Electrochemical oxidation of oxalic acid in the presence of halides at boron doped diamond electrode

Aim of this work is to discuss the electrochemical oxidation of oxalic acid (OA), analyzing the influence of NaCl and NaBr. Experiments were carried out at boron-doped diamond (BDD) electrodes, in alkaline media. BDD electrodes have a poor superficial adsorptivity so their great stability toward oxidation allows the reaction to take place with reactants and intermediates in a non-adsorbed state. The process is significantly accelerated by the presence of a halogen salt in solution; interestingly, the mediated process does not depend on applied current density. Based on the results, bromide was selected as a suitable mediator during OA oxidation at BDD. Br- primarily acts in the volume of the solution, with the formation of strong oxidants; while Cl- action has shown lower improvements in the OA oxidation rate at BDD respect to the results reported using Pt electrode. Finally, the parameters of removal efficiency and energy consumption for the electrochemical incineration of OA were calculated. O objetivo deste trabalho é discutir a oxidação eletroquímica do ácido oxálico (AO), analisando a influência do NaCl e NaBr. Experimentos foram realizados em eletrodos de diamante dopados com boro (DDB), em meio alcalino. Eletrodos DDB têm uma baixa adsortividade superficial, portanto sua grande estabilidade frente à oxidação permite que a reação ocorra com reagentes e intermediários não adsorvidos. O processo é significativamente acelerado pela presença de sal de halogênio na solução; curiosamente, o processo mediado não depende da densidade de corrente aplicada. Com base nos resultados, o brometo foi selecionado como um mediador apropriado durante a oxidação de AO em DDB. Br- age primeiramente no volume da solução, com a formação de oxidantes fortes, enquanto a ação do Cl- mostrou melhoras mais baixas na oxidação do AO em BDD, com relação aos resultados relatados usando eletrodo de Pt. Finalmente, os parâmetros de eficiência de remoção e consumo de energia para a incineração eletroquímica de AO foram calculados

Fe/SBA-15: Characterization and its application to a heterogeneous solar photo-Fenton process in order to decolorize and mineralize an azo dye

Fe/SBA-15 catalyst with different iron (Fe) loads (6% and 10% wt.) was synthesized via incipient wetness impregnation. The potential photocatalytic properties were tested using solar radiation, as a novel catalyst in heterogeneous Fenton approach to degrade Methyl Orange azo dye. A partial pore blocking of the substrate by Fe nanoparticles was detected and the main form of Fe present was Fe2O3. When the Fe(10%)/SBA-15 catalyst was used for heterogeneous solar photo-Fenton reaction, total discoloration of the effluent was achieved in 90 min, and 89% of COD was removed in 240 min. Short-chain linear carboxylic acids were followed over time, as well as inorganic ions.Fil: Arroyo Gómez, José Joaquín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Toncón Leal, Cristian Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: dos Santos, A.J.. Universidade Federal do Rio Grande do Norte; BrasilFil: Moreno, Mario S.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Sapag, Manuel Karim. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Martínez Huitle, C. A.. Universidade Federal do Rio Grande do Norte; Brasi

Photoelectro-Fenton treatment of pesticide triclopyr at neutral pH using Fe(III)-EDDS under UVA light or sunlight

One of the main challenges of electrochemical Fenton-based processes is the treatment of organic pollutants at near-neutral pH. As a potential approach to this problem, this work addresses the use of a low content of soluble chelated metal catalyst, formed between Fe(III) and ethylenediamine-N,N'-disuccinic (EDDS) acid (1:1), to degrade the herbicide triclopyr in 0.050 M Na2SO4 solutions at pH 7.0 by photoelectro-Fenton with UVA light or sunlight (PEF and SPEF, respectively). Comparison with electro-Fenton treatments revealed the crucial role of the photo-Fenton-like reaction, since this promoted the production of soluble Fe(II) that enhanced the pesticide removal. Hydroxyl radicals formed at the anode surface and in the bulk were the main oxidants. A boron-doped diamond (BDD) anode yielded a greater mineralization than an IrO2-based one, at the expense of reduced costeffectiveness. The effect of catalyst concentration and current density on the performance of PEF with BDD was examined. The PEF trials in 0.25 mMNa2SO4 + 0.35mMNaCl medium showed a large influence of generated active chlorine as oxidant, being IrO2 more suitable than RuO2 and BDD. In SPEF with BDD, the higher light intensity from solar photons accelerated the removal of the catalyst and triclopyr, with small effect on mineralization. A plausible route for the herbicide degradation by Fe(III)-EDDS-catalyzed PEF and SPEF is finally proposed based on detected byproducts: three heteroaromatic and four linear Naliphatic compounds, formamide, and tartronic and oxamic acids

