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A comparative study of the electrogeneration of hydrogen peroxide using Vulcan and Printex carbon supports

ASSUMPCAO, M. H. M. T.; SOUZA, R. F. B. De; RASCIO, D. C.; SILVA, J. C. M.; CALEGARO, M. L.; GAUBEUR, I.; PAIXAO, T. R. L. C.; HAMMER, P.; LANZA, M. R. V.; SANTOS, M. C.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
25.75%
A comparative study of two different conductive carbon-black pigments, Vulcan XC-72 R and Printex L6, for the electrogeneration of hydrogen peroxide (H(2)O(2)) by reducing dissolved oxygen in an alkaline solution was performed. The materials were physically characterized by X-ray diffraction (XRD), Fourier transform infrared attenuated total reflection (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). XRD shows the presence of SO(2) and ATR-FTIR technique indicates a difference in NO and SO(2) functional groups between the two carbon pigments. XPS indicated presence of SO and NO and more oxygenated acid species on Printex L6. A rotating ring-disk electrode was used for electrochemical analysis of the oxygen reduction reaction (ORR). The results showed that the Printex L6 was better than Vulcan XC-72 R for H(2)O(2) production. Results also indicate that the number of electrons transferred in the ORR for Printex L6 and Vulcan XC-72 R were 2.2 and 2.9, respectively, while the percentages of H(2)O(2) formed were 88% and 51%. Scanning electrochemistry microscopy images confirmed the higher amount of H(2)O(2) formed in the Printex L6 pigment. Printex L6 was shown to be a more promising for H(2)O(2) production than Vulcan XC-72 R, while the latter was shown to have more potential for fuel cells. (C) 2011 Elsevier Ltd. All rights reserved.; CNPq[577292/2008-0]; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[2005/59992-6]; FAPESP[2008/58789-0]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[2009/09145-6]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[2009/07859-1]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[2010/04539-3]; FAPESP[2007/04759-0]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[2010/07831-7]; UFABC; UFABC[2010/07831-7]; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES[2005/59992-6]; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES[2008/58789-0]; CAPES[2009/09145-6]; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES[2009/07859-1]; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES[2010/04539-3]; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES[2007/04759-0]; CAPES[2010/07831-7]; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Mechanistic changes observed in heavy water for nitrate reduction reaction on palladium-modified Pt(hkl) electrodes

Garcia, Janaina de Souza; Ticianelli, Edson Antonio; Climent, V.; Feliu, J. M.
Fonte: ROYAL SOC CHEMISTRY; CAMBRIDGE Publicador: ROYAL SOC CHEMISTRY; CAMBRIDGE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
25.75%
Reduction of nitrate on palladium-modified platinum single-crystal electrodes has been investigated both voltammetrically and spectroscopically in acidic media (pH = 1). Results obtained in H2O and D2O solvents are compared for the three crystallographic orientations. FTIR and differential electrochemical mass spectrometry (DEMS) results clearly indicate that the isotopic substitution of the solvent has a large effect in the mechanism of the reaction, changing the nature of the detected products. For Pt(111)/Pd and Pt(100)/Pd, N2O is detected as the main product of nitrate reduction when D2O is used as solvent, while no N2O is detected when the reaction is performed in H2O. For Pt(110)/Pd, N2O is detected in both solvents, although the use of D2O clearly favours the preferential formation of this product. The magnitude of voltammetric currents is also affected by the nature of the solvent. This has been analysed considering, in addition to the different product distribution, the existence of different transport numbers and optical constants of the solvent.; MEC (Spain); MEC (Spain) [CTQ 2006-04071/BQU]; CAPES (Brazil); CAPES (Brazil); CNPq (Brazil); CNPq (Brazil)

Low content cerium oxide nanoparticles on carbon for hydrogen peroxide electrosynthesis

