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2019


Natural abundance O-17 MAS NMR and DFT simulations: New insights into the atomic structure of designed micas


Pavon, E; Osuna, FJ; Alba, MD; Delevoye, L
Solid State Nuclear Magnetic Resonance, 100 (2019) 45-51

ABSTRACT

Combining O-17 Magic-Angle Spinning (MAS) NMR at natural abundance with DFT calculations is a promising methodology to shed light on the structure and disorder in tetrahedral sheets of designed micas with enhanced properties. Among brittle micas, synthetic mica is an important alternative to natural ones with a swelling sheet-like structure that results in many applications, by exploiting unique characteristics. Lowenstein's rule is one of the main chemical factor that determines the atomic structure of aluminosilicates and furthermore their properties. In the present article, O-17 MAS NMR spectroscopy is used to validate (or not) the agreement of the Lowenstein's rule with the distribution of Si and Al sites in the tetrahedral sheets of synthetic micas. O-17 MAS spectra of synthetic high-charged micas exhibit two regions of signals that revealed two distinguishable oxygen environments, namely Si-O-X (with X = Si, Al-tet , Mg) and Al-tet -O-Y (Y=Mg or Al-tet). DFT calculations were also conducted to obtain the O-17 chemical shift and other NMR features like the quadrupolar coupling constant, C-Q, for all of the oxygen environments encountered in the two model structures, one respecting the Lowenstein's rule and the other involving Al-tet -O-Al-tet and Si-O-Si environments. Our DFT calculations support the O-17 assignment, by confirming that Al-tet -O-3Mg and Al tet -O-Al tet oxygen environments show chemical shifts under 30 ppm and more important, with quadrupolar coupling constants of about 1 MHz, in line with the spectral observation. By quantifying the O-17 MAS NMR spectra at natural abundance, we demonstrate that one of the synthetic mica compositions does not meet the Lowenstein's rule.


Agosto, 2019 | DOI: 10.1016/j.ssnmr.2019.03.006

Higher hydration performance and bioactive response of the new endodontic bioactive cement MTA HP repair compared with ProRoot MTA white and NeoMTA plus


Jimenez-Sanchez, Maria Del Carmen; Segura-Egea, Juan Jose; Diaz-Cuenca, Aranzazu
Journal of biomedical materials research. Part B, Applied biomaterials, 107 (2019) 2109-2120

ABSTRACT

The aim of this study was to characterize the hydration performance and the bioactive response of the new bioactive endodontic cement MTA HP repair (HP), comparing its physicochemical parameters with those of ProRoot MTA White (Pro) and NeoMTA Plus (Neo). Un-hydrated precursor materials were characterized by X-ray fluorescence, laser diffraction, N2 physisorption and field emission gun scanning electron microscopy (FEG-SEM). Setting time was assessed according to ASTM specification C 266. Hydrated materials were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR) and (FEG-SEM). Bioactivity evaluation in vitro was carried out, by soaking processed cement disk in simulated body fluid (SBF) during 168 h. The cements surface was studied by FT-IR, FEG-SEM, and energy dispersive X-ray. Release to the SBF media of ionic degradation products was monitored using inductively coupled plasma atomic emission spectroscopy. HP showed shorter initial setting time compared to Pro and Neo and produce a quick and effective bioactive response in vitro in terms of phosphate phase surface coating formation. This higher bioactive response for HP is correlated with increasing calcium aluminate content, increasing surface area of un-hydrated powder precursor and the increasing release capacity of Si ionic products of the final hydrated product. The higher bioactive response of MTA HP repair highlights this material, as very interesting to further investigate its performance to improve the outcome of vital pulp therapy procedures. 


