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2020


Optical interference effects on the Casimir-Lifshitz force in multilayer structures


Esteso, V; Carretero-Palacios, S; Miguez, H
Physical Review A, 101 (2020) 033815
Materiales Ópticos Multifuncionales

ABSTRACT

The Casimir-Lifshitz force F(C-L) between planar objects when one of them is stratified at the nanoscale is herein investigated. Layering results in optical interference effects that give rise to a modification of the optical losses, which, as stated by the fluctuation-dissipation theorem, should affect the Casimir-Lifshitz interaction. On these grounds, we demonstrate that, by nanostructuring the same volume of dielectric materials in diverse multilayer configurations, it is possible to access F(C-L) of attractive or repulsive nature, even getting canceled, at specific separation distances.


Marzo, 2020 | DOI: 10.1103/PhysRevA.101.033815

Potentialization of bentonite properties as support in acid catalysts


Amaya, J; Bobadilla, L; Azancot, L; Centeno, M; Moreno, S; Molina, R
Materials Research Bulletin, 123 (2020) 110728
Química de Superficies y Catálisis

ABSTRACT

Enhancement of the main physicochemical properties of a natural bentonite was carried out by means of modifications using surfactant, reflux, microwave treatment and, subsequently, the incorporation of AlZr and AlCe species. The evolution of the main changes in each modification stage was evaluated by means of X-ray diffraction, N-2 sortometry, scanning microscopy (SEM), NH3-TPD, NH3-DRIFTS and CO adsorption at low temperature. For the evaluation of the catalytic behavior, the dehydration-dehydrogenation reactions of 2-propanol and hydro-conversion of decane were used; both of which generate, in addition, information regarding the acidic properties of the materials. The correlation of the number, type and acid strength with the catalytic behavior, allowed establishing the effect produced by both the delamination method and the nature of the incorporated cation. This generated tools that allow controlling the physicochemical properties, and more specifically, the enhancement of the acidity of new supports based on this type of natural clay mineral.


Marzo, 2020 | DOI: 10.1016/j.materresbull.2019.110728

Influence of the Test Configuration and Temperature on the Mechanical Behaviour of WC-Co


Gonzalez, LM; Chicardi, E; Gotor, FJ; Bermejo, R; Llanes, L; Torres, Y
Metals, 10 (2020) 322
Reactividad de Sólidos

ABSTRACT

In this work, the effect of the test configuration and temperature on the mechanical behaviour of cemented carbides (WC-Co) with different carbide grain sizes (d(WC)) and cobalt volume fractions (V-Co), implying different binder mean free paths (lambda (Co)), was studied. The mechanical strength was measured at 600 degrees C with bar-shaped specimens subjected to uniaxial four-point bending (4PB) tests and with disc specimens subjected to biaxial ball-on-three-balls (B3B) tests. The results were analysed within the frame of the Weibull theory and compared with strength measurements performed at room temperature under the same loading conditions. A mechanical degradation greater than 30% was observed when the samples were tested at 600 degrees C due to oxidation phenomena, but higher Weibull moduli were obtained as a result of narrower defect size distributions. A fractographic analysis was conducted with broken specimens from each test configuration. The number of fragments (N-f) and the macroscopic fracture surface were related to the flexural strength and fracture toughness of WC-Co. For a given number of fragments, higher mechanical strength values were always obtained for WC-Co grades with higher K-Ic. The observed differences were discussed based on a linear elastic fracture mechanics (LEFM) model, taking into account the effect of the temperature and microstructure of the cemented carbides on the mechanical strength.


Marzo, 2020 | DOI: 10.3390/met10030322

Pt–TiO2–Nb2O5 heterojunction as effective photocatalyst for the degradation of diclofenac and ketoprofen


Sacco, O.l; Murcia, J.J.; Lara, A.E.; Hernández-Laverde, M.; Rojas, H.; Navío, J.A.; Hidalgo, M.C.; Vaiano, V.
Materials Science in Semiconductor Processing, 107 (2020) 104839
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

