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2021


Kinetics and cyclability of limestone (CaCO3) in presence of steam during calcination in the CaL scheme for thermochemical energy storage


Arcenegui-Troya, J; Sanchez-Jimenez, PE; Perejon, A; Moreno, V; Valverde, JM; Perez-Maqueda, LA
Chemical Engineering Journal, 417 (2021) 129194
Reactividad de Sólidos

ABSTRACT

In the present work, we explore the use of steam in the CaCO3 calcination step of the Calcium Looping process devised for thermochemical energy storage (CaL-TCES). Steam produces a double benefit: firstly, it fastens calcination, allowing a reduction of the temperature needed to attain full calcination in short residence times, as those required in practice, resulting in energy savings. This behaviour is justified on the basis of a kinetics study results obtained from a non-parametric kinetic analysis, which demonstrate that the presence of steam during calcination can reduce the apparent activation energy from 175 kJ/mol to 142 kJ/mol with a steam's partial pressure of 29%. In addition, the results obtained for multicycle CaL-TCES tests show that steam alleviates the deactivation of the sorbent, which is one of the main limiting factors of this technology. This behaviour is explained in terms of the effect of steam on the microstructure of the regenerated CaO. Importantly, the values of residual conversion attained by calcining in steam are higher than those without steam.


Agosto, 2021 | DOI: 10.1016/j.cej.2021.129194

Calcination under low CO2 pressure enhances the calcium Looping performance of limestone for thermochemical energy storage


Sarrion, B; Perejon, A; Sanchez-Jimenez, PE; Amghar, N; Chacartegui, R; Valverde, JM; Perez-Maqueda, LA
Chemical Engineering Journal, 417 (2021) 127922
Reactividad de Sólidos

ABSTRACT

The Calcium Looping performance of limestone for thermochemical energy storage has been investigated under novel favorable conditions, which involve calcination at moderate temperatures under CO2 at low pressure (0.01 and 0.1 bar) and carbonation at high temperature under CO2 at atmospheric pressure. Calcining at low CO2 pressures allows to substantially reduce the temperature to achieve full calcination in short residence times. Moreover, it notably enhances CaO multicycle conversion. The highest values of conversion are obtained for limestone samples calcined under 0.01 bar CO2 at 765 degrees C. Under these conditions, the residual conversion is increased by a factor of 10 as compared to conditions involving calcination under CO2 at atmospheric pressure. The enhancement of CaO conversion is correlated to the microstructure of the CaO samples obtained after calcination. As seen from SEM, BET surface and XRD analysis, calcination under low CO2 pressure leads to a remarkable decrease of pore volume and CaO crystallite size. Consequently, CaO surface area available for carbonation in the fast reaction-controlled regime and therefore reactivity in short residence times is promoted.


Agosto, 2021 | DOI: 10.1016/j.cej.2020.127922

Features of coupled AgBr/WO3 materials as potential photocatalysts


Puga, F.; Navío, J.A.; Hidalgo, M.C.
Journal of Alloys and Compounds, 867 (2021) 159191
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

AgBr/WO3 composite photocatalysts with different selected molar AgBr/WO3 ratios were prepared and widely characterized by XRD, N2-adsorption, SEM, TEM, UV–visible/DRS and XPS techniques. The samples were tested using rhodamine B (RhB) or caffeine, under two illumination conditions (UV and visible light). Although AgBr and WO3 pristine materials have relatively low band gap values (2.6 eV and 2.8 eV, respectively), they exhibit low or no photocatalytic activity under visible light, at least for caffeine degradation. This fact may be mainly related to a high recombination rate of photogenerated charge carriers in these samples. However, the coupling of both leads to a substantial improvement in the degradation of caffeine and RhB under both UV and visible lighting conditions. The increased photocatalytic activity found in the coupled systems with respect to the pristine materials can be attributed to the formation of a type II heterostructure in the coupled AgBr/WO3 samples. Our results show that for AgBr/WO3 coupled systems, kinetic degradation profiles have clear dependence on the molar percentages of the coupled pristine materials, as well as on the nature (sensitizing or not sensitizing effect) of the substrate. For caffeine photodegradation, the best performance was obtained when AgBr/WO3(10–15%) catalysts were used. The AgBr/WO3(20%) sample showed the best photocatalytic activity for rhodamine B degradation, exhibiting also excellent dark adsorption capacity (40–45%). Additionally, studies of activity in five consecutive tests showed a good RhB degradation during the successive reuses being involving a N-de-ethylation mechanism with the main O2•− radicals participation; relatively low mineralization percentages were observed, both under UV and visible light conditions. In these successive runs, no silver leaching to the medium was observed but a change from AgBr towards Ag2CO3 and/or AgxO was produced at the catalyst surface. These features should be known in the use of these systems as potential photocatalysts for practical applications.


