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

Abstract

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.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.Keywords: indirect oxidation, mediators, oxalic acid, halides, boron doped diamond IntroductionElectrochemical treatment is one of the methods used for the removal of organic and inorganic impurities from water and waste water. Consequently, several research groups are attempting to use electrochemical methods as an effective method for detoxification of wastewaters containing biorefractory pollutants. [1][2][3][4][5][6][7][8] The literature has shown that, the electrochemical oxidation represents an alternative in wastewater treatment, [6][7][8][9] and this process can be subdivided in two main categories: "Direct" and "Indirect" as schematized in Table 1. According to information in Table 1, while the electron transfer takes place between electrodes and decomposable species in direct electrochemical oxidation, indirect oxidation mainly uses electrochemically oxidized species as mediators for the destruction of organic compounds. Reactive and high-valent metal ions which are electrochemically generated from stable...

Electrochemical oxidation of succinic acid in aqueous solutions using boron doped diamond anodes

“…The absence of anodic peaks evidences that the succinic acid oxidation on BDD anodes is much more difficult than aromatic compounds' oxidation such as phenols, herbicides, dyes and surfactants (Bensalah et al 2009;Boye et al 2006;Canizares et al 2006b;Louhichi et al 2008b;MartinezHuitle and Brillas 2009;Rodrigo et al 2010;Sires et al 2006;Weiss et al 2008). Similar results were reported by other studies on aliphatic carboxylic acids and alcohols (Canizares et al 2003(Canizares et al , 2008Gandini et al 2000;Ivandini et al 2006;Louhichi et al 2008b;Martinez-Huitle et al 2008;Onofrio et al 2008). Moreover, voltammetric behavior of succinic acid indicates that succinic acid is much more difficult to oxidize than aromatic acids such as benzoic and salicylic acids (Montilla et al 2002;Louhichi et al 2006) which can be explained in terms of chemical structure (aromatic or aliphatic).…”

“…As can be observed, polarization curves showed that no oxidation peaks appeared in the potential region of electrolyte stability. In addition, no oxygen evolution potential shifts were observed in the presence of succinic acid as was observed in the case of other carboxylic acids and glycols (Canizares et al 2003;Gandini et al 2000;Ivandini et al 2006;Louhichi et al 2008b;Martinez-Huitle et al 2008;Onofrio et al 2008). This could be due to the fact that succinic acid oxidation on BDD surface takes place at a potential, very close to that of the electrolyte oxidation.…”

“…It appears that radical intermediates of aromatics are more stable than those of aliphatics because of doublebond delocalization which facilitates electrochemical oxidation of aromatics. Moreover, anodic oxidation of succinic acid on BDD electrode is more difficult than that of aliphatic carboxylic monoacids (oxalic, fumaric, maleic, formic), glycols and aliphatic alcohols (Canizares et al 2003;Gandini et al 2000;Ivandini et al 2006;Kapalka et al 2008c;Louhichi et al 2008b;Martinez-Huitle et al 2008;Onofrio et al 2008). This is probably due to the presence of two carboxyl groups in its chemical structure.…”

“…Also, electrochemical treatment of other bioresistant organic pollutants such as aliphatic compounds was investigated by few researches using BDD anodic oxidation. Additionally, the electrochemical oxidation, especially anodic oxidation on BDD and other anodes of oxalic, acetic, maleic, fumaric, formic and tartaric acids (Canizares et al 2003(Canizares et al , 2008Chailapakul et al 2000;Drogui et al 2007;Gandini et al 2000;Ivandini et al 2006;Kapalka et al 2008c;Martinez-Huitle et al 2008;Onofrio et al 2008) was previously studied. These previous studies (Canizares et al 2003;Gandini et al 2000;Ivandini et al 2006;Martinez-Huitle et al 2008;Onofrio et al 2008) showed that oxalic acid was completely transformed into CO 2 and H 2 O in most cases, which is encouraging to test the feasibility of this process for destruction of succinic acid.…”

Bismuth-Doped Tin Oxide-Coated Carbon Nanotube Network: Improved Anode Stability and Efficiency for Flow-Through Organic Electrooxidation

“…Electrochemical anodic oxidation as well as other advanced oxidation processes (AOPs) have been previously studied for oxalate degradation 36,43,44,45 since it is the most common non-CO 2 end-product during aromatic oxidation 36 due to its slow reaction with the ·OH radical (C 2 O 4 2-+•OH→CO 2 +CO 2 • -;k = 7.7×10 6 M -1 s -1 ). 46 Oxalate and oxalic acid can undergo two-electron oxidation process to carbonate/CO 2 according to the following equations:…”