Agosto, 2019 | DOI: 10.1002/jbm.b.34304

Noble Metal Supported on Activated Carbon for "Hydrogen Free" HDO Reactions: Exploring Economically Advantageous Routes for Biomass Valorisation


Jin, W; Santos, JL; Pastor-Perez, L; Gu, S; Centeno, MA; Reina, TR
Chemcatchem (2019)

ABSTRACT

An innovative route for bio‐compounds upgrading via “hydrogen‐free” hydrodeoxygenation (HDO) is proposed and evaluated using guaiacol as a model compound in a high‐pressure batch reactor. Experimental results showed that noble metal supported on activated carbon catalysts are able to conduct tandem multiple steps including water splitting and subsequent HDO. The activity of Ru/C catalyst is superior to other studied catalysts (i. e. Au/C, Pd/C and Rh/C) in our water‐only HDO reaction system. The greater dispersion and smaller metal particle size confirmed by the TEM micrographs accounts for the better performance of Ru/C. This material also presents excellent levels of stability as demonstrated in multiple recyclability runs. Overall, the proposed novel approach confirmed the viability of oxygenated bio‐compounds upgrading in a water‐only reaction system suppressing the need of external H2 supply and can be rendered as a fundamental finding for the economical biomass valorisation to produce added value bio‐fuels.


Agosto, 2019 | DOI: 10.1002/cctc.201900841

Structural and compositional analysis of Co-based coatings after catalytic tests for the sodium borohydride hydrolysis


Beltran, AM
Materials Research Express, 6 (2019) art. 085511

ABSTRACT

The use of Co-based catalysts for the sodium borohydride hydrolysis for hydrogen production is a well-known process as a source of clean energy, although its mechanisms are still under discussion. With the aim of acquiring a deeper knowledge about this catalytic process, three different catalysts (Co, CoC and CoB) were deposited as a thin film layer by magnetron sputtering onto a polymeric membrane, used as a substrate and analyzed by advance transmission and scanning-transmission electron microscopy techniques (STEM). Structural and compositional characterizations, by electron energy loss spectroscopy (EELS), have been performed on the coatings before and after their use as catalysts on the sodium borohydride reaction for 90 min, to check the production of hydrogen. Results have shown the formation of CoxB nanoflakes and other Co-based compounds over the catalysts and related to their catalytic activity. Knowing the changes in the structure and composition of the catalysts is key to understanding their catalytic behavior, activity and durability. Among the analyzed catalysts, the Co-C presents better activity during the first cycles, which is related to a larger formation of CoxB.


Agosto, 2019 | DOI: 10.1088/2053-1591/ab1e27

MTA HP Repair stimulates in vitro an homogeneous calcium phosphate phase coating deposition


Jiménez-Sánchez, M.D.C.; Segura-Egea, J.J.; Díaz-Cuenca, A.
Journal of Clinical and Experimental Dentistry, 11 (2019) e322-e326

ABSTRACT

Background: To study the mineralization capacity in vitro of the bioceramic endodontic material MTA HP Repair. Material and Methods: Bioactivity evaluation in vitro was carried out, by soaking processed cement disk in simulated body fluid (SBF) during 168 h. The cement surface was studied by Fourier transform infrared spectroscopy (FTIR), field emission gun scanning electron microscopy (FEG-SEM) and energy dispersive X-ray analysis (EDX). Release to the SBF media of ionic degradation products was monitored using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Results: FT-IR showed increasing formation of phosphate phase bands at 1097, 960, 607 and 570 cm -1 with prolonged SBF soaking. FEG-SEM analysis reveals that HP produces a effectively surface covering consisting in homogeneous spherical phosphate phase aggregates with an average diameter of 0.5 -1 .0 μm. EDX analysis comparing un-treated (hydrated), 24 h and 72 h SBF treated surfaces of MTA HP Repair revealed phosphate deposition after 24 h, with high phosphorous/silicon element ratio signal measured after 24 h, indicating a very high phosphate phase deposition for this material. Conclusions: The study shows that MTA HP Repair produces a quick and effective bioactive response in vitro in terms of crystalline calcium phosphate surface coating formation. The high bioactive response of MTA HP Repair makes it an interesting candidate for endodontic use as repair cement. 


