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2019


Materiales y Procesos Catalíticos de Interés Ambiental y Energético

Comprehensive Experimental and Theoretical Study of the CO plus NO Reaction Catalyzed by Au/Ni Nanoparticles

Kyriakou, G; Marquez, AM; Holgado, JP; Taylor, MJ; Wheatley, AEH; Mehta, JP; Sanz, JF; Beaumont, SK; Lambert, RM
ACS Catalysis, 9 (2019) 4919-4929

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The catalytic and structural properties of five different nanoparticle catalysts with varying Au/Ni composition were studied by six different methods, including in situ X-ray absorption spectroscopy and density functional theory (DFT) calculations. The as-prepared materials contained substantial amounts of residual capping agent arising from the commonly used synthetic procedure. Thorough removal of this material by oxidation was essential for the acquisition of valid catalytic data. All catalysts were highly selective toward N-2 formation, with 50-50 Au:Ni material being best of all. In situ X-ray absorption near edge structure spectroscopy showed that although Au acted to moderate the oxidation state of Ni, there was no clear correlation between catalytic activity and nickel oxidation state. However, in situ extended X-ray absorption fine structure spectroscopy showed a good correlation between Au Ni coordination number (highest for Ni50Au50) and catalytic activity. Importantly, these measurements also demonstrated substantial and reversible Au/Ni intermixing as a function of temperature between 550 degrees C (reaction temperature) and 150 degrees C, underlining the importance of in situ methods to the correct interpretation of reaction data. DFT calculations on smooth, stepped, monometallic and bimetallic surfaces showed that N + N recombination rather than NO dissociation was always rate-determining and that the activation barrier to recombination reaction decreased with increased Au content, thus accounting for the experimental observations. Across the entire composition range, the oxidation state of Ni did not correlate with activity, in disagreement with earlier work, and theory showed that NiO itself should be catalytically inert. Au-Ni interactions were of paramount importance in promoting N + N recombination, the rate-limiting step.


Junio, 2019 | DOI: 10.1021/acscatal.8b05154

Materiales Nanoestructurados y Microestructura

Exchange bias and two steps magnetization reversal in porous Co/CoO layer

Ovejero, JG; Godinho, V; Lacroix, B; Garcia, MA; Hernando, A; Fernandez, A
Materials & Design, 171 (2019) 107691

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In this paper Co/CoO thick layers (hundreds of nanometers) of different porosity and oxidation degree were prepared in a magnetron sputtering deposition processby tailoring the DC sputtering power, as well as the process gas and target composition. The control of the synthesis parameters allowed the nanostructuration of the films with a singular distribution of closed pores and a controlled amount of CoO. We observed an exchange bias field of 2.8 KOe for porous Co/CoO composites, similar to Co/CoO bilayers but for coatings thicker than 300 nm. Besides, it was observed that the coating presents bistable magnetic features when cooled under zero field conditions as a result of the unusual exchange coupling.


Junio, 2019 | DOI: 10.1016/j.matdes.2019.107691

Materiales Avanzados

Microbiological induced carbonate (CaCO3) precipitation using clay phyllites to replace chemical stabilizers (cement or lime)

Morales, L; Garzon, E; Romero, E; Sanchez-Soto, PJ
Applied Clay Science, 174 (2019) 15-28

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The objective of the present study is to develop a biotechnological tool for a new application of clay phyllites as stabilized materials in linear works replacing chemical stabilizer (e.g. cement or lime) by natural cement, formed by precipitated calcium carbonate generated by microorganisms of the Bacillaceae family (Bacilluspasteurii). Part of the development process conducting a chemical and mineralogical characterization and an examination of physical and hydromechanical properties. The results of this study show that the effect of bacteria on clay phyllites increases the calcium carbonate content, specific surface area and plasticity values. These increased values are caused by the addition of a non-plastic component to clay phyllites resulting in a more aggregated structure through the precipitation of calcium carbonate from the bacteria, ultimately filling the pores of this material. Microbiological treatments on clay phyllites tends to aggregate the original particles, creating aggregates that are partially associated with the formation of calcium carbonate. Said process is influenced by the curing and compaction procedures conducted on samples, which also cause breakage of carbonated structures formed during treatment. As a result of this breaking process of aggregates, some compaction energy is lost and the treated samples do not reach the maximum dry density of the natural state for the same level of compaction energy applied. Treated samples display a slightly larger friction angle with no cohesion, consistent with filling properties and denser condition. Compressibility is consistently lower than that of the natural state. Comparison of collapse data showsthat the occurrence and amount of collapse are controlled by the as-compacted dry density. It is also determined that higher compaction effort is even more effective than increasing the amount of bacteria introduced to stabilize the sample for the filling of pores (size ranges 3–50 μm) with calcium carbonate. However, the post-ageing compaction destroys the initial binding/cementation effect.


