1,720,974 research outputs found
Anodic oxidation of mecoprop herbicide at lead dioxide
No full textThe electrochemical oxidation of an aqueous solution containing mecoprop (2-(2-methyl-4-chlorophenoxy) propionic acid) has been studied at PbO2 anodes by cyclic voltammetry and bulk electrolysis. The influence of current density, hydrodynamic conditions, temperature and pH on the degradation rate and current efficiency is reported. The results obtained show that the use of PbO2 leads to total mineralization of mecoprop due to the production of oxidant hydroxyl radical electrogenerated from water discharge. The current efficiency for the electrooxidation of mecoprop is enhanced by low current density, high recycle flow-rates and high temperature. In contrast, the pH effect was not significant. It has also been observed that mecoprop decay kinetics follows a pseudo-first-order reaction and the rate constant increases with rising current density
Electrochemical study of self-assembled cysteine monolayers on polycrystalline gold electrodes and functionalization with microperoxidase MP-11.
No full textSelf-assembled monolayers of cysteine (CYST) have been constructed on polycrystalline gold (polyAu) electrode at different immersion times (timmer) in order to characterize them by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Oxidative desorption experiments allowed the calculation of the surface coverage, whereas reductive desorption informed about the binding of CYST to different gold domains.
Desorption products showed different diffusion ability. The maximum coverage was already achieved at short timmer,
although progressive reordering of CYST molecules led to a relevant decrease of the defects at long time, as ascertained
by EIS. Functionalization of polyAu-CYST electrodes with the enzyme microperoxidase MP-11 performed by following two different binding methods showed that the enzymatically catalyzed reduction of H2O2 is enhanced when the –COOH residues of the MP-11 undecapeptide chain are firstly activated and then linked to the –NH2 functional groups of the non-activated CYST layer formed on the polyAu surface
Comparative electrochemical treatments of two chlorinated aliphatic hydrocarbons. Time course of the main reaction by-products
No full textAcidic aqueous solutions of the chlorinated aliphatic hydrocarbons 1,2-dichloroethane (DCA) and 1,1,2,2-tetrachloroethane (TCA) have been treated by the electro-Fenton (EF) process. Bulk electrolyses were performed at constant current using a BDD anode and an air diffusion cathode able to generate H2O2 in situ, which reacts with added Fe2+ to yield •OH from Fenton’s reaction. At 300 mA, almost total mineralization was achieved at 420 min for solutions containing 4 mM of either DCA or TCA. Comparative treatments without Fe2+ (anodic oxidation) or with a Pt anode led to a poorer mineralization. The better performance of the EF process with BDD is explained by the synergistic action of the oxidizing radicals, BDD(•OH) at the anode surface and •OH in the bulk, and the minimization of diffusional limitations. The decay of the initial pollutant accomplished with pseudo first-order kinetics. Chloroacetic and dichloroacetic acids were the major by-products during the degradation of DCA and TCA, respectively. Acetic, oxalic and formic acids were also identified. The proposed reaction pathways include oxidative and reductive (cathodic) dechlorination steps. Chlorine was released as Cl, being further oxidized to ClO3 and, mostly, to ClO4, due to the action of the largely generated BDD(•OH) and •OH
TRATAMIENTO ELECTROQUIMICO DE CONTAMINANTES ORGANOCLORADOS ALIFATICOS. ELUCIDACION DE LOS CAMINOS DE REACCION.
