Comparing the Performance of Supported Ru Nanocatalysts Prepared by Chemical Reduction of RuCl3 and Thermal Decomposition of Ru3(CO)12 in the Sunlight-Powered Sabatier Reaction

The preparation of Ru nanoparticles supported on γ-Al2O3 followed by chemical reduction using RuCl3 as a precursor is demonstrated, and their properties are compared to Ru nanoparticles supported on γ-Al2O3 prepared by impregnation of γ-Al2O3 with Ru3(CO)12 and subsequent thermal decomposition. The Ru nanoparticles resulting from chemical reduction of RuCl3 are slightly larger (1.2 vs. 0.8 nm). In addition, Ru nanoparticles were deposited on Stöber SiO2 using both deposition techniques. These particles were larger than the ones deposited on γ-Al2O3 (2.5 and 3.4 nm for chemical reduction and thermal decomposition, respectively). Taking into account the size differences between the Ru nanoparticles, all catalysts display similar activity (0.14–0.63 mol·gRu−1·h−1) and selectivity (≥99%) in the sunlight-powered Sabatier reaction. Ergo, the use of toxic and volatile Ru3(CO)12 can be avoided, since catalysts prepared by chemical reduction of RuCl3 display similar catalytic performance

Photocatalytic Performance of Undoped and Al-Doped ZnO Nanoparticles in the Degradation of Rhodamine B under UV-Visible Light:The Role of Defects and Morphology

Quasi-spherical undoped ZnO and Al-doped ZnO nanoparticles with different aluminum content, ranging from 0.5 to 5 at% of Al with respect to Zn, were synthesized. These nanoparticles were evaluated as photocatalysts in the photodegradation of the Rhodamine B (RhB) dye aqueous solution under UV-visible light irradiation. The undoped ZnO nanopowder annealed at 400 °C resulted in the highest degradation efficiency of ca. 81% after 4 h under green light irradiation (525 nm), in the presence of 5 mg of catalyst. The samples were characterized using ICP-OES, PXRD, TEM, FT-IR, 27Al-MAS NMR, UV-Vis and steady-state PL. The effect of Al-doping on the phase structure, shape and particle size was also investigated. Additional information arose from the annealed nanomaterials under dynamic N2 at different temperatures (400 and 550 °C). The position of aluminum in the ZnO lattice was identified by means of 27Al-MAS NMR. FT-IR gave further information about the type of tetrahedral sites occupied by aluminum. Photoluminescence showed that the insertion of dopant increases the oxygen vacancies reducing the peroxide-like species responsible for photocatalysis. The annealing temperature helps increase the number of red-emitting centers up to 400 °C, while at 550 °C, the photocatalytic performance drops due to the aggregation tendency

Free Volume Expansion of Poly[1-(trimethylsilyl)-1-propyne] Treated in Supercritical Carbon Dioxide As Revealed by Positron Annihilation Lifetime Spectroscopy

The free volume changes of poly[1-(trimethyl-silyl)-1-propyne] (PTMSP) treated in supercritical CO2 (scCO(2)) were investigated with positron annihilation lifetime spectroscopy (PALS). CO2 is known to plasticize and increase the free volume size of a broad range of polymers. In this work dense PTMSP films were treated with scCO(2) under different pressures and temperatures, resulting in the enlargement of the characteristic channel-like holes (R-3) and the larger free volume cages (R-4) up to 39% and 19%, respectively. The free volume enlargement was found to have a relaxation time of similar to 30 years. At higher temperatures (110-150 degrees C), the o-Ps intensities and gel permeation chromatography (GPC) data revealed chemical changes of the scCO(2)-treated polymer due to the onset of PTMSP's degradation. However, at lower temperatures (40-70 degrees C), significant free volume cavity size increases to 25% for R-3 and 9% for R-4 were also observed

Enhanced performance in pervaporation of supercritical carbon dioxide treated poly[1-(trimethylsilyl)-1-propyne] membranes

