The role of oxygen in the interaction of emeraldine base polyaniline with Cu(II) or Fe(III) ions in NMP solution

The influence of molecular oxygen in the interactions of emeraldine base form of polyaniline (EB-PANI) with Fe(III) or Cu(II) ions in 1-methyl-2-pyrrolidinone (NMP) solutions has been investigated by UV-vis-NIR, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies. Through the set of spectroscopic results it was possible to rationalize the role Of O(2) and to construct a scheme of preferential routes occurring in the interaction of EB-PANI with Fe(III) or Cu(II). Solutions of 4.0 mmol L(-1) EB-PANI with 0.8, 2.0 and 20 mmol L(-1) Fe(III) or Cu(II) ions in NMP were investigated and the main observed reactions were EB-PANI oxidation to pernigraniline (PB-PANI) and EB-PANI doping process by pseudo-protonation, or by a two-step redox process. In the presence Of O(2), PB-PANI is observed in all Fe(III)/EB solutions and EB-PANI doping only occurs in solutions with high Fe(III) concentrations through pseudo-protonation. On the other hand, emeraldine salt (ES-PANI) is formed in all Fe(III)/EB solutions under N(2) atmosphere and, in this case, doping occurs both by the pseudo-protonation and two-step redox mechanisms. In all Cu(II)/EB solutions PB-PANI is formed both in the presence and absence of O(2), and only for solutions with high Cu(II) concentrations doping process occurs in a very low degree. The most important result from EPR spectra was providing evidence for redox steps. The determined Cu(II) signal areas under oxygen are higher than under N(2) and, further. the initial metal proportions (1:2:20) are maintained in these spectra, indicating that Cu(I) formed are re-oxidized by O(2) and. so, Cu(II) ions are being recycled. Consistently, for the solutions prepared under nitrogen, the corresponding areas and proportions in the spectra are much lower, confirming that a partial reduction of Cu(II) ions actually occurs. (C) 2009 Elsevier B.V. All rights reserved.

Photocatalytic decomposition of methylene blue via Fenton mechanisms by silicon wafer doped with Au and Cu: a theoretical and experimental study

In this work, we studied the photocatalytic and the structural aspects of silicon wafers doped with Au and Cu submitted to thermal treatment. The materials were obtained by deposition of metals on Si using the sputtering method followed by fast heating method. The photocatalyst materials were characterized by synchrotron-grazing incidence X-ray fluorescence, ultraviolet-visible spectroscopy, X-ray diffraction, and assays of H(2)O(2) degradation. The doping process decreases the optical band gap of materials and the doping with Au causes structural changes. The best photocatalytic activity was found for thermally treated material doped with Au. Theoretical calculations at density functional theory level are in agreement with the experimental data.

Electroanalytical determination of promethazine hydrochloride in pharmaceutical formulations on highly boron-doped diamond electrodes using square-wave adsorptive voltammetry

The electrochemical oxidation of promethazine hydrochloride was made on highly boron-doped diamond electrodes. Cyclic voltammetry experiments showed that the oxidation mechanisms involved the formation of an adsorbed product that is more readily oxidized, producing a new peak with lower potential values whose intensity can be increased by applying the accumulation potential for given times. The parameters were optimized and the highest current intensities were obtained by applying +0.78 V for 30 seconds. The square-wave adsorptive voltammetry results obtained in BR buffer showed two well-defined peaks, dependent on the pH and on the voltammetric parameters. The best responses were obtained at pH 4.0, frequency of 50 s(-1), step of 2 mV, and amplitude of 50 mV. Under these conditions, linear responses were obtained for concentrations from 5.96 x 10(-7) to 4.76 x 10(-6) mol L-1, and calculated detection limits of 2.66 x 10(-8) mol L-1 (8.51 mu g L-1) for peak 1 and of 4.61 x 10(-8) mol L-1 (14.77 mu g L-1) for peak 2. The precision and accuracy were evaluated by repeatability and reproducibility experiments, which yielded values of less than 5.00% for both voltammetric peaks. ne applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples. All results obtained were compared to recommended procedure by British Pharmacopeia. The voltammetric results indicate that the proposed procedure is stable and sensitive, with good reproducibility even when the accumulation steps involve short times. It is therefore very suitable for the development of the electroanalytical procedure, providing adequate sensitivity and a reliable method.

