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

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

Electrocatalytic properties of PbO2 and SnO2 in the oxidation of the phenoxy acid herbicide 2,4,5 trichlorophenoxyacetic acid (2,4,5-T)

The phenoxyalkanoic acids (2,4,5-T between them) are systemic herbicides widespread in streams and groundwater. These pesticides were classified by the World Health Organization (WHO) as class II toxics, whose maximum concentration for drinking water must be not greater than 100 ppb. Until now, the elimination studies of phenoxyalkanoic acids from aqueous solutions have been restricted to the oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) by using several advanced oxidation processes (AOP’s) but not considering the electrochemical methods. Therefore, in this work the electrochemical degradation of 2,4,5-T in aqueous media on PbO2 and SnO2 anodes under different experimental conditions was investigated. The experiments were carried out using a two compartment electrochemical cell with the auxiliar electrode separated from reaction compartment by a porcelain pot and under galvanostatic conditions. The electrolyzed solution was periodically analyzed for 2,4,5-T and oxidation byproducts by HPLC, GC-MS, UV, DQO and TOC techniques. The anodic oxidation of 2,4,5-T in 0.5 M H2SO4 at 298 K was better observed on SnO2 (70%) than on Pb/PbO2 (50%) anodes at same conditions of applied current density (20 mA cm-2). This oxidation percentage of 2,4,5-T on SnO2 increased until 83% at 30 mA cm-2 with the scarce formation of two aromatic intermediates (2,4,5-threechloropenol: 2,4,5-TCP and 2,5-dihydroxyhydroquinone: 2,5-DHHQ) which seem to disappear through the formation of malonic and acetic acids to give CO2 as final oxidation product. In this work, the influence of the pH and temperature of the electrooxidation were also studied

The role of particle size on the conductive diamond electrochemical oxidation of soil-washing effluent polluted with atrazine

Soil washing using surfactant solutions is a very effective and widely used technique for the remediation of polluted soil. However, it is not a finalistic technology and once the pollutant is transferred to the washing-solution, the resulting aqueous waste has to be treated. In this work, it is studied the feasibility of Conductive - Diamond Electrochemical ? Oxidation (CDEO) to treat the effluent of a surfactant-aided soil washing process and it is pointed out some important mechanistic aspects. Atrazine was selected as the model pesticide and sodium dodecyl sulphate (anionic surfactant) was used as washing agent. Besides COD, TOC, and pollutants concentration, the changes of z-potential and particle size were monitored during electrolysis in order to clarify the degradation mechanisms involved in the electrochemical treatment of emulsions. The results show that CDEO enables a complete reduction in the organic load of the waste. However, the process efficiency seems to be influenced by the size of particles present in the reaction media, which decreases continuously during the treatment. Steric hindrance of the large micelles (mean size 1100 um) seems to prevent direct oxidation of micelles on the anodic surface and hence only mediated processes can explain the results obtained. In this case, it may be assumed that peroxocarbonate (from carbonate salts added as supporting electrolyte) and peroxosulphate ions (formed from the oxidation of sulphate ions released from SDS molecule) are the main species expected according to the washing fluid compositio