Junio, 2021 | DOI: 10.1016/j.jallcom.2021.159191

Dehydration of glucose to 5-Hydroxymethlyfurfural on bifunctional carbon catalysts


Bounoukta, CE; Megias-Sayago, C; Ammari, F; Ivanova, S; Monzon, A; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 286 (2021) 119938
Química de Superficies y Catálisis

ABSTRACT

The proposed study tries to reply on one important question concerning glucose dehydration: What is the role of bare or tandem Lewis/Bronsted acid sites in the reaction and which are better? A series of mono and bifunctional catalyst are designed and screened for the glucose dehydration reaction. The results clearly reveal that catalyst activity is a function of catalyst composition. The presence of Lewis sites the reaction toward first step isomerization, while the Brunsted acid dehydrate directly glucose to HMF via levoglucosane intermediate. This study proposed also a kinetic modelling of the included reactions and their contrast with the empirical observations.


Junio, 2021 | DOI: 10.1016/j.apcatb.2021.119938

In-situ HDO of guaiacol over nitrogen-doped activated carbon supported nickel nanoparticles


Jin, Wei; Pastor-Perez, Laura; Villora-Pico, Juan J.; Mercedes Pastor-Blas, M.; Odriozola, Jose A.; Sepulveda-Escribano, Antonio; Ramirez Reina, Tomas
Applied Catalysis A-General, 620 (2021) 118033
Química de Superficies y Catálisis

ABSTRACT

In-situ hydrodeoxygenation of guaiacol over Ni-based nitrogen-doped activated carbon supported catalysts is presented in this paper as an economically viable route for bio-resources upgrading. The overriding concept of this paper is to use water as hydrogen donor for the HDO reaction, suppressing the input of external highpressure hydrogen. The effect of nitrogen sources, including polypyrrole (PPy), polyaniline (PANI) and melamine (Mel) on the structural, electronic and ultimately of catalytic features of the designed materials have been addressed. Nitrogen-doped samples are more active than the undoped counterparts in the "H2-free" HDO process. For instance, the conversion of guaiacol increased by 8 % for Ni/PANI-AC compared to that of Ni/AC catalysts. The superior performance of Ni/NC can be attributed to the acid-base properties and modified electronic properties, which favours the C-O cleavage and water activation as well as enhances dispersion of Ni particles on the catalysts' surface.


Junio, 2021 | DOI: 10.1016/j.apcata.2021.118033

Pectin-cellulose nanocrystal biocomposites: Tuning of physical properties and biodegradability


Moreno, Ana Gonzalez; Guzman-Puyol, Susana; Dominguez, Eva; Benitez, Jose J.; Segado, Patricia; Lauciello, Simone; Ceseracciu, Luca; Porras-Vazquez, Jose M.; Leon-Reina, Laura; Heredia, Antonio; Heredia-Guerrero, Jose A.
International Journal of Biological Macromolecules, 180 (2021) 709-717
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

The fabrication of pectin-cellulose nanocrystal (CNC) biocomposites has been systematically investigated by blend-ing both polysaccharides at different relative concentrations. Circular free-standing films with a diameter of 9 cm were prepared by simple solution of these carbohydrates in water followed by drop-casting and solvent evaporation. The addition of pectin allows to finely tune the properties of the biocomposites. Textural characterization by AFM showed fibrous morphology and an increase in fiber diameter with pectin content. XRD analysis demonstrated that pectin incorporation also reduced the degree of crystallinity though no specific interaction between both poly-saccharides was detected, by ATR-FTIR spectroscopy. The optical properties of these biocomposites were character-ized for the first time and it was found that pectin in the blend reduced the reflectance of visible light and increased UV absorbance. Thermal stability, analyzed by TGA, was improved with the incorporation of pectin. Finally, pectin-cellulose nanocrystal biocomposites showed a good biodegradability in seawater, comparable to other common bioplastics such as cellulose and low-molecular weight polylactide, among others.