Electroanalytical determination of N-nitrosamines in aqueous solution using a boron-doped diamond electrode

The electrochemical methods cyclic and square-wave voltammetry were applied to develop an electroanalytical procedure for the determination of N-nitrosamines (N-nitrosopyrrolidine, N-nitrosopiperidine and N-nitrosodiethylamine) in aqueous solutions. Cyclic voltammetry was used to evaluate the electrochemical behaviors of N-nitrosamines on boron-doped diamond electrodes. It was observed an irreversible electrooxidation peak located in approximately 1.8 V (vs. Ag/AgCl) for both N-nitrosamines. The optimal electrochemical response was obtained using the following square-wave voltammetry parameters: f = 250 Hz, E(sw) = 50 mV and E(s) = 2 mV using a Britton-Robinson buffer solution as electrolyte (pH 2). The detection and quantification limits determined for total N-nitrosamines were 6.0 x 10(-8) and 2.0 x 10(-7) mol L(-1), respectively.

Anodic oxidation of wastewater containing the Reactive Orange 16 Dye using heavily boron-doped diamond electrodes

Boron-doped diamond (BDD) films grown on the titanium substrate were used to study the electrochemical degradation of Reactive Orange (RO) 16 Dye. The films were produced by hot filament chemical vapor deposition (HFCVD) technique using two different boron concentrations. The growth parameters were controlled to obtain heavily doped diamond films. They were named as E1 and E2 electrodes, with acceptor concentrations of 4.0 and 8.0 x 10(21) atoms cm(-3), respectively. The boron levels were evaluated from Mott-Schottky plots also corroborated by Raman`s spectra, which characterized the film quality as well as its physical property. Scanning Electron Microscopy showed well-defined microcrystalline grain morphologies with crystal orientation mixtures of (1 1 1) and (1 00). The electrode efficiencies were studied from the advanced oxidation process (AOP) to degrade electrochemically the Reactive Orange 16 azo-dye (RO16). The results were analyzed by UV/VIS spectroscopy, total organic carbon (TOC) and high-performance liquid chromatography (HPLC) techniques. From UV/VIS spectra the highest doped electrode (E2) showed the best efficiency for both, the aromaticity reduction and the azo group fracture. These tendencies were confirmed by the TOC and chromatographic measurements. Besides, the results showed a direct relationship among the BDD morphology, physical property, and its performance during the degradation process. (C) 2011 Elsevier B.V. All rights reserved.

On the activation and physical degradation of boron-doped diamond surfaces brought on by cathodic pretreatments

The electrochemical activation and physical degradation of boron-doped diamond (BDD) electrodes with different boron doping levels after repeated cathodic pretreatments are reported. Galvanostatic cathodic pretreatment passing up to -14000 C cm(-2) in steps of -600 C cm(-2) using -1 A cm(-2) caused significant physical degradation of the BDD surface, with film detachment in some areas. Because of this degradation, a great increase in the electrochemically active area was observed in Tafel plots for the hydrogen evolution reaction (HER) in acid media. The minimum cathodic pretreatment needed for the electrochemical activation of the BDD electrodes without producing any observable physical degradation on the BDD surfaces was determined using electrochemical impedance spectroscopy (EIS) measurements and cyclic voltammetry: -9 C cm(-2), passed at -1 A cm(-2). This optimized cathodic pretreatment can be safely used when electrochemical experiments are carried out on BDD electrodes with doping levels in the range between 800 and 8000 ppm.

Methanol and ethanol electro-oxidation on Pt-SnO(2) and Pt-Ta(2)O(5) sol-gel-modified boron-doped diamond surfaces

The search for more efficient anode catalyst than platinum to be used in direct alcohol fuel cell systems is an important challenge. In this study, boron-doped diamond film surfaces were modified with Pt, Pt-SnO(2) and Pt-Ta(2)O(5) nano-crystalline deposits by the sol-gel method to study the methanol and ethanol electro-oxidation reactions in acidic medium. Electrochemical experiments carried out in steady-state conditions demonstrate that the addition of SnO(2) to Pt produces a very reactive electrocatalyst that possibly adsorbs and/or dissociate ethanol more efficiently than pure Pt changing the onset potential of the reaction by 190 mV toward less positive potentials. Furthermore, the addition of Ta(2)O(5) to Pt enhances the catalytic activity toward the methanol oxidation resulting in a negative shift of the onset potential of 170 mV. These synergic effects indicate that the addition of these co-catalysts inhibits the poisoning effect caused by strongly adsorbed intermediary species. Since the SnO(2) catalyst was more efficient for ethanol oxidation, it could probably facilitate the cleavage of the C-C bond of the adsorbed intermediate fragments of the reaction. (C) 2009 Elsevier B.V. All rights reserved.

