17 research outputs found
Screening process for activity determination of conductive oxide electrodes for organic oxidation
A modified method for the calculation of the normalized faradaic charge (q fN) is proposed. The method involves the simulation of an oxidation process, by cyclic voltammetry, by employing potentials in the oxygen evolution reaction region. The method is applicable to organic species whose oxidation is not manifested by a defined oxidation peak at conductive oxide electrodes. The variation of q fN for electrodes of nominal composition Ti/RuX Sn1-X O2 (x = 0.3, 0.2 and 0.1), Ti/Ir0.3Ti0.7O2 and Ti/Ru0.3Ti0.7O2 in the presence of various concentrations of formaldehyde was analyzed. It was observed that electrodes containing SnO2 are the most active for formaldehyde oxidation. Subsequently, in order to test the validity of the proposed model, galvanostatic electrolyses (40 mA cm-2) of two different formaldehyde concentrations (0.10 and 0.01 mol dm-3) were performed. The results are in agreement with the proposed model and indicate that this new method can be used to determine the relative activity of conductive oxide electrodes. In agreement with previous studies, it can be concluded that not only the nature of the electrode material, but also the organic species in solution and its concentration are important factors to be considered in the oxidation of organic compounds.Um método modificado para o cálculo da carga faradaica normalizada (q fN) é proposto. O método envolve a simulação de um processo de oxidação, por voltametria cíclica, empregando potenciais na região da reação de desprendimento de oxigênio (RDO). Este método é aplicável a espécies orgânicas, cuja oxidação não é manifestada por um pico de oxidação definido em eletrodos de óxidos condutores. A variação de q fN para eletrodos de composição nominal Ti/RuX Sn1-X O2 (x = 0,3; 0,2 e 0,1), Ti/Ir0,3Ti0,7O2 e Ti/Ru0,3Ti0,7O2, na presença de diferentes concentrações de formaldeído foi investigada. Foi observado que eletrodos contendo SnO2 são os mais ativos frente à oxidação de formaldeído. Subseqüentemente, para investigar a aplicabilidade do modelo proposto, eletrólises galvanostáticas (40 mA cm-2) de formaldeído foram efetuadas em duas concentrações distintas (0,10 e 0,01 mol dm-3). Os resultados estão de acordo com o modelo proposto e indicam que este novo método pode ser usado para determinar a atividade relativa de eletrodos de óxido. De acordo com trabalhos prévios, pode ser concluído que não somente a natureza do material eletródico, mas também a espécie orgânica em solução e a sua concentração são fatores importantes a serem considerados na oxidação de espécies orgânicas.FAPES
Cyclic voltammetric behaviour of dimensionally stable anodes in the presence of C1 - C3 aldehydes
Electrochemical degradation of the dye reactive orange 16 using electrochemical flow-cell
Electrochemical removals of color and organic load from solutions containing the dye reactive orange 16 (RO16) were performed in an electrochemical flow-cell, using a platinum working electrode. The influence of the process variables flow-rate, such as NaCl concentration, applied potential and solution pH, were studied. The best color removal achieved was 93% (λ = 493 nm) after 60 min at 2.2 V vs. RHE electrolysis, using 1.00 g L-1 NaCl as supporting electrolyte. The rises in the concentration of NaCl and applied potential increased the color removal rate. The best total organic carbon removal (57%) was obtained at 1.8 V, without the separating membrane, indicating that the ideal conditions for the color removal are not necessarily the same as those to remove the total organic carbon. The degradation efficiency decreased with the solution pH decrease.As remoções eletroquímicas de cor e do conteúdo orgânico de soluções do corante laranja reativo 16 (RO16) foram efetuadas usando uma célula em fluxo e um eletrodo de trabalho de Pt. As influências das variáveis do sistema, tais como fluxo, concentração de NaCl, potencial aplicado e pH da solução, foram estudadas. A melhor remoção de cor foi de 93% (λ = 493 nm) após 60 min de eletrólise potentiostática a 2,2 V vs. ERH, usando 1,00 g L-1 NaCl como eletrólito suporte. Os aumentos na concentração de NaCl e do potencial aumentam a velocidade de remoção de cor. A melhor remoção de carbono orgânico total (57%) foi obtida com a aplicação de 1,8 V, sem membrana de separação, indicando que as melhores condições para remoção de cor não são necessariamente as melhores para remover conteúdo orgânico. A eficiência de degradação diminui com a diminuição do pH da solução.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPES
Electrochemical degradation of the dye reactive orange 16 using electrochemical flow-cell
Electrochemical removal of CuII in the presence of humic acid
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.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.651658Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES
Antimicrobial activity and chemical constituents of essential oils and oleoresins extracted from eight pepper species
Cyclic voltammetric behaviour of dimensionally stable anodes in the presence of C1 - C3 aldehydes
This work describes the cyclic voltammetry study of three aliphatic aldehydes: formaldehyde, acetaldehyde and propionaldehyde at dimensionally stable anodes (DSA®). Electrodes of nominal composition Ti/Ru0.3M0.7O2 (where M = Ti ou Sn) were used in 0.5 mol dm-3 H2SO4 in a filter-press cell. Both electrodes exhibit behaviour typical of such materials in the presence of formaldehyde. However, with acetaldehyde and propionaldehyde non-typical behaviour is observed. This is characterised by a fall in the normalised faradaic anodic charge (q nf) and also a decrease in the current density associated with the oxygen evolution reaction (OER). A possible reaction mechanism, considering the direct oxidation of the aldehyde at the electrode surface, is suggested
The galvanostatic oxidation of aldehydes to acids on Ti/Ru0.3Ti0.7O2 electrodes using a filter-press cell
Results for the galvanostatic oxidation of formaldehyde, acetaldehyde, propionaldehyde and n-butyraldehyde in 0.5 mol dm-3 H2SO4 at Ti/Ru0.3Ti0.7O2 DSA® type electrodes, using a filter-press cell, are presented. The observed products are the respective carboxylic acids and CO2. In the case of formaldehyde the additional presence of CO3(2-) is detected as a product. The carbon balance is observed to decrease with electrolysis time due to the partial liberation of the aldehyde in solution as a gas. The partial liberation of aldehyde gases increases with chain length and in this way the conversion of reactants to products decreases, as does the efficiency of the electro-oxidation process
Cyclic voltammetric behaviour of dimensionally stable anodes in the presence of C1 - C3 aldehydes
This work describes the cyclic voltammetry study of three aliphatic aldehydes: formaldehyde, acetaldehyde and propionaldehyde at dimensionally stable anodes (DSA®). Electrodes of nominal composition Ti/Ru0.3M0.7O2 (where M = Ti ou Sn) were used in 0.5 mol dm-3 H2SO4 in a filter-press cell. Both electrodes exhibit behaviour typical of such materials in the presence of formaldehyde. However, with acetaldehyde and propionaldehyde non-typical behaviour is observed. This is characterised by a fall in the normalised faradaic anodic charge (q nf) and also a decrease in the current density associated with the oxygen evolution reaction (OER). A possible reaction mechanism, considering the direct oxidation of the aldehyde at the electrode surface, is suggested