1,720,988 research outputs found
Ru, Co and Ca-based catalysts for artificial photosynthesis
Get PDFLa fotosíntesis artificial ofrece una alternativa al panorama energético actual, basado en el consumo de combustibles fósiles. Tratando de emular la fotosíntesis de las plantas, este campo de estudio trata de utilizar la luz solar para producir electrones, protones y oxígeno a partir del agua, para más tarde utilizar los electrones para producir hidrógeno u otros combustibles, y almacenar de esta forma la energía solar en forma de enlaces químicos. Para hacer energéticamente viables estos dos procesos es necesario el uso de catalizadores, comúnmente basados en metales de transición.
En el primer capítulo se introduce brevemente la motivación que ha llevado a la realización de la tesis, discutiéndose también los aspectos mecanísticos más relevantes de la catálisis de oxidación de agua, así como la reducción de protones, dando una visión general de los catalizadores en ambos campos más relevantes hasta la fecha.
El segundo capítulo se centra en los objetivos de este trabajo. El objetivo principal de esta tesis es la síntesis y caracterización estructural y electroquímica de varios catalizadores de Ru, Cu y Co, y el posterior estudio de su reactividad en catálisis de oxidación de agua y/o reducción de protones. El objetivo final es comprender sus mecanismos de reacción y los factores que afectan a su actividad catalítica para ayudar al diseño futuro de catalizadores más eficientes y robustos.
En el tercer capítulo se presenta la síntesis, caracterización y reactividad de una nueva familia de complejos de Ru. Un estudio espectroscópico y cinético detallado ha permitido identificar la formación de nuevas especies tras oxidación de los complejos en soluciones acuosas, las cuales tienen una implicación directa en su comportamiento en catálisis de oxidación de agua. El cuarto capítulo aborda la síntesis y caracterización de una nueva familia de complejos de Cu, estudiándose su reactividad en catálisis de oxidación de agua y comparándose con la de los complejos de cobre más relevantes reportados hasta la fecha en la bibliografía. Finalmente, en el quinto capítulo se presenta la desactivación de un cluster molecular de CoII/CoIII cuando este se somete a potenciales de reducción, dando lugar a la formación de nanopartículas de CoO o CoO(OH) depositadas sobre un electrodo de carbono. Dichas nanopartículas han sido probadas en catálisis de reducción de protones y su reactividad relacionada con su morfología y naturaleza.
En el sexto capítulo se incluyen las conclusiones más relevantes del trabajo realizado. Finalmente, el último capítulo contiene un anexo que incluye otros trabajos realizados y publicados durante esta tesis relacionados con el tema principal de esta tesis.Artificial photosynthesis offers a viable alternative to the actual energetic model based mainly in the consumption of fossil fuels. Trying to emulate the photosynthesis process in higher plants, this area of study attempts to use sunlight in order to produce electrons, protons and oxygen from water, with the aim of using the released electrons for producing hydrogen or other useful fuels. Within this context, the use of catalysts usually based in transition metals is necessary to make these two processes viable.
The first chapter contains a brief introduction about the motivation for the research presented in this thesis. The most relevant general mechanistic aspects for water oxidation (WO) as well as proton reduction catalysis are also presented, giving a general view of most relevant catalysts reported to date.
The second chapter is focused in the objectives of this work. The main goal of this PhD thesis is the synthesis and the structural and electrochemical characterization of a series of Ru, Co and Cu-based catalysts and the ulterior study of their reactivity towards water oxidation and/or proton reduction catalysis. The final objective is to fully understand the mechanistic pathways and the factors that affect their catalytic performance for helping in the future rational design of more efficient and robust catalysts.
In the third chapter, the synthesis, characterization and reactivity of a new family of Ru complexes is presented. A series of detailed electrochemical, spectroscopic and kinetic studies allows the identification of new species formed after oxidation of the complexes in aqueous solution that proved to be key for further understanding their catalytic behavior in water oxidation. The fourth chapter presents the synthesis and characterization of a new family of Cu complexes. Their reactivity towards water oxidation has been studied and compared with that of the most relevant Cu-based WO catalysts reported in the literature. Finally, in the fifth chapter we present the deactivation of a CoII/CoIII molecular cluster after application of reductive potentials, giving rise to the formation of CoO or CoO(OH) nanoparticles deposited onto a glassy carbon electrode. The ability of these nanoparticles for reducing protons has been tested, and their catalytic performance discussed on the basis of the nature of the species obtained and their morphology .
