Sílvio C. de Oliveira

An Organic Aqueous Gel as Electrolyte for Application in Electrochromic Devices Based in Bismuth Electrodeposition

The purpose of this work was to study the deposition/dissolution behavior of bismuth in an aqueous electrolytic gel media from the point of view of electrochromic phenomena. The gel was made from a derivative polymer of animal protein. This polymer is extremely consistent, and it becomes a transparent gel from 350 to 850 nm ~visible region!. Moreover, voltammetry and chronoamperometry experiments have shown that the bismuth deposition/dissolution has excellent electrochemical reversibility with a large variation of transmittance values ~around 60%! when Cu

Application of Different Advanced Oxidation Processes for the Degradation of Organic Pollutants

Water is not only an economic, but also an increasingly important social commodity. Potable water is an essential resource for sustaining economic and social development in all sectors. A safe water supply and appropriate sanitation are the most essential components for a healthy and prosperous life. However, increases in human activities have led to exposure of the aqueous environment to chemical, microbial and biological pollutants as well as to micropollutants. Thus, liquid effluents containing toxic substances are generated by a variety of chemistry-related industrial processes, as well as by a number of common household or agricultural applications.

Degradation of 4-aminoantipyrine by electro-oxidation with a boron-doped diamond anode: Optimization by central composite design, oxidation products and toxicity

Electro-oxidation with electrogenerated H2O2 (EO-H2O2) was applied to treat acidic aqueous solutions of 4-aminoantipyrine (4-AA), a persistent drug metabolite of dipyrone, in sulfate medium. Trials were made using a boron-doped diamond anode in the presence of H2O2 electrogenerated on site. A 24 central composite design (CCD) was employed to evaluate the effect of four independent variables, namely current density (j), pH, 4-AA concentration and electrolysis time, on the percentages of degradation and mineralization, as well as on mineralization current efficiency (MCE). Predicted responses agreed with observed values, showing linear trendlines with good R2 and R2adj values. The degradation was optimum at j=77.5mAcm-2, pH3.5 and 62.5mgL-1 4-AA, leading to 63% and 99% removal after 3 and 7min, respectively. For those solutions, the largest mineralization was found at j=77.5mAcm-2, attaining 45% abatement at 175min. Low MCE values were obtained in all electrolyses. An initial route for 4-AA degradation is proposed based on one dimer and eleven aromatic and aliphatic intermediates detected in the treated solutions at pH3.5 by LC-MS. The initial 62.5mgL-1 solution at pH3.5 presented acute toxicity on Artemia salina larvae, with LC50=13.6mgL-1, being substantially reduced after 3 and 7min of EO-H2O2 at j=77.5mAcm-2 due to the formation of less toxic derivatives.

Influence of chelation on the Fenton-based electrochemical degradation of herbicide tebuthiuron

This study describes the performance of electro-Fenton (EF) and photoelectro-Fenton (PEF) processes to degrade the herbicide tebuthiuron (TBH) in 0.050 M Na2SO4 at pH = 3.0. Experiments were performed in an undivided cell equipped with a boron-doped diamond (BDD) or Pt anode and an air-diffusion cathode that produces H2O2. Physisorbed hydroxyl radicals (M(OH)) generated from water oxidation at the anode and/or free OH formed from Fentons reaction acted as main oxidants. All processes became much more effective using a BDD anode because of the higher oxidation power of BDD(OH). Sulfate and nitrate were the predominant ions released during TBH destruction. In both, EF and PEF treatments, two distinct kinetic regimes were observed, the first one corresponding to the oxidation of free TBH by OH and the second one to that of the Fe(III)-TBH complex by M(OH). The effect of Fe2+ and TBH concentrations on the kinetics of both regions has been examined. Moreover, a poor mineralization was reached with Pt anode, whereas almost total mineralization was attained by EF and PEF with BDD. Both processes showed analogous mineralization rates because the intermediates produced could not be photodegraded by UVA light. Gas chromatography-mass spectrometry analysis of electrolyzed solutions revealed the generation of eight heteroaromatics along with 1,3-dimethylurea, which have been included in a reaction pathway proposed for the initial degradation of TBH.

