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Artículos SCI



2020


Influence of Water on the Oxidation of NO on Pd/TiO2 Photocatalysts


M.J. Hernández Rodríguez; E. Pulido Melián; J. Araña; J.A. Navío; O.M. González Díaz; Dunia E. Santiago; J.M. Doña Rodríguez
Nanomaterials, 10 (2020) 2354
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

Two series of new photocatalysts were synthesized based on modification with Pd of the commercial P25 photocatalyst (EVONIK®). Two techniques were employed to incorporate Pd nanoparticles on the P25 surface: photodeposition (series Pd-P) and impregnation (series Pd-I). Both series were characterized in depth using a variety of instrumental techniques: BET, DRS, XRD, XPS, TEM, FTIR and FESEM. The modified series exhibited a significant change in pore size distribution, but no differences compared to the original P25 with respect to crystalline phase ratio or particle size were observed. The Pd0 oxidation state was predominant in the Pd-P series, while the presence of the Pd2+ oxidation state was additionally observed in the Pd-I series. The photoactivity tests were performed in a continuous photoreactor with the photocatalysts deposited, by dip-coating, on borosilicate glass plates. A total of 500 ppb of NO was used as input flow at a volumetric flow rate of 1.2 L·min−1, and different relative humidities from 0 to 65% were tested. The results obtained show that under UV-vis or Vis radiation, the presence of Pd nanoparticles favors NO removal independently of the Pd incorporation method employed and independently of the tested relative humidity conditions. This improvement seems to be related to the different interaction of the water with the surface of the photocatalysts in the presence or absence of Pd. It was found in the catalyst without Pd that disproportionation of NO2 is favored through its reaction with water, with faster surface saturation. In contrast, in the catalysts with Pd, disproportionation took place through nitro-chelates and adsorbed NO2 formed from the photocatalytic oxidation of the NO. This different mechanism explains the greater efficiency in NOx removal in the catalysts with Pd. Comparing the two series of catalysts with Pd, Pd-P and Pd-I, greater activity of the Pd-P series was observed under both UV-vis and Vis radiation. It was shown that the Pd0 oxidation state is responsible for this greater activity as the Pd-I series improves its activity in successive cycles due to a reduction in Pd2+ species during the photoactivity tests.


Diciembre, 2020 | DOI: 10.3390/nano10122354

Control of experimental conditions in reaction flash-sintering of complex stoichiometry ceramics


Gil-Gonzalez, E; Perejon, A; Sanchez-Jimenez, PE; Roman-Gonzalez, D; Perez-Maqueda, LA
Ceramics International, 46 (2020) 29413-29420
Reactividad de Sólidos

ABSTRACT

The inherent potential of reaction flash-sintering for the preparation of complex oxides is evidenced by the one-step synthesis and densification of a ceramic of complex stoichiometry. The system Bi0.93La0.07FeO3, a multi-ferroic ceramic with promising technological applications, has been chosen. This system presents three different metals in its composition and it is extremely challenging to prepare by conventional procedures. Non-stoichiometric materials with unwilling secondary phases are usually obtained by conventional methods, due to the high volatility of bismuth oxide at the temperatures required for inducing the solid-solid reactions. Here, it is demonstrated that a careful control of the experimental flash conditions (applied electric field and selected current density limit) is required to obtain a high quality ceramic. Small deviations from the optimum conditions result in either non-stoichometric or poorly densified samples.


Diciembre, 2020 | DOI: 10.1016/j.ceramint.2020.05.091

Thin film electroluminescent device based on magnetron sputtered Tb doped ZnGa2O4 layers


Gil-Rostra, J; Valencia, FY; Gonzalez-Elipe, AR
Journal of Luminescence, 228 (2020) 117617
Nanotecnología en Superficies y Plasma

ABSTRACT

Photoluminescent (PL) layers and electroluminescent (EL) systems prepared by different methods have been systematically studied for the fabrication of flat panel displays, monitoring screens, and lighting systems. In this work we report about a new procedure of preparing Tb doped ZnGa2O4 green luminescent thin films at low temperature that consists of the simultaneous reactive magnetron sputtering (R-MS) deposition of a Zn-Ga mixed oxide acting as a matrix and the plasma decomposition (PD) of evaporated terbium acetylacetonate. The resulting films were transparent and presented a high PL efficiency making them good candidates for EL applications. Layers of this phosphor film with thickness in the order of hundreds nanometers were sandwiched between two dielectric layers of Y2O3 and AlSiNxOy that were also prepared by R-MS. The response of the resulting EL device was characterized as a function of the applied voltage and the type of AC excitation signal. The high luminance and long-term stability of these thin film electroluminescent devices (TFELDs) proves the reliability and efficiency of this kind of transparent R-MS multilayer system (with a total thickness in order of 650 nm) for display and lighting applications.


