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2018


Study of the effectiveness of the flocculation-photocatalysis in the treatment of wastewater coming from dairy industries


Murcia, J.J., Hernández-Laverde, M., Rojas, Muñoz, E., Navío, J.A., Hidalgo, M.C.
Journal of Photochemistry and Photobiology A: Chemistry, 358 (2018) 256-264

ABSTRACT

The aim of the present work was to evaluate the effectiveness of flocculation-photocatalysis as combined processes in the treatment of dairy industries wastewater. Different commercial and lab prepared flocculants and photocatalysts were evaluated. All the materials prepared were extensively characterized. Commercial materials presented the best physicochemical properties and performance in the treatment of the studied wastewater. On one hand, all the photocatalysts evaluated showed bactericidal activity for E. Coli, total coliforms and other enterobacteriaceae. Total elimination of E. coli was obtained by using commercial TiO2 P25 Evonik, under 120 W/m2 of UV–vis light intensity and 5 h of total illumination time. Other species of bacteria remained after treatment under these conditions. It was also found that the highest light intensity of 120 W/m2 led to increase the Chemical Oxygen Demand and Total Organic Carbon in the samples treated, it can be due to the faster formation of new organic compounds as intermediaries during the photocatalytic reactions at the highest photonic flux. Flocculation pre-treatment of the wastewater samples led to improve the effectiveness of the photocatalytic treatment; thus, the combination of flocculation-photocatalysis treatments at low light intensity of 30 W/m2 leads to achieve the total elimination of E. coli, and under this intensity the elimination of total coliforms and other enterobacteriaceae increased 5.48% compared to the photocatalytic treatment alone. These treatment conditions led to comply the Colombian regulations for dairy wastewater.


Mayo, 2018 | DOI: 10.1016/j.jphotochem.2018.03.034

Influence of the Mn content on the TiNbxMn alloys with a novel fcc structure


Chicardi, E; Aguilar, C; Sayagues, MJ; Garcia-Garrido, C
Journal of Alloys and Compounds, 746 (2018) 601-610

ABSTRACT

This work studies the structural evolution of TiNbxMn alloys (x: 0-12 wt%) synthetized by mechanical alloying in a planetary ball mill with different milling times between 1 h and 120 h. The specimens were characterized by X-ray diffraction patterns, scanning and transmission electron microscopies and Energy-dispersive X-ray spectroscopy. It was observed an evolution of the alloys developed from the raw Ti, Nb and Mn elements to bcc-TiNbxMn alloys and, finally, novel fcc-TiNbxMn alloys, with Fm3m space group symmetry, not previously observed. The presence of Mn promotes other interesting effects: a) the decreasing of the crystallite and the particle sizes, reaching values close to 4 nm and 400 nm, respectively, b) the partial amorphization of the fcc-TiNbxMn alloys due to the combined effect of the Mechanical Alloying and the difference of Mn atomic size in comparison with Ti and Nb and c) the presence of Mn that decreases the Fe amount (from milling media) in the as-milled powders. 


Mayo, 2018 | DOI: 10.1016/j.jallcom.2018.02.306

Crystallization Kinetics of Nanocrystalline Materials by Combined X-ray Diffraction and Differential Scanning Calorimetry Experiments


Gil-Gonzalez, E; Perejon, A; Sanchez-Jimenez, PE; Medina-Carrasco, S; Kupcik, J; Subrt, J; Criado, JM; Perez-Maqueda, LA
Crystal Growth & Design, 18 (2018) 3107-3116

ABSTRACT

Crystallization is one key aspect in the resulting properties of nanocrystalline functional materials, and much effort has been devoted to understanding the physical mechanisms involved in these processes as a function of temperature. The main problems associated with crystallization kinetic studies come from the limitations of the employed techniques, and the obtained results may vary significantly depending on the choice of the measurement method. In this work, a complete description of the thermal crystallization event of nanocrystalline BiFeO3 has been performed by combining the information obtained from three different experimental techniques: in situ high-temperature X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Interestingly, the kinetic analysis of the X-ray diffraction and differential scanning calorimetry data yields almost identical results, although the physical properties measured by both techniques are different. This allows the unambiguous determination of the kinetic parameters. The importance of a proper definition of the conversion degree, which is limited by the employed measurement technique, is also highlighted.