Assumpcao, M. H. M. T.; Moraes, A.; Souza, R. F. B. de; Gaubeur, I.; Oliveira, R. T. S.; Antonin, V. S.; Malpass, G. R. P.; Rocha, R. S.; Calegaro, M. L.; Lanza, M. R. V.; Santos, M. C.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
25.75%
A comparative study using different proportions of CeO2/C (4%, 9% and 13% CeO2) was performed to produce H2O2, a reagent used in the oxidation of organic pollutants and in electro-Fenton reactions for the production of the hydroxyl radical (OH center dot), a strong oxidant agent used in the electrochemical treatment of aqueous wastewater. The CeO2/C materials were prepared by a modified polymeric precursor method (PPM). X-ray diffraction analysis of the CeO2/C prepared by the PPM identified two phases. CeO2 and CeO2. The average size of the crystallites in these materials was close to 7 nm. The kinetics of the oxygen reduction reaction (ORR) were evaluated by the rotating ring-disk electrode technique. The results showed that the 4% CeO2/C prepared by the PPM was the best composite for the production of H2O2 in a 1 mol L-1 NaOH electrolyte solution. For this material, the number of electrons transferred and the H2O2 percentage efficiency were 3.1 and 44%, respectively. The ring-current of the 4% CeO2/C was higher than that of Vulcan carbon, the reference material for H2O2 production, which produced 41% H2O2 and transferred 3.1 electrons per molecule of oxygen. The overpotential for this reaction on the ceria-based catalyst was substantially lower (approximately 200 mV)...

Remocao de cobre (II) em eletrodos de platina-polipirrol e carbono vitreo reticulado

Hasse, Eloisa Elena Schwartz
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
25.75%
A remoção de íons Cu²+ de soluções ácidas diluídas é investigada utilizando eletrodos de Pt recobertos com polipirrol previamente reduzido (PPl) e eletrodos de carbono vítreo reticulado (CVR). O estudo tem por objetivo a redução de Cu²+ sobre ppl via reação espontânea e eletroredução a -0,40 V vs. eletrodo de calomelano saturado (ECS), e a eletroredução sobre CVR. Nestes experimentos, a concentração de íons Cu²+ remanescentes na solução é monitorada por voltametria de varredura linear ou por voltametria potenciodinâmica em um ultramicroeletrodo de platina (UME). Também o monitoramento por espectrometria de absorção atômica (EAA) foi realizado nos processos de remoção por eletrodeposição. Foi mostrado que o CVR é o material mais adequado para este fim. O cobre depositado sobre platina em meio sulfúrico exibe uma, duas ou três ondas de redissolução anódica, que correspondem respectivamente à oxidação de uma camada de cobre adsorvida sobre a platina, à oxidação de um filme fino depositado sobre a camada adsorvida e à oxidação do depósito de cobre denso que cresce sobre o filme fino. Este comportamento foi evidenciado por ciclos potenciodinâmicos impostos a um UME de disco de Pt na faixa de concentrações de Cu²+ entre 10-5 e 10-4 M em meio sulfúrico.; The removal of CU²+ ions from dilute acidic solutions is studied at Pt electrodes recovered with electrically neutral polypyrrole and at reticulated vitreous carbon electrodes...

Electrochemical Oxidation of Hydroxylamine on Gold in Aqueous Acidic Electrolytes: An in Situ SERS Investigation

Godoi, Denis R. M.; Chen, Youjiang; Zhu, Huanfeng; Scherson, Daniel
Fonte: Amer Chemical Soc Publicador: Amer Chemical Soc
Tipo: Artigo de Revista Científica Formato: 15711-15713
ENG
Relevância na Pesquisa
25.75%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); The electrooxidation of hydroxylamine (HAM) on roughened Au electrodes has been examined in aqueous buffered electrolytes (pH 3) using in situ surface-enhanced Raman scattering (SERS). Two distinct spectral features were observed at potentials, E, within the range in which HAM oxidation was found to ensue, centered at 803 cm(-1) for 0.55 < E < 0.8 V and at 826 cm(-1) for 1.0 < E < 1.40 V versus SCE, attributed, respectively, to adsorbed nitrite and adsorbed NO(2). Similar experiments performed in solutions containing nitrite instead of HAM under otherwise identical conditions displayed only the peak ascribed to adsorbed nitrite over the range of 0.1 < E < 0.8 V versus SCE with no additional features at higher potentials. These observations strongly suggest that under the conditions selected for these studies the oxidation of HAM on Au proceeds at least in part through a pathway that does not involve nitrite as a solution-phase intermediate.

Adsorption of dihydrogen phosphate ion on platinum electrodes in aqueous media monitored by probe-beam deflection

Bidoia, Ederio Dino
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1-4
ENG
Relevância na Pesquisa
25.75%
Probe-beam deflection (PBD) was used to monitor concentration gradients of anions adjacent to the surface of a platinum electrode in acidic aqueous media containing H3PO4. PBD can measure the potential-dependent extent of adsorption of H2PO4- on the Pt electrode surface and permits the Langmuir isotherm to be fitted to the experimental data. The value thus obtained for the surface concentration was 1.3 × 10-11 mol mm -2, or 1.7 atoms of Pt per H2PO4-. Also, the electron transfer number obtained was 0.24, signifying an incomplete transfer of charge, and the equilibrium constant is 1.80 suggesting a reversible adsorption process. © 2005 Elsevier B.V. All rights reserved.