Pt–TiO2–Nb2O5 heterojunction was synthetized and studied for the photocatalytic removal of diclofenac (DCF) and ketoprofen (KTF) under UV light irradiation. The physical-chemical properties of the prepared catalysts were analysed by different characterization techniques revealing that the lowest platinum nanoparticle size and the better metal distribution was observed in Pt–TiO2–Nb2O5 sample. The Pt–TiO2–Nb2O5 heterojunction possessed the best photocatalytic activity toward both the photodegradation and mineralization of the two selected pollutants. The optimal photocatalyst showed a DCF and KTF mineralization rate of 0.0555 and 0.0746 min−1, respectively, which were higher than those of Pt–TiO2 (0.0321 min−1 for DCF and 0.0597 min−1 for KTF). The experiments driven to analyse the effects of free radical capture showed that ·OH, ·O2− and h+ have a primary role in reactive during the photocatalytic reaction. The improved photocatalytic performances of the Pt–TiO2–Nb2O5 heterojunction could be argue by a direct Z-scheme mechanism in which the Pt0 nanoparticles could act as a bridge between TiO2 and Nb2O5, improving the electron-hole separation and, ultimately, enhancing the photocatalytic removal rate of both DCF and KTF.


Marzo, 2020 | DOI: 10.1016/j.mssp.2019.104839

Role of particle size on the multicycle calcium looping activity of limestone for thermochemical energy storage


Duran-Martin, JD; Jimenez, PES; Valverde, JM; Perejon, A; Arcenegui-Troya, J; Trinanes, PG; Maqueda, LAP
Journal of Advanced Research, 22 (2020) 67-76
Reactividad de Sólidos

ABSTRACT

The calcium looping process, based on the reversible reaction between CaCO3 and CaO, is recently attracting a great deal of interest as a promising thermochemical energy storage system to be integrated in Concentrated Solar Power plants (CaL-CSP). The main drawbacks of the system are the incomplete conversion of CaO and its sintering-induced deactivation. In this work, the influence of particle size in these deactivation mechanisms has been assessed by performing experimental multicycle tests using standard limestone particles of well-defined and narrow particle size distributions. The results indicate that CaO multicycle conversion benefits from the use of small particles mainly when the calcination is carried out in helium at low temperature. Yet, the enhancement is only significant for particles below 15 μm. On the other hand, the strong sintering induced by calcining in CO2 at high temperatures makes particle size much less relevant for the multicycle performance. Finally, SEM imaging reveals that the mechanism responsible for the loss of activity is mainly pore-plugging when calcination is performed in helium, whereas extensive loss of surface area due to sintering is responsible for the deactivation when calcination is carried out in CO2 at high temperature.


Marzo, 2020 | DOI: 10.1016/j.jare.2019.10.008

An insight on the design of mercapto functionalized swelling brittle micas


Osuna, FJ; Pavon, E; Alba, MD
Journal of Colloid and Interface Science, 561 (2020) 533-541
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Surface modification of natural clay minerals with reagents containing metal chelating groups has great environmental value. The functionalization by adsorption or grafting guarantees a durable immobilization of the reactive organic groups, preventing their leaching when they are used in liquid media. The aim of this research was the designed mercapto functionalization of swelling brittle micas, Na-Mn, thorough both chemical and physical mechanisms. Na-Mn were functionalized with 2-mercaptoethylammonium (MEA), 2,3-dimercapto-1-propanol (BAL) and (3-mercaptopropyl)trimethoxysilane (MPTMS). The thiol concentration on swelling brittle micas is higher than the observed value for others adsorbents. The cation exchange reaction with MEA and one-step grafting with MPTMS in acid medium are the most efficient mercapto functionalization mechanism.


Marzo, 2020 | DOI: 10.1016/j.jcis.2019.11.028

Development by Mechanochemistry of La0.8Sr0.2Ga0.8Mg0.2O2.8 Electrolyte for SOFCs


Garcia-Garcia, FJ; Tang, YQ; Gotor, FJ; Sayagues, MJ
Materials, 13 (2020)
Reactividad de Sólidos

