior in strong oxidant solutions.
February, 2015 · DOI: 10.1016/j.surfcoat.2014.12.047
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
Effective photoreduction of a nitroaromatic environmental endocrine disruptor by AgNPs functionalized on nanocrystalline TiO2
Hernandez-Gordillo, A; Obregon, S; Paraguay-Delgado, F; Rodriguez-Gonzalez, VRSC Advances, 5 (2015) 15194-15197 DOI: 10.1039/c5ra00094g
Abstract
Unprecedented photoactivity of silver nanoparticles photodeposited on nanocrystalline TiO2 for the efficient reduction of 4-nitrophenol at room temperature is reported. The use of Na2SO3 as a harmless scavenger agent for the reduction of a nitroaromatic endocrine disruptor yields a valuable 4-aminophenol reagent.
February, 2015 · DOI: 10.1039/c5ra00094g
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
Evolution of H-2 photoproduction with Cu content on CuOx-TiO2 composite catalysts prepared by a microemulsion method
Kubacka, A; Munoz-Batista, MJ; Fernandez-Garcia, M; Obregon, S; Colon, GApplied Catalysis B: Environmental, 163 (2015) 214-222 DOI: 10.1016/j.apcatb.2014.08.005
Abstract
Copper oxides in contact with anatase correspond to promising materials with high activity in the photo-production of hydrogen by aqueous reforming of alcohols. By a single pot microemulsion method we obtained a series of Cu-Ti composite systems with controlled copper content in the 0-25 wt.% range. The scanning of such a wide range of composition led to the discovery of two well differentiated maxima in the photo-reaction performance. These maxima present rather high and relatively similar reaction rates and photonic efficiencies but are ascribed to the presence of different copper species. A multi-technique analysis of the materials indicates that the maxima obtained comes from optimizing different steps of the reaction; while the first would be connected with a positive effect on anatase charge handling performance the second seems exclusively related to electron capture by surface copper species.
February, 2015 · DOI: 10.1016/j.apcatb.2014.08.005
Materiales Ópticos Multifuncionales - Nanotecnología en Superficies y Plasma
Flexible Distributed Bragg Reflectors from Nanocolumnar Templates
Calvo, ME; Gonzalez-Garcia, L; Parra-Barranco, J; Barranco, A; Jimenez-Solano, A; Gonzalez-Elipe, AR; Miguez, HAdvanced Optical Materials, 3 (2015) 171-175 DOI: 10.1002/adom.201400338
Abstract
A flexible distributed Bragg reflector is made by the infiltration of a nanocolumnar array with polydimethyl siloxane oligomers. The high optical reflectance displayed by the final material is a direct consequence of the high refractive index contrast of the columnar layers whereas the structural stability is due to the polymer properties.
February, 2015 · DOI: 10.1002/adom.201400338
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
Photocatalytic activity of bismuth vanadates under UV-A and visible light irradiation: Inactivation of Escherichia coli vs oxidation of methanol
Adan, C; Marugan, J; Obregon, S; Colon, GCatalysis Today, 240 (2015) 93-99 DOI: 10.1016/j.cattod.2014.03.059
Abstract
Four bismuth vanadates have been synthesized by using two different precipitating agents (NH3 and triethylamine) following a hydrothermal treatment at 100 °C for 2 h and at 140 °C for 20 h. Then, solids were characterized by X-ray diffraction, BET surface area, UV–vis spectroscopy and scanning microscopy techniques. The characterization of the synthesized materials showed a well crystallized scheelite monoclinic structure with different morphologies. All materials display optimum light absorption properties for visible light photocatalytic applications. The photocatalytic activity of the catalysts was investigated for the inactivation of Escherichia coli bacteria and the oxidation of methanol under UV–vis and visible light irradiation sources. Main results demonstrate that BiVO4 are photocatalytically active in the oxidation of methanol and are able to inactivate bacteria below the detection level. The activity of the catalyst decreases when using visible light, especially for methanol oxidation, pointing out differences in the reaction mechanism. In contrast with bacteria, whose interaction with the catalyst is limited to the external surface, methanol molecules can access the whole material surface.