Diciembre, 2020 | DOI: 10.1016/j.jlumin.2020.117617

Efficient third harmonic generation from FAPbBr(3) perovskite nanocrystals


Rubino, A; Huq, T; Dranczewski, J; Lozano, G; Calvo, ME; Vezzoli, S; Miguez, H; Sapienza, R
Journal of Materials Chemistry C, 8 (2020) 15990-15995
Materiales Ópticos Multifuncionales

ABSTRACT

The development of versatile nanostructured materials with enhanced nonlinear optical properties is relevant for integrated and energy efficient photonics. In this work, we report third harmonic generation from organic lead halide perovskite nanocrystals, and more specifically from formamidinium lead bromide nanocrystals, ncFAPbBr(3), dispersed in an optically transparent silica film. Efficient third order conversion is attained for excitation in a wide spectral range in the near infrared (1425 nm to 1650 nm). The maximum absolute value of the modulus of the third order nonlinear susceptibility of ncFAPbBr(3), chi((3)NC), is derived from modelling both the linear and nonlinear behaviour of the film and is found to be chi((3)NC) = 1.46 x 10(-19) m(2) V-2 (or 1.04 x 10(-11) esu) at 1560 nm excitation wavelength, which is of the same order as the highest previously reported for purely inorganic lead halide perovskite nanocrystals (3.78 x 10(-11) esu for ncCsPbBr(3)). Comparison with the experimentally determined optical constants demonstrates that maximum nonlinear conversion is attained at the excitonic resonance of the perovskite nanocrystals where the electron density of states is largest. The ease of synthesis, the robustness and the stability provided by the matrix make this material platform attractive for integrated nonlinear devices.


Diciembre, 2020 | DOI: 10.1039/d0tc04790b

High-temperature solar-selective coatings based on Cr(Al)N. Part 2: Design, spectral properties and thermal stability of multilayer stacks


Rojas, TC; Caro, A; Escobar-Galindo, R; Sanchez-Lopez, JC
Solar Energy Materials and Solar Cells, 218 (2020) 110812
Tribología y Protección de Superficies

ABSTRACT

Two multilayer solar selective absorber coatings [Al/CrN0.95/Cr0.96Al0.04N1.08/Cr0.53Al0.47N1.12/Al2O3 (stack #1) and Cr0.96Al0.04N0.89/Cr0.62Al0.38N1.00/Cr0.53Al0.47N1.12/Al2O3 (stack #2)] were deposited on 316L steel by combining direct current (DC) and high power impulse magnetron sputtering (HiPIMS) technologies with the aim of increasing the working limit temperature. The composition and thickness of the constituent layers were optimized using CODE software to achieve a high solar absorptance (alpha) and low values of thermal emittance (epsilon) in the infrared region. The deposited multilayered stacks were heated during 2 h in air at 600, 700 and 800 degrees C to study their thermal stability and optical performance. Compositional, structural and optical characterization of the stacks (as-prepared and after thermal treatment) was performed. Both stacks presented a good solar selectivity with alpha > 95% and epsilon < 15%, were stable up to 600 degrees C and fulfilled the performance criterion PC < 5% after 600 and 700 degrees C treatments. Despite the stacks suffered chemical transformations above 600 degrees C, partial oxidation (stack #1) and Cr2N formation (stack #1 and #2), the optical properties were optimum up to 700 degrees C for stack #1 (alpha = 94%, epsilon((25 degrees C)) = 12%) and 600 degrees C for stack #2 (alpha = 93%, epsilon((25 degrees C)) = 13%). The solar-to-mechanical energy conversion efficiencies (eta) of the as-deposited and annealed (600 and 700 degrees C) samples were up to 20% points higher than the absorber paint commercially used (Pyromark). At 800 degrees C, they underwent a further structural transformation, provoked by the oxidation of the inner layers, and they consequently lost their solar selectivity.


