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Scientific Papers in SCI

2021


Facile synthesis and characterization of a novel 1,2,4,5-benzene tetracarboxylic acid doped polyaniline@zinc phosphate nanocomposite for highly efficient removal of hazardous hexavalent chromium ions from water


Abdelghani Hsini, Yassine Naciri, Mohamed Benafqir, Zeeshan Ajmal, Nouh Aarab, Mohamed Laabd, J.A. Navío, F. Puga, Rabah Boukherroub, Bahcine Bakiz, Abdallah Albourine
Journal of Colloid and Interface Science, 585 (2021) 560-573

ABSTRACT

The present study describes the preparation of a novel 1,2,4,5-benzene tetracarboxylic acid doped polyaniline@zinc phosphate (BTCA-PANI@ZnP) nanocomposite via a facile two-step procedure. Thereafter, the as-prepared composite material adsorption characteristics for Cr(VI) ions removal were evaluated under batch adsorption. Kinetic approach studies for Cr(VI) removal, clearly demonstrated that the results of the adsorption process followed the pseudo second order and Langmuir models. The thermodynamic study indicated a spontaneous and endothermic process. Furthermore, higher monolayer adsorption was determined to be 933.88 mg g1 . In addition, the capability study regarding Cr(VI) ions adsorption over BTCA-PANI@ZnP nanocomposite clearly revealed that our method is suitable for large scale application. X-ray photoelectron spectroscopy (XPS) analysis confirmed Cr(VI) adsorption on the BTCA-PANI@ZnP surface, followed by its subsequent reduction to Cr(III). Thus, the occurrence of external mass transfer, electrostatic attraction and reduction phenomenon were considered as main mechanistic pathways of Cr(VI) ions removal. The superior adsorption performance of the material, the multidimensional characteristics of the surface and the involvement of multiple removal mechanisms clearly demonstrated the potential applicability of the BTCA-PANI@ZnP material as an effective alternative for the removal of Cr(VI) ions from wastewater.


March, 2021 | DOI: 10.1016/j.jcis.2020.10.036

Functionalized biochars as supports for Pd/C catalysts for efficient hydrogen production from formic acid


Santos, JL; Megias-Sayago, C; Ivanova, S; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 282 (2021) 119615

ABSTRACT

Biomass waste product was used to generate biochars as catalytic supports for selective hydrogen production from formic acid. The supports were obtained after pyrolysis in CO2 atmosphere of non-pretreated and che-mically ZnCl2 activated raw materials (vine shoot and crystalline cellulose). The support series includes materials with different textural properties and surface chemistry. The support nature and especially textural properties firstly affects significantly Pd size and dispersion and its interaction with the support and secondly influence in a great extent the catalytic behavior of the final material. The presence of prevailing mesoporous character appeared to be the most important parameter influencing formic acid dehydrogenation and overall hydrogen production.


March, 2021 | DOI: 10.1016/j.apcatb.2020.119615

Enhanced UV and visible light photocatalytic properties of synthesized AgBr/SnO2 composites


Puga, F.; Navío, J.A.; Hidalgo, M.C.
Separation and Purification Tecnology, 257 (2021) 117948

ABSTRACT

Composites (AgBr/SnO2) comprised of AgBr and SnO2 with different molar % of bare SnO2, have been synthesized by simple precipitation methods; the bare SnO2 used, was synthesized by hydrothermal procedure. Samples have been characterized by X-ray diffraction (XRD), N2-adsorption, UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of the as-prepared photocatalysts was evaluated through photocatalytic degradation of rhodamine B (RhB) and caffeic acid (CAFA) under UV and Visible illumination. In photocatalytic degradation studies, for both substrates, conversion rates of around 95% were found in 45 min of both UV-illumination and 85% under visible lighting. These conversion rates were superior than the conversion rates of pure parental components, AgBr and SnO2 under the same experimental conditions. At least, for RhB no loss of photocatalytic activity has been observed after five recycles although the mineralization degree progressively diminished along the recycles. The enhanced photocatalytic degradation of AgBr/SnO2 compounds was attributed, in part, to a synergistic increase in adsorption viability, as well as to the effective separation of photoinduced load carriers that resulted from the formation of a heterojunction according to the type II junction. Radical scavengers’ experiments indicated that active oxidant species as O2.−, ·OH and h+ all are involved in this photocatalytic system, although it seems that O2.− played the major role in the photocatalytic degrading of RhB by AgBr/SnO2 composites. In summary, coupling AgBr with SnO2 remarkably improves the photocatalytic activity under both UV and visible-illumination with respect to the parental components. These features open the route to future applications of this material in the field of environmental remediation.