Agosto, 2019 | DOI: 10.4317/jced.55661

Physicochemical parameters - hydration performance relationship of the new endodontic cement MTA Repair HP


Jiménez-Sánchez, M.D.C.; Segura-Egea, J.J.; Díaz-Cuenca, A.
Journal of Clinical and Experimental Dentistry, 11 (2019) e739-e744

ABSTRACT

Background: To characterize the chemical composition and textural parameters of the MTA Repair HP precursor powder and their influence to hydration performance. Material and Methods: Un-hydrated precursor material was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence (XRF), laser diffraction (LD), N2 physisorption and field emission gun scanning electron microscopy (FEG-SEM). Setting time was assessed according to ASTM specification C 266. Hydrated material was analysed by XRD, FT-IR, energy dispersive X-ray (EDX) analysis and FEG-SEM. Results: Ca3SiO5 and Ca2SiO4, in addition to CaWO4 as radiopacifier are the main compositional phases. Other measured parameters indicate high specific surface area of 4.8 m2 g-1, high aluminium content of 1.7 wt.% and low initial and final setting times of 12 and 199 min, respectively. Singular microstructural features consisting of high aspect ratio nanoparticles are main constituents of un-hydrated precursor. Besides, FEM-SEM observation shows notably growth of hexagonal shaped plate-like morphologies homogeneously distributed along the sample during hydration process. Conclusions: The short setting time measured for HP Repair, is correlated with high surface area of precursor powder, high Al content and the absence of compositional sulphate phases. 


Agosto, 2019 | DOI: 10.4317/jced.56013

Bio-based composite fibers from pine essential oil and PLA/PBAT polymer blend. Morphological, physicochemical, thermal and mechanical characterization


Hernandez-Lopez, M; Correa-Pacheco, ZN; Bautista-Banos, S; Zavaleta-Avejar, L; Benitez-Jimenez, JJ; Sabino-Gutierrez, MA; Ortega-Gudino, P
Materials Chemistry and Physics, 234 (2019) 345-353

ABSTRACT

Biodegradable aliphatic polyesters are an alternative to reduce the use of synthetic plastic materials that cause severe damage to the environment. Formulations based on poly (lactic acid) (PLA) and poly (butylene adipate-co-terephthalate) (PBAT), were mixed in a 60:40 ratio, adding different concentrations of pine essential oil through the use of extrusion technology to obtain biodegradable polymer fibers. Some formulations were coated with chitosan. All the elaborated fibers were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy-Attenuated Total Reflection (FTIR-ATR), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and mechanical properties. The SEM studies showed that the PBAT improves the tenacity and provides greater elasticity promoting the interaction between the blends phases with fibril formation. In the FTIR-ATR analysis, compatibility between the blends was observed due to a possible interaction of the carbonyl group of PBAT with PLA. The DSC and the mechanical properties showed partial miscibility of the blends, indicating, that the plasticizing action of the essential oil gave greater mobility, flexibility, less rigidity and crystallization in the blends. A lower Young's modulus and greater elongation at break was also observed.


Agosto, 2019 | DOI: 10.1016/j.matchemphys.2019.01.034

Processing and properties of Bi0.98R0.02FeO3 (R = La, Sm, Y) ceramics flash sintered at similar to 650 degrees C in <5 s


Gil-Gonzalez, E; Perejon, A; Sanchez-Jimenez, PE; Raj, R; Perez-Maqueda, LA
Journal of the American Ceramic Society, (2019)

ABSTRACT

We show that flash sintering produces single‐phase, nanograin‐sized polycrystals of isovalent‐substituted multiferroic ceramics of complex compositions. Single‐phase polycrystals of Bi0.98R0.02FeO3 (R = La, Sm, Y) were produced at a furnace temperature of ~650°C in a few seconds by the application of an electric field of 50 V cm−1, with the current limit set to 40 mA mm−2. The dielectric and insulating properties compared favorably with expected values. Impedance spectroscopy suggests electrically homogenous microstructure, except for the sample Bi0.98La0.02FeO3 that shows a small grain boundary contribution to the impedance. These results reinforce the enabling nature of flash sintering for ceramics which pose difficulties in conventional sintering because they contain low melting constituents or develop secondary phases during the sintering protocol.