Diciembre, 2020 | DOI: 10.1016/j.solmat.2020.110812

Ru-Ni/MgAl2O4 structured catalyst for CO2 methanation


Navarro, Juan C.; Centeno, Miguel A.; Laguna, Oscar H.; Odriozola, Jose A.
Renewabel Energy, 161 (2020) 120-132
Química de Superficies y Catálisis

ABSTRACT

Novel catalytic systems should be tested for the valorization of CO2 through the Sabatier reaction, since this process is gaining great importance within strategic sectors of the chemical industry. Therefore, this work explores the feasibility of structuring a catalyst (0.5%Ru-15%Ni/MgAl2O4) for CO2 methanation using metal micromonoliths. The coating of the catalyst over the surface of the micromonoliths is carried out by means of the washcoating procedure and different characterization techniques are applied to establish possible changes in the catalyst during structuring.
Regarding the performance in the Sabatier reaction, the structured systems are tested as well as the powder catalyst in order to establish the possible effects of the structuring processes. For this, variables such as catalyst loading, space velocity, inclusion of water in the feed-stream and the pressurization of the process were studied.
In general, the structuring of the proposed catalyst by the reported procedure is absolutely feasible. There are no substantial changes in the main features of the catalyst and this means that its catalytic performance is not altered after the structuring process either. Furthermore, the structured system exhibits high stability in a long-term test and is comparable with other CO2 methanation catalysts reported in research to date. 


Diciembre, 2020 | DOI: 10.1016/j.renene.2020.07.055

Tailoring CrNx stoichiometry and functionality by means of reactive HiPIMS


Sanchez-Lopez, JC; Caro, A; Alcala, G; Rojas, TC
Surface & Coatings Technology, 401 (2020) 126235
Tribología y Protección de Superficies

ABSTRACT

This work presents a complete study of the influence of HiPIMS pulse characteristics on the microstructure, chemical composition, mechanical and oxidation resistance properties of CrN thin films. The investigated parameters were frequency and pulse length at two different nitrogen fluxes, maintaining constant the duty cycle conditions (2%). The effect of a negative bias of 100 V was investigated in a particular case. By changing the synthesis conditions, it was possible to tailor the N/Cr ratio and thus to control the CrNx stoichiometry from x = 0.63 to 1.10. The selection of longer pulses (shorter frequencies) generates more disordered structures with lower N/Cr ratios. This is reflected in higher hardness and elastic modulus values on despite of a lower oxidation resistance due to existence of larger concentration of N vacancies. The best oxidation resistance is obtained at the highest peak current combined with additional ion bombardment provided by substrate biasing. The present results open the possibilities of modifying chemical composition and engineering surfaces by changing exclusively the pulse conditions in HiPIMS deposition processes.


Noviembre, 2020 | DOI: 10.1016/j.ceramint.2020.09.024

Advances in the implementation of PVD-based techniques for the preparation of metal catalysts for the hydrolysis of sodium borohydride


Arzac, GM; Fernandez, A
International Journal of Hydrogen Energy, 58 (2020) 33288-33309
Materiales Nanoestructurados y Microestructura

ABSTRACT

Sodium borohydride constitutes a safe alternative for the storage of hydrogen with a high gravimetric content. Catalytic hydrolysis of sodium borohydride permits on-demand hydrogen generation for multiple applications. In this field, the rational design of efficient metal catalysts deposited on structured supports is highly desirable. For most reactions, chemical methods are the most commonly used methods for the preparation of supported metal catalysts. Physical vapour deposition techniques are emerging as an alternative for the preparation of catalytic materials because of their multiple advantages. They permit the one-step deposition of catalysts on structured supports with controlled microstructure and composition, avoiding the multi-step procedures and the generation of hazardous by-products associated with chemical routes.

In this short review, we will describe the available literature on the application of physical vapour deposition techniques for the preparation of supported metal catalysts for the hydrolysis of sodium borohydride. The effects of the deposition parameters on the properties of the catalytic materials will be discussed, and strategies for further improvement will be proposed. Here, we also present our new results on the study of nanoporous Pt catalysts that are prepared through the chemical dealloying of magnetron sputtered Pt-Cu thin films for the hydrolysis of sodium borohydride. We discuss the capabilities of the technique to tune the microstructure from columnar to closed porous microstructures, which, coupled with dealloying, produces more active supported catalysts with lower noble metal loading. At the end, we briefly mention the application of PVD for the preparation of supported catalysts for the hydrolysis of ammonia borane, another hydrogen generating reaction of high interest nowadays.