February, 2021 | DOI: 10.1016/j.seppur.2020.117948

Impact of Tb4+ and morphology on the thermal evolution of Tb-doped TiO2 nanostructured hollow spheres and nanoparticles


Colomer, MT; Rodriguez, E; Moran-Pedroso, M; Vattier, F; de Andres, A
Journal of Alloys and Compounds, 853 (2021) 156973

ABSTRACT

Tb-doped TiO2 hollow spheres (HSs) in the range 0.0-2.0 at.% have been synthesized by the first time to the best of our knowledge. The HSs are compared with nanoparticles (NPs) to evaluate the impact of morphology on their physicochemical and photoluminescence (PL) behavior upon increasing calcination temperature. After calcination at 550 degrees C, the particles are anatase with a primary average size of 10.0 +/- 0.2 nm for the NPs and 12.0 +/- 0.2 nm for those that form the micron sized hollow spheres of 1.8 +/- 0.2 mu m diameter and ca. 64 nm shell thickness. The temperature of the anataseerutile transition is found to be strongly dependent on the presence of Tb as well as on morphology. Contrarily to the usual stabilization of anatase when doping with trivalent rare-earth ions, the transition temperature is reduced when doping with Tb. The rutile phase is further favored for the HSs compared to the NPs probably related to the low density of the HSs and/or a more efficient packing density and/or a bigger crystal size of the nanoparticles that form those spheres with respect to the packing and the size of the NPs and/or the crystal size of the nanoparticles of the HSs with respect to the size of the NPs. Only a slight unit-cell volume increase for the anatase structure is observed upon Tb doping, in both the NPs and in the HSs, contrary to the expected increment due to the larger ionic radius of Tb3+ compared to Ti4+. In addition, the intensity of the characteristic f-f Tb3+ emission bands is extremely weak both in the anatase and rutile phases. The transition is accompanied with the emergence of an infrared emission band centered at 810 nm related to the formation of defects during the structural transformation providing deep levels in the gap that partly quench the f-f emissions in the rutile phase. The results are consistent with the presence of Tb in both +3 and +4 valence states. XPS measurements confirmed the presence of Tb3+ as well as of Tb4+ in both HSs and NPs. The large fraction of Tb4+ present in the samples originates the weak f-f emission intensity, an only slight increase of the cell parameters and the destabilization of the anatase phase. 


February, 2021 | DOI: 10.1016/j.jallcom.2020.156973

Sol-gel synthesis of ZnWO4-(ZnO) composite materials. Characterization and photocatalytic properties


Jaramillo-Páez, C., Navío, J.A., Puga, F., Hidalgo, M.C.
Journal of Photochemistry & Photobiology, A: Chemistry, 404 (2021) 112962

ABSTRACT

ZnWO4 based powder photocatalyst have been successfully prepared by calcining a co-precipitated precursor (ZnWO) obtained from aqueous Zn2+ and WO4 2− solutions at pH = 7, without surfactants addition. The as-formed sample was characterized by XRD, N2-absorption, SEM, TEM, DRS and XPS. Both techniques, XRD and XPS results showed that prepared sample corresponds to a crystalline, Zn-enriched composition, ZnWO4 indicating the formation of a ZnWO4-(ZnO) composite, whit ca. 10 wt.-% of ZnO confirmed by XRF analysis. Photocatalytic activities towards degradation of Rhodamine B (RhB), Methyl Orange (MO) and Phenol, under UV-illumination, was investigated not only by monitoring the percentages of conversion of substrates, but also by estimating the corresponding percentages of mineralization that accompany the photocatalytic process. Comparative substrateconversion rates estimated per surface area unit of catalyst, showed that the activity for ZnWO4-(ZnO) composite is similar to that for TiO2(P25), at least for MO and RhB, and even higher that for TiO2(P25) in respect to phenol conversion. By adding TEA to the synthesis procedure, a composite named as ZnWO4-ZnO-(pH = 10)-600 is generated, which has a higher proportion of ZnO (ca. 39 %) and superior specific surface area than the so-called ZnWO4-(ZnO) sample. Furthermore, the photocatalytic degradation of MO using the former material indicates that it is superior to ZnWO4-(ZnO) and even that TiO2(P25) itself under the same operational conditions. 