Electrodeposited lead dioxide coatings

Lead dioxide coatings on inert substrates such as titanium and carbon now offer new opportunities for a material known for 150 years. It is now recognised that electrodeposition allows the preparation of stable coatings with different phase structures and a wide range of surface morphologies. In addition, substantial modification to the physical properties and catalytic activities of the coatings are possible through doping and the fabrication of nanostructured deposits or composites. In addition to applications as a cheap anode material in electrochemical technology, lead dioxide coatings provide unique possibilities for probing the dependence of catalytic activity on layer composition and structure (critical review, 256 references)

Electro-oxidation of cyanide on active and non-active anodes: Designing the electrocatalytic response of cobalt spinels

[EN] The feasibility of the electrochemical technologies for wastewater treatment greatly relies on the design of efficient but inexpensive electrocatalysts. It is generally accepted that the so-called ¿non-active¿ anodes (like the boron-doped diamond (BDD) or SnO2-based anodes), producing highly oxidizing hydroxyl radicals, are the most promising candidates for pollutants abatement. In this work, the electrocatalytic performance of various cobalt oxides, pure and doped with Cu or Au, for CN¿ oxidation has been studied and compared with that of conventional graphite, BDD, SnO2-Sb and SnO2-Sb-Pt. The metal oxide electrodes were prepared by thermal decomposition of the salt precursors onto Ti. For the M-doped Co3O4 electrodes, the nominal M/Co ratios were Cu/ Co=0.07¿1.00; and Au/Co=0.05¿0.20. The electrodes were characterized by different techniques (XRD, SEM, EDX, XPS) and their electrocatalytic response was studied by cyclic voltammetry and galvanostatic electrolysis in a H-type cell in aqueous 0.1M NaOH. The obtained results show that the nature of the dopant plays a key role on the electrocatalytic behavior of cobalt spinels. Thus, while Cu catalyzes the CN¿ electro-oxidation, Au declines it. This is explained by the fact that, unlike Au (which segregates as Au-rich particles), Cu is effectively incorporated into the spinel structure by forming a solid solution (CuxCo3-xO4). In this solid solution, atomic scale Cu(spinel)-CN¿ specific interactions occur to catalyze the reaction, whereas in segregated Au particles the oxidation is hindered probably by a too-strong adsorption of cyanide and/or its inaccessibility to oxide active sites. Electrolysis runs have revealed that ¿active¿ over-saturated Cu-doped spinels (Cu/Co=1.00) exhibit higher current efficiencies than conventional graphite and ¿non-active¿ BDD and SnO2-based anodes. Hence, we hereby demonstrate that an inexpensive ¿active¿ electrocatalyst can show even higher efficiency than the most powerful BDD anode. These results highlight the significance of anode design in the application of the electrochemical technique for wastewater treatment.Financial support from the Spanish Ministerio de Economia y Competitividad and FEDER funds (MAT2016-76595-R, IJCI-2014-20012) is gratefully acknowledgedBerenguer, R.; Quijada, C.; La Rosa-Toro, A.; Morallón, E. (2019). Electro-oxidation of cyanide on active and non-active anodes: Designing the electrocatalytic response of cobalt spinels. Separation and Purification Technology. 208:42-50. https://doi.org/10.1016/j.seppur.2018.05.024S425020

Cobalt mediated electro-scrubbers for the degradation of gaseous perchloroethylene