Mayo, 2018 | DOI: 10.1021/acs.cgd.8b00241

Photo-induced processes on Nb2O5 synthesized by different procedures


Jaramillo-Páez, C., Sánchez-Fernández, F.J., Navío, J.A., Hidalgo, M.C.
Journal of Photochemistry and Photobiology A: Chemistry, 359 (2018) 40-52

ABSTRACT

The properties of Nb2O5 strongly depend on its synthesis procedure as well as the conditions of ulterior thermal treatment. We report the synthesis of Nb2O5 powders prepared by sol-gel precipitation method using niobium(V) ethoxide as precursor. Two chemical routes were chosen: the presence of tryethyl amine (TEA) as precipitant/template agent, or the oxidant peroxide method. In addition, microwave-assisted activation was also used. The as-prepared samples by the above procedures were amorphous. Structural changes upon heating from room temperature up to 800 °C were investigated by X-ray powder diffraction technique combined with thermogravimetric analysis. The sequential thermal treatment up to 800 °C promotes the crystallization of hexagonal phase to orthorhombic phase whereas the ulterior cooling to room temperature lead to a mixture of both phases. Samples calcined at selected temperatures of either 600 °C or 800 °C for 2 h, were characterized by XRD, SEM, N2-adsorption and diffuse reflectance spectroscopy (DRS). The synthetic approach routes as well as the combined microwave activation followed by ulterior thermal treatment lead to changes not only on particle size but also on the textural properties of the synthesized catalysts. The catalysts synthesized have been evaluated using Rhodamine B (RhB) as a substrate, under both UV and visible lighting conditions. None of the catalysts synthesized showed activity in the visible. Under UV-illumination conditions, some of the catalysts exhibited a relatively low photoactivity in the degradation of RhB, which is associated with a photo-sensitizing effect. However, the addition of Ag+ ions considerably increased the activity of all the catalysts in the degradation of RhB under UV-illumination conditions. A mechanism is proposed to explain the photo-induced processes obtained, leaving the door open to the possible implications of the observed results in relation to the interaction of RhB dye with noble metal nanoparticles such as silver.


Mayo, 2018 | DOI: 10.1016/j.jphotochem.2018.03.040

Chemical CO2 recycling via dry and bi reforming of methane using Ni-Sn/Al2O3 and Ni-Sn/CeO2-Al2O3 catalysts


Stroud, T; Smith, TJ; Le Sache, E; Santos, JL; Centeno, MA; Arellano-Garcia, H; Odriozola, JA; Reina, TR
Applied Catalysis B-Environmental, 224 (2018) 125-135

ABSTRACT

Carbon formation and sintering remain the main culprits regarding catalyst deactivation in the dry and bi-reforming of methane reactions (DRM and BRM, respectively). Nickel based catalysts (10 wt.%) supported on alumina (Al2O3) have shown no exception in this study, but can be improved by the addition of tin and ceria. The effect of two different Sn loadings on this base have been examined for the DRM reaction over 20 h, before selecting the most appropriate Sn/Ni ratio and promoting the alumina base with 20 wt.% of CeO2. This catalyst then underwent activity measurements over a range of temperatures and space velocities, before undergoing experimentation in BRM. It not only showed good levels of conversions for DRM, but exhibited stable conversions towards BRM, reaching an equilibrium H-2/CO product ratio in the process. In fact, this work reveals how multicomponent Ni catalysts can be effectively utilised to produce flexible syngas streams from CO2/CH4 mixtures as an efficient route for CO2 utilisation.