Electrochemical study of arsenopyrite weathering

Almeida, CMVB; Giannetti, B. F.
Fonte: Royal Soc Chemistry Publicador: Royal Soc Chemistry
Tipo: Artigo de Revista Científica Formato: 604-610
ENG
Relevância na Pesquisa
25.75%
Cyclic voltammograms and capacitance measurements are presented to characterize the mineral response at relatively moderate environmental conditions, pH 4.5 and T = 25degreesC. The experiments involve examining the rates of oxidation and the surface morphology of arsenopyrite, which is oxidized abiotically. The semiconducting properties of the mineral have been investigated in attempt to gain additional information of FeAsS dissolution behavior in acidic solutions at potentials close to the open circuit potential of the mineral. A mechanistic pathway for the anodic dissolution of arsenopyrite in open circuit conditions is also suggested. At high overpotentials, anodic reactions produce mainly sulfate and arsenate ions and may be described as hole limited. The reduction of orpiment-like compounds at potentials more negative than the open circuit potential is discussed.

Caracterização de oxidos de manganes (IV) suportados em polietileno

Marcelo Ganzarolli de Oliveira
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/06/1987 PT
Relevância na Pesquisa
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Este trabalho teve como objetivo a caracterização de óxidos de manganês(IV) (MnO2) suportados em polietileno de alta e de baixa densidade (PEAD e PEBD) e obtidos por imersão cIos polímeros em soluções ácidas (H2SO4 e HNO3) de permanganato de potássio a 80°C. Os óxidos foram caracterizados morfologicamente e quanto à sua capacidade de adsorção de íon zinco, tendo esta sido relacionada à sua área superficial. Foi verificado que: a) as massas de MnO2 suportadas aumentam com o tempo de imersão e são maiores quando obtidas na presença de HN03 e sobre PEAD do que quando obtidas na presença de H2S04 e sobre PEBD. b) A área superficial dos óxidos diminui com o tempo de imersão e é maior para os óxidos obtidos na presença de HN03 e sobre PEAD do que para os óxidos obtidos na pre- sença de H2S04 e sobre PEBD. c) Tanto a secagem do óxido quando o seu envelhecimento levam a uma diminuição da área superficial. d) Micrografias de varredura eletrônica revelam que o óxido seco tem a forma de um gel macroporoso com muitas rachaduras. e) No processo de deposição a superfície do polímero é oxidada. A influência dos íons SO4 e NO¨ foi atribuída a adsorção dos mesmos sobre as cadeias poliméricas de MnO2. As maiores massas obtidas sobre PEBD foram relacionadas à maior mobilidade das cadeias do substrato. A diminuição da área superficial e a abertura de macroporos e rachaduras foi atribuída à contração do gel...

Estudo do pre-tratamento superficial de fios de aço inoxidavel ABNT 304 L para o processo de trefilação

Mara Terumi Fukunaga
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 02/03/1999 PT
Relevância na Pesquisa
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O tratamento térmico de recozimento é uma das etapas do processo de conformação plástica dos metais de trefilação para a produção de fios, devolvendo ao material a ductilidade perdida no estiramento. No entanto, provoca a formação de camadas de óxido prejudiciais a continuidade do processo de trefilação. A decapagem química tem como objetivo eliminar os produtos da oxidação, além de propiciar uma condição superficial que permita o recobrimento ou ancoragem do lubrificante antes do seguimento do processo. Com isso, pode-se notar que a realização do pré-tratamento na superfície do fio na trefilação tem grande importância e influencia na qualidade superficial do produto trefilado. Este trabalho apresenta o estudo do processo de pré-tratamento superficial através da utilização de vários ácidos decapantes, determinando qual a melhor composição da solução decapante, a concentração mais adequada, a temperatura e o melhor tempo de imersão no pré-tratamento de fios de aço inoxidável ABNT 304L nos diâmetros de 1,60mm e 3,00mm. Os resultados analisados estatisticamente e apresentados graficamente através da análise da rugosidade superficial e ganho de massa do lubrificante mostraram que a solução decapante de ácidos nítrico e clorídrico...