Noviembre, 2020 | DOI: 10.1016/j.ijhydene.2020.09.041

Graphene-coated Ti-Nb-Ta-Mn foams: A promising approach towards a suitable biomaterial for bone replacement


Lascano, S; Chavez-Vasconez, R; Munoz-Rojas, D; Aristizabal, J; Arce, B; Parra, C; Acevedo, C; Orellana, N; Reyes-Valenzuela, M; Gotor, FJ; Arevalo, C; Torres, Y
Surface & Coatings Technology, 401 (2020) 126250
Reactividad de Sólidos

ABSTRACT

The design of bone implants with proper biological and mechanical properties remains a challenge in medical implantology. The use of bioactive coatings has been shown to improve the biocompatibility of the implant surface. In this study, a new approach including porous scaffolds, beta-Ti alloys and nanocoatings to design new bone implants is presented. Porous Ti-Nb-Ta-xMn alloys (x: 2, 4, and 6 wt%) substrates were obtained by powder metallurgy and the effect of the porosity and Mn content on mechanical properties was studied. CVD single-layer graphene was transferred onto the porous substrates that presented the best mechanical response (x: 4 wt%) for further evaluation of in vitro cell behavior (biocompatibility and cell adhesion). Cytotoxicity and biocompatibility tests confirmed that cell adhesion and proliferation were successfully achieved on graphene-coated porous substrates, confirming these systems are potential candidates for using in partial bone tissue replacement.


Noviembre, 2020 | DOI: 10.1016/j.surfcoat.2020.126250

Dust filter of secondary aluminium industry as raw material of geopolymer foams


Eliche-Quesada, D; Ruiz-Molina, S; Perez-Villarejo, L; Castro, E; Sanchez-Soto, PJ
Hournal of Building Engineering, 32 (2020) 101656
Materiales Avanzados

ABSTRACT

In this work, the use of waste dust filter of secondary aluminum industry (DFA) to obtain geopolymer foams has been studied. The waste was used as source of alumina and foaming agent. As precursor and principal reactive silica supplier rice husk ash was used. Precursors were chemically activated by means of a sodium hydroxide aqueous solution and a commercial sodium silicate solution. The influence of the DFA content or Si/Al molar ratio (4-7) were determined by keeping the Si/Na molar ratio of 0.7 M constant and the concentration of sodium hydroxide in the activating solution equal to 8.5 M. The geopolymer foams obtained were studied by X-ray Diffraction (XRD), adsorption/desorption of nitrogen, infrared spectroscopy (FTIR), and scanning electron microscope (SEM) techniques. The results indicated that geopolymer foams presented low values of bulk density (643-737 kg/m(3)) high values of apparent porosity (62-70%), low, but sufficient values of compressive strength (0.5-1.7 MPa) and good values of thermal conductivity (0.131-0.157 W/mK). Lower values of thermal conductivity were obtained for Si/Al = 4 and 5 M ratios, due to the highest apparent porosity and the highest total pore volume. These geopolymer foam materials have similar properties to other construction materials sector such as gypsum boards, foamed concrete, or insulating materials. In addition, its use in other applications of interest such as catalyst support or gas filtration materials could be investigated.


Noviembre, 2020 | DOI: 10.1016/j.jobe.2020.101656

Plasma-Enabled Amorphous TiO2 Nanotubes as Hydrophobic Support for Molecular Sensing by SERS


Filippin, N; Castillo-Seoane, J; Lopez-Santos, MC; Rojas, CT; Ostrikov, K; Barranco, A; Sanchez-Valencia, JR; Borras, A
ACS Applied Materials & Interfaces, 12 (2020)
Nanotecnología en Superficies y Plasma - Tribología y Protección de Superficies