This work focuses on the treatment of gaseous perchloroethylene (PCE) using electro-scrubbing with diamond electrodes and cobalt mediators. PCE was obtained by direct desorption from an aqueous solution containing 150 mg L−1, trying to a real pollution case. The electro-scrubber consisted of a packed absorption column connected with an undivided electrochemical cell. Diamond anodes supported on two different substrates (tantalum and silicon) were used and the results indicated that Ta/BDD was more successful in the production of Co (III) species and in the degradation of PCE. Three experimental systems were studied for comparison purposes: absorbent free of Co (III) precursors, absorbent containing Co (III) precursors, and absorbent containing Co (III) precursors undergoing previous electrolysis to the electro-scrubbing to facilitate the accumulation of oxidants. The most successful option was the last, confirming the important role of mediated electrochemical processes in the degradation of PCE. Trichloroacetic acid (TCA) and carbon tetrachloride (CCl4) were found as the primary reaction products and ethyl chloroacetate esters were also identified. A comprehensive mechanism of the processes happening inside electro-scrubber is proposed.Este trabajo se centra en el tratamiento del percloroetileno gaseoso (PCE) mediante electro-fregado con electrodos de diamante y mediadores de cobalto. El PCE se obtuvo por desorción directa de una solución acuosa que contenía 150 mg L -1 , tratando de un caso de contaminación real. El electrodepurador constaba de una columna de absorción empaquetada conectada con una celda electroquímica no dividida. Se utilizaron ánodos de diamante soportados sobre dos sustratos diferentes (tantalio y silicio) y los resultados indicaron que Ta / BDD tuvo más éxito en la producción de especies de Co (III) y en la degradación de PCE. Se estudiaron tres sistemas experimentales con fines comparativos: absorbente libre de precursores de Co (III), absorbente que contiene precursores de Co (III) y absorbente que contiene precursores de Co (III) sometidos a electrólisis previa.al electro-fregado para facilitar la acumulación de oxidantes. La opción más exitosa fue la última, lo que confirma el importante papel de los procesos electroquímicos mediados en la degradación del PCE. Se encontraron ácido tricloroacético (TCA) y tetracloruro de carbono (CCl 4 ) como productos de reacción primarios y también se identificaron ésteres de cloroacetato de etilo. Se propone un mecanismo integral de los procesos que ocurren dentro del electrodepurador

Treatment of toluene gaseous streams using packed column electro-scrubbers and cobalt mediators

An absorption system has been combined with an electrochemical cell to treat a gaseous stream polluted with toluene. Toluene retention in 3 h operation tests was higher than 87.0% in the case of treating the gaseous stream with single scrubbing, 97.0% in the case of using electro-scrubbing and over 99.0% in using cobalt-mediated electro-scrubbing. It was found that the amount of toluene that escapes from the electro-scrubber does not only depend on the flow rate but also on the current density and the presence of the metallic mediator. The higher the current densities are, the higher the amount of electrochemically degraded toluene is. In addition to the mediating effect of the metal catalyst, the results also suggest an important participation of the redox sulfate/persulfate pair in the degradation of toluene. Only methyl-cyclohexane (at very low concentrations) is observed as intermediate, despite carboxylic acids were also initially expected. The formation of this compound can be explained in terms of the hydrogenation of toluene. The very low concentrations absorbed, and the very high current densities, support the occurrence of an electrochemical cold combustion in the electro-scrubber.Se ha combinado un sistema de absorción con una celda electroquímica para tratar una corriente gaseosa contaminada con tolueno. La retención de tolueno en las pruebas de funcionamiento de 3 h fue superior al 87,0% en el caso del tratamiento de la corriente gaseosa con lavado simple, al 97,0% en el caso de electro-fregado y superior al 99,0% con electro-fregado con cobalto. Se encontró que la cantidad de tolueno que escapa del electrodepurador no solo depende del caudal sino también de la densidad de la corriente y de la presencia del mediador metálico. Cuanto mayores sean las densidades de corriente, mayor será la cantidad de tolueno degradado electroquímicamente. Además del efecto mediador del catalizador metálico, los resultados también sugieren una participación importante del par redox sulfato / persulfato en la degradación del tolueno. Sólo metilciclohexano (a concentraciones muy bajas) se observa como intermedio, a pesar de que inicialmente también se esperaban ácidos carboxílicos. La formación de este compuesto se puede explicar en términos de hidrogenación de tolueno. Las muy bajas concentraciones absorbidas y las altísimas densidades de corriente favorecen la aparición de una combustión electroquímica en frío en el electrodepurador