ABSTRACT

In this work, a mechanochemical process using high-energy milling conditions was employed to synthesize La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) powders from the corresponding stoichiometric amounts of La2O3, SrO, Ga2O3, and MgO in a short time. After 60 min of milling, the desired final product was obtained without the need for any subsequent annealing treatment. A half solid oxide fuel cell (SOFC) was then developed using LSGM as an electrolyte and La0.8Sr0.2MnO3 (LSM) as an electrode, both obtained by mechanochemistry. The characterization by X-ray diffraction of as-prepared powders showed that LSGM and LSM present a perovskite structure and pseudo-cubic symmetry. The thermal and chemical stability between the electrolyte (LSGM) and the electrode (LSM) were analyzed by dynamic X-ray diffraction as a function of temperature. The electrolyte (LSGM) is thermally stable up to 800 and from 900 °C, where the secondary phases of LaSrGa3O7 and LaSrGaO4 appear. The best sintering temperature for the electrolyte is 1400 °C, since at this temperature, LaSrGaO4 disappears and the percentage of LaSrGa3O7 is minimized. The electrolyte is chemically compatible with the electrode up to 800 °C. The powder sample of the electrolyte (LSGM) at 1400 °C observed by HRTEM indicates that the cubic symmetry Pm-3m is preserved. The SOFC was constructed using the brush-painting technique; the electrode–electrolyte interface characterized by SEM presented good adhesion at 800 °C. The electrical properties of the electrolyte and the half-cell were analyzed by complex impedance spectroscopy. It was found that LSGM is a good candidate to be used as an electrolyte in SOFC, with an Ea value of 0.9 eV, and the LSM sample is a good candidate to be used as cathode


Marzo, 2020 | DOI: 10.3390/ma13061366

Platinum nanoparticles stabilized by N-heterocyclic thiones. Synthesis and catalytic activity in mono- and di-hydroboration of alkynes


Moraes, LCC; Figueiredo, RCC; Espinos, JPP; Vattier, F; Franconetti, A; Jaime, C; Lacroix, B; Rojo, J; Lara, P; Conejero, S
Nanoscale, 12 (2020) 6821-6831
Nanotecnología en Superficies y Plasma

ABSTRACT

N-Heterocyclic Thiones (NHT) proved to be efficient ligands for the stabilization of small platinum nanoparticles (1.3-1.7 nm), synthesized by decomposition of [Pt(dba)(2)], under a H-2 atmosphere, in the presence of variable sub-stoichiometric amounts of the NHT. Full characterization by means of TEM, HR-TEM, NMR, ICP, TGA and XPS have been carried out, providing information about the nature of the metal nanoparticles and the interaction of the NHT ligands to the metal surface. Importantly, DFT calculations indicate that some NHT ligands interact with the metal through the C & xe001;C double bond of the imidazole fragment in addition to the sulfur atom, thus providing additional stabilization to the nanoparticles. According to XPS, TGA and ICP techniques, the surface coverage by the ligand increases by decreasing the size of the substituents on the nitrogen atom. The platinum nanoparticles have been used as catalyst in the hydroboration of alkynes. The most active system is that with a less covered surface area lacking an interaction of the ligand by means of the C & xe001;C double bond. This catalyst hydroborates alkynes with excellent selectivities towards the monoborylated anti-Markovnikov product (vinyl-boronate) when one equiv. of borane is used. Very interestingly, aliphatic alkynes undergo a second hydroborylation process leading to the corresponding 1,1- and 1,2-diboroylated species with good selectivities towards the former.


Marzo, 2020 | DOI: 10.1039/d0nr00251h

Recent advances in selective oxidation of biomass-derived platform chemicals over gold catalysts


Megias-Sayago, C; Navarro-Jaen, S; Castillo, R; Ivanova, S
Current Opinion in Green and Sustainable Chemistry, 21 (2020) 50-55
Química de Superficies y Catálisis

ABSTRACT

Gold is without a doubt the best known metal for chemical oxidation. The noblest of the noble metals gained its place because of its resistance to overoxidation, low temperature of operation, especially in gas-phase oxidation, and fairly good selectivity when required. The aim for sustainable development and the need for new technologies open the possibility to introduce new raw materials and new catalyst formulation. That is why new horizons appear in the otherwise uncertain future of gold catalysis. The old glory becomes now a glorious alternative, and this mini-review gives only a small example of it.