ABSTRACT

We devise a unique heteronanostructure array to overcome a persistent issue of simultaneously utilizing the surface-enhanced Raman scattering, inexpensive, Earth-abundant materials, large surface areas, and multifunctionality to demonstrate near single-molecule detection. Room-temperature plasma-enhanced chemical vapor deposition and thermal evaporation provide high-density arrays of vertical TiO2 nanotubes decorated with Ag nanoparticles. The role of the TiO2 nanotubes is 3-fold: (i) providing a high surface area for the homogeneous distribution of supported Ag nanoparticles, (ii) increasing the water contact angle to achieve superhydrophobic limits, and (iii) enhancing the Raman signal by synergizing the localized electromagnetic field enhancement (Ag plasmons) and charge transfer chemical enhancement mechanisms (amorphous TiO2) and by increasing the light scattering because of the formation of vertically aligned nanoarchitectures. As a result, we reach a Raman enhancement factor of up to 9.4 × 107, satisfying the key practical device requirements. The enhancement mechanism is optimized through the interplay of the optimum microstructure, nanotube/shell thickness, Ag nanoparticles size distribution, and density. Vertically aligned amorphous TiO2 nanotubes decorated with Ag nanoparticles with a mean diameter of 10–12 nm provide enough sensitivity for near-instant concentration analysis with an ultralow few-molecule detection limit of 10–12 M (Rh6G in water) and the possibility to scale up device fabrication.


Noviembre, 2020 | DOI: 10.1021/acsami.0c14087

Anisotropic Resistivity Surfaces Produced in ITO Films by Laser-Induced Nanoscale Self-organization


Lopez-Santos, C; Puerto, D; Siegel, J; Macias-Montero, M; Florian, C; Gil-Rostra, J; Lopez-Flores, V; Borras, A; Gonzalez-Elipe, AR; Solis, J
Advanced Optical Materials, (2020)2001086
Nanotecnología en Superficies y Plasma

ABSTRACT

Highly anisotropic resistivity surfaces are produced in indium tin oxide (ITO) films by nanoscale self-organization upon irradiation with a fs-laser beam operating at 1030 nm. Anisotropy is caused by the formation of laser-induced periodic surface structures (LIPSS) extended over cm-sized regions. Two types of optimized structures are observed. At high fluence, nearly complete ablation at the valleys of the LIPSS and strong ablation at their ridges lead to an insulating structure in the direction transverse to the LIPSS and conductive in the longitudinal one. A strong diminution of In content in the remaining material is then observed, leading to a longitudinal resistivity rho(L) approximate to 1.0 omega center dot cm. At a lower fluence, the material at the LIPSS ridges remains essentially unmodified while partial ablation is observed at the valleys. The structures show a longitudinal conductivity two times higher than the transverse one, and a resistivity similar to that of the pristine ITO film (rho approximate to 5 x 10(-4) omega center dot cm). A thorough characterization of these transparent structures is presented and discussed. The compositional changes induced as laser pulses accumulate, condition the LIPSS evolution and thus the result of the structuring process. Strategies to further improve the achieved anisotropic resistivity results are also provided.


Noviembre, 2020 | DOI: 10.1002/adom.202001086

Flexible syngas production using a La2Zr2-xNixO7-delta pyrochlore-double perovskite catalyst: Towards a direct route for gas phase CO2 recycling


le Sache, E; Pastor-Perez, L; Garcilaso, V; Watson, DJ; Centeno, MA; Odriozola, JA; Reina, TR
Catalysis Today, 357 (2020) 583-589
Química de Superficies y Catálisis

ABSTRACT

The bi-reforming of methane (BRM) has the advantage of utilising greenhouse gases and producing H2 rich syngas. In this work Ni stabilised in a pyrochlore-double perovskite structure is reported as a viable catalyst for both Dry Reforming of Methane (DRM) and BRM. A 10 wt.% Ni-doped La2Zr2O7 pyrochlore catalyst was synthesised, characterised and tested under both reaction conditions and its performance was compared to a supported Ni/La2Zr2O7. In particular the effect of steam addition is investigated revealing that steam increases the H2 content in the syngas but limits reactants conversions. The effect of temperature, space velocity and time on stream was studied under BRM conditions and brought out the performance of the material in terms of activity and stability. No deactivation was observed, in fact the addition of steam helped to mitigate carbon deposition. Small and well dispersed Ni clusters, possibly resulting from the progressive exsolution of Ni from the mixed oxide structure could explain the enhanced performance of the catalyst.