Cations extraction of sandy-clay soils from Cavado valley, Portugal, using sodium salts solutions

Silva, João Eudes da; Castro, F.
Fonte: Universidade de São Paulo Publicador: Universidade de São Paulo
Tipo: Artigo de Revista Científica
Publicado em //2002 ENG
Relevância na Pesquisa
25.75%
Cases of contamination by metals in the water wells of the Cavado Valley in north-west Portugal can be attributed to the heavy leaching of clay soils due to an excess of nitrogen resulting from the intensive use of fertilisers in agricultural areas. This work focuses on the natural weathering characteristics of soils, particularly the clay material, through the study of samples collected near the River Cavado. Samples taken from various sites, after physico-chemical characterisation, were subjected to clay dissolution tests, using sodium salts of different ionic forces, to detect the relationship between certain physico-chemical parameters of water, such as pH, nitrate, chloride and sulphate content, in the dissolution of clay and the subsequent extraction of such cations as Al, Fe and K. In acidic sandy clay soils, the mineralogical composition of which was characterised by a predominance of quartz, micas, kaolinite and K-feldspars, decreases of the clay material/water pH ratio increases dissolution of the micaceous and K-feldspars phases. The presence of nitrates in the aqueous solution apparently advanced the extraction of all three cations Al, Fe and K. The specific surface area of the clay material showed a significant correlation with the main kinetic parameters of cation extraction.; Têm ocorrido casos de contaminações de águas de poços...

Removal of Cr(VI) from aqueous solutions by a bacterial biofilm supported on zeolite : optimisation of the operational conditions and scale-up of the bioreactor

Pazos, M.; Branco, Mónica; Neves, Isabel C.; Sanromán, M. A.; Tavares, M. T.
Fonte: John Wiley & Sons, Inc. Publicador: John Wiley & Sons, Inc.
Tipo: Artigo de Revista Científica
Publicado em /12/2010 POR
Relevância na Pesquisa
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The aim of this study was to investigate the feasibility of a bioreactor system and its scale-up to remove Cr(VI) from solution. The bioreactor is based on an innovative process that combines bioreduction of Cr(VI) to Cr(III) by the bacterium Arthrobacter viscosus and Cr(III) sorption by a specific zeolite. Batch studies were conducted in a laboratory-scale bioreactor, taking into account different operating conditions. Several variables, such as biomass concentration, pH and zeolite pre-treatment, were evaluated to increase removal efficiency. The obtained results suggest that the Cr removal efficiency is improved when the initial biomass concentration is approximately 5 g L–1 and the pH in the system is maintained at an acidic level. Under the optimised conditions, approximately 100 % of the Cr(VI) was removed. The scale-up of the developed biofilm process operating under the optimised conditions was satisfactorily tested in a 150-L bioreactor.; Xunta de Galicia - programa Angeles Alvariño

Enhanced selective metal adsorption on optimised agroforestry waste mixtures

Rosales, E.; Ferreira, Laura; Sanromán, M. A.; Tavares, M. T.; Pazos, M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2015 ENG
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The aim of this work is to ascertain the potentials of different agroforestry wastes to be used as biosorbents in the removal of a mixture of heavy metals. Fern (FE), rice husk (RI) and oak leaves (OA) presented the best removal percentages for Cu(II) and Ni(II), Mn(II) and Zn(II) and Cr(VI), respectively. The performance of a mixture of these three biosorbents was evaluated, and an improvement of 10% in the overall removal was obtained (19.25 mg/g). The optimum mixture proportions were determined using simplexcentroid mixture design method (FE:OA:RI = 50:13.7:36.3). The adsorption kinetics and isotherms of the optimised mixture were fit by the pseudo-first order kinetic model and Langmuir isotherm. The adsorption mechanism was studied, and the effects of the carboxylic, hydroxyl and phenolic groups on metal–biomass binding were demonstrated. Finally, the recoveries of the metals using biomass were investigated, and cationic metal recoveries of 100% were achieved when acidic solutions were used.

Eléctrodos de filme fino de mercúrio para análise de metais vestigiais - estudos de optimização