Full text linkLos hidrocarburos alifáticos clorados conjugan toxicidad con una alta estabilidad química, capacidad de bioacumulación y difusión de largo alcance. Los cloroetanos son particularmente ubicuos en la industria y en los productos domésticos, y su introducción en el medio ambiente puede entrañar riesgos para los seres vivos. Actualmente, la USEPA (US Environmental Protection Agency) está llevando a cabo el llamado “Endocrine Disruptor Screening Program (EDSP)”, en el cual tanto el 1,2-dicloroetano (DCA) como el 1,1,2,2-tetracloroetano (TCA) son considerados prioritarios debido a sus efectos potenciales sobre el sistema endocrino. El DCA se encuentra también en la lista de substancias prioritarias establecida recientemente por la Comisión Europea.1 Para evitar o, cuando menos, minimizar la entrada de cloroetanos en el medio acuático es necesaria la aplicación de tecnologías de tratamiento de aguas más eficaces que las tradicionalmente empleadas en las plantas de tratamiento de aguas residuales, como por ejemplo los procesos de oxidación avanzada (AOPs). De entre éstos, los AOPs electroquímicos (EAOPs) como la oxidación anódica (OA) y el proceso electro-Fenton (EF) vienen suscitando un gran interés para la degradación de compuestos orgánicos debido a sus excepcionales características técnicas y al uso reducido de compuestos químicos de elevado coste. Sin embargo, hasta la fecha, la electrorreducción con cátodos de plata ha sido el método electroquímico más utilizado para la destrucción de cloroetanos, observándose en general una conversión parcial de los contaminantes iniciales en lugar de su mineralización total.
En este trabajo, se han tratado disoluciones acuosas ácidas de DCA y TCA mediante los procesos EF y OA. Las electrólisis se han realizado a corriente constante usando un ánodo de diamante dopado con boro (BDD) y un cátodo a difusión de aire (ADE) capaz de generar H2O2 in situ, el cual reacciona con el Fe2+ añadido para obtener •OH en el seno de la disolución a partir de la conocida reacción de Fenton. A los 420 min de tratamiento EF a 300 mA, se alcanzó la mineralización prácticamente total de disoluciones con 4 mM de DCA o TCA. Tratamientos comparativos en ausencia de Fe2+ (es decir, OA) o con un ánodo de menor poder oxidante como el Pt condujeron a una mineralización más pobre. Los resultados tan positivos obtenidos mediante el proceso EF con BDD se pueden atribuir a la acción sinérgica de los radicales oxidantes, es decir, BDD(•OH) en la superficie del ánodo y •OH en el seno de la disolución, además de la minimización de las limitaciones difusivas. El descenso de la concentración del contaminante inicial se ajusta perfectamente a una cinética de pseudo primer orden. Los subproductos acumulados en mayor concentración durante la degradación del DCA y el TCA son los ácidos cloroacético y dicloroacético, respectivamente. Así mismo, se han identificado los ácidos acético, oxálico y fórmico. Los caminos de reacción propuestos incluyen etapas de decloración oxidativa y reductiva (catódica). Por otra parte, se ha encontrado que el cloro se libera inicialmente como ion Cl, el cual es oxidado a ion ClO3 y, fundamentalmente, a ion ClO4, gracias a la acción de los radicales BDD(•OH) y •OH generados en gran proporción.
En conclusión, se ha demostrado que el proceso EF con una celda BDD/ADE es una tecnología muy efectiva para la descontaminación de disoluciones acuosas de DCA y TCA, así como de mezclas de ambos, lo cual constituye un resultado importante de cara a proseguir con su tratamiento en matrices de agua real.
Referencias
1. European Commission, Identification of Priority Hazardous Substances under the Water Framework Directive, Directorate-General Environment, 2000
A critical review on latest innovations and future challenges of electrochemical technology for the abatement of organics in water
Full text linkUpdated water directives and ambitious targets like the United Nations’ Sustainable Development Goals (SDGs) have emerged in the last decade to tackle water scarcity and contamination. Although numerous strategies have been developed to remove water pollutants, it is still necessary to enhance their effectiveness against toxic and biorefractory organic molecules. Comprehensive reviews have highlighted the appealing features of the electrochemical technologies, but much progress has been made in recent years. In this timely review, a critical discussion on latest innovations and perspectives of the most promising electrochemical tools for wastewater treatment is presented. The work describes the performance of electrocatalytic anodes for direct electrochemical oxidation, the oxidation mediated by electrogenerated active chlorine, the electrocatalytic reduction as well as coupled approaches for synchronous anodic and cathodic processes combined with homogeneous and heterogeneous catalysis. The last section is devoted to the assessment of scale-up issues and the increase in the technology readiness level
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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