The Direct Black 22 dye was electrooxidized at 30 mA cm-2 in a flow cell using a BDD or β-PbO2 anode, varying pH (3, 7, 11), temperature (10, 25, 45 °C), and [NaCl] (0 or 1.5 g L-1). In the presence of NaCl, decolorization rates were similar for all conditions investigated, but much higher than predicted through a theoretical model assuming mass-transport control; similar behavior was observed for COD removal (at pH 7, 25 °C), independently of the anode. With no NaCl, COD removals were also higher than predicted with a theoretical model, which suggests the existence of distinct dye degradation pathways.

A remoção de íons Pb2+ a partir de soluções diluídas foi estudada, em condições galvanostáticas, usando uma célula de fluxo sem membrana com eletrodos de esponja de aço inoxidável (SSW). A metodologia de superfície de resposta (variáveis independentes: corrente elétrica e vazão) foi usada para obter as condições ótimas para a remoção de Pb2+ a partir de 2 L de uma solução de Pb(NO3)2 50 mg L-1 em NaNO3 0,10 mol L-1 + H3BO3 0,10 mol L-1 (pH 4,8). A partir das superfícies de respostas, concluiu-se que a vazão (59-341 L h-1) não influencia significativamente no processo de remoção de Pb2+. Por outro lado, o aumento da corrente elétrica leva a uma maior remoção de Pb2+, com valores significantemente melhores de consumo de energia específica e eficiência de corrente quando comparados àqueles relatados na literatura. Para um experimento realizado na região de condições ótimas (70 mA e 200 L h-1), uma conversão de Pb2+ de 99,6% foi atingida depois de 90 min de eletrólise. A utilização da célula de fluxo sem membrana com eletrodos de SSW, além de ser energeticamente mais eficiente, levou à remoção de Pb2+ em ambos os eletrodos, mais predominantemente no anodo, sobre o qual 95% dos íons Pb2+ foram convertidos a PbO2.

The removal of Pb2+ ions from dilute solutions was investigated under galvanostatic conditions using a membrane-less flow-through cell with stainless steel wool (SSW) electrodes. The response surface methodology (independent variables: electric current and volumetric flow rate) was used to find the optimal conditions for Pb2+ removal from 2 L of an aqueous solution of 50 mg L-1 Pb(NO3)2 in 0.10 mol L-1 NaNO3 + 0.10 mol L-1 H3BO3 (pH 4.8). The obtained response surfaces revealed that the volumetric flow rate (59-341 L h-1) does not substantially affect the Pb2+ removal process. On the other hand, the electric current increase led to higher Pb2+ removal, with significantly improved values of specific energy consumption and current efficiency when compared with those reported in the literature. For an experiment carried out in the optimum-condition region (70 mA and 200 L h-1), a Pb2+ conversion of 99.6% was attained after 90 min of electrolysis. The use of the membrane-less flow-through cell with SSW electrodes, besides being significantly more energy efficient, led to Pb2+ removal on both electrodes, but predominantly in the SSW anode, on which more than 95% of the Pb2+ ions were converted to PbO2.

The electrochemical performance of electrodeposited Ti/β-PbO2 and Ti-Pt/β-PbO2 anodes was galvanostatically evaluated (batch mode, 50 mA cm-2) to degrade the Direct Yellow 86 dye (100 or 200 mg L-1 in 0.1 mol L-1 Na2SO4 + 1.5 g L-1 NaCl), investigating the effect of pH and temperature. Similar results were obtained for both electrodes and the best conditions for removal of color and chemical oxygen demand are pH 7 and 40 °C, when 90% decolorization is attained by passing a charge of only ~0.13 A h L-1 and total mineralization is achieved with expenditure of ~5 kW h m-3.

A degradação eletroquímica do corante Vermelho Reativo 141 foi investigada por meio da aplicação da metodologia de superfície de respostas, utilizando reator filtro-prensa com anodo de β-PbO2. A carga requerida para 90% de descoloração (Q90) e a remoção da demanda química de oxigênio após 30 min de eletrólise (COD30) foram utilizadas para modelar o sistema. As variáveis investigadas foram a densidade de corrente, pH, concentração de NaCl e temperatura. Baixos valores de Q90 (0,2-0,3 A h L-1) foram obtidos em condições ácidas (pH 1-3) e em altas concentrações de NaCl (1,0-2,0 g L-1), quando as espécies oxidantes Cl2 e HOCl estão presentes. Os melhores valores para COD30 foram obtidos com altas densidades de corrente e em condições de pH ácido a neutro; entretanto, o consumo energético resultante torna o processo economicamente não viável. Para soluções extremamente ácidas foram obtidos valores reduzidos de consumo de energia, relacionado ao Q90, em torno de 0,79 kW h m-3.