January, 2021 | DOI: 10.1016/j.jphotochem.2020.112962

Photocatalytic activity of ZnO nanoparticles and the role of the synthesis method on their physical and chemical properties


Uribe-Lopez, MC; Hidalgo-Lopez, MC; Lopez-Gonzalez, R; Frias-Marquez, DM; Nunez-Nogueira, G; Hernandez-Castillo, D; Alvarez-Lemus, MA
Journal of Photochemistry & Photobiology, A: Chemistry, 404 (2021) 112866

ABSTRACT

In the present study, we report on the effect of the synthesis method in the photoactivity of ZnO-NPs. The nanoparticles were prepared by precipitation and sol-gel procedures using zinc nitrate and zinc (II) acetylacetonate as ZnO precursors, respectively. The obtained samples were named as ZnO-PP (precipitation method) and ZnO-SG (sol-gel method). The powders were calcined at 500 degrees C and further characterized by Fourier Transform Infrared spectroscopy, X-ray Powder Diffraction, N-2 adsorption, thermal analysis, Diffuse Reflectance UV-Vis spectroscopy, and Electron Microscopy. Both methods of synthesis lead to formation of pure ZnO with hexagonal-wurtzite crystalline structures with average crystallite sizes similar to 30 nm. The specific surface area was affected by the synthesis method, since SBET values were 5 m(2)/g and 13 m(2)/g for sol-gel and precipitation method, respectively. The electron microscopy revealed significant changes in morphology for the obtained nanoparticles, as sol-gel directed the hexagonal rod-like geometries (similar to 50 nm in diameter) while quasi-spherical nanoparticles (similar to 100 nm in diameter) were formed using precipitation method. Photocatalytic activity was estimated by degrading phenol (50 ppm) as probe molecule under UVA irradiation (lambda = 356 nm), the results demonstrated that ZnO-PP reached 100 % of degradation after 120 min and 90 % of the pollutant was mineralized, whereas for ZnO-SG the results were 80 % and 48 % respectively. Fluorescence test using terephthalic acid (TA) demonstrated higher formation of OH center dot radicals for ZnO synthesized by precipitation method, which could explain the higher photodegradation and mineralization observed. These results support that even slight differences in physical and chemical properties of ZnO, have a significant impact on the photocatalytic performance of such nanoparticles.


January, 2021 | DOI: 10.1016/j.jphotochem.2020.112866

2020


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


Gil-Rostra, J; Valencia, FY; Gonzalez-Elipe, AR
Journal of Luminescence, 228 (2020) 117617

ABSTRACT

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


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

Efficient third harmonic generation from FAPbBr(3) perovskite nanocrystals


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

ABSTRACT

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


December, 2020 | DOI: 10.1039/d0tc04790b

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


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

ABSTRACT

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


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

Ru-Ni/MgAl2O4 structured catalyst for CO2 methanation


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

ABSTRACT

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


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

Elucidating the Promotional Effect of Cerium in the Dry Reforming of Methane


Rodriguez-Gomez, A; Lopez-Martin, A; Ramirez, A; Gascon, J; Caballero, A
Chemcatchem

ABSTRACT

A series of Ni-Ce catalysts supported on SBA-15 has been prepared by co-impregnation, extensively characterized and evaluated in the carbon dioxide reforming of methane (DRM). The characterization by TEM, XRD and TPR has allowed us to determine the effect of metal loading on metal dispersion. Cerium was found to improve nickel location inside the mesopores of SBA-15 and to suppress coke formation during the DRM reaction. The analysis by XPS allowed us to associate the high cerium dispersion with the presence of low-coordinated Ce3+ sites, being main responsible for its promotional effect. A combination of XAS and XPS has permitted us to determine the physicochemical properties of metals under reduction conditions. The low nickel coordination number determined by XAS in N-Ce doped systems after reduction suggests the generation of very small nickel particles which showed greater catalytic activity and stability in the reaction, and a remarkable resistance to coke formation.


December, 2020 | DOI: 10.1002/cctc.202001527

Wetting and spreading of liquid lithium onto nanocolumnar tungsten coatings tailored through the topography of stainless steel substrates


Munoz-Pina, S; Garcia-Valenzuela, A; Oyarzabal, E; Gil-Rostra, J; Rico, V; Alcala, G; Alvarez, R; Tabares, FL; Palmero, A; Gonzalez-Elipe, AR
Nuclear Fusion, 60 (2020) 126033