February, 2015 · DOI: 10.1016/j.cattod.2014.03.059
Nanotecnología en Superficies y Plasma
Laser Treatment of Ag@ZnO Nanorods as Long-Life-Span SERS Surfaces
Macias-Montero, M; Pelaez, RJ; Rico, VJ; Saghi, Z; Midgley, P; Afonso, CN; Gonzalez-Elipe, AR; Borras, AACS Applied Materials & Interfaces, 7 (2015) 2331-2339 DOI: 10.1021/am506622x
Abstract
UV nanosecond laser pulses have been used to produce a unique surface nanostructuration of Ag@ZnO supported nanorods (NRs). The NRs were fabricated by plasma enhanced chemical vapor deposition (PECVD) at low temperature applying a silver layer as promoter. The irradiation of these structures with single nanosecond pulses of an ArF laser produces the melting and reshaping of the end of the NRs that aggregate in the form of bundles terminated by melted ZnO spherical particles. Well-defined silver nanoparticles (NPs), formed by phase separation at the surface of these melted ZnO particles, give rise to a broad plasmonic response consistent with their anisotropic shape. Surface enhanced Raman scattering (SERS) in the as-prepared Ag@ZnO NRs arrays was proved by using a Rhodamine 6G (Rh6G) chromophore as standard analyte. The surface modifications induced by laser treatment improve the stability of this system as SERS substrate while preserving its activity.
February, 2015 · DOI: 10.1021/am506622x
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
Structural and chemical reactivity modifications of a cobalt perovskite induced by Sr-substitution. An in situ XAS study
Hueso, JL; Holgado, JP; Pereniguez, R; Gonzalez-DelaCruz, VM; Caballero, AMaterials Chemistry and Physics, 151 (2015) 29-33 DOI: 10.1016/j.matchemphys.2014.11.015
Abstract
LaCoO3 and La0.5Sr0.5O3O3-delta perovskites have been studied by in situ Co K-edge XAS. Although the partial substitution of La(III) by Sr(II) species induces an important increase in the catalytic oxidation activity and modifies the electronic state of the perovskite, no changes could be detected in the oxidation state of cobalt atoms. So, maintaining the electroneutrality of the perovskite requires the generation of oxygen vacancies in the network. The presence of these vacancies explains that the substituted perovskite is now much more reducible than the original LaCoO3 perovskite. As detected by in situ XAS, after a consecutive reduction and oxidation treatment, the original crystalline structure of the LaCoO3 perovskite is maintained, although in a more disordered state, which is not the case for the Sr doped perovskite. So, the La0.5Sr0.5CoO3-delta perovskite submitted to the same hydrogen reduction treatment produces metallic cobalt, while as determined by in situ XAS spectroscopy the subsequent oxidation treatment yields a Co(III) oxide phase with spinel structure. Surprisingly, no Co(II) species are detected in this new spinel phase.
February, 2015 · DOI: 10.1016/j.matchemphys.2014.11.015
Reactividad de Sólidos
Synthesis of a nanosilica supported CO2 sorbent in a fluidized bed reactor
Soria-Hoyo, C; Valverde, JM; van Ommen, JR; Sanchez-Jimenez, PE; Perez-Maqueda, LA; Sayagues, MJApplied Surface Science, 328 (2015) 548-553 DOI: 10.1016/j.apsusc.2014.12.106
Abstract
CaO has been deposited on a nanosilica powder matrix by a procedure based on atomic layer deposition (ALD) in a fluidized bed reactor at atmospheric pressure following a potentially scalable process. In previous works ALD in gas fluidized bed has been mostly performed under reduced pressure, which hampers scaling-up the production technology. The material synthesized in the present work is tested as CO2 solid sorbent at calcium looping conditions. Multicyclic thermogravimetric analysis (TGA) shows that the nanosilica support stabilizes the capture capacity of CaO. EDX-STEM analysis illustrates the presence of Ca well distributed on the surface of the SiO2 nanoparticles.