The electrochemical degradation of the Reactive Red 141 dye using a filter-press reactor with a β-PbO2 anode was investigated through the application of the response surface methodology. The charge required for 90% decolorization (Q90) and the chemical oxygen demand removal percentage after 30 min electrolysis (COD30) were used to model the system. The investigated independent variables were the current density, pH, NaCl concentration, and temperature. Low values of Q90 (0.2-0.3 A h L-1) were obtained at acidic conditions (pH 1-3) and high concentrations of NaCl (1.0-2.0 g L-1), when Cl2 and HOCl are the predominant oxidant species. The best values of COD30 were obtained at high current densities and acidic to neutral conditions (pH 5-7); however, the consequent energy consumption makes the process not economically feasible under these conditions. For strongly acidic solutions, specific energy consumptions associated to Q90 as low as 0.79 kW h m-3 were attained.

The physical and electrochemical properties of Ti-SnO2/Sb electrodes obtained by the thermal decomposition of solutions of the precursor salts SnCl2×2H2O/SbCl3 and SnSO4/Sb2(SO4)3 were investigated. The reversibility of the cyclic voltammetric response of the Fe(CN)6(4-)/Fe(CN)6(3-) redox couple was assessed using the obtained electrodes. Their catalytic activity for the oxygen-evolving reaction and maximum capacity for electronic transfer were also evaluated by potential and current linear scans in 0.5 mol L-1 H2SO4. Additionally, scanning electron microscopy analyses allowed the visualization of the morphology of the oxide films obtained. The best results were presented by the electrodes obtained from the chloride salt precursors.

Filmes de óxidos coloridos foram crescidos sobre amostras de aço inoxidável AISI 304 por métodos químico e eletroquímicos usando diferentes tempos de coloração. Os métodos eletroquímicos utilizados foram pulsos alternados de potencial e varreduras triangulares de corrente. Os filmes coloridos foram caracterizados na região do visível por espectrofotometria no modo de refletância. A resistência à corrosão por pites das diferentes amostras coloridas foi avaliada a 25 ºC em NaCl 0,62 mol L-1, usando curvas de polarização potenciodinâmicas, e em HCl 0,40 mol L-1, por espectroscopia de impedância eletroquímica. Independentemente do método de coloração usado, os filmes de óxido colorido apresentam um efeito protetor contra a corrosão por pites somente nas primeiras horas de exposição. Para tempos de exposição mais longos (8-10 h), as amostras de aço coloridas ou não coloridas apresentaram comportamentos semelhantes.

Colored oxide films were grown on AISI-304 stainless-steel samples by chemical and electrochemical methods using different coloring times. The electrochemical methods involved the use of alternating potential pulses and triangular current scans. The colored films were characterized in the visible region by reflectance spectrophotometry. Pitting corrosion resistance of the different colored steel samples was evaluated at 25 ºC in 0.62 mol L-1 NaCl, using potentiodynamic polarization curves, and in 0.4 mol L-1 HCl, by electrochemical impedance spectroscopy. Independently of the coloring method used, the colored oxide films showed a protective effect against pitting corrosion only in the first hours of exposition. For longer exposition times (8-10 h) the colored and non-colored steel samples presented similar behaviors.

As propriedades eletroquímicas de compósitos do tipo Pani(DMcT-íon Cu)/fibra de carbono, obtidos eletroquimicamente, são analisadas em função tanto do procedimento de preparação como do sal de cobre (CuCl2.2H2O ou CuSO4) utilizado para a incorporação de íons Cu2+ no compósito. Dois procedimentos foram utilizados: adicionando-se o sal de cobre diretamente ao eletrólito durante a eletropolimerização da polianilina (procedimento A), ou adsorvendo-se os íons cobre juntamente com o DMcT sobre a fibra de carbono antes da eletropolimerização (procedimento B). A estabilidade eletroquímica, as propriedades elétricas e a morfologia desses compósitos foram analisadas, por voltametria cíclica, espectroscopia de impedância eletroquímica e microscopia eletrônica de varredura, respectivamente.