Agosto, 2019 | DOI: 10.1111/jace.16718

Large gap atmospheric pressure barrier discharges using ferroelectric materials


Navascues, P.; Gonzalez-Elipe, A. R.; Cotrino, J.; Gomez-Ramirez, A.
Plasma Sources Sciences & Tecnology,

ABSTRACT

Does grain size have an influence on intrinsic mechanical properties and conduction mechanism of near fully-dense boron carbide ceramics?


Moshtaghioun, BM; Laguna-Bercero, MA; Gomez-Garcia, D; Pena, JI
Journal of Alloys and Compounds, 795 (2019) 408-415

ABSTRACT

This work is concentrated on getting a reply to the following question: how does the grain size of boron carbide specimens influence on their mechanical and electrical response? It is a common issue that both essential properties are usually affected by the grain boundaries. To this purpose, a set of near fully-dense boron carbide specimens were prepared by spark plasma sintering. In order to reduce residual porosity and grain-size effects, nanoindentation tests at room temperature were conducted. DC conductivity was measured through four-point test technique from room temperature up to 800 °C. The results show that hardness can reach values as high as ∼60 GPa and plasticity onset takes place at around 23 GPa by dislocation nucleation. Regarding the conductivity, it is found that grain boundaries can block the mobility of bipolarons in an effective way. A simple additive law is provided to account for the resistivity of boron carbide polycrystals.


Julio, 2019 | DOI: 10.1016/j.jallcom.2019.05.037

Effects of Boron Addition on the Microstructure and Mechanical Properties of (Ti,Ta)(C,N)-Co Based Cermets


Chicardi, E; Martinez, FJG
Metals, 9 (2019) art. 787

ABSTRACT

In this work, a titanium-tantalum carbonitride based cermet, with cobalt as the binder phase and boron as a sintering additive, was developed by a mechanically induced self-sustaining reaction process using two different methodologies. The boron additive was added to prevent the formation of brittle intermetallic compounds generally formed during the liquid phase sintering step due to the excessive ceramic dissolution into the molten binder phase. A systematic study was carried out to understand the effects of boron addition on the nature of the phases, microstructure, and mechanical properties of cermets. With the boron addition, the formation of two different boride solid solutions, i. e., (Ti, Ta)B-2 and (Ti, Ta)(3)B-4, was observed. Moreover, the nature of the binder was also modified, from the (Ti, Ta)Co-2 brittle intermetallic compound (for cermets without boron addition) to ductile and tough (Ti, Ta)Co-3 and alpha-Co phases (for cermets with boron addition). These modifications caused, as a general trend, the increase of hardness and toughness in cermets.


Julio, 2019 | DOI: 10.3390/met9070787

Bionanocomposites based on chitosan intercalation in designed swelling high-charged micas


Alba, MD; Cota, A; Osuna, FJ; Pavon, E; Perdigon, AC; Raffin, F
Scientific Reports, 9 (2019) art. 10265

ABSTRACT

Bionanocomposites based on layered inorganic components, as clays, and polymers of biological origin, as chitosan, have a major impact in medical and environmental fields, being economical and environmentally friendly materials. Na-Mn micas (n = 2 and 4) with controlled surface charge, high cation exchange capacity and swelling behaviour, are attractive inorganic composite components that exhibit improved adsorption properties compared to other inorganic solids which makes them potentially useful for bionanocomposites. The goal of this research was to explore the potential use of those synthetic brittle micas to form eco-friendly bionanocomposites with chitosan biopolymer. Hence, chitosan-mica bionanocomposites were prepared by ion-exchange reaction between chitosan solution and synthetic high charge mica. X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis, MAS-NMR spectroscopy and zeta-potential have been employed for bionanocomposites characterization. The results showed that the adsorption of chitosan is effective, although a chitosan portion remains in the outer surface being hydrogen-bonded to the tetrahedral sheet of the silicate.