Junio, 2021 | DOI: 10.1016/j.ijbiomac.2021.03.126

Structural Evolution in Iron-Catalyzed Graphitization of Hard Carbons


Gomez-Martin, A; Schnepp, Z; Ramirez-Rico, J
Chemistry of Materials, 33 (2021) 3087-3097
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Despite the recent interest in catalytic graphitization to obtain graphite-like materials from hard-carbon sources, many aspects of its mechanism are still poorly unknown. We performed a series of in situ experiments to study phase transformations during graphitization of a hard-carbon precursor using an iron catalyst at temperatures up to 1100 degrees C and ex situ total scattering experiments up to 2000 degrees C to study the structural evolution of the resulting graphitized carbon. Our results show that upon heating and cooling, iron undergoes a series of reductions to form hematite, magnetite, and wustite before forming a carbide that later decomposes into metallic iron and additional graphite and that the graphitization fraction increases with increasing peak temperature. Structural development with temperature results in decreasing sheet curvature and increased stacking, along with a decrease in turbostratic disorder up to 1600 degrees C. Higher graphitization temperatures result in larger graphitic domains without further ordering of the graphene sheets. Our results have implications for the synthesis of novel biomass-derived carbon materials with enhanced crystallinity.


Mayo, 2021 | DOI: 10.1021/acs.chemmater.0c04385

Synthesis of clay geopolymers using olive pomace fly ash as an alternative activator. Influence of the additional commercial alkaline activator used


Gomez-Casero, MA; Moral-Moral, FJ; Perez-Villarejo, L; Sanchez-Soto, PJ; Eliche-Quesada, D
Journal of Materials Research and Technology-JMR&T 12 (2021) 1762-1776
Materiales Avanzados

ABSTRACT

In this research, the use of olive pomace fly ash (OPFA) as an alkaline source for the activation of calcined clays (CC) from Bailen (Jaen, Spain) was studied. The optimal composition was obtained for 70 wt % CC and 30 wt % OPFA. The physical, mechanical and thermal properties of control geopolymers that use water as a liquid medium have been studied and compared with geopolymers that use additional activating solutions as sodium or potassium hydroxide solutions (8 M), or a mixture of alkaline hydroxide and alkaline silicate solution (NaOH-Na2SiO3 or KOH-K2SiO3). The results showed that OPFA can be used as an alkaline activator, showing mechanical properties slightly lower than those obtained when additional alkaline hydroxide activating solutions were used. The best compressive strength was obtained for geopolymers that use alkaline silicates as an activating solution. However, the best thermal insulation properties were obtained for control geopolymers. The microstructural characteristics of the geopolymers were evaluated by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM-EDS) that corroborate the formation of geopolymeric gel in all the specimens, being the amount of gel formed greater in samples using commercial potassium activating solutions. These results demonstrate the feasibility of using this type of waste, OPFA, as activating reagents in the manufacture of geopolymers or alkaline activated materials. The manufactured geopolymers can be used as compressed earth blocks for walls and partitions, since the specimens pursue mechanical properties that comply with current regulations, presenting better thermal insulation properties. 


Mayo, 2021 | DOI: 10.1016/j.jmrt.2021.03.102

High-temperature solar-selective coatings based on Cr(Al)N. Part 1: Microstructure and optical properties of CrNy and Cr1-xAlxNy films prepared by DC/HiPIMS


Rojas, TC; Caro, A; Lozano, G.; Sanchez-Lopez, JC
Solar Energy Materials and Solar Cells, 223 (2021) 110951
Materiales Ópticos Multifuncionales - Tribología y Protección de Superficies