Mayo, 2018 | DOI: 10.1016/j.apcatb.2017.10.047

Development of a novel TiNbTa material potentially suitable for bone replacement implants


Chicardi, E; Gutierrez-Gonzalez, CF; Sayagues, MJ; Garcia-Garrido, C
Materials & Design, 145 (2018) 88-96

ABSTRACT

A novel (beta + gamma)-TiNbTa alloy has been developed by a combined low energy mechanical alloying (LEMA) and pulsed electric current sintering process (PECS). Microstructurally, this material presents interesting characteristics, such as a submicrometric range of particle size, a body-centered phase (beta-TiNbTa) and, mainly, a novel face-centered cubic Ti-based alloy (gamma-TiNbTa) not previously reported. Related to mechanical performance, the novel (beta + gamma)-TiNbTa shows a lower E (49 +/- 3 GPa) and an outstanding yield strength (sigma(y) 1860 MPa). This combination of original microstructure and properties makes to the (beta + gamma)-TiNbTa a novel material potentially suitable as biomaterial to fabricate bone replacement implants, avoiding the undesirable and detrimental stressshielding problem and even the usual damage on the mechanical strength of Ti-based foams biomaterials. 


Mayo, 2018 | DOI: 10.1016/j.matdes.2018.02.042

Carbonation of Limestone Derived CaO for Thermochemical Energy Storage: From Kinetics to Process Integration in Concentrating Solar Plants


Ortiz, C; Valverde, JM; Chacartegui, R; Perez-Maqueda, LA
ACS Sustainable Chemistry & Engineering, 6 (2018) 6404-6417

ABSTRACT

Thermochemical energy storage (TCES) is considered as a promising technology to accomplish high energy storage efficiency in concentrating solar power (CSP) plants. Among the various possibilities, the calcium-looping (CaL) process, based on the reversible calcination–carbonation of CaCO3 stands as a main candidate due to the high energy density achievable and the extremely low price, nontoxicity, and wide availability of natural CaO precursors such as limestone. The CaL process is already widely studied for CO2 capture in fossil fuel power plants or to enhance H2 production from methane reforming. Either one of these applications requires particular reaction conditions to which the sorbent performance (reaction kinetics and multicycle conversion) is extremely sensitive. Therefore, specific models based on the conditions of any particular application are needed. To get a grip on the optimum conditions for the carbonation of limestone derived CaO in the CaL-CSP integration, in the present work is pursued a multidisciplinary approach that combines theoretical modeling on reaction kinetics, lab-scale experimental tests at relevant CaL conditions for TCES, process modeling, and simulations. A new analytic equation to estimate the carbonation reaction rate as a function of CO2 partial pressure and temperature is proposed and validated with experimental data. Using the kinetics analysis, a carbonator model is proposed to assess the average carbonation degree of the solids. After that, the carbonator model is incorporated into an overall process integration scheme to address the optimum operation conditions from thermodynamic and kinetics considerations. Results from process simulations show that the highest efficiencies for the CaL-CSP integration are achieved at carbonator absolute pressures of ∼3.5–4 bar, which leads to an overall plant efficiency (net electric power to net solar thermal power) around 41% when carbonation is carried out at 950 °C under pure CO2


Mayo, 2018 | DOI: 10.1021/acssuschemeng.8b00199

Tribological properties of TiC/a-C:H nanocomposite coatings prepared via HiPIMS


Sanchez-Lopez, JC; Dominguez-Meister, S; Rojas, TC; Colasuonno, M; Bazzan, M; Patelli, A
Applied Surface Science, 440 (2018) 458-466