Simultaneous Differential Pulse Voltammetric Determination of Ascorbic Acid and Caffeine in Pharmaceutical Formulations Using a Boron-Doped Diamond Electrode

A cathodically pretreated boron-doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry Linear calibration curves (r = 0 999) were obtained from 1 9 x 10(-5) to 2 I x 10(-4) mol L(-1) for AA and from 9 7 x 10(-6) to 1 1 x 10-4 mol L(-1) for CAF. with detection limits of 19 wool L(-1) and 7 0 mu nol L(-1). respectively This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations. with results equal to those obtained using a HPLC reference method

Simultaneous voltammetric determination of paracetamol and caffeine in pharmaceutical formulations using a boron-doped diamond electrode

A simple and highly selective electrochemical method was developed for the single or simultaneous determination of paracetamol (N-acetyl-p-aminophenol, acetaminophen) and caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) in aqueous media (acetate buffer, pH 4.5) on a boron-doped diamond (BDD) electrode using square wave voltammetry (SWV) or differential Pulse voltammetry (DPV). Using DPV with the cathodically pre-treated BDD electrode, a separation of about 550 mV between the peak oxidation potentials Of paracetamol and caffeine present in binary mixtures was obtained. The calibration curves for the simultaneous determination of paracetamol and caffeine showed an excellent linear response, ranging from 5.0 x 10(-7) mol L(-1) to 8.3 x 10(-7) mol L(-1) for both compounds. The detection limits for the simultaneous determination of paracetamol and caffeine were 4.9 x 10(-7) mol L-1 and 3.5 x 10(-8) mol L(-1), respectively. The proposed method Was Successfully applied in the simultaneous determination of paracetamol and caffeine in several pharmaceutical formulations (tablets), with results similar to those obtained using a high-performance liquid chromatography method (at 95% confidence level). (C) 2008 Elsevier BY. All rights reserved.

Application Of Real-Time Control Strategy To Improve Nitrogen Removal In Wastewater Treatment

Biological nitrogen removal is an important task in the wastewater treatment. However, the actual removal of total nitrogen (TN) in the wastewater treatment plant (WWTP) is often unsatisfactory due to several causes, one of which is the insufficient availability of carbon source. One possible approach to improve the nitrogen removal therefore is addition of external carbon source, while the amount of which is directly related to operation cost of a WWTP. It is obviously necessary to determine the accurate amount of addition of external carbon source according to the demand depending on the influent wastewater quality. This study focused on the real-time control of external carbon source addition based on the on-line monitoring of influent wastewater quality. The relationship between the influent wastewater quality (specifically the concentration of COD and ammonia) and the demand of carbon source was investigated through experiments on a pilot-scale A/O reactor (1m3) at the Nanjing WWTP, China. The minimum doses of carbon source addition at different situations of influent wastewater quality were determined to ensure the effluent wastewater quality meets the discharge standard. The obtained relationship is expected to be applied in the full-scale WWTPs. .

Synthesis and characterization of lanthanum- and yttrium-doped Fe2O3 pigments

MELO, D. M. A. et al. Synthesis and charactezarion of lanthanum and yttrium doped Fe2O3 pigments. Cerâmica, São Paulo, v. 53, p. 79-82, 2007.

Use of Bioscreen C for growth of Mucor hiemalis in different carbon and nitrogen sources

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Draft Genome Sequence of the Nitrogen-Fixing Symbiotic Bacterium Bradyrhizobium elkanii 587

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Solubilization of CaHPO4 and AlPO4 by Aspergillus niger in culture media with different carbon and nitrogen sources

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Sewage sludge as nitrogen and phosphorus source for cane-plant and first ratoon crops

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)