Paulo Rogério Pinto Rodrigues

Electrochemical and spectroelectrochemical (SERS) studies of the reduction of methylene blue on a silver electrode

The electrochemical behavior of methylene blue (MB+) on a silver electrode has been investigated by cyclic voltammetry, the rotating disk electrode technique, chronoamperometry and surface-enhanced Raman spectroscopy (SERS). The electrochemical results have shown that MB+ is reduced in two one-electron steps and that these two reduction processes are, at least partially, controlled by mass transport. The electrochemical measurements have also shown that the reduction of MB+ on the surface of a silver electrode promotes the formation of two different films. The SERS spectra have shown the presence of distinct species on the electrode surface as the potential is made more negative. Such a dependence on the potential allowed the characterization of the chemical species associated with the first and second film formation. They are, respectively, the radical cation (HMB+) and leucomethylene blue (LMB).

Estudo do comportamento eletroquímico do benzotriazol e benzimidazol na oxidação do aço inoxidável tipo ABNT 304

This work reports a study of the inhibiting action of benzotriazole (BTAH) and benzimidazole (BZM) on the corrosion of 304 austenitic stainless steel (SS) in 4.5 mol/L H2SO4. All solutions were prepared with analytical degree reagents and highly purified water. The concentrations used were: [BTAH]= 1x10-5 mol.L-1 and [BZM]= 1x10-3 mol/L. The experiments were carried out at a room temperature of 26 ± 2°C. Open circuit potential (OCP), anodic potentiostatic polarisation curves (AP), electrochemical impedance spectroscopy (EIS) and optical microscopy (OM) were used in the experiments. The results of OM for BTAH + BZM showed a corrosion-inhibiting synergic effect for 304 SS. The OCP measures in the presence of BTAH, BZM or BTAH+BZM indicate an increase in corrosion potential (Ecorr), suggesting that BTAH, BZM and BTAH+BZM acted as anodic corrosion inhibitors. AP curves in the presence BTAH and BZM, individually, suggested catalytic corrosion action for 304 SS, but in the presence of BTAH+BZM, inhibitor corrosion was observed. The results of the experiments were confirmed by EIS diagrams obtained in Ecorr.

A corrosão do aço inoxidável austenítico 304 em biodiesel

Fuel distribution uses 304 stainless steel containers for the storage of biofuels, however, there are few reports in the literature about the corrosive aspects this steel in biodiesel. The objective of this research is to study the corrosive behavior of 304 austenitic stainless steel in the presence of biodiesel, unwashed and washed, with aqueous solutions of citric, oxalic, acetic and ascorbic acids 0,01 mol L-1, and compare with results obtained for the copper (ASTM D130). The employedtechniques were: atomic absorption spectrometry (AAS) and optical microscopy (OM). The results of EAA showed a low rate of corrosion for the stainless steel, the alloys elements studied were Cr, Ni and Fe, the highest rate was observed for the chrome, 1.78 ppm / day in biodiesel with or without washing. The OM of the 304 steel, when compared with that of copper, has a low corrosion rate in the 304 steel/biodiesel system. Not with standing, this demonstrates that not only the 304 steel, but also the copper, corrodes in biodiesel.

Electrochemical behavior of indole for AISI 430 stainless steel in changing the media from 1 mol L-1 H2SO4 to 1 mol L-1 HCl

The adsorption of organic substances in metals and in different media has been attributed to different effects, such as the carbon chain size, type or number of heteroatom in the molecule structure, reactivity, the steric effect, among others. The objective of this work is to study the electrochemical indole behavior for AISI 430 stainless steel (SS), when changing the study media from H2SO4 1 mol L-1 to HCl 1 mol L-1. The experimental techniques used are as follows: the open-circuit potential, anodic and cathodic potentiodinamic polarization, electrochemical impedance spectroscopy, optical microscopy and scanning electron microscopy. These results suggest that the adsorption of indole in the presence of SO4-2 is lower than in the medium containing Cl-, which is justified by the indole action as a weak acid, because it has only a single pair of electrons, which is displaced and takes part in the π-electron aromatic system; thus the first step of the indole reaction in acid media is the protonation and generation of an indole cation.

(Microbiological corrosion of 316 austenitic steel in Na 2 SO 4 0,5 mol L -1 the absence and presence of Escherichia coli)

Microbiological corrosion is a current problem and impacts the steel industry. This research studied the infl uence of Escherichia coli (Ec) in the corrosion of 316 austenitic stainless steel (SS) in Na 2 SO 4 0.5 mol L -1 . The techniques imployed were: open circuit potential, anodic potentiodynamic polarisation (APP), electrochemical impedance spectroscopy (EIS) and optical microscopy (OM). The APP curves showed that the 316 SS is passive from -400 up to +1050 mV versus a reference electrode of mercurous sulfate (ESM). In the transpassive region, APP observed that the presence of 0.1% Ec was the generator of a biofi lm, allowing a decrease in the current of density (j), when compared to APP in the absence of Ec. However it was found that with 1% and 10% Ec, j again increased in this region, probably due to biofi lm displacement on the surface of the 316 SS. The diagrams of EIS and the OM confi rmed the results.