ABSTRACT

High power impulse magnetron sputtering (HiPIMS) technology has been employed to prepare TiC/a-C:H nanocomposite coatings from a titanium target in acetylene (C2H2) reactive atmospheres. Gas fluxes were varied from 1.3 to 4.4 sccm to obtain C/Ti ratios from 2 to 15 as measured by electron probe microanalysis (EPMA). X-ray diffraction and transmission electron microscopy demonstrate the presence of TiC nanocrystals embedded in an amorphous carbon-based matrix. The hardness properties decrease from 17 to 10 GPa as the carbon content increases. The tribological properties were measured using a pinon-disk tribometer in ambient air (RH = 30-40%) at 10 cm/s with 5 N of applied load against 6-mm 100Cr6 balls. The friction coefficient and the film wear rates are gradually improved from 0.3 and 7 x 10(-6) mm(3)/N m to 0.15 and 2 x 10(-7) mm(3)/N m, respectively, by increasing the C2H2 flux. To understand the tribological processes appearing at the interface and to elucidate the wear mechanism, microstructural and chemical investigations of the coatings were performed before and after the friction test. EPMA, X-ray photoelectron and electron energy-loss spectroscopies were employed to obtain an estimation of the fraction of the a-C:H phase, which can be correlated with the tribological behavior. Examination of the friction counterfaces (ball and track) by Raman microanalysis reveals an increased ordering of the amorphous carbon phase concomitant with friction reduction. The tribological results were compared with similar TiC/a-C(:H) composites prepared by the conventional direct current process. 


Mayo, 2018 | DOI: 10.1016/j.apsusc.2018.01.135

Obituary Note: Prof. Jose Manuel Criado


Perez-Maqueda, L; Koga, N; Malek, J
Thermochimica Acta, 663 (2018) A1

ABSTRACT

The late Prof. Jose Manuel Criado (1944.6.13–2018.2.27)

It is with the profoundest regret that we must report the passing of Prof. José Manuel Criado on February 27, 2018 at the age of 73. We express our most sincere condolences to his family, colleagues and friends.

Prof. Criado was born in Sevilla, Spain, on June 13th, 1944. He studied chemistry at the University of Seville and recieved his PhD from the same university under the supervision of Prof. Francisco González García and Prof. José María Trillo. He held a position as assistant professor at the Department of Inorganic Chemistry of the University of Seville from 1968 until 1972. Then, he joined the Consejo Superior de Investigaciones Científicas (CSIC) or National Research Council of Spain. In this institution he was junior researcher, senior researcher and, from 1986, full professor. Moreover, he has been visiting professor in a number of international institutions such as Stanford University (USA), CNRS Thermodynamics and Microcalorimetry Center in Marseille (France), University of Salford (UK), Macaulay Research Institute (UK), Institute of Inorganic Chemistry (Czech Republic), University of Chile (Chile). He had long-lasting collaborations with scientists from all over the world and visited labs in many countries. For many years, he used to spend some weeks abroad in the frame of collaboration projects with a number of international research groups, of special importance where his projects with the Czech Republic or Chile that lasted for over 20 years. He also served as an editorial board member of Thermochimica Acta for a long time and contributed largely to the further development of our academic field.

First research works of Prof. Criado were done within the field of heterogeneous catalysis, but very soon, he got interested in reactivity of solids and thermal analysis. Thus, most of his scientific career has been devoted to the study of kinetics of solid-state processes and mechanochemisty. He published about 240 papers in international journals. In the field of kinetics of solid-state processes, he made significant contributions, such as showing the limitations of using single linear heating rate experiments for extracting kinetic parameters, the proposal of master curves for discerning the kinetic model followed by the process or the combined analysis of experimental data obtained under different heating schedules. Moreover, after learning about the sample controlled thermal analysis (SCTA) method directly from Prof. Rouquerol in Marseille (France) and Profs. Paulik brothers in Budapest (Hungary), he constructed several of these instruments and extended the use of SCTA to the kinetic analysis of heterogeneous reactions, highlighting its advantages over conventional heating. Additionally, he used the kinetic control of solid-state processes by SCTA for the preparation of a number of functional and structural materials with controlled microstructures and properties. In the field of mechanochemistry, he made substantial contributions to the preparation of materials by gas–solid reaction using high energy planetary ball mills specially modified by him to work under controlled gas atmosphere.