ABSTRACT

The use of liquid metal as an alternative to cover the plasma-exposed areas of fusion reactors has called for the development of substrates where refilling and metal spreading occur readily and at reasonably low temperatures. In the search for common materials for this purpose, we show that nanostructured tungsten coatings deposited on stainless steel (SS) by magnetron sputtering at oblique angles (MS-OAD) is a good option, provided that the surface microstructure of substrate is properly engineered. Tungsten thin films with nominal thicknesses of 500 and 2500 nm were deposited onto SS plates subjected to conventional surface finishing treatments (sand blasting, sand paper abrasion and electrochemical polishing) to modify the surface topography and induce the appearance of different groove patterns. In the first part of this work we show how the topographical features of the SS substrates affect the typical nanocolumnar microstructure of OAD thin films of tungsten. Subsequently, we characterize the spreading behavior of liquid lithium onto these tungsten nanocolumnar surfaces and critically discuss whether nanocolumnar tungsten thin films are a suitable option for the wetting and spreading of molten lithium. As a result, we reveal that the features of the tungsten nanocolumnar coating, characterized by a given height and void spaces between nanocolumns in the order of 1–2 μm, is critical for the spreading of molten lithium, while the existence of wider channels affects it very weakly. Moreover, it is shown that tungsten films deposited by MS-OAD on SS substrates subjected to conventional finishing procedures represent a good alternative to other more complex surface engineering procedures utilized for this purpose.


December, 2020 | DOI: 10.1088/1741-4326/abb53e

Robust anti-icing superhydrophobic aluminum alloy surfaces by grafting fluorocarbon molecular chains


Rico, V; Mora, J; Garcia, P; Aguero, A; Borras, A; Gonzalez-Elipe, AR; Lopez-Santos, C
Applied Materials Today, 21 (2020) 100815

ABSTRACT

Infusion of low surface tension liquids in nanostructured surfaces is currently used to promote an anti icing response, although the long term stability of these systems is often jeopardized by losses of the infused liquid. In this work, we propose an alternative to the infusion procedure to induce a more effective and long lasting anti-icing capacity. The method consists of a combination of surface nanostructuration with the chemical grafting of fluorocarbon molecules. Al6061 substrates have been subjected to laser roughening and further modified with a nanostructured Al2O3 thin film to achieve a dual roughness and porous surface state. These surfaces have been subjected to a grafting treatment with perfluorooctyltriethoxysilane (PFOTES) vapor or, for comparative purposes, infused with a low surface tension liquid. A comparative analysis of the wetting, water condensation and anti-icing properties of these two systems showed an outstandingly better performance for the grafted surfaces with respect to the infused ones. Grafted surfaces were markedly superhydrophobic and required higher water vapor pressures to induce condensation. When looking for their anti-icing capacity, they presented quite long freezing delay times for supercooled water droplets (i.e. almost four hours) and exhibited a notably low ice accretion in a wind tunnel test. The high aging resistance and durability of these grafted surfaces and the reproducibility of the results obtained when subjected to successive ice accretion cycles show that molecular grafting is an efficient anti-icing methodology that, in aggressive media, may outperform the classical infusion procedures. The role of the fluorocarbon chains anchored on the surface in inducing an anti-icing functionality is discussed.


December, 2020 | DOI: 10.1016/j.apmt.2020.100815

(NH4)4[NiMo6O24H6].5H2O / g-C3N4 materials for selective photo-oxidation of Csingle bondO and Cdouble bondC bonds


Caudillo-Flores, U; Ansari, F; Bachiller-Baeza, B; Colon, G; Fernandez-Garcia, M; Kubacka, A
Applied Catalysis B-Environmental, 278 (2020) 119299

ABSTRACT

Novel composite photo-catalysts having (NH4)(4)[NiMo6O24H6]center dot 5H(2)O Polyoxometalate (POM) species deposited over g-C3N4 are synthesized. Materials were characterized through a multitechnique approach showing the stability of the carbon nitride component both through the synthesis process and under reaction. Contrarily, the POM component evolves under reaction conditions to maximize the interaction with the support. Such a behavior renders, as measured by the quantum efficiency, highly active photo-catalysts in the photo-oxidation of 2-propanol and styrene both under UV and sunlight illumination, setting up the basis for a green catalytic process. The material having a 4 wt. % POM showed improved activity with respect to both parent constituents but also higher selectivity to the partial oxidation of the alcohol and the aromatic hydrocarbon to generate added value chemical compounds. A multitechnique approach investigating charge carrier fate demonstrates the key role played by the interaction between components to promote activity and selectivity in selective oxidation reactions.


December, 2020 | DOI: 10.1016/j.apcatb.2020.119299

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


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

ABSTRACT

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


December, 2020 | DOI: 10.3390/nano10122354

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


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

ABSTRACT

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


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

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


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

ABSTRACT

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


November, 2020 | DOI: 10.1002/adom.202001086

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


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

ABSTRACT

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


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

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


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

ABSTRACT

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


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

Tailoring CrNx stoichiometry and functionality by means of reactive HiPIMS


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

ABSTRACT

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


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

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