Febrero, 2020 | DOI: 10.1016/j.cogsc.2019.12.001

Role of Fe(III) in aqueous solution or deposited on ZnO surface in the photoassisted degradation of rhodamine B and caffeine


Tanji, Karim; Navio, J A; Martin-Gomez, A N; Hidalgo, M C; Jaramillo-Paez, C; Naja, Jamal; Hassoune, Hicham; Kherbeche, Abdelhak
Chemosphere, 241 (2020) 125009
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

Iron (III) was incorporated, to the surface of a synthesized ZnO, using two nominal molar percentages of Fe (III): 1% and 5% Fe relative to ZnO. Samples dried and calcined at 200 °C and 400 °C for 2 h, were characterized by XRD, XPS, XRF, N2-adsorption-BET and (UV–vis)-DRS. Photocatalytic activities of the catalysts were assessed based on the degradation of rhodamine B (RhB) and caffeine (CAF) in aqueous solution under two irradiation conditions: UV and visible light illumination. Prior to the photocatalytic tests, the interaction of each one of the substrates with either Fe(III) or Fe(II) was studied in homogeneous medium under UV-illumination and oxygenated environment. It was found that Fe (III) can play an important role in homogeneous media in the photoassisted degradation, both of rhodamine B and caffeine, while Fe (II) does not exert a relevant role in the photoassisted degradation of the referred substrates. Fe–ZnO samples display similar or poorer performance than pure ZnO in the presence of UV light for both studied substrates. The phenomenon can be attributed to the formation of either goethite or ZnFe2O4 at the ZnO surface where the coupled Fe3+/Fe2+ can act as recombination centers for the photogenerated charges. On the contrary, all Fe–ZnO samples showed enhanced photocatalytic activity under visible illumination which seems to be independent of the iron content. In this context, the mechanisms for photoassisted degradation of both the substrates in homogeneous medium and photocatalytic degradation are discussed, as well as the role of Fe in the photodegradation processes.


Febrero, 2020 | DOI: 10.1016/j.chemosphere.2019.125009

Monolithic stirrer reactor: The selective lactose oxidation in liquid phase over Au/Al2O3 nanostructured catalysts


Regenhardt, SA; Meyer, CI; Sanz, O; Sebastian, V; Ivanova, S; Centeno, MA; Odriozola, JA; Montes, M; Marchi, AJ; Garetto, TF
Molecular Catalysis, 481 (2020) 110219
Química de Superficies y Catálisis

ABSTRACT

The performance of rotating metallic monolith stirrer reactor was studied for selective lactose oxidation in liquid phase at 65 degrees C, atmospheric pressure and with air as oxidant agent. The Au/Al(2)O(3)deposition on metallic substrates was performed by wash-coating, producing catalyst coating thicknesses between 5 and 20 mu m. Monoliths with different configuration (channel size between 0.36 and 1.06 mm) were used as stirrer blades in a batch reactor. Internal and external mass transfer limitations were observed during liquid phase lactose oxidation. For stirring rates equal or higher than 600 rpm there were no important external diffusional restrictions and this was also independent of the monolith configuration. Coating with thickness higher than 15 mu m presents loss of catalyst effectiveness due to internal diffusional restrictions. Excellent stability in the catalytic tests was obtained after three regeneration-reaction cycles. Regeneration was carried out at 400 degrees C in air flow. Gold particle size distribution in the monolith washcoat, determined by TEM before and after reaction, was homogeneous with a medium size of around 5 nm. This is in agreement with the very good reproducibility and stability obtained in the catalytic tests. After calcination at 500 degrees C, some sintering and a heterogeneous distribution of metal particle size was observed, accompanied by a slight loss in catalyst activity. It is concluded that metallic monolith stirrer reactors are a promising application for selective lactose oxidation in liquid phase.


Febrero, 2020 | DOI: 10.1016/j.mcat.2018.10.014

Synthesis of Mn2+-doped ZnS by a mechanically induced self-sustaining reaction


Aviles, MA; Cordoba, JM; Sayagues, MJ; Gotor, FJ
Journal of Materials Science, 55 (2020) 1603-1613
Reactividad de Sólidos

ABSTRACT

The mechanochemical process denoted as a mechanically induced self-sustaining reaction was successfully applied in obtaining Mn-doped ZnS samples with Mn content between 0 and 5 mol%. The process consists in milling Zn/Mn/S powder elemental mixtures with the appropriate stoichiometry, which promotes after approximately 80 min the induction of a combustion reaction. The doping level was properly adjusted by controlling the atomic ratio of the starting mixture. A complete characterization of samples was carried out, including X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, energy-dispersive X-ray spectroscopy, Raman spectroscopy, diffuse reflectance UV-Vis spectroscopy and emission and excitation photoluminescence measurements. A wurtzite structure, in which Mn2+ replaces Zn2+, was obtained with a nanometric character. The photoluminescence of samples showed the characteristic (Mn2+T1)-T-4-(6)A(1) emission that was highly dependent on the doping level. The maximum luminescence efficiency through the ZnS excitation was found for a doping value of 1 mol%. The photoluminescence showed virtually no contribution from the host emission, which confirmed that samples were properly doped.