Probably, the main contribution of Prof. Criado as a scientist has been as teacher and mentor for many of us. Despite of spending most of his scientific career in a research center rather than in a university, his laboratories were always full of students, postdocs and visitors from all over the world. He devoted a great effort to motivate and stimulate young people to pursue a career in science. His enthusiasm for science was sincere, as he loved science and research. Thus, he worked until the very last days and, even, when he could not go to the institute because he did not feel well, he worked in a small lab at home. He was very generous and always shared his knowledge with others. Thus, he expended long hours teaching about kinetics, making the complex equations easy to understand. Only those with a deep knowledge have this ability! It is not rare that many of his former students, postdocs and coworkers have permanent positions as professors and scientist in a number of international institutions. Another significant feature of Prof. Criado was his hospitality. He and his wife Maria Jesús Dianez, who joined his research group few years ago, has always his home doors open to any coworker or visitor.

We will all miss him not only as a scientist with a deep knowledge but as a friend we loved so much.


Mayo, 2018 | DOI: 10.1016/j.tca.2018.05.004

Multicomponent Ni-CeO2 nanocatalysts for syngas production from CO2/CH4 mixtures


le Sache, E.; Santos, J. L.; Smith, T. J.; Centeno, M. A.; Arellano-Garcia, H.; Odriozola, J. A.; Reina, T. R.
Journal of CO2 utilization, 25 (2018) 68-78

ABSTRACT

The dry reforming of methane with CO2 is a common route to transform CO2/CH4 mixtures into added value syngas. Ni based catalysts are highly active for this goal but suffer from deactivation, as such promoters need to be introduced to counteract this, and improve performance. In this study, mono- and bi-metallic formulations based on 10 wt.% Ni/CeO2-Al2O3 are explored and compared to a reference 10 wt.% Ni/gamma-Al2O3. The effect of Sn and Pt as promoters of Ni/CeO2-Al2O3 was also investigated. The formulation promoted with Sn looked especially promising, showing CO2 conversions stabilising at 65% after highs of 95%. Its increased performance is attributed to the additional dispersion Sn promotion causes. Changes in the reaction conditions (space velocity and temperature) cement this idea, with the Ni-Sn/CeAl material performing superiorly to the mono-metallic material, showing less deactivation. However, in the long run it is noted that the mono- metallic Ni/CeAl performs better. As such the application is key when deciding which catalyst to employ in the dry reforming process.


Mayo, 2018 | DOI: 10.1016/j.jcou.2018.03.012

In Vitro Comparative Study of Oxygen Plasma Treated Poly(Lactic-Co-Glycolic) (PLGA) Membranes and Supported Nanostructured Oxides for Guided Bone Regeneration Processes


Torres-Lagares, D; Castellanos-Cosano, L; Serrera-Figallo, MA; Lopez-Santos, C; Barranco, A; Rodriguez-Gonzalez-Elipe, A; Gutierrez-Perez, JL
Materials, 11 (2018) art. 752

ABSTRACT

(1) Background: The use of physical barriers to prevent the invasion of gingival and connective tissue cells into bone cavities during the healing process is called guided bone regeneration. The objective of this in-vitro study was to compare the growth of human osteoblasts on Poly(Lactic-co-Glycolic) (PLGA) membranes modified with oxygen plasma and Hydroxyapatite (HA), silicon dioxide (SiO2), and titanium dioxide (TiO2) composite nanoparticles, respectively. (2) Methods: All the membranes received a common treatment with oxygen plasma and were subsequently treated with HA nanostructured coatings (n = 10), SiO2 (n = 10) and TiO2 (n = 10), respectively and a PLGA control membrane (n = 10). The assays were performed using the human osteoblast line MG-63 acquired from the Center for Scientific Instrumentation (CIC) from the University of Granada. The cell adhesion and the viability of the osteoblasts were analyzed by means of light-field microphotographs of each condition with the inverted microscope Axio Observer A1 (Carl Zeiss). For the determination of the mitochondrial energy balance, the MitoProbe (TM) JC-1 Assay Kit was employed. For the determination of cell growth and the morphology of adherent osteoblasts, two techniques were employed: staining with phalloidin-TRITC and staining with DAPI. (3) Results: The modified membranes that show osteoblasts with a morphology more similar to the control osteoblasts follow the order: PLGA/PO2/HA > PLGA/PO2/SiO2 > PLGA/PO2/TiO2 > PLGA (p < 0.05). When analysing the cell viability, a higher percentage of viable cells bound to the membranes was observed as follows: PLGA/PO2/SiO2 > PLGA/PO2/HA > PLGA/PO2/TiO2 > PLGA (p < 0.05), with a better energy balance of the cells adhered to the membranes PLGA/PO2/HA and PLGA/PO2/SiO2. (4) Conclusion: The membrane in which osteoblasts show characteristics more similar to the control osteoblasts is the PLGA/PO2/HA, followed by the PLGA/PO2/SiO2.