ABSTRACT

In order to explore the potentialities of Cr1-x(Al)xNy materials in multilayer-based solar selective coatings (SSC) for high temperature applications (T > 500 °C), the optical behavior of Cr1-x(Al)xNy films is studied in this work. Two sets of layers (CrNy and Cr1-xAlxNy) were prepared by direct current (DC) and high-power impulse magnetron sputtering (HiPIMS) technology. The deposition parameters: N2 flux, HiPIMS frequency and aluminum sputtering power, were modified to get a wide variety of stoichiometries. The composition, morphology, phases and electronic structure of the films were characterized in depth. The optical behavior was determined by UV–Vis–NIR and FTIR spectroscopies, and the optical constants were obtained from the measured transmittance and reflectance spectra based on appropriate dielectric function models. Our results indicate that small changes in the layer composition influence the optical constants. In particular, a metallic-like behavior was obtained for CrNy layers with N vacancies (CrN0.95 and CrN0.67 films) while a semiconductor-like behavior was observed for CrN1.08. Thus, the CrNy films can be used as effective absorber layer in multilayer-based SSC, and namely, the CrN0.67 film as an IR reflector/absorber layer too. Likewise, the optical properties of Cr1-xAlxNy layers can also be tuned from metallic to semiconductor-like behavior depending on the chemical composition. Indeed, the absorption coefficients of Cr1-xAlxNy films with optimized Al content and N-vacancies are comparable to those reported for state-of-the-art materials such as TiAlN or TiAlCrN. In addition, a Cr0.96Al0.04N0.89 film was found to be a suitable IR reflector/absorber layer.


Mayo, 2021 | DOI: 10.1016/j.solmat.2020.110951

Effect of the sulphonating agent on the catalytic behavior of activated carbons in the dehydration reaction of fructose in DMSO


Bounoukta, CE; Megias-Sayago, C; Ivanova, S; Penkova, A; Ammari, F; Centeno, MA; Odriozola, JA
Applied Catalysis A-General, 617 (2021) 118108
Química de Superficies y Catálisis

ABSTRACT

A series of -SO3R functionalized activated carbons (R=H, O, aryl) were prepared and applied in fructose dehydration reaction to 5-hydroxymethylfurfural. Different sulphonating methods introduce groups on catalyst surface with distinct donor-acceptor and hydrophilic properties. Their nature influences significantly not only activated carbon?s textural and chemical properties but also the product yields and selectivity in fructose dehydration reaction. The viability of the solvent free reaction was also investigated and compared to the performance of the catalyst series in presence of DMSO, where the best catalytic results were obtained.


Mayo, 2021 | DOI: 10.1016/j.apcata.2021.118108

Synthesis and Characterization of a Nearly Single Bulk Ti2AlN MAX Phase Obtained from Ti/AlN Powder Mixture through Spark Plasma Sintering


Salvo, C; Chicardi, E; Poyato, R; Garcia-Garrido, C; Jimenez, JA; Lopez-Pernia, C; Tobosque, P; Mangalaraja, RV
Materials, 14 (2021) 2217
Reactividad de Sólidos

ABSTRACT

MAX phases are an advanced class of ceramics based on ternary carbides or nitrides that combine some of the ceramic and metallic properties, which make them potential candidate materials for many engineering applications under severe conditions. The present work reports the successful synthesis of nearly single bulk Ti2AlN MAX phase (>98% purity) through solid-state reaction and from a Ti and AlN powder mixture in a molar ratio of 2:1 as starting materials. The mixture of Ti and AlN powders was subjected to reactive spark plasma sintering (SPS) under 30 MPa at 1200 degrees C and 1300 degrees C for 10 min in a vacuum atmosphere. It was found that the massive formation of Al2O3 particles at the grain boundaries during sintering inhibits the development of the Ti2AlN MAX phase in the outer zone of the samples. The effect of sintering temperature on the microstructure and mechanical properties of the Ti2AlN MAX phase was investigated and discussed.


Mayo, 2021 | DOI: 10.3390/ma14092217

Effects of an Illite Clay Substitution on Geopolymer Synthesis as an Alternative to Metakaolin


Eliche-Quesada, D; Bonet-Martinez, E; Perez-Villarejo, L; Castro, E; Sanchez-Soto, PJ
Journal of Materials in Civil Engineering, 33 (2021) 04021072
Materiales Avanzados