Julio, 2019 | DOI: 10.1038/s41598-019-46495-z

On‐Surface Synthesis and Characterization of Acene‐Based Nanoribbons Incorporating Four‐Membered Rings


Sanchez-Sanchez, C; Dienel, T; Nicolai, A; Kharche, N; Liang, LB; Daniels, C; Meunier, V; Liu, JZ; Feng, XL; Mullen, K; Sanchez-Valencia, JR; Groning, O; Ruffieux, P; Fasel, R
Chemistry-A European Journal

ABSTRACT

A bottom up method for the synthesis of unique tetracene-based nanoribbons, which incorporate cyclobutadiene moieties as linkers between the acene segments, is reported. These structures were achieved through the formal [2+2] cycloaddition reaction of ortho-functionalized tetracene precursor monomers. The formation mechanism and the electronic and magnetic properties of these nanoribbons were comprehensively studied by means of a multitechnique approach. Ultra-high vacuum scanning tunneling microscopy showed the occurrence of metal-coordinated nanostructures at room temperature and their evolution into nanoribbons through formal [2+2] cycloaddition at 475 K. Frequency-shift non-contact atomic force microscopy images clearly proved the presence of bridging cyclobutadiene moieties upon covalent coupling of activated tetracene molecules. Insight into the electronic and vibrational properties of the so-formed ribbons was obtained by scanning tunneling microscopy, Raman spectroscopy, and theoretical calculations. Magnetic properties were addressed from a computational point of view, allowing us to propose promising candidates to magnetic acene-based ribbons incorporating four-membered rings. The reported findings will increase the understanding and availability of new graphene-based nanoribbons with high potential in future spintronics.


Julio, 2019 | DOI: 10.1002/chem.201901410

Size-tailored Ru nanoparticles deposited over gamma-Al2O3 for the CO2 methanation reaction


Navarro-Jaen, S; Navarro, JC; Bobadilla, LF; Centeno, MA; Laguna, OH; Odriozola, JA
Applied Surface Science, 483 (2019) 750-761

ABSTRACT

By means of the polyol method, a series of 5 wt% Ru/Al2O3 catalysts was synthesized controlling the particle size of the ruthenium species. The physico-chemical characterization demonstrated the successful particle size control of the Ru species, in such a way that higher the Ru/PVP ratio, higher the Ru particle size. Moreover, there are evidences that suggest preferential growth of the RuO2 clusters depending on the Ru/PVP ratio. Regarding the catalytic activity during the CO2 methanation, the total conversion and the CH4 yield increased with the particle size of Ru. Nevertheless, a considerable enhancement of the catalytic performance of the most active system was evidenced at 4 bar, demonstrating the improvement of the thermodynamics (superior total conversion) and kinetics (superior reaction rate) of the CO2 methanation at pressures above the atmospheric one. Finally, the in situ DRIFTS study allowed to establish that CO2 was dissociated to CO* and O* species on the metallic Ru particles, followed by the consecutive hydrogenation of CO* towards CHO*, CH2O*, CH3O*, and finally CH4 molecules, which were further desorbed from the catalyst. Thus from the mechanistic point of view, a suitable particle size of the Ru nanoparticles along with the high-pressure effects results in the enhancement of the availability of hydrogen and consequently in the formation of CHxO species that enhance the cleavage of the C-O bond, which is the rate-determining step of the overall CO2 methanation process.


Julio, 2019 | DOI: 10.1016/j.apsusc.2019.03.248

Influence of the preparation method in the metal-support interaction and reducibility of Ni-Mg-Al based catalysts for methane steam reforming


Azancot, L; Bobadilla, LF; Santos, JL; Cordoba, JM; Centeno, MA; Odriozola, JA
International Journal of Hydrogen Energy, 44 (2019) 19827-19840

ABSTRACT

Ni-Mg-Al based catalysts were prepared using different preparation methods (impregnation, impregnation-coprecipitation and coprecipitation) and tested in steam reforming of methane. The differences observed in catalytic activity were directly correlated to the physicochemical properties and the different degree of Ni-Mg-Al interaction. The reducibility results showed that the catalyst prepared by the impregnation-coprecipitation method presented the most optimal metal-support interaction to reduce the NiO preserving the Ni-0 particles highly dispersed on the support surface. These results demonstrate that the structure and catalytic performance of Ni-Mg-Al based catalysts can be tuned by controlling the metal-support interaction through of the preparation method.