Mayo, 2018 | DOI: 10.3390/ma11050752

High-temperature compressive creep of novel fine-grained orthorhombic ZrO2 ceramics stabilized with 12 mol% Ta doping


Sponchia, G; Moshtaghioun, BM; Riello, P; Benedetti, A; Gomez-Garcia, D; Dominguez-Rodriguez, A; Ortiz, AL
Journal of the European Ceramic Society, 38 (2018) 2445-2448

ABSTRACT

A novel fine-grained orthorhombic ZrO2 ceramic stabilized with 12 mol% Ta doping was fabricated by spark plasma sintering from home-made powders, and its high-temperature mechanical properties evaluated for the first time by compressive creep tests in both Ar and air. It was found that the high-temperature plasticity of the ceramic deformed in Ar, under which the Ta-doped orthorhombic ZrO2 is a black suboxide with abundant oxygen vacancies in its crystal structure, is controlled by grain boundary sliding (stress exponent similar to 2, and activation energy similar to 780-800 kJ/mol). However, the high-temperature plasticity of the ceramic deformed in air, under which the Ta-doped orthorhombic ZrO2 is a white oxide due to the elimination in situ of oxygen vacancies, is controlled by recovery creep (stress exponent 3, and activation energy similar to 750 kJ/mol). It was also observed that black Ta-doped orthorhombic ZrO2 is more creep resistant than its white counterpart with the same grain size, and that the former deforms as the more conventional Y2O3-stabilized ZrO2 does.


Mayo, 2018 | DOI: 10.1016/j.jeurceramsoc.2017.12.055

Microemulsion Assisted Sol-Gel Method as Approach to Load a Model Anticancer Drug inside Silica Nanoparticles for Controlled Release Applications


Jaramillo, N; Paucar, C; Fernandez, A; Negrete, CG; Garcia, C
Collid and Interface Science Communications, 24 (2018) 13-17

ABSTRACT

Silica nanoparticles are attractive carriers due to their improved safety and effectiveness in drug delivery. Silica nanoparticles were synthesized by using microemulsion assisted sol-gel method, and a model anticancer drug 5-fluorouracil (5-FU) was added to the silica precursor before hydrolysis and condensation reactions start. The obtained materials were characterized by Transmission Electron Microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FTIR). Drug encapsulation within silica nanoparticles causes an increase in particle size. However, particle morphology is not affected. The drug release profile was obtained through high performance liquid chromatography (HPLC). The encapsulation approach showed to be effective for sustaining a continuous and increasing release during testing time (98 h). Further studies were performed to evaluate the cytotoxic effects of silica nanoparticles with loaded 5-FU on Chinese hamster ovary cells (CHO-K1). Materials are non-cytotoxic for all concentration tested (5-200 mu g/mL).