Febrero, 2020 | DOI: 10.1007/s10853-019-04138-8

Catalytic Performance of Bulk and Al2O3-Supported Molybdenum Oxide for the Production of Biodiesel from Oil with High Free Fatty Acids Content


Navajas, A; Reyero, I; Jimenez-Barrera, E; Romero-Sarria, F; Llorca, J; Gandia, LM
Catalysts, 10 (2020) 158
Química de Superficies y Catálisis

ABSTRACT

Non-edible vegetable oils are characterized by high contents of free fatty acids (FFAs) that prevent from using the conventional basic catalysts for the production of biodiesel. In this work, solid acid catalysts are used for the simultaneous esterification and transesterification with methanol of the FFAs and triglycerides contained in sunflower oil acidified with oleic acid. Molybdenum oxide (MoO3), which has been seldom considered as a catalyst for the production of biodiesel, was used in bulk and alumina-supported forms. Results showed that bulk MoO3 is very active for both transesterification and esterification reactions, but it suffered from severe molybdenum leaching in the reaction medium. When supported on Al2O3, the MoO3 performance improved in terms of active phase utilization and stability though molybdenum leaching remained significant. The improvement of catalytic performance was ascribed to the establishment of MoO3-Al2O3 interactions that favored the anchorage of molybdenum to the support and the formation of new strong acidic centers, although this effect was offset by a decrease of specific surface area. It is concluded that the development of stable catalysts based on MoO3 offers an attractive route for the valorization of oils with high FFAs content.


Febrero, 2020 | DOI: 10.3390/catal10020158

Effect of Gold Particles Size over Au/C Catalyst Selectivity in HMF Oxidation Reaction


Megias-Sayago, C; Lolli, A; Bonincontro, D; Penkova, A; Albonetti, S; Cavani, F; Odriozola, JA; Ivanova, S
Chemcatchem, 12 (2020) 1177-1183
Química de Superficies y Catálisis

ABSTRACT

A series of gold nanoparticles in the 4-40 nm range were prepared, immobilized on activated carbon and further tested, at low base concentration, in the catalytic oxidation of 5-hydroxymethyl furfural (HMF) to 2,5-furandicarboxylic acid (FDCA). Gold particles size variation has no influence on HMF conversion but significantly affects product selectivity and carbon balance. This behavior is ascribed to the thermodynamically favorable oxygen reduction reaction on Au(100) faces. As the gold particle size decreases the Au(100)/Au(111) exposure ratio, estimated by using the van Hardeveld-Hartog model, increases as well as the FDCA selectivity. The smaller the gold particle size the smaller the 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) to FDCA ratio pointing to the gold size dependent behavior of the oxidation of the alcohol function of the HMF molecule.


Febrero, 2020 | DOI: 10.1002/cctc.201901742

Mesoporous Matrices as Hosts for Metal Halide Perovskite Nanocrystals


Rubino, A; Calio, L; Garcia-Bennett, A; Calvo, ME; Miguez, H
Advanced Optical Materials, (2020) 201901868
Materiales Ópticos Multifuncionales

ABSTRACT

Several works have recently demonstrated that perovskite nanocrystals can be controllably formed within a variety of porous matrices employing diverse synthetic strategies. By means of the fine tuning of the pore size distribution, the thickness and composition of the walls, the geometry of the void network and its topology, strict control over the structural and morphological parameters of the hosted semiconductor can be achieved, determining its optical absorption and emission properties. Furthermore, porous hosts provide the guest semiconductor with enhanced stability and versatility in terms of processing, which favors its integration in devices. This article provides a comprehensive review of the different approaches proposed, as well as a discussion on the relevance they may have for the development of nanostructured perovskite-based optoelectronics. A critical assessment of the optical quality of the hybrid perovskite nanomaterials so obtained is presented, as well as an analysis of the fundamental and applied aspects of the nanocrystal-matrix interaction and a projected prospect of their impact in the fields of artificial lighting and renewable energy.


