A crescente ocorrência de antibióticos e seus metabólitos estão cada vez maiores em águas superficiais e subterrâneas, causando impactos significativos no meio ambiente e necessitando de desenvolvimento de novos tratamentos para a remoção completa de tais contaminantes. Este trabalho apresenta o estudo da eletrogeração de peróxido de hidrogênio (H2O2) em meio ácido e a degradação do analgésico dipirona em um reator de fluxo eletroquímico usando um eletrodo de difusão gasosa (GDE) modificado com 5,0% ftalocianina de cobalto (II) (CoPc) e pressurizado com O2. A maior produção de H2O2 alcançada foi de 133 mg L-1 a um potencial aplicado de -2,1 V (vs. Pt//Ag/AgCl/KCl s) e os melhores resultados para a degradação da dipirona foram obtidos sob condições eletro-Fenton, em que o carbono orgânico total (TOC) foi reduzido 62,8% após 90 min de reação e 49,1 kW h de energia foi consumida por kg de dipirona degradada.

The increasing occurrence of antibiotics and their metabolites in surface and ground waters is causing a significant impact on the environment and needing of developing novel treatments for the complete removal of such contaminants. This paper presents the study of the electrogeneration of hydrogen peroxide (H2O2) in acidic medium and the degradation of the analgesic dipyrone in an electrochemical flow reactor using a gas diffusion electrode (GDE) modified with 5.0% cobalt (II) phthalocyanine (CoPc) and pressurized with O2. The highest yield of H2O2 (133 mg L-1) was achieved after 90 min of electrolysis at an applied potential of -2.1 V (vs. Pt//Ag/AgCl/KCl s) and the best results for degradation of dipyrone were obtained under electro-Fenton conditions, where the total organic carbon (TOC) was reduced 62.8% after 90 min of reaction and 49.1 kW h of energy was consumed per kg of dipyrone degraded.

This work reports the development of GDE for electrogeneration of H2O2 and their application in the degradation process of Reactive Blue 19 dye. GDE produced by carbon black with 20% polytetrafluoroethylene generated up to 500 mg L-1 of H2O2 through the electrolysis of acidic medium at -0.8 V vs Ag/AgCl. Reactive Blue 19 dye was degraded most efficiently with H2O2 electrogenerated in the presence of Fe(II) ions, leading to removal of 95% of the original color and 39% of TOC at -0.8 V vs Ag/AgCl.

A remoção de CuII (10 mg L-1) complexado por ácido húmico comercial (100 mg L-1) foi estudada a diferentes densidades de corrente (30-80 mA cm-2) usando uma célula filtro-prensa, ânodo de Ti/Ru0.3Ti0.7O2 e cátodo de aço inoxidável. As eletrólises foram feitas com e sem membrana separando os compartimentos da célula [aniônica homogênea (Nafion R117), catiônica heterogênea (Ionac MC-3470) e aniônica heterogênea (Ionac MA-3475)]. A influência da membrana na velocidade de remoção de CuII foi maior com as catiônicas. Foi obtida eficiência de corrente de ca. 55% (Ionac MC-3470) para remoção de CuII a 30 mA cm-2. Combinando oxidação e redução, foi obtida remoção de 100% de CuII com eficiência de corrente de 75%. A etapa principal para a remoção é interação eletrostática com o ânodo, seguida pela difusão através da membrana e deposição sobre o cátodo. Adicionalmente, a degradação oxidativa de ácido húmico contribui com a velocidade de remoção de CuII.

The removal of CuII (10 mg L-1) complexed by commercial humic acid (100 mg L-1) was studied at different current densities (30-80 mA cm-2) using a filter-press cell, Ti/Ru0.3Ti0.7O2 anode and stainless steel cathode. The electrolyses were performed with and without membrane separating the cell compartments [(homogeneous anionic (Nafion R117), heterogeneous cationic (Ionac MC-3470) and heterogeneous anionic (Ionac MA-3475)]. The influence of the membrane on the rate of CuII removal was bigger for cationic membranes. Current efficiencies up to ca. 55% (Ionac MC-3470) for CuII removal at 30 mA cm-2 were obtained. By combining oxidation and reduction, 100% CuII removal was achieved at current efficiencies of 75%. The main path for the removal is the electrostatic interaction with the anode followed by diffusion through the membrane and deposition at the cathode. Additionally, the oxidative degradation of humic acid contributes to the rate of CuII removal.