Mayo, 2018 | DOI: 10.1016/j.colcom.2018.03.002

The nanostructure of porous cobalt coatings deposited by magnetron sputtering in helium atmosphere


Lacroix, B; Godinho, V; Fernandez, A
Micron, 108 (2018) 49-54

ABSTRACT

In this work, (scanning) transmission electron microscopy has been used to study the nanostructure of porous cobalt coatings obtained by magnetron sputtering using helium as process gas. This nanostructure consists of closed pores of different nanometric size (about 4-20 nm) that are distributed all over a nanocrystalline Co matrix and filled with the deposition gas. Spatially resolved electron energy-loss spectroscopy analysis was applied to measure and map, with high lateral resolution, the relevant physical properties (density, pressure and He-K edge shift) of helium trapped inside these individual nanopores, in order to provide new insights about the growth mechanism involved in such systems. In particular, a coefficient of proportionality, C = 0.039 eV nm(3), between the blue shift of the He K-edge and the He density has been found. In addition, very high He densities (10-100 at./nm(3)) and pressures in the gigapascal range (0.05-5.0 GPa) have been measured. The linear dependence of these parameters as a function of the inverse radii obeying to the Laplace-Young law for most of the pores suggests that their formation during the coating's growth takes place in regime of elastic deformation of the Co matrix.


Mayo, 2018 | DOI: 10.1016/j.micron.2018.02.004

Influence of gold particle size in Au/C catalysts for base-free oxidation of glucose


Megias-Sayago, C; Santos, JL; Ammari, F; Chenouf, M; Ivanova, S; Centeno, MA; Odriozola, JA
Catalysis Today, 306 (2018) 183-190

ABSTRACT

A series of gold colloids were prepared and immobilized on commercial activated carbon. The influence of the colloid preparation and stability were studied and related to the gold particle size in the final catalyst. The catalysts show an important activity in the glucose to gluconic acid oxidation reaction, leading to gluconic acid yield close to 90% in base free mild conditions (0.1 MPa O-2 and 40 degrees C). The size-activity correlation and probable mechanism were also discussed. Finally, the viability of the catalyst was tested by recycling it up to four times. 


Mayo, 2018 | DOI: 10.1016/j.cattod.2017.01.007

Absorption and Emission of Light in Optoelectronic Nanomaterials: The Role of the Local Optical Environment


Jimenez-Solano, Alberto; Galisteo-Lopez, Juan F.; Miguez, Hernan
Journal of Physical Chemistry Letters, 9 (2018) 2077-2084

ABSTRACT

Tailoring the interaction of electromagnetic radiation with matter is central to the development of optoelectronic devices. This becomes particularly relevant for a new generation of devices offering the possibility of solution processing with competitive efficiencies as well as new functionalities. These devices, containing novel materials such as inorganic colloidal quantum dots or hybrid organic-inorganic lead halide perovskites, commonly demand thin (tens of nanometers) active layers in order to perform optimally and thus maximizing the way electromagnetic radiation interacts with these layers is essential. In this Perspective, we discuss the relevance of tailoring the optical environment of the active layer in an optoelectronic device and illustrate it with two real-world systems comprising photovoltaic cells and light emitting devices.


Abril, 2018 | DOI: 10.1021/acs.jpclett.8b00848

Is an alumina-whisker-reinforced alumina composite the most efficient choice for an oxidation-resistant high-temperature ceramic?


Tamura, Y; Moshtaghioun, BM; Zapata-Solvas, E; Gomez-Garcia, D; Dominguez-Rodriguez, A; Cerecedo-Fernandez, C; Valcarcel-Juarez, V
Journal of the European Ceramic Society, 38 (2018) 1812-1818

ABSTRACT

The search of a competitive ceramic material for structural applications demands several requisites: a simple microstructure with easy reproducibility, good intrinsic mechanical properties and most of all, an optimal oxidation resistance. This later point is a challenging point for most ultrahigh refractory materials. 
In this work an alumina (Al2O3) whisker-reinforced Al2O3 composite prepared by spark plasma sintering (SPS) is studied. It will be shown that, although the microstructure is quite similar to that of pure monolithic one, there is a notorious enhancement of the high-temperature deformation resistance, reaching up to one order of magnitude over the pure Al2O3 specimen. On the other hand, the activation energy of these composites increases notably. The results are explained in terms of an original model. A comparison with reported data shows that such composite is as efficient as a SiC-whisker-reinforced Al2O3 composite, with the advantage of its oxidation resistance and much less fabrication cost.