The effect of a supercritical carbon dioxide (scCO(2)) treatment on the free volume of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) and PTMSP-silica nanohybrid membranes was investigated with positron annihilation lifetime spectroscopy (PALS) and correlated with their performance in pervaporation. Treatment of dense unfilled PTMSP and silica filled PTMSP (2.5, 10 and 20 wt.% silica) membranes with scCO(2) at different pressures and temperatures, resulted in a clear increase in the mean free volume size and an enhanced performance in the pervaporative separation of an aqueous ethanol mixture. Specific permeation rate increases up to 76% were observed for the unfilled membranes treated with scCO(2) at 70 degrees C and 24 MPa. The scCO(2)-treatment could thus be seen as an effective alternative to PTMSP-silica (50 wt.%) membranes, which cause a 72% increase in specific permeation rate. Moreover, the ethanol concentration in the permeate increases significantly upon treating the membranes with scCO(2). (C) 2011 Elsevier B.V. All rights reserved

BiFeO3 thin films via aqueous solution deposition: a study of phase formation and stabilization

© 2015, Springer Science+Business Media New York. This paper reports a thorough microstructural investigation of bismuth ferrite (BFO) thin films subjected to various processing conditions and discusses their influence on the stability of the BiFeO3 perovskite phase. The formation of secondary phases in BFO thin films is studied as a function of annealing temperature and time, film thickness, Bi excess, and Ti substitution. While films annealed at 600 °C consist of the desired BiFeO3 phase, higher temperatures induce the decomposition leading to a significant amount of secondary phases, particularly the iron-rich Bi2Fe4O9 phase. A longer annealing time at 700 °C further enhances the decomposition of BiFeO3. Qualitative microstructural analysis of the films is performed by electron backscattered diffraction which provides phase analysis of individual grains. The morphology of the single-crystalline Bi2Fe4O9 grains that are embedded in the BiFeO3 matrix drastically changes as a function of the film thickness. Nucleation of these Bi2Fe4O9 grains probably occurs at the film/substrate interface, after which grain growth continues toward the surface of the film through the depletion of the BFO phase. Addition of Bi excess or the substitution of Fe with Ti in the precursor solutions significantly reduces the formation of an iron-rich secondary phase. Influence of the secondary phases as well as Ti substitution on magnetic properties of BFO films was investigated.status: publishe

Understanding the importance of Cu(I) intermediates in self-reducing molecular inks for flexible electronics

Fast and scalable low-temperature deposition of microscale metallic features is of utmost importance for the development of future flexible smart applications including sensors, wireless communication, and wearables. Recently, a new class of metal organic decomposition (MOD) copper inks was developed, consisting of self-reducing copper formate containing amine complexes. From these novel inks, copper metal features with outstanding electrical conductivity (+/- 10(5) S cm(-1)) are deposited at a temperature of 150 degrees C or less, which is well below the reduction temperature of orthorhombic alpha-copper formate (around 225 degrees C). However, the underlying principle of this reaction mechanism and the relationship between the corresponding temperature shift and the amine coordination are still under debate. The current study provides a full explanation for the shift in reduction temperatures via in situ characterization. The results clearly indicate that the structural resemblance and stability of the Cu(II) starting compound and the occurring Cu(I) intermediate during the in situ reduction are the two main variables that rationalize the temperature shift. As such, the thermal compatibility of copper MOD inks with conventional plastic substrates such as polyethylene terephthalate can be explained, based on metal-organic complex properties

Crosslinked poly[1-(trimethylsilyl)-1-propyne] membranes: Characterization and pervaporation of aqueous tetrahydrofuran mixtures