Noviembre, 2020 | DOI: 10.1016/j.cattod.2019.05.039

Thermo-optic response of MEH-PPV films incorporated to monolithic Fabry-Perot microresonators


Rostra, JG; Soler-Carracedo, K; Martin, LL; Lahoz, F; Yubero, F
Dyes and Pigments, 182 (2020) 108625
Nanotecnología en Superficies y Plasma

ABSTRACT

Poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) is a semiconducting optically active polymer widely used in optoelectronics research. MEH-PPV can be commercially acquired in a large range of molecular weights. However, the influence of this property on the optical performance of the polymer is often disregarded. In this paper, the thermal dependence of the refractive index of MEH-PPV thin films prepared from high and medium molecular weight polymers is investigated. Thus, monolithic Fabry-Perot (FP) microcavities are fabricated, in which the active polymer film is part of their defect layer. It is found that when these devices are used as optical temperature sensors, the position of the emission band of the microcavities excited with a blue diode laser shifts to lower wavelengths when temperature increases with sensitivities in the 0.2-0.3 nm/degrees C range. This effect is ascribed to the variation in the refractive index of the polymer active layer within the resonator with temperature. According to theoretical simulations of optical transmittance by classical transfer matrix method and the evaluation of the optical eigenmodes by finite element methods of the manufactured FP resonator cavities, it is found that the MEH-PPV films present negative thermo-optic coefficients of about-0.018 K-1 and-0.0022 K-1 for high and medium molecular weight polymers, respectively, in the temperature range between 20 and 60 degrees C. These values are about the highest reported so far, to the best of our knowledge, and points to high performance thermal sensor applications.


Noviembre, 2020 | DOI: 10.1016/j.dyepig.2020.108625

Internal quantum efficiency and time signals from intensity-modulated photocurrent spectra of perovskite solar cells


Riquelme, A; Galvez, FE; Contreras-Bernal, L; Miguez, H; Anta, JA
Journal of Applied Physics, 128 (2020) 133103
Materiales Ópticos Multifuncionales

ABSTRACT

Intensity Modulated Photocurrent Spectroscopy (IMPS) is a small-perturbation optoelectronic technique that measures the quantum efficiency of a photoelectrochemical device as a function of optical excitation frequency. Metal Halide Perovskites (MHPs) are mixed electronic-ionic semiconductors with an extraordinary complex optoelectronic behavior and a record efficiency surpassing 25%. In this paper, we propose a simplified procedure to analyze IMPS data in MHPs based on the analysis of the internal quantum efficiency and the time signals featuring in the frequency spectra. In this procedure, we look at the change of each signal when optical excitation wavelength, photon flux, and temperature are varied for an archetypical methyl ammonium lead iodide solar cell. We use drift-diffusion modeling and comparison with relatively simpler dye-sensitized solar cells (DSC) with viscous and non-viscous electrolytes to help us to understand the origin of the three signals appearing in MHP cells and the measurement of the internal quantum efficiency.


Octubre, 2020 | DOI: 10.1063/5.0013317

Upgrading the PtCu intermetallic compounds: The role of Pt and Cu in the alloy


Castillo, R; Garcia, ED; Santos, JL; Centeno, MA; Sarria, FR; Daturi, M; Odriozola, JA
Catalysis Today, 356 (2020) 390-398
Química de Superficies y Catálisis

ABSTRACT

This work is devoted to the study of the role of both metals in the intermetallic PtxCuy/ γ Al2O3 catalysts commonly employed in CO-PROX reaction. Therefore, monometallic Pt and Cu based catalysts and PtCu intermetallic compound with different molar ratios (Pt3Cu1 and Pt1Cu3) supported catalysts were carefully synthesized and deeply characterized. Room temperature CO adsorptions by FTIR spectroscopy were carried out on the mono- and intermetallic catalysts being the monometallic catalyst determinant for the study. From the analysis of the nature of the platinum surface in Pt/ γ Al2O3, we have demonstrated that the role of Pt sites is based in the CO dissociation for the CO2 formation and also how the platinum surface is partially blocked by leftovers from the synthesis. Moreover, the study of the Cu/ γ Al2O3 and the bimetallic catalysts PtxCuy/ γ Al2O3 allowed elucidating the effect of the copper in the metallic site and support interphase as well as the role of copper in the hydrocarbon oxidation.


Octubre, 2020 | DOI: 10.1016/j.cattod.2019.11.026

Tribological performance of Nb-C thin films prepared by DC and HiPIMS


Sala, N; Abad, MD; Sanchez-Lopez, JC; Cruz, M; Caro, J; Colominas, C
Materials Letters, 277 (2020) 12834
Tribología y Protección de Superficies

ABSTRACT

Nanostructured NbC thin films with variable contents of Nb and C were prepared by direct current (DC) magnetron sputtering, and for the first time, via high power impulse magnetron sputtering (HiPIMS) searching for an improvement in the tribological properties. X-ray diffraction shows that increasing the carbon incorporation, the crystalline composition evolves from Nb2C to NbC phase. Further carbon enrichment leads to a nanocomposite structure formed by small NbC crystals (8-14 nm) dispersed in a-C matrix. The friction coefficient varied from high friction (0.8) to low friction (0.25) and the hardness values between 20 and 11 GPa depending on the film composition. A densification of the coatings by changing the methodology from DC to HiPIMS was not observed. 


