Electrochemical oxidation of p -chlorophenol on SnO2-Sb2O5 based anodes for wastewater treatment

The influence of an IrO2 interlayer between the Ti substrate and the SnO2-Sb2O5 coating on the electrode service life and on the efficiency of p-chlorophenol (p-CP) oxidation for wastewater treatment has been investigated. The results have shown that if the loading of the SnO2-Sb2O5 coating relative to the IrO2 interlayer loading (γ ratio defined by Equation 1) is high (γ = 20-30) the service life of the electrode can be increased without modification of the ability of this electrode to perform p-CP oxidation. This suggests that the oxidation of p-CP using a Ti/IrO2/SnO2-Sb2O5 electrode with high γ ratio (γ > 20) occurs only through the SnO2-Sb2O5 component of the electrode, with no interference of the IrO2 interlayer. However, the electrode potential at a given current density is considerably lower in the case of the Ti/IrO2/SnO2-Sb2O5 electrode. In order to explain this decrease in electrode potential we speculate that water is firstly discharged on IrO2, which is present in small amounts on the surface, forming hydroxyl radicals at a relatively low potential. These active hydroxyl radicals then migrate (spill over) towards the SnO2-Sb2O5 coating, where they are physiosorbed and react with p-CP leading to complete combustio

Mechanistic implications of zinc(II) ions on the degradation of phenol by the fenton reaction

A study of the interference of Zn2+ ions on phenol degradation by Fenton reaction (Fe2+/Fe3+ + H2O2) is reported. One of the first intermediates formed in the reaction, catechol, can reduce Fe3+ to Fe2+ and, in the presence of H2O2 initiates an efficient catalytic redox cycle. In the initial stages of the reaction, this catechol-mediated cycle becomes the principal route of thermal degradation of phenol and its oxidation products. The Zn2+ ion addition enhances the persistence time of catechol, probably by stabilization of the corresponding semiquinone radical via complexation

Interference of inorganic ions on phenol degradation by the Fenton reaction

The addition of Cu2+ ions to the classical Fenton reaction (Fe2+ plus H2O2 at pH 3) is found to accelerate the degradation of organic compounds. This synergic effect causes an approximately 15 % additional reduction of the total organic carbon (TOC), representing an overall improvement of the efficiency of the mineralization of phenol. Although Fe2+ exhibits a high initial rate of degradation, the degradation is not complete due to the formation of compounds refractory to the hydroxyl radical. The interference of copper ions on the degradation of phenol by the Fenton reaction was investigated. In the presence of Cu2+, the degradation is slower, but results in a greater reduction of TOC at the end of the reaction (t = 120 min). In the final stages of the reaction, when the Fe3+ in the solution is complexed in the form of ferrioxalate, the copper ions assume the role of the main catalyst of the degradation.Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), BrasiliaConselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), BrasiliaFUNDECTFUNDECTCNPqCNPqINCT CatalysisINCT- CatalysisFAPEALFAPEA

A influência do clareamento dental sobre a resistência de união de sistemas adesivos ao esmalte

Este estudo apresenta como o clareamento dos dentes afeta a resistência da união no esmalte dentário e o tipode fratura de três adesivos distintos - um adesivo convencional, auto-condicionante e um universal. Osincisivos bovinos foram preparados por aplainamento da superfície labial. Parte dos corpos de prova foisubmetida ao tratamento de clareamento com um produto à base de peróxido (WhiteGold Office® 35%). Osprodutos Single Bond®, AdheSE® e Single Bond Universal® foram utilizados para aderir em um bloco deresina restauradora à superfície plana dos dentes. Foram preparados corpos de prova em formato palitos comos dentes no tamanho de 10x1x1 mm, submetidos em testes de microtensão que também foram empregadospara examinar o tipo de fratura. Os resultados foram estatisticamente analisados pelo método ANOVA dedois fatores. Tanto para os corpos de prova não clareados como os clareados, os sistemas adesivos nãoapresentaram valores de resistência de tração estatisticamente diferentes. O estudo permitiu a tipificação de 4formas distintas de fratura, em que o tipo de fratura variava de coesiva do esmalte para as amostras clareadasaté o tipo fratura predominantemente coesiva à resina para os dentes não clareados, levando à conclusão deque o processo de clareamento exerceu um evidente efeito de enfraquecimento no esmalte, mesmo após 21dias pós-tratamento.Palavras-chave: Clareamento de dentes; sistemas adesivos; resistência de adesão; fratura; sistemarestaurador

Desenvolvimento de metodologia eletroquímica para degradação da ciprofloxacina por agentes oxidantes gerados in situ