Febrero, 2020 | DOI: 10.1002/adom.201901868

Evaluation of Au–ZnO, ZnO/Ag2CO3 and Ag–TiO2 as Photocatalyst for Wastewater Treatment


Murcia, J.J.; Hernández, J.S.;Rojas, H.; Moreno-Cascante, J.; Sánchez-Cid, P.; Hidalgo, M.C.; Navío, J.A.; Jaramillo-Páez, C.
Topics in Catalysis, (2020)
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

In this work series of photocatalysts based on ZnO modified by Au and Ag2CO3 addition and Ag–TiO2 materials were synthesized and evaluated in the treatment of handicrafts factories wastewater and water samples taken from a highly polluted river. In general, it was found that ZnO series were more effective in the bacteria elimination than the commonly used TiO2 semiconductor. It was also observed that the metal (Au, Ag) or silver carbonate addition significantly increases the photocatalytic activity of ZnO and TiO2. It was determined that the content of the metal or carbonate added is an important factor to take into account in order to obtain suitable efficiency in the photocatalytic process, so, for example in the case of the river water samples the increase of Ag2CO3 content from 1 to 5%, had a detrimental effect over the bacteria elimination. The optimal conditions for dyes photodegradation and bacteria elimination were found by using a response surface study and the Au–ZnO (1%) photocatalyst. From this study it was determined that even after recycling this material leads to obtain a removal percentage of these pollutants over than 94%.


Febrero, 2020 | DOI: 10.1007/s11244-020-01232-z

Hybrid ZnO/Ag3PO4 photocatalysts, with low and high phosphate molar percentages


Martín-Gómez, A.N.;Navío, J.A.;Jaramillo-Páeza, C.;Sánchez-Cid, P.;Hidalgo, M.C.
Journal of Photochemistry and Photobiology A: Chemistry, (2020) 112196
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

In this work, a previously optimized synthesized ZnO photocatalyst was modified with different molar percentages of Ag3PO4 through a facile in situ precipitation–deposition method and then characterized by different techniques (XRD, XRF, BET, UV–vis DRS, SEM, TEM and XPS). The incorporation of Ag3PO4 produces important changes in the light absorption properties with a significant absorbance in the visible region observed for ZnO modified with different amounts of Ag3PO4; the optical absorption intensity in the visible region of the coupled ZnO/Ag3PO4 increases as the molar percentages of Ag3PO4 increases, evidencing a clear dependence on the content of Ag3PO4. However, this work shows that the incorporation of Ag3PO4 in almost all cases reduces the photocatalytic capacity of ZnO, except when it is used in a specific percentage of 10 % and only being more active against rhodamine B and not on the Caffeine. SEM images and elemental mapping indicate that Ag3PO4 disperses very well in the ZnO particles, exhibiting an almost homogeneous distribution, showing zones with cumulus of Ag3PO4 (rich in P-Ag) in contact with ZnO-zones (rich in Zn). All the prepared photocatalysts were tested in the photocatalytic degradation of rhodamine B as a dye, and caffeine as a toxic and persistent emerging compound under UV and visible light illumination. It is reported that not only the ZnO:Ag3PO4 ratio is an important factor that influences the photocatalytic process of substrate degradation, but also the nature of the substrate has an important influence on the photocatalytic behavior of the materials under both UV and visible illumination. Thus, pristine Ag3PO4 showed high photocatalytic degradation for rhodamine B, while for caffeine negligible photocatalytic degradation was found in both the UV and visible regions. The thermal- and photo-stability of the coupled system was also studied. At least, for rhodamine B no loss of photocatalytic activity has been observed after five recycles although the mineralization degree progressively diminished along the recycles.


Febrero, 2020 | DOI: 10.1016/j.jphotochem.2019.112196

Modulation of the acidity of a vermiculite and its potential use as a catalytic support


Amaya, J; Bobadilla, L; Azancot, L; Centeno, M; Moreno, S; Molina, R
Journal of Materials Science, 55 (2020) 6482-6501
Química de Superficies y Catálisis

ABSTRACT

The modulation and characterization of the acidity of a vermiculite were carried out, which was modified by delamination by means of hydrothermal and acid treatments with the subsequent incorporation of AlZr and AlCe species to modulate the acidity. The effect of these species was evaluated regarding the structural (XRD, XPS and IR), textural (N-2 sortometry) and acidity properties (NH3-TPD, NH3-DRIFTS and CO adsorption at low temperature). The catalytic performance was studied in the dehydration-dehydrogenation reactions of 2-propanol and the hydroconversion of decane, which generate important information about the acidity properties such as the type, number and strength of acidic sites. The correlation between the number, type and acid strength with the catalytic behavior allowed to establish the important effect regarding the nature of the mineral, its method of delamination and the nature of the incorporated cation, thus generating tools for controlled processes for the potentiation of the acidity of new supports from raw vermiculite.