Mendes, Sandra Cristina Conde Monterroso
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
POR
Relevância na Pesquisa
25.75%
No presente trabalho re-visitou-se a técnica electroanalítica de voltametria de redissolução anódica (ASV) aliada ao uso de eléctrodos de filme fino de mercúrio (TMFE) e de eléctrodos de filme fino de mercúrio revestidos com polímeros de troca iónica, principalmente para a determinação de metais vestigiais, mas também de compostos moleculares. Foram avaliados os efeitos combinados do pH, do ião tiocianato e do potencial de deposição nas características de eléctrodos de filme de mercúrio depositados em superfícies de carbono vítreo. Foi avaliada a sensibilidade do método de voltametria de redissolução anódica para a determinação de chumbo com eléctrodos de filme fino de mercúrio produzidos in-situ e ex-situ. Provou-se que, em condições acídicas (pH 3,4) e com potenciais de deposição bastante negativos (-1,3 V) o ião tiocianato promove não só a formação do filme fino de mercúrio, no que diz respeito tanto à quantidade de mercúrio depositada como à velocidade de deposição de mercúrio, mas também o processo de remoção do filme fino de mercúrio. Para além disso, a metodologia usando o TMFE produzido in-situ em meio de tiocianato teve que ser re-formulada de forma a permitir a determinação simultânea de cobre e de chumbo em água do mar. O valor de concentração de tiocianato a usar teve que ser alterado para 0...

Electrochemical impedance and current fluctuations analysis during slow strain rate test of a UNS S30400 stainless steel in low pH media

Bastos,Ivan N.; Nogueira,Ricardo P.; Ponciano,José A. C.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2005 EN
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This paper is aimed at investigating the electrochemical behavior of austenitic stainless steel UNS S30400 under stress corrosion cracking conditions in acidic solutions at room temperature. Electrochemical impedance spectroscopy and electrochemical current noise measurements were performed at different stress levels during slow strain rate tests at pH 0.00 and 1.00 in order to evaluate the influence of mechanical deformation on the evolution of the electrochemical responses of the interface. Results have shown that, differently to what happens at pH 1.00, the corrosive attack at pH 0.00 is characterized by intensive cracking concomitantly to the progressive spreading out of uniform corrosion on the metallic surface. The coupling of both electrochemical impedance and current noise techniques provided complementary information about the interplay between dissolution and cracking of the stainless steel exposed to electrolytes of different aggressiveness.

Degradation of the insecticides Thiamethoxam and Imidacloprid in aqueous solution as promoted by an innovative Feº/Fe3O4 composite

Urzedo,Ana P. F. M. de; Nascentes,Clésia C.; Augusti,Rodinei
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 EN
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The performance of an innovative Feº/Fe3O4 composite to degrade the insecticides Thiamethoxam and Imidacloprid in aqueous solution was evaluated. Factorial designs were built to investigate the influence of a number of crucial variables on such degradation processes: H2O2 concentration, solution pH, and composite mass. The solution pH was the most influential variable; hence, significant degradation rates (> 90%) was accomplished exclusively in acidic solutions (pH=2). In addition, the composite was highly efficient in promoting the degradation of both insecticides either in the presence or unpredictably in the absence of H2O2. These results thus indicated that the composite possess a dual behavior, acting as either an oxidizing or a reducing agent.

Modeling controlled potassium release from phlogopite in solution: exploring the viability of using crushed phlogopitite rock as an alternative potassium source in Brazilian soil

Silva,Adriana de A. S. da; Sampaio,João A.; Luz,Adão B. da; França,Sílvia C. A.; Ronconi,Célia M.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2013 EN
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The chemical and mineralogical properties of phlogopitite, a rock containing the mineral phlogopite, were studied aiming at employment as an alternative source of potassium. Mineralogical characterization of this rock was performed using X-ray diffractometry, X-ray fluorescence, scanning electron microscopy and infrared spectroscopy. According to the results, phlogopite contains approximately 82.6 g K2O kg-1 (ca. 9%). The kinetics involved in the release of the potassium ions from the mineral were examined using acidic solutions (nitric, citric, oxalic and Mehlich-1) and a salt solution (sodium tetraphenylboron, Na[B(C6H5)4]). The experimental results from the kinetic studies were used to determine the mathematical relationship between the concentration of potassium released and the reaction time.

Electrochemical degradation of dimethyl phthalate ester on a DSA® electrode

Souza,Fernanda L.; Aquino,José M.; Miwa,Douglas W.; Rodrigo,Manuel A.; Motheo,Artur J.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2014 EN
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The electrochemical degradation of dimethyl phthalate (DMP) using a one-compartment filter press flow cell and a commercial dimensionally stable anode (DSA®) is presented. The best electrolysis conditions were determined by the analysis of the influence of the nature and concentration of the support electrolyte, pH, current density and temperature. The abatement of DMP concentration and total organic carbon (TOC) removal were superior in the presence of NaCl, as well as the apparent first order kinetic constants. Using constant ionic strength at 0.15 mol dm-3 by adding Na2SO4, DMP concentration decreases faster at relative low NaCl concentrations while the TOC removal after 1 h of electrolysis increases with NaCl concentration. The DMP removal was very similar for all the current densities investigated at acidic solutions. When electric energy saving is considered, since the electrochemical system was under mass transport conditions, the best operational option is to use low current density values.