Estudo do comportamento eletroquímico de azóis para o aço inoxidável AISI 430 em H2SO4 1 mol L-1

Corrosion is an undesirable process that occurs in metallic materials. Studied was the effect of inhibiting Benzotriazole (BTAH), Benzimidazole (BZM) and Indole in different concentrations for the stainless steel (SS) AISI 430 in H2SO4 1 mol L-1. The techniques employed this research were: anodic potenciostatic polarisation, electrochemical impedance spectroscopy, optical microscopy and scanning electron microscopy. The curves of anodic polarisation showed that BTAH, BZM and Indol act as corrosion inhibitors for 430 SS, at concentrations of 1x10-3 and 5x10-4 mol L-1, but do not inhibit corrosion for concentrations equal to or less than 1x10-4 mol L-1. The in-crease of the efficiency in relation to the inhibitory substances studied followed this order: Indol <BZM <BTAH. The anodic polarization curve results were supported by electrochemical impedance spectroscopy, and microscopic analysis.

A influência do Thiobacillus Thiooxidans na corrosão do aço inoxidável 430 em H2SO4 1 mol L-1

A corrosao microbiologica e um dos grandes problemas industriais da atualidade. O objetivo desse trabalho e estudar a influencia da Thiobacillus Thiooxidans (TT) na corrosao do aco inoxidavel 430 em H2SO4 1mol L-1. Nesse trabalho, foram empregadas as tecnicas de: medidas gravimetricas, polarizacao anodica potenciostatica (PA) e potenciodinâmica ciclica (PC), espectroscopia de impedância eletroquimica (EIE), microscopia optica e eletronica de varredura (MEV). Os resultados gravimetricos mostraram que, em 180 minutos de imersao do aco no meio contendo TT, ha a formacao de biofilme, o qual, inicialmente, bloqueia a corrosao do metal. A PA mostrou que o TT atua catalisando a reacao de oxidacao do aco 430 nesse meio, sendo que resultados semelhantes foram obtidos pela EIE. A aplicacao da PC, na regiao passiva do aco 430, nesse meio, gera a inibicao da geracao de biofilmes em sua superficie, resultado este comprovado pela MEV.

Study of TiO2 Hybrid Solar Cells with Natural Dyes

Celulas solares sensibilizadas por corante (CSSC) sao dispositivos que aproveitam a luz do sol para gerar energia e possuem na composicao um oxido semicondutor e um fotossensibilizador adequado. Devido ao custo elevado, a pesquisa por novos materiais aplicados nas celulas solares desperta grande interesse. Este trabalho tem como objetivo estudar celulas solares hibridas de interface FTO/TiO2/corante produzidas com diferentes fotossensibilizadores naturais de baixo custo, extraidos em solucao etanoica acidificada, de diferentes produtos naturais: ameixa, uva, urucum e berinjela. As tecnicas de caracterizacao utilizadas foram: Espectroscopia na regiao do ultravioleta-visivel (UV-VIS), Espectroscopia na regiao do Infravermelho por Transformada de Fourier (IV-TF), medidas do Potencial de Circuito Aberto em funcao do tempo (Eca), curvas Fotocronoamperometricas (FCA) e Curvas de Densidade de Fotocorrente em funcao do Potencial (j-E). Os corantes testados nas CSSC apresentaram caracter de fotossensibilidade, com adsorcao nos filmes de TiO2 e absorcao maxima na regiao do visivel. A CSSC com melhores parâmetros fotovoltaicos foi empregando-se o corante extraido da ameixa, gerando uma celula solar com ƞ = 0,12±0,03, Eca = 572±12 mV, FF = 0,57±0,01 e jcc = 0,40±0,09 mA cm-2.

Recombination Study of Dye Sensitized Solar Cells with Natural Extracts

Natural dyes can be used in dye sensitized solar cells (DSSCs) to generate low-cost devices, although with low light harvesting because of energy losses from the recombination process. This study investigates recombination reactions in DSSCs with natural dyes extracted from eggplants, plums, and hibiscus flowers. Titanium dioxide films were coated on a fluorine-doped tin oxide glass conductor substrate by the doctor blading method and impregnated in a dye solution for 24 h. Electrodeposited platinum was used as the cathode, and I3/I as the redox couple. The techniques employed were: intensity modulated photovoltage spectroscopy, intensity modulated photocurrent spectroscopy, electrochemical impedance spectroscopy, charge extraction, and cyclic voltammetry. The results show that cells containing plum dye exhibited the best photovoltaic parameters, with high values of gap, charge extraction, and potential, being less resistive to charge transfer with an electron lifetime of 0.51 s, collection time of 8.54 ms, and charge efficiency collection of 0.99.

Photoelectrochemical Behavior of the Cell FTO/TiO 2 /CeO 2 /N719 Obtained from the Pechini and Precipitation of Cerium Oxide Methods

Renewable energy sources have received much attention in recent years due to concerns about global climate and environmental changes. Solar energy appears to be a promising alternative, especially dye-sensitized solar cells (DSSC), which, according to the literature, can achieve a power conversion efficiency in excess of 11%, depending on the semiconductor oxide used in their fabrication. The aim of this paper is to investigate the performance of DSSCs using cerium oxide (CeO2), titanium oxide (TiO2), and commercial dye N719. CeO2 was obtained using the Pechini and precipitation methods. The characterization techniques employed were x-ray diffraction, Raman spectroscopy, scanning electron microscopy, ultraviolet–visible spectroscopy, dynamic light scattering, and photoelectrochemical measurements. The results indicate that the efficiency of the DSSC CeO2/TiO2 obtained using the precipitation method was about 20% higher than that of the DSSC TiO2.