February, 2015 · DOI: 10.1016/j.apsusc.2014.12.106
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
Water splitting performance of Er3+-doped YVO4 prepared from a layered K3V5O14 precursor
Obregon, S; Colon, GChemical Engineering Journal, 262 (2015) 29-33 DOI: 10.1016/j.cej.2014.09.073
Abstract
Erbium-doped YVO4 have been synthesized by means of a simple solution method having good photo activities under UV-like excitation for the water splitting half reactions. From the structural and morphological characterization it has been stated that the presence of Er3+ induces the promotion of luminescence. Moreover the incorporation of erbium clearly affects to the morphology YVO4 leading to 200 nm size well-defined spindle-like particles. The improved photocatalytic performance might be associated to a better electron–hole separation mechanism, probably due to the slight increase of band-gap value. The obtained photoactivities for H2 and O2 evolution reactions make this material a promising candidate for water splitting reactions.
February, 2015 · DOI: 10.1016/j.cej.2014.09.073
Química de Superficies y Catálisis
Glycerol steam reforming on bimetallic NiSn/CeO2-MgO-Al2O3 catalysts: Influence of the support, reaction parameters and deactivation/regeneration processes
Bobadilla, LP; Penkova, A; Alvarez, A; Dominguez, MI; Romero-Sarria, F; Centeno, MA; Odriozola, JAApplied Catalysis A: General, 492 (2015) 38-47 DOI: 10.1016/j.apcata.2014.12.029
Abstract
NiSn bimetallic catalysts supported over Al2O3 modified with different promoter (Mg and/or Ce) were prepared and characterized by powder X-ray diffraction (XRD), N2 sorptometry, and temperature programmed reduction (TPR). Hydrogen production by glycerol steam reforming over these catalysts was investigated. Among the catalysts, NiSn/AlMgCe catalyst shows the highest hydrogen yield as well as the best stability during the reaction. The effect of reaction temperature, water/glycerol molar ratio and space velocity on the glycerol steam reforming over NiSn/AlMgCe were also investigated. Finally, it was verified that the catalyst can be regenerated by oxidation of carbonaceous deposits.
February, 2015 · DOI: 10.1016/j.apcata.2014.12.029
Química de Superficies y Catálisis - Fotocatálisis Heterogénea: Aplicaciones
Synthesis and application of layered titanates in the photocatalytic degradation of phenol
Ivanova, S; Penkova, A; Hidalgo, MD; Navio, JA; Romero-Sarria, F; Centeno, MA; Odriozola, JAApplied Catalysis B: Environmental, 163 (2015) 23-29 DOI: 10.1016/j.apcatb.2014.07.048
Abstract
This study proposes a direct synthetic route to single titanate sheets through the mild and versatile conditions of the “chimie douce”. The stages of the production include the complexation of the titanium alkoxide precursor by benzoic acid, the formation of titanium oxo-clusters and their controlled transformation into single sheet titanates during the hydrolysis stage. The resulted material appears to be an excellent precursor for self-organized TiO2 nanotubes formation which presents an excellent activity as photocatalyst in the photo-degradation of phenol.
February, 2015 · DOI: 10.1016/j.apcatb.2014.07.048
Reactividad de Sólidos
Influence of the Processing Route on the Carbon Nanotubes Dispersion and Creep Resistance of 3YTZP/SWCNTs Nanocomposites
Castillo-Rodriguez, M; Munoz, A; Morales-Rodriguez, A; Poyato, R; Gallardo-Lopez, A; Dominguez-Rodriguez, AJournal of the American Ceramic Society, 98 (2015) 645-653 DOI: 10.1111/jace.13348
Abstract
3YTZP matrix composites containing 2.5 vol% of single-walled carbon nanotubes (SWCNT) were fabricated by Spark Plasma Sintering (SPS) at 1250°C, following different processing routines with the aim of optimizing the SWCNTs dispersion throughout the ceramic matrix. Microstructural characterization of the as-fabricated samples has been performed by means of scanning electron microscopy (SEM). The specimens have been crept at 1200°C to correlate creep resistance and SWCNTs distribution. There are no creep experimental results on these nanocomposites reported in literature. Mechanical results show that the incorporation of SWCNTs into a 3YTZP matrix produces an increase in the strain rate at high temperature with respect to monolithic zirconia. The creep resistance of these nanocomposites decreases with the improvement of the SWCNTs dispersion, where a smaller SWCNTs agglomerate size and consequently a higher concentration of carbon nanotubes surrounding the 3YTZP grain boundaries is found. This fact indicates that SWCNTs act as a lubricant making grain-boundary sliding easier during deformation of these composites.