Cations extraction of sandy-clay soils from cavado valley, portugal, using sodium salts solutions

Silva,João Eudes da; Castro,Fernando
Fonte: São Paulo - Escola Superior de Agricultura "Luiz de Queiroz" Publicador: São Paulo - Escola Superior de Agricultura "Luiz de Queiroz"
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2002 EN
Relevância na Pesquisa
25.75%
Cases of contamination by metals in the water wells of the Cavado Valley in north-west Portugal can be attributed to the heavy leaching of clay soils due to an excess of nitrogen resulting from the intensive use of fertilisers in agricultural areas. This work focuses on the natural weathering characteristics of soils, particularly the clay material, through the study of samples collected near the River Cavado. Samples taken from various sites, after physico-chemical characterisation, were subjected to clay dissolution tests, using sodium salts of different ionic forces, to detect the relationship between certain physico-chemical parameters of water, such as pH, nitrate, chloride and sulphate content, in the dissolution of clay and the subsequent extraction of such cations as Al, Fe and K. In acidic sandy clay soils, the mineralogical composition of which was characterised by a predominance of quartz, micas, kaolinite and K-feldspars, decreases of the clay material/water pH ratio increases dissolution of the micaceous and K-feldspars phases. The presence of nitrates in the aqueous solution apparently advanced the extraction of all three cations Al, Fe and K. The specific surface area of the clay material showed a significant correlation with the main kinetic parameters of cation extraction.

Insights into preventive measures for dental erosion

Magalhães,Ana Carolina; Wiegand,Annette; Rios,Daniela; Honório,Heitor Marques; Buzalaf,Marília Afonso Rabelo
Fonte: Faculdade De Odontologia De Bauru - USP Publicador: Faculdade De Odontologia De Bauru - USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2009 EN
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Dental erosion is defined as the loss of tooth substance by acid exposure not involving bacteria. The etiology of erosion is related to different behavioral, biological and chemical factors. Based on an overview of the current literature, this paper presents a summary of the preventive strategies relevant for patients suffering from dental erosion. Behavioral factors, such as special drinking habits, unhealthy lifestyle factors or occupational acid exposure, might modify the extent of dental erosion. Thus, preventive strategies have to include measures to reduce the frequency and duration of acid exposure as well as adequate oral hygiene measures, as it is known that eroded surfaces are more susceptible to abrasion. Biological factors, such as saliva or acquired pellicle, act protectively against erosive demineralization. Therefore, the production of saliva should be enhanced, especially in patients with hyposalivation or xerostomia. With regard to chemical factors, the modification of acidic solutions with ions, especially calcium, was shown to reduce the demineralization, but the efficacy depends on the other chemical factors, such as the type of acid. To enhance the remineralization of eroded surfaces and to prevent further progression of dental wear...

Factors affecting Staphylococcus epidermidis growth in peritoneal dialysis solutions.

McDonald, W A; Watts, J; Bowmer, M I
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1986 EN
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Staphylococcus epidermidis is the most frequent cause of peritonitis complicating continuous ambulatory peritoneal dialysis. We studied factors that might influence the growth of S. epidermidis in commercially available peritoneal dialysis solution (PDS). Test strains were inoculated into PDS and incubated overnight at 37 degrees C. Samples were removed at appropriate intervals, bacterial counts were performed, and growth curves were constructed. We studied the effects of various osmolarities, the neutralization and acidification of fresh and spent PDS, and the effect of intraperitoneal dwell time on the ability PDS to support growth of S. epidermidis. In fresh PDS, numbers of bacteria remained constant after 24 h. No significant differences in growth were observed among PDS with 0.5, 1.5, 2.5, and 4.25% glucose. Neutralizing acidic fresh PDS had no effect on bacterial growth. However, growth did occur in spent PDS. PDS which was recovered after only 2 h in the peritoneal cavity supported growth to the same extent as did PDS recovered after 4 to 6 h. Mean log10 changes after 24 h of incubation were as follows: for fresh PDS, -1.3; after 2 h dwell time, 2.9; after 4 h dwell time, 1.9; and after 6 h dwell time, 1.3. Acidification of spent PDS to less than pH 6.35 produced less rapid growth; mean log10 increases after 24 h of incubation were 1.9 for pH 7.75...