ABSTRACT

In this study, a calcined illite clay from Bailen, Jaen, Spain, was valorized as a substitute of metakaolin in the synthesis of new geopolymeric materials. The raw materials, raw clay and commercial kaolin, were pretreated at 750 degrees C (4 h). Several samples (0%-100% by weight of clay) were activated by mixing NaOH solution and sodium silicate solution. The specimens were cured (60 degrees C and 99% relative humidity) for 24 h, then demolded and kept at ambient conditions for 7, 28, and 90 days. The prepared geopolymers were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Physical, mechanical, and thermal properties were determined. The results indicated that the specimens based on the illite raw clay and metakaolin present an amorphous consolidated appearance, characteristic of the polycondensation reactions. The incorporation of up to 50% by weight of raw clay provided geopolymers with higher mechanical strength (39.6 MPa) and bulk density (1,455 kg/m(3)), lower apparent porosity (19.6%), and similar although slightly higher thermal conductivity (0.25 W/mK) than control geopolymers containing only metakaolin as a precursor after 28 days of curing. Control geopolymers presented compressive strength, bulk density, apparent porosity, and thermal conductivity of 23 MPa, 1,251 kg/m(3), 41.03% and 0.224 W/mk, respectively, at the same age of cured geopolymers. The mechanical properties increased with curing time due to a greater advance of the geopolymerization reaction. Therefore, this illite clay can be thermally activated together with metakaolin to obtain geopolymers with suitable technological properties. The results demonstrate that the finished materials can be used for construction applications.


Mayo, 2021 | DOI: 10.1061/(ASCE)MT.1943-5533.0003690

IR spectroscopic insights into the coking-resistance effect of potassium on nickel-based catalyst during dry reforming of methane


Azancot, L; Bobadilla, LF; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 285 (2021) 119822
Química de Superficies y Catálisis

ABSTRACT

Dry reforming of methane (DRM) is an effective catalytic route for transforming CO2 and CH4 into valuable syngas and thus potentially attractive for mitigating the emission of environmental harmful gases. Therefore, it is crucial to develop rationally Ni-based catalysts highly resistant to coking and sintering. In this scenario, the addition of small amounts of potassium to nickel catalyst increases their resistance to coking during dry reforming of methane. Nonetheless, the specific role of potassium in these catalysts not have been fully understood and there are still important discrepancies between the different reported studies. This work provides a new approach on the anticoking nature of a K-promoted Ni catalyst by means of a combined IR spectroscopic study of in situ characterization by CO adsorption under static conditions and operando DRIFTS measurements under dynamic conditions of DRM reaction. The involved surface species formed during the reaction were elucidated by transient and steady-state operando DRIFTS studies. It was revealed that the existence of Ni-K interfacial sites favours the gasification of carbonaceous deposits towards reverse Boudouard reaction and reduces the sticking probability of CO2 dissociative adsorption. Moreover, the presence of strongly Mg-O-K basic sites leads to the formation of carbonate intermediates that are subsequently reduced into CO gaseous towards the associative mechanism by RWGS reaction. These results provide a fundamental understanding of the relevant anticoking effect of potassium on Ni-based catalysts.


Mayo, 2021 | DOI: 10.1016/j.apcatb.2020.119822

Mechanochemically synthesized ternary chalcogenide Cu3SbS4 powders in a laboratory and an industrial mill


Dutkova, E; Sayagues, MJ; Fabian, M; Balaz, M; Achimovicova, M
Materials Letters, 291 (2021) 129566
Reactividad de Sólidos

ABSTRACT

In this work, we demonstrate the use of elemental precursors (Cu, Sb, S) to synthesize famatinite Cu3SbS4 using a laboratory planetary ball milling and an industrial eccentric vibratory milling. Cu3SbS4 was prepared for 120 min and 180 min in laboratory and industrial mill, respectively, with the utilization of protective atmosphere. The Cu3SbS4 prepared in the laboratory and industrial mill with crystallite size 14 nm and 10 nm, respectively, was confirmed by both LeBail refinement of the X-ray powder diffraction data and transmission electron microscopy. The determined band gap energy 1.31 eV and 1.24 eV is blue-shifted relative to the bulk Cu3SbS4. The synthesis of Cu3SbS4 by a scalable milling process represents a prospective route for mass production of material with potential photovoltaic properties. In this work, we demonstrate the use of elemental precursors (Cu, Sb, S) to synthesize famatinite Cu3SbS4 using a laboratory planetary ball milling and an industrial eccentric vibratory milling. Cu3SbS4 was prepared for 120 min and 180 min in laboratory and industrial mill, respectively, with the utilization of protective atmosphere. The Cu3SbS4 prepared in the laboratory and industrial mill with crystallite size 14 nm and 10 nm, respectively, was confirmed by both LeBail refinement of the X-ray powder diffraction data and transmission electron microscopy. The determined band gap energy 1.31 eV and 1.24 eV is blue-shifted relative to the bulk Cu3SbS4. The synthesis of Cu3SbS4 by a scalable milling process represents a prospective route for mass production of material with potential photovoltaic properties. 