Julio, 2019 | DOI: 10.1016/j.ijhydene.2019.05.167

Laboratory multi-technique study of Spanish decorated leather from the 12th to 14th centuries


Franquelo, ML; Duran, A; Perez-Rodriguez, JL
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 218 (2019) 331-341

ABSTRACT

This work comprises an exhaustive study of Spanish decorative leathers dating from the 12th to 14th centuries. These paintings are considered a key example of a crucible of artistic styles: Gothic, Islamic and Florentine Trecento. The goal of this work was to use the scientific information provided by a number of experimental techniques – namely EDX, micro-FTIR, micro-Raman and micro-XRD – to assess the dating of the wooden vault, leather preparation and filling fibres. Another goal was to assess the artistic technique based on the characterization of pigments and the differentiation between original materials and those added throughout its history. Gypsum was the original preparation layer extended over the leather. A new preparation stratum was added in further interventions with the artwork. The original pictorial materials and those used during refurbishments have been identified. Original pigments were: red lead, Mars red, red lake, cinnabar, lapis lazuli, red ochres, raw sienna, white lead and charcoal black. Gilding was also found. Pigments added during restoration were: barite, emerald green, rutile, anatase, Mars red, cadmium red, lithopone, cadmium yellow, charcoal black and orpiment.


Julio, 2019 | DOI: 10.1016/j.saa.2019.04.012

Plasma Enabled Conformal and Damage Free Encapsulation of Fragile Molecular Matter: from Surface-Supported to On-Device Nanostructures


Alcaire, M; Aparicio, FJ; Obrero, J; Lopez-Santos, C; Garcia-Garcia, FJ; Sanchez-Valencia, JR; Frutos, F; Ostrikov, K; Borras, A; Barranco, A
Advanced Functional Materials, (2019) art. 1903535

ABSTRACT

Damage-free encapsulation of molecular structures with functional nanolayers is crucial to protect nanodevices from environmental exposure. With nanoscale electronic, optoelectronic, photonic, sensing, and other nanodevices based on atomically thin and fragile organic matter shrinking in size, it becomes increasingly challenging to develop nanoencapsulation that is simultaneously conformal at atomic scale and does not damage fragile molecular networks, while delivering added device functionality. This work presents an effective, plasma-enabled, potentially universal approach to produce highly conformal multifunctional organic films to encapsulate atomically thin graphene layers and metalorganic nanowires, without affecting their molecular structure and atomic bonding. Deposition of adamantane precursor and gentle remote plasma chemical vapor deposition are synergized to assemble molecular fragments and cage-like building blocks and completely encapsulate not only the molecular structures, but also the growth substrates and device elements upon nanowire integration. The films are insulating, transparent, and conformal at sub-nanometer scale even on near-tip high-curvature areas of high-aspect-ratio nanowires. The encapsulated structures are multifunctional and provide effective electric isolation, chemical and environmental protection, and transparency in the near-UV-visible-near-infrared range. This single-step, solvent-free remote-plasma approach preserves and guides molecular building blocks thus opening new avenues for precise, atomically conformal nanofabrication of fragile nanoscale matter with multiple functionalities.