Ciprofloxacin is second generation quinolones flour, which is very soluble in water. This drug can be found in Sewage Treatment Plants (STPs) and natural waters at concentrations of μg L-1 and ng L-1. Electrolysis was carried out using Ag/AgCl as reference electrode and as cathode and anode plates of Ti/TiO2 were used. To study the role of supporting electrolyte were used H2SO4, HCl, NaCl, NaNO3, KCl, and Na2SO4. Were applied current densities (DC) between 20 and 160 mA.cm-2. The electrodic process indicates be dependent on pH and ionic strength. Through electrolysis, the degradation /mineralization occurs more easily in the presence of Cl-

Transition Metals Doped Nanocrystals: Synthesis, Characterization, and Applications

Doping is a technique that makes it possible to incorporate substitutional ions into the crystalline structure of materials, generating exciting properties. This book chapter will comment on the transition metals (TM) doped nanocrystals (NCs) and how doping and concentration influence applications and biocompatibility. In the NCs doped with TM, there is a strong interaction of sp-d exchange between the NCs’ charge carriers and the unpaired electrons of the MT, generating new and exciting properties. These doped NCs can be nanopowders or be embedded in glass matrices, depending on the application of interest. Therefore, we show the group results of synthesis, characterization, and applications of iron or copper-doped ZnO nanopowders and chromium-doped Bi2S3, nickel-doped ZnTe, and manganese-doped CdTe quantum dots in the glass matrices

Electrochemical oxidation of p -chlorophenol on SnO2–Sb2O5 based anodes for wastewater treatment

The influence of an IrO2 interlayer between the Ti substrate and the SnO2-Sb2O5 coating on the electrode service life and on the efficiency of p-chlorophenol (p-CP) oxidn. for wastewater treatment has been investigated. The results have shown that if the loading of the SnO2-Sb2O5 coating relative to the IrO2 interlayer loading (g ratio defined by Equation 1) is high (g = 20-30) the service life of the electrode can be increased without modification of the ability of this electrode to perform p-CP oxidn. This suggests that the oxidn. of p-CP using a Ti/IrO2/SnO2-Sb2O5 electrode with high g ratio (g > 20) occurs only through the SnO2-Sb2O5 component of the electrode, with no interference of the IrO2 interlayer. However, the electrode potential at a given c.d. is considerably lower in the case of the Ti/IrO2/SnO2-Sb2O5 electrode. In order to explain this decrease in electrode potential we speculate that water is firstly discharged on IrO2, which is present in small amts. on the surface, forming hydroxyl radicals at a relatively low potential. These active hydroxyl radicals then migrate (spill over) towards the SnO2-Sb2O5 coating, where they are physiosorbed and react with p-CP leading to complete combustion

ESTUDO MECANÍSTICO DAS REAÇÕES FENTON E CUPRO-FENTON POR ANÁLISE VOLTAMÉTRICA IN SITU

Although the classical Fenton process exhibits a high initial rate of the organic compounds degradation, this process is not complete due to the formation of refractory compounds which resist the attack of the hydroxyl radicals. In the presence of Cu(II), the degradation is slower, but results in a greater reduction of TOC (total organic carbon) measurements of net mineralization at the end of the reaction (t=120min). The addition of Cu(II) ions to classical Fenton reaction conditions (Fe(II) plus H2O2 at pH 3) is shown to accelerate the degradation of organic compounds. This synergic effect causes an approximately 15% additional reduction of the TOC. Voltammetric studies confirm the catalytic role of catechol in the presence of Fe(III)/Fe(II) and Cu(II)/Cu(I). Addition of aliphatic acids to the reaction medium, did not interfere with the cupro-Fenton reaction, but had an inhibitory effect on the classical Fenton reaction, consistent with the following order of interaction with the ion Fe(III): Oxalic Acid (OA) >> Formic Acid (FA) ~ Acetic acid (AA)

PROSPECÇÃO TECNOLÓGICA DA APLICAÇÃO DE TRATAMENTO ELETROQUÍMICO E REAÇÃO DE FENTON NA REMEDIAÇÃO DE ÁGUA DE PRODUÇÃO DE BIODIESEL

Visando promover um mapeamento dos trabalhos relacionados ao uso de processos eletroquímicos e/ou da reação de Fenton na remediação de efluentes da produção de biocombustíveis, utilizou-se bancos de patentes (INPI, Derwent Innovations Index, WIPO, Espacenet e Lens) e de artigos (Periódicos), de forma a elucidar as tendências científicas e tecnológicas impostas a estas fontes alternativas de energia. Identificou-se a liderança de EUA e China tanto na produção científica quanto patentária no tema. Países como Brasil, Tailândia, Coreia do Sul e Colômbia foram identificados como bons desenvolvedores científicos, apesar da modesta produção tecnológica. Não foram encontradas citações de trabalhos ou patentes que agregassem simultaneamente a produção de biodiesel e o tratamento por meio de reação de Fenton e pela via eletro-oxidação. A maior parte das patentes identificadas com o tema está classificada com os códigos C02F, C12P, C10L e B01D