Mayo, 2021 | DOI: 10.1016/j.matlet.2021.129566

Toward Commercialization of Stable Devices: An Overview on Encapsulation of Hybrid Organic-Inorganic Perovskite Solar Cells


Aranda, Clara A.; Calio, Laura; Salado, Manuel
Crystals, 11 (2021) 519
Materiales Ópticos Multifuncionales

ABSTRACT

Perovskite solar cells (PSCs) represent a promising technology for energy harvesting due to high power conversion efficiencies up to 26%, easy manufacturing, and convenient deposition techniques, leading to added advantages over other contemporary competitors. In order to promote this technology toward commercialization though, stability issues need to be addressed. Lately, many researchers have explored several techniques to improve the stability of the environmentally-sensitive perovskite solar devices. Challenges posed by environmental factors like moisture, oxygen, temperature, and UV-light exposure, could be overcome by device encapsulation. This review focuses the attention on the different materials, methods, and requirements for suitable encapsulated perovskite solar cells. A depth analysis on the current stability tests is also included, since accurate and reliable testing conditions are needed in order to reduce mismatching involved in reporting the efficiencies of PSC.


Mayo, 2021 | DOI: 10.3390/cryst11050519

Fluorinated and platinized Titania for Glycerol oxidation


Murcia, J.J.; Bautista, E; Ávila Martínez, E.G.; Rangel R.N.; Romero, R.; Cubillos Lobo, J.A.; Rojas Sarmiento, H.A.; Hernández, J.S.; Cárdenas, O.; Hidalgo, M.C.; Navío, J.A.; Baeza, R.
Materials Proceedings, 4 (2021) 37
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

In this research, photocatalysts based on TiO2 modified by fluorination and platinum addition were evaluated in the glycerol oxidation. These materials were characterized by different instrumental analysis techniques to determine the physicochemical properties. It was found that the surface modification lead to improve the materials absorption in the Visible region of the electromagnetic spectra and to increase the surface area of TiO2. By HPLC analysis was possible to observed that the photocatalysts 0.5% Pt-F-TiO2 showed the highest yield and selectivity towards glyceraldehyde (GAL). It was also observed that the increase in the platinum content until values of 2% had a negative effect in the effectiveness of fluorinated Titania in the glycerol photo-oxidation. The fluorination and platinum addition modify some physicochemical properties of TiO2, leading also to modify the reaction mechanism and selectivity during glycerol partial photo-oxidation and the dose of photocatalysts is an important reaction condition to obtain GAL and Dyhidroxyacetone (DHA) with yields above to 70%.


Abril, 2021 | DOI: 10.3390/IOCN2020-07792

Holmium phosphate nanoparticles as negative contrast agents for high-field magnetic resonance imaging: Synthesis, magnetic relaxivity study and in vivo evaluation


Gomez-Gonzalez, E; Caro, C; Martinez-Gutierrez, D; Garcia-Martin, ML; Ocana, M; Becerro, AI
Journal of Colloid and Interface Science, 587 (2021) 131-140
Materiales Coloidales

ABSTRACT

The increasing use of high magnetic fields in magnetic resonance imaging (MRI) scanners demands new contrast agents, since those used in low field instruments are not effective at high fields. In this paper, we report the synthesis of a negative MRI contrast agent consisting of HoPO4 nanoparticles (NPs). Three different sizes (27 nm, 48 nm and 80 nm) of cube-shaped NPs were obtained by homogeneous precipitation in polyol medium and then coated with poly(acrylic) acid (PAA) to obtain stable colloidal suspensions of HoPO4@PAA NPs in physiological medium (PBS). The transverse relaxivity (r2) of aqueous suspensions of the resulting NPs was evaluated at both 1.44 T and 9.4 T. A positive correlation between r2 values and field strength as well as between r2 values and particle size at both magnetic field strengths was found although this correlation failed for the biggest NPs at 9.4 T, likely due to certain particles aggregation inside the magnet. The highest r2 value (489.91 mM-1s−1) was found for the 48 nm NPs at 9.4 T. Toxicity studies demonstrated that the latter NPs exhibited low toxicity to living systems. Finally, in vivo studies demonstrated that HoPO4@PAA NPs could be a great platform for next-generation T2-weighted MRI contrast agents at high magnetic field.