The electrochemical properties of Pani(DMcT-Cu ion)/carbon fiber composites, obtained by electrochemical means, are analysed as a function of the preparation procedure and the different copper salts (CuCl2.2H2O or CuSO4) used as source of Cu2+ ions to be incorporated into the Pani(DMcT)/carbon fiber composite. The composites were prepared according to two procedures: by adding the copper salt directly to the electrolyte during the polyaniline electrosynthesis (procedure A), or by allowing the copper ion to be physically adsorbed onto the carbon fiber prior to the polymer electroformation (procedure B). The electrochemical stability, electrical properties and morphology of the composites were analysed by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy, respectively.

Estudos sobre a estabilidade de óxidos anódicos crescidos sobre zircônio e suas ligas biocompatíveis Ti-50Zr %at. e Zr-2,5Nb %m., em solução fisiológica de Ringer aerada, a 25 e 37 ºC, foram feitos por meio da comparação entre as cargas de sua formação e de sua reconstrução após dissolução a circuito aberto na solução fisiológica. A estabilidade de óxidos crescidos na solução de Ringer e em solução de Na2SO4 0,15 mol L-1 foi comparada. Os resultados obtidos mostram que a estabilidade desses óxidos é aumentada por envelhecimento sob condições potenciostáticas e que ela pode ser decrescida pela presença de íons cloreto no eletrólito durante o processo de anodização.

Studies on the stability of anodic oxides grown on zirconium and its biocompatible alloys Ti-50Zr at.% and Zr-2.5Nb wt.%, in aerated Ringer physiological solution, at 25 and 37 °C, were carried out by comparing their formation charge and their reconstruction charge after dissolution at open circuit in the physiological solution. The stability of oxides grown in the Ringer solution and in a 0.15 mol L-1 Na2SO4 solution was compared. The obtained results show that the stability of these oxides is increased by aging under potentiostatic conditions and can be decreased by the presence of chloride ions in the electrolyte during the anodization process.

An analysis of the different activities carried out during the first twenty annual meetings (1978-1997) of the Brazilian Chemical Society (SBQ) is presented. The number of papers in the abstract book increased from around 300 in the biennium 78/79 to around 1230 in 96/97. The papers contained in the different sections of the abstract book in the 1st (1978), 10th (1987) and 19th (1996) annual meetings were grouped according to the regions of Brazil the authors' institutions were from, or abroad, and also considering whether the paper came from one institution or was a collaboration between two or more institutions. The relative contribution of the southeastern and northern regions decreased from 77% and 3.0% of the total in 1978 to 63% and 1.2% in 1996, respectively, while those of the northeastern, southern and midwestern regions increased from 12%, 4.8% and 0.6% to 15%, 13%, and 2.6%, respectively; the relative contribution of institutions from abroad also increased from 2.4% to 4.0%. Chemistry of Natural Products and Organic Chemistry decreased their relative contribution from around 55% in 1978 to around 28% in 1996, an evolution towards a more balanced development of the different areas of chemistry in Brazil.

Utilizando-se a espectroscopia de impedância eletroquímica, foram estudadas as propriedades elétricas e semicondutoras de filmes anódicos passivos formados potenciostaticamente (1 V £ Ef £ 5 V vs. ecs) sobre eletrodos de nióbio policristalino em soluções aquosas de H3PO4 0,5 mol/L (pH 1,3), a temperatura ambiente. Os dados foram analisados com uma função de transferência usando uma rotina de ajuste não-linear, supondo que a resistência do filme está acoplada em série com a impedância faradaica da reação Nb(0) Nb(V) e estas em paralelo com a capacitância da interface filme/eletrólito. A permissividade relativa dos filmes foi estimada como cerca de 44. Encontrou-se que a concentração em número de doadores (N D) nos filmes decresce com Ef (isto é, à medida que a espessura do filme aumenta). A partir de gráficos de Mott-Schottky, também obteve-se um valor de -0,72 V para o potencial de banda plana.

The electrical and semiconducting properties of thin anodic passive films potentiostatically formed (1 V £ Ef £ 5 V vs. sce) on polycrystalline niobium electrodes in aqueous 0.5 mol/L H3PO4 solutions (pH 1.3) were studied, at room temperature, using electrochemical impedance spectroscopy. The data were analysed with a transfer function using a non-linear fitting routine, assuming that the resistance of the film is coupled in series with the faradaic impedance of the Nb(0) Nb(V) reaction, and these in parallel with the capacitance of the passive film/electrolyte interface. The relative permittivity of the films was estimated as about 44. The number concentration of donors (N D) in the films was found to decrease with Ef (i.e., with increasing film thickness). A flat band potential value of -0.72 V was also obtained from Mott-Schottky plots.