Junio, 2019 | DOI: 10.1016/j.clay.2019.03.018

Fotocatálisis Heterogénea: Aplicaciones

Preparation, characterization and photocatalytic degradation of Rhodamine B dye over a novel Zn3(PO4)2/BiPO4 catalyst

Naciri,Y.;Chennah,A.;Jaramillo-Páez,C.;Navío,J.A.;Bakiz, B.;Taoufyq,A.;Ezahri,M.;Villain,S.;Guinneton,F.;Benlhachemi,A.
Journal of Environmental Chemical Engineering, 7 (2019) 103075

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In this work, a facile method was used to synthesize the Zn3(PO4)2/BiPO4 composite photocatalysts with different Bi contents followed by heat treatment at 900 °C for 3 h. The as-prepared samples were studied by a variety of characterization techniques including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) combined with energy dispersive X-ray diffraction (EDX), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (DRS). The UV–vis spectroscopy was used to analyze the evolution of Rhodamine B discoloration in presence of the synthesized phosphate photocatalysts. The XRD, SEM-EDX, TEM, DRS and XPS analyses confirmed the formation of heterojunction structure between both materials, during the process of co-precipitation and ulterior heat treatment. The photocatalytic tests showed that photocatalytic ability of the 70% Bi-Zn3(PO4)2 composites was higher than that of pure Zn3(PO4)2 and BiPO4 after 1 h of UV-illumination. The obviously enhanced photocatalytic activity of the 70% Bi-Zn3(PO4)2 sample could be mainly attributed to the formation of the heterojunction, accelerating the separation of photogenerated charge carriers. A plausible mechanism of the photocatalytic degradation of RhB on Zn3(PO4)2/BiPO4 composites is proposed. The reduction in the Chemical Oxygen Demand (COD) revealed the mineralization of dye along with color removal. Thus, it can be suggested that the 70% Bi-Zn3(PO4)2 can serve as a promising photocatalyst in the degradation of organic contaminants under UV light.


Junio, 2019 | DOI: 10.1016/j.jece.2019.103075

Nanotecnología en Superficies y Plasma

Multifunctional antimicrobial chlorhexidine polymers by remote plasma assisted vacuum deposition

Mora-Boza, A; Aparicio, FJ; Alcaire, M; Lopez-Santos, C; Espinos, JP; Torres-Lagares, D; Borras, A; Barranco, A
Frontiers of chemical science and engineering, 13 (2019) 330-339

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Novel antibacterial materials for implants and medical instruments are essential to develop practical strategies to stop the spread of healthcare associated infections. This study presents the synthesis of multifunctional antibacterial nanocoatings on polydimethylsiloxane (PDMS) by remote plasma assisted deposition of sublimated chlorhexidine powders at low pressure and room temperature. The obtained materials present effective antibacterial activity against Escherichia coli K12, either by contact killing and antibacterial adhesion or by biocide agents release depending on the synthetic parameters. In addition, these multifunctional coatings allow the endure hydrophilization of the hydrophobic PDMS surface, thereby improving their biocompatibility. Importantly, cell-viability tests conducted on these materials also prove their non-cytotoxicity, opening a way for the integration of this type of functional plasma films in biomedical devices.


Junio, 2019 | DOI: 10.1007/s11705-019-1803-6

 

 

 

 

 

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