Febrero, 2020 | DOI: 10.1007/s10853-020-04445-5

Robust label-free CuxCoyOz electrochemical sensors for hexose detection during fermentation process monitoring


Lopez-Fernandez, E; Gil-Rostra, J; Espinos, JP; Gonzalez, R; Yubero, F; de Lucas-Consuegra, A; Gonzalez-Elipe, AR
Sensors and Actuators B-Chemical, 304 (2020) 127360
Nanotecnología en Superficies y Plasma

ABSTRACT

Label free electrochemical sensors of glucose are used whenever long-term operation and stable response are required. For this purpose, various metals and oxides of the first transition series have been proposed as alternative to more expensive noble metal electrochemical sensors. In this work we propose a new formulation consisting of copper-cobalt mixed oxides which, in the form of porous and nanostructured thin films with well controlled Co/Cu ratio, are prepared at room temperature in one step by a modification of the magnetron sputtering oblique angle deposition procedure. Films with various compositions were electrochemically characterized by cyclic voltammetry to determine their amperometric response to glucose as a function of voltage and NaOH electrolyte concentration. This analysis showed that films with a Co/Cu atomic ratio equal 3.4 presented a maximum sensitivity (0.710 A M−1 cm−2), a small limit of detection (0.105 μM) and a resilient behaviour upon cycling operation and long storage periods that clearly overpassed the performance of copper and cobalt single oxides. The CuxCoyO electrocatalysts also presented a good selectivity towards glucose and fructose in the presence of common interference compounds found in biological fluids (e.g., ascorbic acid, acetaminophen and uric acid), sucrose and ethanol, this latter present in many agrofood liquids. The possibilities of this sensor electrocatalyst have been tested for the analysis of a wine synthetic fermentation process. The comparison of the electrochemical results with conventional analytical methods showed a lineal amperometric response with respect hexose contents in a must at different stages of its transformation into wine.


Febrero, 2020 | DOI: 10.1016/j.snb.2019.127360

Enhanced Stability of Perovskite Solar Cells Incorporating Dopant-Free Crystalline Spiro-OMeTAD Layers by Vacuum Sublimation


Barranco, A; Lopez-Santos, MC; Idigoras, J; Aparicio, FJ; Obrero-Perez, J; Lopez-Flores, V; Contreras-Bernal, L; Rico, V; Ferrer, J; Espinos, JP; Borras, A; Anta, JA; Sanchez-Valencia, JR
Advanced Energy Materials, (2020) 1901524
Nanotecnología en Superficies y Plasma

ABSTRACT

The main handicap still hindering the eventual exploitation of organometal halide perovskite-based solar cells is their poor stability under prolonged illumination, ambient conditions, and increased temperatures. This article shows for the first time the vacuum processing of the most widely used solid-state hole conductor (SSHC), i.e., the Spiro-OMeTAD [2,2 ',7,7 '-tetrakis (N,N-di-p-methoxyphenyl-amine) 9,9 '-spirobifluorene], and how its dopant-free crystalline formation unprecedently improves perovskite solar cell (PSC) stability under continuous illumination by about two orders of magnitude with respect to the solution-processed reference and after annealing in air up to 200 degrees C. It is demonstrated that the control over the temperature of the samples during the vacuum deposition enhances the crystallinity of the SSHC, obtaining a preferential orientation along the pi-pi stacking direction. These results may represent a milestone toward the full vacuum processing of hybrid organic halide PSCs as well as light-emitting diodes, with promising impacts on the development of durable devices. The microstructure, purity, and crystallinity of the vacuum sublimated Spiro-OMeTAD layers are fully elucidated by applying an unparalleled set of complementary characterization techniques, including scanning electron microscopy, X-ray diffraction, grazing-incidence small-angle X-ray scattering and grazing-incidence wide-angle X-ray scattering, X-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy.


Enero, 2020 | DOI: 10.1002/aenm.201901524

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