The anodic oxidation of methamidophos (MMD), a highly toxic pesticide used worldwide, was studied in a sodium sulfate aqueous solution on Pb/PbO2, Ti/SnO2, and Si/BDD (boron doped diamond) electrodes at 30 degrees C. Under galvanostatic conditions, it was observed thatthe performance of the electrode material is influenced by pH and current density as shown by HPLC and ATR-FTIR analysis of MMD and its oxidation products along the electrolysis. It was found that MMD degradation using Pb/PbO2 in acid media (pH 2.0 and 5.6) generates formaldehyde asthe main product of the reaction giving evidence of an indirect mineralization mechanism. Under the same conditions, Ti/SnO2 showed poor formaldehyde production compared to the Pb/PbO2 electrode. On Si/BDD electrodes formaldehyde production was not observed, instead the ATR-FTIR results showed the formation of phosphate as the reaction progressed suggesting a complete MMD mineralization on this electrode. In addition, HPLC results showed that the electrode efficiency is also dependent on the applied current density. This current density influence is remarkably clear on the Si/BDD electrodes where it was evident that the most efficient current density toward a complete MMD mineralization was reached with the application of 50 mA/cm2.

Photolysis (254 nm) of 2-azidopyrimidine (AP) in glassy ethanol (EtOH) at 77 K produces the EPR spectrum of 2-pyrimidylnitrene (D = 1.15 cm-1) in its triplet ground state. Photolysis (254 nm) of AP in EtOH at 77 K leads to bleaching of the absorption of the azide (λmax = 242 nm) and formation of a broad absorption band between 300 and 400 nm and a highly structured band between 400 and 450 nm. A more highly resolved but similar spectrum was observed by photolysis of AP in argon at 14 K. The appearance of these bands in argon is accompanied by the formation of a series of IR transitions. The experimentally observed IR spectrum was consistent with the spectrum of triplet 2-pyrimidylnitrene (3PN) predicted by density functional theory with the 6-31G* basis set. The UV−vis spectrum is attributed to 3PN based on the IR and EPR results. Laser flash photolysis (LFP) of AP in dichloromethane at ambient temperature produced 3PN with its characteristic structured absorption between 400 and 450 nm. The triplet nitrene was formed in an exponential process (k OBS = 8 ± 2 × 107 s-1, τ ∼ 13 ns, λmax = 429 nm) following the laser flash. The transient absorption observed at 455 nm decays with the same time constant and is attributed to singlet 2-pyrimdylnitrene (1PN). Simple expectations based on anti-aromaticity arguments and density functional theory calculations agree that cyclization of singlet 2-pyrimidylnitrene to form a 1H-benzodiazirine is more endothermic than the corresponding process in unsubstituted singlet phenylnitrene if the singlet−triplet gaps of the two nitrenes are comparable. The rate constant of intersystem crossing of 1PN is more than 200 times faster than that of parent singlet phenylnitrene. Cyclization of 1PN to the benzo 1H-diazirine is not observed, and the hypothetical process is at least 13 times slower than that of singlet phenylnitrene to a benzazirine at ambient temperature. 3PN decays over tens of microseconds in a second order process, presumably to form the azo dimer, and reacts with molecular oxygen.

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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...

The surface of glassy carbon (GC) electrode has been modified by oxidation of L-cysteine. The covalent modified GC electrode with L-Cysteine has been studied, according the supporting electrolyte used. Favourable interactions between the L-cysteine film and DA enhance the current response compared to that at the Nafion GC and bare GC electrodes, achieving better performances than those other electrodes. This behaviour was as result of the adsorption of the cysteine layer film, compact and uniform formation; depending on L-cysteine solution (phosphate buffer or chloridric acid supporting electrolyte) used for modifying GC surface. In cyclic voltammetric measurements, modified electrodes can successfully separate the oxidation/reduction DA peaks in different buffer solutions, but an evident dependence in the response was obtained as function of pH and modified electrode. The modified electrode prepared with L-cysteine/HCl solution was used to obtain the calibration curve and it exhibited a stable and sensitive response to DA. The results are described and discussed in the light of the existing literature.

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The inhibition of copper corrosion in 3.5% NaCl solution has been studied at 25 o C using three inhibitors: 1-phenyl-2,4-dithiobiuret(Inh I), 1-p-methoxyphenyl-2,4-dithiobiuret(Inh II) and 1-p-chlorophenyl-2,4-dithiobiuret(Inh III). The inhibition efficiencies of these compounds have been evaluated by weight loss and electrochemical methods (impedance spectroscopy and polarisation curves). The surface study was done by using SEM and ESCA techniques. The inhibition efficiencies of the inhibitors follow the sequence Inh II > Inh I > Inh III. The inhibitors Inh I, Inh II and Inh III appear to inhibit corrosion process through the formation of a protective film which was found to consist of Cu(I)-inhibitor complex, cuprous chloride CuCl or CuCl 2 -complex ions or both on the surface. .

The aim of this work is to study the viability of using TiO2 nanotube arrays decorated with PbO2 to electrochemically produce persulfate