Octubre, 2020 | DOI: 10.1016/j.matlet.2020.128334

Microstructure and thermal conductivity of Si-Al-C-O fiber bonded ceramics joined to refractory metals


Vera, MC; Martinez-Fernandez, J; Singh, M; Casalegno, V; Balagna, C; Ramirez-Rico, J
Materials Letters, 276 (2020) 128203
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

We explore joining Si-Al-C-O fiber-bonded ceramics to Cu-clad-Mo using an Ag-Ti-Cu brazing alloy. A temperature of 900 degrees C and times in the range of 10-20 min are required to obtain sound joints irrespectively of the fiber orientation. The reaction layer is 1-2 mu m thick and free of pores and defects. The thermal conductivity of the joined samples is well described considering that the metal and the ceramic are in series for thermal resistance. This implies that the joint is highly conductive and forms an almost perfect 


Octubre, 2020 | DOI: 10.1016/j.matlet.2020.128203

Unraveling Discharge and Surface Mechanisms in Plasma-Assisted Ammonia Reactions


Navascues, P; Obrero-Perez, JM; Cotrino, J; Gonzalez-Elipe, AR; Gomez-Ramirez, A
ACS Sistainable Chemistry & Engineering, 8 (2020) 14855-14866
Nanotecnología en Superficies y Plasma

ABSTRACT

Current studies on ammonia synthesis by means of atmospheric pressure plasmas respond to the urgent need of developing less environmentally aggressive processes than the conventional Haber-Bosch catalytic reaction. Herein, we systematically study the plasma synthesis of ammonia and the much less investigated reverse reaction (decomposition of ammonia into nitrogen and hydrogen). Besides analyzing the efficiency of both processes in a packed-bed plasma reactor, we apply an isotope-exchange approach (using D-2 instead of H-2) to study the reaction mechanisms. Isotope labeling has been rarely applied to investigate atmospheric plasma reactions, and we demonstrate that this methodology may provide unique information about intermediate reactions that, consuming energy and diminishing the process efficiency, do not effectively contribute to the overall synthesis/decomposition of ammonia. In addition, the same methodology has demonstrated the active participation of the interelectrode material surface in the plasma-activated synthesis/decomposition of ammonia. These results about the involvement of surface reactions in packed-bed plasma processes, complemented with data obtained by optical emission spectroscopy analysis of the plasma phase, have evidenced the occurrence of inefficient intermediate reaction mechanisms that limit the efficiency and shown that the rate-limiting step for the ammonia synthesis and decomposition reactions are the formation of NH* species in the plasma phase and the electron impact dissociation of the molecule, respectively.


Octubre, 2020 | DOI: 10.1021/acssuschemeng.0c04461

Multiple pollutants removal by functionalized heterostructures based on Na-2-Mica


Pazos, MC; Bravo, LR; Ramos, SE; Osuna, FJ; Pavon, E; Alba, MD
Applied Clay Science, 196 (2020) 105749
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Organomica, C8-2-Mica, was obtained from a high charged synthetic mica, Na-2-Mica, by cation exchange reaction with octylammonium cations and these were used to host other bulky guest species such as polyhydroxy aluminium cations, Al(13)20. The hydrolization of 3-mercaptopropyltrimethoxysilane (MPTMS) allowed the covalent attachment with hydroxyl groups of the oligomeric cation, providing thiol groups that create specific adsorption sites, Al(13)20/SH. The structure of the adsorbents was analysed by XRD and Infrared spectroscopy and these were tested as an adsorbent for the removal of zinc and herbicide MCPA from aqueous solutions. C8-2-Mica was the best adsorbent for MCPA and thiol groups favoured the adsorption of Zn2+. Moreover, Al(13)20/SH showed excellent adsorptive properties for the simultaneous adsorption of MCPA and Zn2+.


Octubre, 2020 | DOI: 10.1016/j.clay.2020.105749

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