Este trabalho apresenta um estudo comparativo da eficiência eletroquímica na eletrogeração de peróxido de hidrogênio in situ usando eletrodos da difusão gasosa modificados com os catalisadores orgânicos redox: 2-etilantraquinona, 2-terc-butilantraquinona e azobenzeno em meio de 0,1 mol L-1 H2SO4 + 0,1 mol L-1 K2SO4, pH = 1. A produção de peróxido de hidrogênio está diretamente relacionada ao potencial aplicado e a concentração dos catalisadores adicionados. A modificação dos eletrodos resultou em um aumento significativo no rendimento de H2O2 (30%) alcançando 850 mg L-1 e o sobrepotencial da reação de redução do oxigênio foi deslocado para valores menos negativos (400 mV vs Ag/AgCl para os eletrodos modificados com quinonas e 300 mV vs. Ag/AgCl para os eletrodos modificados com azobenzeno) comparado ao eletrodo de difusão gasosa não modificado, reduzindo o consumo de energia de 596,5 para 232,4 kWh kg-1. Os resultados indicaram que o melhor eletrodo para a eletrogeração do H2O2 é o eletrodo de difusão gasosa modificado com 10% de 2-etilantraquinona, o qual apresentou a melhor relação custo/benefício.

This paper reports a comparative study of the electrochemical performance of in situ hydrogen peroxide electrogeneration on gas diffusion electrodes modified by organic redox catalysts 2-ethylanthraquinone, 2-terc-butylanthraquinone and azobenzene in medium of 0.1 mol L-1 H2SO4 plus 0.1 mol L-1 K2SO4, pH = 1. Hydrogen peroxide generation proved strongly dependent on the applied potential and on the concentration of added catalysts. Electrode modifications led to a significant increase in H2O2 yield (30%) reaching 850 mg L-1, and the overpotential for oxygen reduction shifted to less negative values (400 mV vs Ag/AgCl for electrodes modified by quinones and 300 mV vs Ag/AgCl for electrodes modified by azobenzene) compared to noncatalyzed gas diffusion electrodes, resulting in reduced energy consumption of 596.5 to 232.4 kWh kg-1. The results indicated that the best electrode for H2O2 electrogeneration is the gas diffusion electrode modified with 10% of 2-ethylanthraquinone, offering the best cost to benefit ratio.

This paper presents some results that may be used as previous considerations to a hydrogen peroxide electrogeneration process design. A kinetic study of oxygen dissolution in aqueous solution is carried out and rate constants for oxygen dissolution are calculated. Voltammetric experiments on vitreous carbon cathode shown that the low saturation concentration drives the oxygen reduction process to a mass transfer controlled process which exhibits low values of limiting currents. Results have shown that the hydrogen peroxide formation and its decomposition to water are separated by 400 mV on the vitreous carbon surface. Diffusion coefficients for oxygen and hydrogen peroxide are calculated using data taken from Levich and Tafel plots. In a series of bulk electrolysis experiments hydrogen peroxide was electrogenerated at several potential values, and concentration profiles as a function of the electrical charged passed were obtained. Data shown that, since limiting current plateaus are poorly defined onto reticulated vitreous carbon, cathodic efficiency may be a good criterion for choosing the potential value in which hydrogen peroxide electrogeneration should be carried out.

This investigation reports the results of linear polarization of hot upset Ti-6Al-7Nb bar samples. Current-potential curves recorded in Hank’s solution were analyzed by correlating characteristics of passivation and microstructures obtained after processing. Results have shown that it is important to select temperature process and deformation rate as parameters when more noble potential values are required. Low deformation rate facilitates the formation of beta phase that is retained in the structure at room temperature shifting the corrosion potential to more positive values. However, samples hot compressed from 750°C to 1030 °C showed passive layer stability over a wide range of potentials extending from -0.15 V to 1.75 V vs SCE . Furthermore, passive films grown onto the Ti-6Al-7Nb samples surfaces have shown no sign of rupture for the processing conditions selected for this study.

Pure titanium shows very interesting characteristics such as high strength-to-weight ratio, very good corrosion resistance and excellent biocompatibility, which make this material appropriate for use in orthopedic and dental implants. Due to the mechanical properties of pure titanium, its use in implants is restricted to applications which involve moderate mechanical stress, such as dental implants. In applications where high mechanical strength is necessary, like orthopedic implants, it is appropriate to employ titanium-based alloys, which have better properties than pure titanium. The present work is related to the microstructure and corrosion resistance characterization of the Ti-6Al-7Nb alloy, designed to be used in orthopedic prostheses.

The removal of lead from an acid borate-nitrate solution containing Pb(II) was used to characterize the mass transport properties of an electrolytic reactor with reticulated vitreous carbon cathodes, operated in the flow-through mode. Current potential curves recorded at a rotating vitreous carbon disc electrode were used to determine the diffusion coefficient for Pb(II) under the conditions of the experiments. The performance and figures of merit of the electrolytic reactor were investigated by using different flowrates and cathode porosities. Dimensionless Sherwood and Reynolds numbers were correlated to characterize the mass transport properties of the reactor, and they were fitted to the equation Sh=24Re0.32Sc0.33.