Julio, 2019 | DOI: 10.1002/adfm.201903535

Au/CeO2-ZnO/Al2O3 as Versatile Catalysts for Oxidation Reactions: Application in Gas/Liquid Environmental Processes


Megias-Sayago, C; Reina, TR; Ivanova, S; Odriozola, JA
Frontiers in Chemistry, 7 (2019) art. 504

ABSTRACT

The present work showcases the versatility of nanogold systems supported on Zn-doped ceria when applied in two important environmental processes, the total CO oxidation, and the liquid phase oxidation of glucose to gluconic acid. In the CO oxidation the suitability of these materials is clearly demonstrated achieving full conversions even at sub-ambient conditions. Regarding the glucose oxidation our materials display high conversion values (always over 50%) and very importantly full or almost full selectivity toward gluconic acid-an added value platform chemical in the context of biomass upgrading routes. The key factors controlling the successful performance on both reactions are carefully discussed and compared to previous studies in literature. To our knowledge this is one of the very few works in catalysis by gold combining liquid and gas phase reactions and represents a step forward in the flexible behavior of nano gold catalysts.


Julio, 2019 | DOI: 10.3389/fchem.2019.00504

2D compositional self-patterning in magnetron sputtered thin films


Garcia-Valenzuela, A; Alvarez, R; Rico, V; Espinos, JP; Lopez-Santos, MC; Solis, J; Siegel, J; del Campo, A; Palmero, A; Gonzalez-Elipe, AR
Applied Surface Science, 480 (2019) 115-121

ABSTRACT

Unlike topography patterning, widely used for numerous applications and produced by means of different technologies, there are no simple procedures to achieve surface compositional patterning at nanometric scales. In this work we have developed a simple method for 2D patterning the composition of thin films. The method relies on the magnetron sputtering deposition at oblique angles onto patterned substrates made by laser induced periodic surface structures (LIPSS). The method feasibility has been demonstrated by depositing SiOx thin films onto LIPSS structures generated in Cr layers. A heterogeneous and aligned distribution of O/Si ratios (and different Sin+ chemical states) along the LIPSS structure in length scales of some hundreds nm's has been proven by angle resolved X-ray photoelectron spectroscopy and a patterned arrangement of composition monitored by atomic force microscopy-Raman analysis. The obtained results are explained by the predictions of a Monte Carlo simulation of this deposition process and open the way for the tailored one-step fabrication of surface devices with patterned compositions.


Junio, 2019 | DOI: 10.1016/j.apsusc.2019.02.206

Comprehensive Experimental and Theoretical Study of the CO plus NO Reaction Catalyzed by Au/Ni Nanoparticles


Kyriakou, G; Marquez, AM; Holgado, JP; Taylor, MJ; Wheatley, AEH; Mehta, JP; Sanz, JF; Beaumont, SK; Lambert, RM
ACS Catalysis, 9 (2019) 4919-4929

ABSTRACT

The catalytic and structural properties of five different nanoparticle catalysts with varying Au/Ni composition were studied by six different methods, including in situ X-ray absorption spectroscopy and density functional theory (DFT) calculations. The as-prepared materials contained substantial amounts of residual capping agent arising from the commonly used synthetic procedure. Thorough removal of this material by oxidation was essential for the acquisition of valid catalytic data. All catalysts were highly selective toward N-2 formation, with 50-50 Au:Ni material being best of all. In situ X-ray absorption near edge structure spectroscopy showed that although Au acted to moderate the oxidation state of Ni, there was no clear correlation between catalytic activity and nickel oxidation state. However, in situ extended X-ray absorption fine structure spectroscopy showed a good correlation between Au Ni coordination number (highest for Ni50Au50) and catalytic activity. Importantly, these measurements also demonstrated substantial and reversible Au/Ni intermixing as a function of temperature between 550 degrees C (reaction temperature) and 150 degrees C, underlining the importance of in situ methods to the correct interpretation of reaction data. DFT calculations on smooth, stepped, monometallic and bimetallic surfaces showed that N + N recombination rather than NO dissociation was always rate-determining and that the activation barrier to recombination reaction decreased with increased Au content, thus accounting for the experimental observations. Across the entire composition range, the oxidation state of Ni did not correlate with activity, in disagreement with earlier work, and theory showed that NiO itself should be catalytically inert. Au-Ni interactions were of paramount importance in promoting N + N recombination, the rate-limiting step.


Junio, 2019 | DOI: 10.1021/acscatal.8b05154

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