To enhance their applicability in a broader range of pervaporation feed streams, poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes have been successfully crosslinked, using a 3,3'-diazido-diphenylsulfone crosslinker. Both photochemical and thermal processes were used to activate the bis(azide) and thus initiate the crosslink reaction. The presented photochemical crosslink process, has an insufficient efficiency, due to the unreacted bis(azide) and the formation of by-products such as carboxylic acids. On the other hand, thermal annealing at temperatures of at least 160 degrees C allows successful crosslinking of FTMSP. In contrast to photochemical crosslinking, the bis(azide) completely decomposes after thermal treatment, rendering the membranes insoluble in solvents that dissolve the uncrosslinked polymer, such as tetrahydrofuran (THF), n-heptane and methyl-tert-butyl ether. All membranes were extensively characterized by means of infrared analysis, solid-state H-1-wideline NMR, positron annihilation lifetime spectroscopy, swelling capacity measurements and pervaporation measurements. These techniques, allowed to gain insight in the crosslink reaction mechanism, crosslinking density of the crosslinked polymer network, changes in the free volume cavity sizes, solvent resistance and pervaporation performance, respectively. The potential of the thermally crosslinked PTMSP membranes in the removal of demanding solvents from aqueous mixtures was illustrated by pervaporation tests on dilute THF/water mixtures. The membrane containing 15 wt.% of crosslinker and treated at 180 degrees C during 1.5 h showed specific permeation rates that are approximately 4 times higher than those of the commercially available polydimethylsiloxane-based membranes, combined with competitive THF/water separation factors. Feed streams containing 10 wt.% THF could be enriched up to 84 wt.% THF in the permeate. (C) 2011 Elsevier B.V. All rights reserved

Obtención de láminas delgadas del sistema compuesto BiFeO3-Bi4Ti3O12 mediante procesamiento disolución-gel en medio acuoso

[EN] Thin film multiferroic composites, with a high quantity of interfaces between the different materials, represent a more feasible alternative to single phase systems in which the multifunctional response is usually hampered due to intrinsic physical constraints. Nowadays some of these composites can be produced by applying deposition techniques such as PLD, CVD, MBE or the like, which allow a high degree of crystallographic control. However, despite their effectiveness, all these techniques also involve a high consumption of energy in terms of temperature and/or vacuum. Within this frame, the present contribution proposes a sustainable chemical solution deposition process to prepare thin films of the multiferroic BiFeO–BiTiO composite system. More specifically an aqueous solution-gel plus spin-coating methodology is employed which also avoids the organic solvents typically used in a conventional sol–gel method, so further keeping an eye on the environmentally friendly conditions. Attempts are conducted that demonstrate how by systematically controlling the processing parameters it is possible to obtain thin film composites with a promising 3-3 type connectivity at temperatures as low as 600 °C.[ES] Los materiales compuestos (composites) multiferroicos en forma de lámina delgada y conun gran número de intercaras entre los distintos componentes, representan una alternativa más práctica y viable frente a los sistemas monofásicos, en los cuales la respuestamultiferroica se encuentra típicamente impedida debido a restricciones físicas de carácter intrínseco. Actualmente algunos de estos composites son obtenidos mediante diversas técnicas de deposición tales como PLD, CVD, MBE o similares, las cuales permiten un alto grado de control a nivel cristalográfico. No obstante, a pesar de su efectividad, todas estas técnicas también engloban un alto consumo de energía en términos de temperatura y/o vacío. En este contexto, el presente trabajo de investigación propone un método de deposición química en disolución para obtener láminas delgadas del sistema multiferroico compuesto BiFeO3-Bi4Ti3O12. En concreto se plantea la utilización de una metodología disolución-gel en medio acuoso seguida de deposición por spin coating, metodología con la que además se evita el empleo de los disolventes orgánicos típicamente utilizados en un método sol-gel convencional y que por tanto acentúa el carácter sostenible del proceso. Para ello se han llevado a cabo diferentes experimentos con los cuales se pone de manifiesto cómo llevando a cabo un control sistemático de las distintas variables del proceso, es posible obtener composites en forma de lámina delgada con una prometedora configuración 3-3 a temperaturas no superiores a 600 ◦C.This work was supported by the Spanish Ministry of Economy and Competitiveness, MINECO (Projects MAT2016-80182-Rand MAT2014-59210-JIN). This work was also conducted in theframe of “Grupo de Propiedades Ópticas, Eléctricas y Magnéticas y sus Aplicaciones”, (UPM), Unidad Asociada al Instituto de Cerámica y Vidrio (CSIC)