February, 2015 · DOI: 10.1111/jace.13348
Nanotecnología en Superficies y Plasma - Materiales Nanoestructurados y Microestructura
STEM-EELS analysis reveals stable highdensity He in nanopores of amorphous silicon coatings deposited by magnetron sputtering
Schierholz, Roland; Lacroix, Bertrand; Godinho, Vanda; Caballero-Hernandez, Jaime; Duchamp, Martial; Fernandez, AsuncionNanotechnology, 26 (2015) 075703 DOI: 10.1088/0957-4484/26/7/075703
Abstract
A broad interest has been showed recently on the study of nanostructuring of thin films and surfaces obtained by low-energy He plasma treatments and He incorporation via magnetron sputtering. In this paper spatially resolved electron energy-loss spectroscopy in a scanning transmission electron microscope is used to locate and characterize the He state in nanoporous amorphous silicon coatings deposited by magnetron sputtering. A dedicated MATLAB program was developed to quantify the helium density inside individual pores based on the energy position shift or peak intensity of the He K-edge. A good agreement was observed between the high density (~35–60 at nm−3) and pressure (0.3–1.0 GPa) values obtained in nanoscale analysis and the values derived from macroscopic measurements (the composition obtained by proton backscattering spectroscopy coupled to the macroscopic porosity estimated from ellipsometry). This work provides new insights into these novel porous coatings, providing evidence of high-density He located inside the pores and validating the methodology applied here to characterize the formation of pores filled with the helium process gas during deposition. A similar stabilization of condensed He bubbles has been previously demonstrated by high-energy He ion implantation in metals and is newly demonstrated here using a widely employed methodology, magnetron sputtering, for achieving coatings with a high density of homogeneously distributed pores and He storage capacities as high as 21 at%.
February, 2015 · DOI: 10.1088/0957-4484/26/7/075703
Nanotecnología en Superficies y Plasma
Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance
Longtin, R; Sanchez-Valencia, JR; Shorubalko, I; Furrer, R; Hack, E; Elsener, H; Groning, O; Greenwood, P; Rupesinghe, N; Teo, K; Leinenbach, C; Groning, PScience and Technology of Advanced Materials, 16 (2015) 015005 (11 pp) DOI: 10.1088/1468-6996/16/1/015005
Abstract
The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 degrees C with a Ag-Cu-Ti alloy and at 880 degrees C with a Cu-Sn-Ti-Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Omega. The improved interfacial transport properties in the brazed films lead to superior electron fieldemission properties when compared to the as-grown films. An emission current of 150 mu A was drawn from the brazed nanotubes at an applied electric field of 0.6 V mu m(-1). The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.
February, 2015 · DOI: 10.1088/1468-6996/16/1/015005
Propiedades mecánicas, modelización y caracterización de cerámicos avanzados
Ultra-fast and energy-efficient sintering of ceramics by electric current concentration
Zapata-Solvas, E; Gomez-Garcia, D; Dominguez-Rodriguez, A; Todd, RIScientific Reports, 5 (2015) art n. 8513 DOI: 10.1038/srep08513
Abstract
Electric current activated/assisted sintering (ECAS) techniques, such as electrical discharge sintering (EDS) or resistive sintering (RS), have been intensively investigated for longer than 50 years. In this work, a novel system including an electrically insulated graphite die for Spark Plasma Sintering (SPS) is described, which allows the sintering of any refractory ceramic material in less than 1 minute starting from room temperature with heating rates higher than 2000°C/min and an energy consumption up to 100 times lower than with SPS. The system alternates or combines direct resistive sintering (DRS) and indirect resistive sintering (IRS). Electrical insulation of the die has been achieved through the insertion of a film made of alumina fibers between the graphite die and the graphite punches, which are protected from the alumina fiber film by a graphite foil. This system localized the electric current directly through the sample (conductive materials) as in DRS and EDS, or through the thin graphite foil (non-conductive materials) as in IRS, and is the first system capable of being used under EDS or RS conditions independently combining current concentration/localization phenomena.
February, 2015 · DOI: 10.1038/srep08513
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