Abril, 2021 | DOI: 10.1016/j.jcis.2020.11.119

Pb2+, Cd2+ and Hg2+ removal by designed functionalized swelling high-charged micas


Osuna, FJ; Pavon, E; Alba, MD
Science of The Total Environment, 764 (2021) 142811
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

The increasing accumulation of toxic heavy metals in the environment has generated the need of efficient removal systems, being the adsorption method the most popular one applied in aqueous solutions. Of particular concern is the case of Pb2+, Cd2+ and Hg2+ due to their high potential hazard. In this paper, we describe the feasibility of a new family of nanomaterials, swelling high charge micas, in the removal of these cations from aqueous solutions. Batch adsorption experiments were carried out in the as-made micas, NaMn, and after functionalization with ethylammonium, EA-Mn, and mercaptoethylammonium, MEA-Mn. The results have demonstrated that all of them are efficient heavy metal adsorbents, being Na-M2 the best adsorbent for Pb2+ and Cd2+, and, MEA-M2 for Hg2+.


Abril, 2021 | DOI: 10.1016/j.scitotenv.2020.142811

Elucidating the nature of Mo species on ZSM-5 and its role in the methane aromatization reaction


Lopez-Martin, A.; Platero, F; Colon, G.; Caballero, A.
Reaction Chemistry & Engineering
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT

The valorization of methane is one of the most important goals during the transition period to the general use of renewable energies. Its transformation into a valuable chemical like benzene by direct aromatization of methane (DAM) reaction has been extensively studied in the past years, mainly using Mo/ZSM-5 catalytic systems. Although viable, this DAM reaction poses a number of issues mainly derived from poor conversion and deactivation processes. Therefore, a deeper knowledge of these systems is needed. Herein, by combining chemical (TPR), spectroscopic (XPS), HAADF and other techniques, we have identified the different Mo precursors stabilized in the calcined ZSM-5 support, their nature (monomers, dimers and bulk Mo oxides), location in the zeolite framework (external surface or micropores), and the partial segregation of aluminum during the preparation of catalysts. The role of each Mo phase promoting or hindering the transformation of methane in aromatics has been also clarified.


Abril, 2021 | DOI: 10.1039/d1re00044f

Electrochromic response and porous structure of WO3 cathode layers


Louloudakis, D; Mouratis, K; Gil-Rostra, J; Koudoumas, E; Alvarez, R; Palmero, A; Gonzalez-Elipe, AR
Electrochimica Acta, 376 (2021) 138049
Nanotecnología en Superficies y Plasma

ABSTRACT

Maximizing the electrochromic response of tungsten oxide-based systems demands highly porous electrode layers that facilitate the incorporation of electrolyte cations during the reduction process. In this work, amorphous and porous WO3 thin films were grown on indium tin dioxide glass substrates by magnetron sputtering at oblique angles at two different plasma gas pressures. Remarkably, the film that showed higher porosity presented a worse electrochromic response in terms of durability, time response and charge density capacity. This result is analyzed and explained on the basis of the features of the porous structure of the films: While the typical nanostructure developed at low pressures possesses large and connected pore voids with few ramifications, the nanostructure generated at a higher pressure presents a rather sponge-like porous structure with numerous and small well-connected voids. A general discussion on the role of the porous structure and, particularly, on the accessible pore volume and area is carried out. It is concluded that not only the accessible pore volume, defining the volume of electrolyte that stays inside the layer, but also the accessible pore area, which defines the efficiency of the incorporation/release of Li+ cations within the electrode material, determine the efficiency and reversibility of the electrochromic response.


Abril, 2021 | DOI: 10.1016/j.electacta.2021.138049

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