Nitrate reduction on Pt single crystals with Pd multilayer

Nitrate reduction on palladium multilayers deposited on platinum single crystal electrodes was studied by cyclic voltammetry and FTIR spectroscopy in acid and alkaline media. The results are compared with those obtained with bulk palladium single crystals. The reaction is sensitive to the electrode surface structure, the reactivity depending on the solution pH. In acid solution nitrate was reduced at potentials below the potential of zero total charge (pztc), when the electrode is negatively charged. Competition between nitrate, hydrogen and anion adsorption and NO formation and accumulation at the surface are proposed as the main reasons for the slow reaction rate. On the bulk palladium single crystal electrodes, NO formation leads to a fast blockage of the surface resulting in a very low activity for nitrate reduction. In alkaline solution, nitrate is reduced at more positive potentials with significantly higher current being measured on the Pd multilayer on Pt(100) electrode. (C) 2008 Elsevier Ltd. All rights reserved.

Cassava wastewater as a substrate for the simultaneous production of rhamnolipids and polyhydroxyalkanoates by Pseudomonas aeruginosa

Glycerol, cassava wastewater (CW), waste cooking oil and CW with waste frying oils were evaluated as alternative low-cost carbon substrates for the production of rhamnolipids and polyhydroxyalkanoates (PHAs) by various Pseudomonas aeruginosa strains. The polymers and surfactants produced were characterized by gas chromatography-mass spectrophotometry (MS) and by high-performance liquid chromatography-MS, and their composition was found to vary with the carbon source and the strain used in the fermentation. The best overall production of rhamnolipids and PHAs was obtained with CW with frying oil as the carbon source, with PHA production corresponding to 39% of the cell dry weight and rhamnolipid production being 660 mg l(-1). Under these conditions, the surface tension of the culture decreased to 30 mN m(-1), and the critical micelle concentration was 26.5 mg l(-1). It would appear that CW with frying oil has the highest potential as an alternative substrate, and its use may contribute to a reduction in the overall environmental impact generated by discarding such residues.

Evaluation of the antioxidant activity of passion fruit (Passiflora edulis and Passiflora alata) extracts on stimulated neutrophils and myeloperoxidase activity assays

The antioxidant activity of methanol extracts from Passiflora edulis and Passiflora alata pulp, and P. edulis rinds, healthy or infected with the passion fruit woodiness virus (PWV), was investigated using the oxidant activities of the neutrophil and the neutrophil granule enzyme myeloperoxidase (MPO), both playing key roles in inflammation. The reactive oxygen species produced by stimulated neutrophils were evaluated by lucigenin-enhanced chemiluminescence (CL) and the activity of purified MPO was measured by SIEFED (Specific Immunological Extraction Followed by Enzymatic Detection), a technique for studying the direct interaction of a compound with the enzyme. The rind extracts of P. edulis possessed higher and dose-dependent inhibitory effects on CL response and on the peroxidase activity of MPO than total pulp extracts from both passion fruit species. The quantification of isoorientin in the extracts showed a correlation with their antioxidant activity, suggesting the potential of P. edulis rinds as functional food or as a possible source of natural flavonoids. (C) 2011 Elsevier Ltd. All rights reserved.

Synthesis, Characterization, and Electrocatalytic Activity toward Methanol Oxidation of Carbon-Supported Pt(x)-(RuO(2)-M)(1-x) Composite Ternary Catalysts (M = CeO(2), MoO(3), or PbO(x))

Carbon-supported platinum is commonly used as an anode electrocatalyst in low-temperature fuel cells fueled with methanol. The cost of Pt and the limited world supply are significant barriers for the widespread use of this type of fuel cell. Moreover, Pt used as anode material is readily poisoned by carbon monoxide produced as a byproduct of the alcohol oxidation. Although improvements in the catalytic performance for methanol oxidation were attained using Pt-Ru alloys, the state-of-the-art Pt-Ru catalyst needs further improvement because of relatively low catalytic activity and the high cost of noble Pt and Ru. For these reasons, the development of highly efficient ternary platinum-based catalysts is an important challenge. Thus, various compositions of ternary Pt(x)-(RuO(2)-M)(1-x)/C composites (M = CeO(2), MoO(3), or PbO(x)) were developed and further investigated as catalysts for the methanol electro-oxidation reaction. The characterization carried out by X-ray diffraction, energy-dispersive X-ray analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry point out that the different metallic oxides were successfully deposited on the Pt/C, producing small and well-controlled nanoparticles in the range of 2.8-4.2 nm. Electrochemical experiments demonstrated that the Pt(0.50)(RuO(2)-CeO(2))(0.50)/C composite displays the higher catalytic activity toward the methanol oxidation reaction (lowest onset potential of 207 mV and current densities taken at 450 mV, which are 140 times higher than those at commercial Pt/C), followed by the Pt(0.75)(RuO(2)-MoO(3))(0.25)/C composite. In addition, both of these composites produced low quantities of formic acid and formaldehyde when compared to a commercially available Pt(0.75)-Ru(0.25)/C composite (from E-Tek, Inc.), suggesting that the oxidation of methanol occurs mainly by a pathway that produces CO(2) forming the intermediary CO(ads).