In the sixth chapter the most relevant conclusions of this work are discussed. Finally, the last chapter includes an annex containing other works that have been carried out and published during this PhD thesis and that are closely related with the work carried out during the PhD
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Robust Molecular Anodes for Electrocatalytic Water Oxidation Based on Electropolymerized Molecular Cu Complexes
Get PDFA multistep synthesis of a new tetra-amidate macrocyclic ligand functionalized with alkyl-thiophene moieties, 15,15-bis(6-(thiophen-3-yl)hexyl)-8,13-dihydro-5H-dibenzo[b,h][1,4,7,10]tetraazacyclotridecine-6,7,14,16(15H,17H)-tetraone, H4L, is reported. The reaction of the deprotonated ligand, L4−, and Cu(II) generates the complex [LCu]2−, that can be further oxidized to Cu(III) with iodine to generate [LCu]−. The H4L ligand and their Cu complexes have been thoroughly characterized by analytic and spectroscopic techniques (including X-ray Absorption Spectroscopy, XAS). Under oxidative conditions, the thiophene group of [LCu]2− complex polymerizes on the surface of graphitic electrodes (glassy carbon disks (GC), glassy carbon plates (GCp), carbon nanotubes (CNT), or graphite felts (GF)) generating highly stable thin films. With CNTs deposited on a GC by drop casting, hybrid molecular materials labeled as GC/CNT@p-[LCu]2− are obtained. The latter are characterized by electrochemical techniques that show their capacity to electrocatalytically oxidize water to dioxygen at neutral pH. These new molecular anodes achieve current densities in the range of 0.4 mA cm−2 at 1.30 V versus NHE with an onset overpotential at ≈250 mV. Bulk electrolysis experiments show an excellent stability achieving TONs in the range of 7600 during 24 h with no apparent loss of catalytic activity and maintaining the molecular catalyst integrity, as evidenced by electrochemical techniques and XAS spectroscopy.Fil: Amthor, Sebastian. Barcelona Institute Of Science And Technology. Institut Català D'investigació Química.; EspañaFil: Ranu, Koushik. Barcelona Institute Of Science And Technology. Institut Català D'investigació Química.; EspañaFil: Bellido, Carlos G.. Barcelona Institute Of Science And Technology. Institut Català D'investigació Química.; EspañaFil: Salomón, Fernando Federico. Barcelona Institute Of Science And Technology. Institut Català D'investigació Química.; España. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Piccioni, Alberto. Università di Bologna; ItaliaFil: Mazzaro, Raffaello. Università di Bologna; ItaliaFil: Boscherini, Federico. Università di Bologna; ItaliaFil: Pasquini, Luca. Università di Bologna; ItaliaFil: Gil Sepulcre, Marcos. Barcelona Institute Of Science And Technology. Institut Català D'investigació Química.; EspañaFil: Llobet, Antoni. Barcelona Institute Of Science And Technology. Institut Català D'investigació Química.; Españ
Powerful Bis-facially Pyrazolate-Bridged Dinuclear Ruthenium Epoxidation Catalyst
Get PDFA new bis-facial dinuclear ruthenium complex, {[RuII(bpy)]2(μ-bimp)(μ-Cl)}2+, 22+, containing a hexadentate pyrazolate-
bridging ligand (Hbimp) and bpy as auxiliary ligands has been synthesized and fully characterized in solution by spectrometric, spectroscopic, and electrochemical techniques. The new compound has been tested with regard to its capacity to oxidize water and alkenes. The in situ generated bis-aqua complex, {[RuII(bpy)(H2O)]2(μ-bimp)}3+, 33+, is an excellent catalyst for the epoxidation of a wide range of alkenes. High turnover numbers (TN), up to 1900, and turnover frequencies (TOF), up to 73 min−1, are achieved using PhIO as oxidant. Moreover, 33+ presents an outstanding stereospecificity for both cis and trans olefins toward the formation of their corresponding epoxides due to specific interactions transmitted by its ligand scaffold. A mechanistic analysis of the epoxidation process has been performed based on density functional theory (DFT) calculations in order to better understand the putative cooperative effects within this dinuclear catalystSupport form MINECO (Grants CTQ2011-26440, CTQ-2013-49075-R and CTQ2010-21532-C02-02) and the DFG (Grant Me1313/9-1) is gratefully acknowledged. J.A. is grateful for the award of a PIF doctoral grant from UAB. A.P. thanks the Spanish MINECO for the project CTQ2014-59832-JIN and the European Commission for a Career Integration Grant (No.CIG09-GA-2011-293900
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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