Abril, 2018 | DOI: 10.1016/j.jeurceramsoc.2017.10.006

Bimetallic Ni-Co/SBA-15 catalysts for reforming of ethanol: How cobalt modifies the nickel metal phase and product distribution


Rodriguez-Gomez, A; Caballero, A
Molecular Catalysis, 449 (2018) 122-130

ABSTRACT

In this study, five mono and bimetallic xNi-(10-x)Co/SBA-15 catalysts (x = 10, 8, 5, 2 and 0, with a total metallic content of 10 wt%) have been synthesized using a deposition-precipitation (DP) methodology. Catalytic performances on the steam reforming of ethanol reaction (SRE) have been determined and correlated with their physical and chemical state. A nickel content of 5% or higher yields catalytic systems with good activity, high selectivity to hydrogen and a low production of acetaldehyde (less than 5%). However, in the systems where the cobalt is the main component of the metallic phase (8-10%), the selectivity changes, mainly due to the production of an excess of acetaldehyde, which is also reflected in the larger H-2/CO2 ratio. In agreement with previous findings, this important modification in the selectivity comes from the formation of a cobalt carbide phase, where only takes place in the cobalt enriched systems, and is inhibited with nickel content larger than 5%. The formation of this carbide phase seems to be responsible for the decrease of cobalt particle size during the SRE reaction. Even though this cobalt carbide phase is thermodynamically metastable against decomposition to metallic cobalt and graphite carbon, our results have shown that it only reacts and decomposes after a hydrogen treatment at 600 degrees C.


Abril, 2018 | DOI: 10.1016/j.mcat.2018.02.011

Spark plasma sintering of titanium nitride in nitrogen: Does it affect the sinterability and the mechanical properties?


Moshtaghioun, BM; Gomez-Garcia, D; Dominguez-Rodriguez, A
Journal of the European Ceramic Society, 38 (2018) 1190-1196

ABSTRACT

Titanium nitride ceramics have an intrinsic interest due to its optical and structural applications. However, the conditions for sintering of dense pieces are not still clarified. This research work is focused on the spark plasma sintering (SPS) of near-fully dense fine-grained TiN. The main goal is giving a response to a longstanding debate: can the external atmosphere favor sintering? Different sintering atmospheres, either vacuum or a nitrogen flow, have been used during SPS heating to this purpose. X ray diffraction analysis has showed the presence of TiN as the main phase with traces of Ti4O7 in optimal SPS conditions (1600 °C, one minute dwell time). Our results show that the use of a nitrogen flow while heating can improve sinterability very slightly, but mechanical properties are essentially unaltered within the experimental uncertainty. The hardness reaches values as high as 20GPa whereas fracture toughness can be evaluated around 4 MPam1/2.


Abril, 2018 | DOI: 10.1016/j.jeurceramsoc.2017.12.029

Phase-pure BiFeO3 produced by reaction flash-sintering of Bi2O3 and Fe2O3


Gil-Gonzalez, E; Perejon, A; Sanchez-Jimenez, PE; Sayagues, MJ; Raj, R; Perez-Maqueda, LA
Journal of Materials Chemistry A, 6 (2018) 5356-5366

ABSTRACT

Mixed powders of Bi2O3 and Fe2O3 are shown to yield single-phase, dense nanostructured polycrystals of BiFeO3 in reaction flash sintering experiments, carried out by applying a field of 50 V cm(-1) and with the current limit set to 35 mA mm(-2). The furnace was heated at a constant rate with the reaction sintering taking place abruptly upon reaching 625 degrees C. Remarkably, an intermediate bismuth-rich phase of the oxide that forms just before reaching the flash temperature transforms, and at the same time sinters, into singlephase BiFeO3 within a few seconds after the onset of the flash. The BiFeO3 so produced is electrically insulating, a property that is critical to its applications. This one-step synthesis of single-phase polycrystals of complex oxides from their basic constituents, by reaction flash sintering, is a significant development in the processing of complex oxides, which are normally difficult to sinter by conventional methods.


Abril, 2018 | DOI: 10.1039/c7ta09239c

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