Use of Natural Rubber Membranes as Support for Powder TiO2and Ag/TiO2 Photocatalysts

The purpose of this study was to synthesize TiO2-polymer composites able to act as photocatalyst membranes. TiO2 catalysts were prepared using the sol-gel method to contain 0.0, 0.5, 1.0, and 2.0 wt.% of embedded Ag particles, subsequently incorporated into natural rubber latex at a weight fraction of 15%. Samples of these ceramic powders were suspended in a latex emulsion (natural rubber), cast in Petri dishes and slowly dried in an oven. The resulting materials were evaluated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, diffuse reflectance spectroscopy, differential scanning calorimetry, thermogravimetry, and photocatalytic assaying using methylene blue as an organic pollutant reference. All composite membranes exhibited good photoactivity conferred by TiO2 powder, with 98% dye fading after 300 min of ultraviolet irradiation.

H2O2-assisted photoelectrocatalytic degradation of Mitoxantrone using CuO nanostructured films: Identification of by-products and toxicity

CuO nanostructured thin films supported on silicon with 6.5 cm2 area (geometric area greater than the studies reported in the literature) were synthesized by a chemical bath deposition technique. The electrodes were characterized by MEV, XRD, XPS, contact angle, cyclic voltammetry and electrochemical impedance spectroscopy analyses. To evaluate the photoelectrochemical properties of the CuO films, photocurrent-voltage measurements were performed using linear voltammetry. The catalytic activities of CuO nanostructures were evaluated by monitoring photodegradation of Mitoxantrone (MTX) under UV-A light irradiation. The method of photoelectrocatalysis (PEC), applying a voltage of 1.5 V and assisted by adding H2O2, was undertaken. To the best of our knowledge, no studies on the degradation of anticancer agents using PEC process have been found in the literature. For comparison purposes, experiments were performed under the same conditions by assisted photocatalysis (PC) with H2O2 and direct photolysis. CuO deposits consist of a needle-like morphology. The presence of CuO in the tenorite phase was evidenced by XRD and the XPS spectra showed the presence of copper(II) oxide. The increase in current under illumination shows that CuO exhibits photoactivity. The PEC system showed a 75% level of MTX degradation, while the level achieved using PC was 50%. Under UV-A light alone only 3% removal was obtained after 180 min. Up to 10 by-products were identified by chromatography-mass spectrometry (LC-MS) with m/z values ranging between 521 and 285 and a plausible degradation route has been proposed. It is worth mentioning that 9 by-products identified in this work, were not found in the literature in other studies of degradation or products generated as metabolites. The toxicity tests of MTX before and after PEC treatment with Artemia Salina and Allium cepa showed a decrease in the acute toxicity of the medium as the antineoplastic was degraded.

Influence of electrolysis conditions on the treatment of herbicide bentazon using artificial UVA radiation and sunlight. Identification of oxidation products

The main objective of this work is to demonstrate the viability of solar photoelectro-Fenton (SPEF) process to degrade pesticides in urban wastewater matrix, selecting the herbicide bentazon as a model molecule. In order to provide a correct assessment of the role of the different oxidants and catalysts involved, bentazon was comparatively treated by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and UVA-assisted EF (i.e., PEF) processes as well, either in sulfate or chloride media. Trials were made in a stirred tank reactor with an air-diffusion cathode and a boron-doped diamond (BDD), RuO2-based or Pt anode. In chlorinated matrices, the herbicide disappeared more rapidly using a RuO2-based anode because of the generated active chlorine. The best mineralization performance was always obtained using BDD due to its higher oxidation power, which allowed the complete destruction of refractory chloroderivatives. A concentration of 0.50 mM Fe2+ was found optimal to catalyze Fentons reaction, largely enhancing the mineralization process under the action of OH. Among photo-assisted treatments, sunlight was proven superior to a UVA lamp to promote the photolysis of intermediates, owing to its greater UV irradiance and contribution of visible photons, although PEF also allowed achieving a large mineralization. In all cases, bentazon decay obeyed a pseudo-first-order kinetics. SPEF treatment in urban wastewater using BDD at only 16.6 mA cm-2 yielded 63.2% mineralization. A thorough, original reaction pathway for bentazon degradation is proposed, including seven non-chlorinated aromatics, sixteen chloroaromatics and two chloroaliphatics identified by GC-MS, most of them not previously reported in literature. Ion-exclusion HPLC allowed the detection of seven short-chain linear carboxylic acids.

Kobalt (III) Oksihidroksit Yardımıyla Fipronilin Elektrokimyasal Tespiti İçin Matematiksel Açıklama

Bu calismada, kobalt (III) oksihidroksit kullanilarak fipronil pestisidinin elektrokimyasal tespit olasiligi belirlenmistir. Bu islemde redoks cifti CoO(OH)/CoO 2 kullanilmistir. Karsilik gelen matematiksel model, dogrusal kararlilik teorisi ve bifurkasyon analizi vasitasiyla gelistirilmis ve analiz edilmistir. Oksihidroksidin, notr ve hafif alkali ortamda fipronilin saptanmasinda etkili bir elektrot degistirici olarak uygulanabilecegi gosterilmistir. Elektrokimyasal cevabin acik ve kolay anlasilir oldugu belirlenmistir. Titresimli ve monotonik istikrarsizlik olasiligi da calismada dogrulanmistir.

Kinetic studies of the reaction between pesticides and hydroxyl radical generated by laser flash photolysis

BACKGROUND Due to contamination of the environment by pesticides and their mishandling, there is the need for treatment of contaminated sites and correct disposal of materials containing them. Thus, studies with advanced oxidation processes are expanding and can determine the rate constant of the hydroxyl radical with organic compounds of great importance in environmental contamination. In this context, the use of laser flash photolysis has been shown to be viable for the determination of these constants. RESULTS The reaction rate constants of different pesticides with HO(•) in degassed acetonitrile have been determined. They were 1.6 × 10(9)  M(-1)  s(-1), 0.6 × 10(9)  M(-1)  s(-1), 1.2 × 10(9)  M(-1)  s(-1), 2.4 × 10(9)  M(-1)  s(-1) and 2.2 × 10(9)  M(-1)  s(-1) for the pesticides carbaryl, propoxur, fenoxycarb, ethoxysulfuron and chlorimuron-ethyl, respectively. These values are about an order of magnitude smaller than the diffusion controlled rate and correlate with the relative rates of disappearance of the pesticides in the photo-Fenton reaction in water. CONCLUSION The correlation of the relative rate constants determined by laser flash photolysis with the relative rates of photo-Fenton degradation of the pesticides is compelling evidence for the participation of the hydroxyl radical in the degradation of these pesticides in the latter system.

Electrochromic Behavior of Vanadium Oxide Nanostructures Synthesized by Melt Sonoquenching

This paper reports a new procedure for V2O5 synthesis using the combination of two traditional methods, melt quenching and sonochemistry, called melt sonoquenching. The resulting nanomaterial was characterized by several methods in order to verify physical and chemical characteristics, and its possible use as electrochromic electrode material. Scanning electron micrographs revealed V2O5 nanofibers with lengths varying from 140 to 160 nm, and diameters varying from 10 to 15 nm, X-ray diffraction experiments pointed to an amorphous structure with an interlamellar spacing of 13.3 Å. Chemical composition was estimated by TGA, suggesting that the composition for such xerogel oxide was V2O5.1.8H2O. Besides these, spectroelectrochemical characterization showed a transmittance variation of 45 % at 410 nm, with coloration persistence of 91.3 %, response times for the oxidation and reduction were, respectively, 1 s and 3.5 s, being such electrochomic efficiency of 55 cmC in throughout 100 cycles of color changes from blue-green-orange.