Electrocatalysis of ethanol oxidation on Pt monolayers deposited on carbon-supported Ru and Rh nanoparticles

Pt monolayers deposited on carbon- supported Ru and Rh nanoparticles were investigated as electrocatalysts for ethanol oxidation. Electronic features of the Pt monolayers were studied by in situ XANES (X-ray absorption near-edge structure). The electrochemical activity was investigated by cyclic voltammetry and cronoamperometric experiments. Spectroscopic and electrochemical results were compared to those obtained on carbon-supported Pt-Ru and Pt-Rh alloys, and Pt E-TEK. XAS results indicate a modification of the Pt 5d band due to geometric and electronic interactions with the Ru ant Rh substrates, but the effect of withdrawing electrons from Pt is less pronounced in relation to that for the corresponding alloys. Electrochemical stripping of adsorbed CO, which is one of the intermediates, and the currents for the oxidation of ethanol show faster kinetics on the Pt monolayer deposited on Ru nanoparticles, and an activity that exceeds that of conventional catalysts with much larger amounts of platinum. (c) 2007 Elsevier B.V. All rights reserved.

Ethanol electro-oxidation on carbon-supported Pt-Ru, Pt-Rh and Pt-Ru-Rh nanoparticles

This work investigates the effects of carbon-supported Pt, Pt-Ru, Pt-Rh and Pt-Ru-Rh alloy electrocatalysts oil the yields of CO2 and acetic acid as electro-oxidation products of ethanol. Electronic and structural features of these metal alloys were studied by in situ X-ray absorption spectroscopy (XAS). The electrochemical activity was investigated by polarization experiments and the reaction intermediates and products were analyzed by in situ Fourier Transform Infra-Red Spectroscopy (FTIR). Electrochemical stripping of CO. which is one of the adsorbed intermediates, presented a faster oxidation kinetics on the Pt-Ru electrocatalyst, and similar rates of reaction on Pt-Rh and Pt. The electrochemical current of ethanol oxidation showed a higher value and the onset potential was less positive oil Pt-Ru. However, in situ FTIR spectra evidenced that the CO2/acetic acid ratio is higher for the materials with Rh, mainly at lower potentials. These results indicate that the Ru atoms act mainly by providing oxygenated species for the oxidation of ethanol intermediates, and point out ail important role of Rh on the C-C bond dissociation. (C) 2007 Elsevier Ltd. All rights reserved.

Development and Application of a Highly Selective Biomimetic Sensor for Detection of Captopril, an Important Ally in Hypertension Control

A biomimetic sensor is proposed as a promising new analytical method for determination of captopril in different classes of samples. The sensor was prepared by modifying a carbon paste electrode with iron (II) phthalocyanine bis(pyridine) [FePe(dipy)] complex. Amperometric measurements in a batch analytical mode were first carried out in order to optimize the sensor response. An applied potential lower than 0.2 V vs Ag vertical bar AgCl in 0.1 mol L(-1) of TRIS buffer at pH 8.0 provided the best response, with a linear range of 2.5 x 10(-5) to 1.7 x 10(-4) mol L(-1). A detailed investigation of the selectivity of the sensor, employing seventeen other drugs, was also performed. Recovery studies were carried out using biological and environment samples in order to evaluate the sensor`s potential for use with these sample classes. Finally, the performance of the biomimetic sensor was optimized in a flow injection (FIA) system using a wall jet electrochemical cell. Under optimized flow conditions, a broad linear response range, from 5.0 x 10(-4) to 2.5 x 10(-2) mol L(-1), was obtained for captopril, with a sensitivity of 210 +/- 1 mu A L mol(-1).

Solubilizacao e interacao de pigmentos com solventes organicos e agentes tenso-ativos

A Mg e Mn-Ftalocianina (Mg e Mn-Pc) foram solubilizados à 25°C em dimetilsulfóxido (DMSO); N, N-dimetilacetamida (DMA); N,N-dimetilformamida (DMF); N-metil-formamida, formamida, piridina, o-diclorobenzeno, monoclorobenzeno, tolueno, metanol, etanol, propanol-1, propanol-2, butanol-1 e octanol-1. Alguns valores representativos obtidos para o logarítimo da absortividade molar (E) da Mn-Pc, são os seguintes: o-diclorobenzeno (E = 4,94); DMSO (E = 4,39); octanol-1 (E = 3,90). Valores correspondentes para Mg-Pc são: o-diclarobenzeno (E = 4,93); DMSO (E = 5,22) e Octanol-1 ( E = 5,06). Em função de interação com solventes, pode-se classificar a Mg-Pc como um indicador básico e a Mn-Pc como indicador ácido. Os pigmentos Mg e Mn-Pc foram também solubillzados em soluções aquosas contendo vários surfatantes à 25°C. A Mg-Pc apresentou solubilidade significativa em água contendo brometo de cetiltrimetilamônio (CTAB), Brij-35, cloreto de cetilpiridinio (CPC1), brometo de cetilpiridínio (CPBr,) Triton X-100, cloreto de metildodecilbenziltrimetilamônio, brometo de cetildimetiletilamõnio e brometo de laurilisoquinolínio. A Mn-Pc foi solúvel em soluções aquosas de Brij-35 e Triton X-100. Em função de sua interação com surfatantes a Mg-Pc é classificada como corante catiônico e a Mn-Pc como corante aniônico. O corante comercial quinóide Oil Blue A [1,4-di(isopropilarnina)-antraquinona - 9,10 foi solubilizado à 25°C em DMF, DMSO, DMA, monoclorobenzeno, benzeno, tolueno, piridina, metanol, etanol, propanol-1, propanol-2, butanol-1 e octanol-1. Foi também solubilizado em soluções aquosas de surfatantes, tais como sódio lauril-sulfato (NaLS), cloreto de cetiltrimetilamônio (CTAB), brometo de cetildimetiletilamônio, Triton X-100, cloreto de cetilpiridínio (CPCl), Brij-35, cloreto de rnetildodecilbenziltrimetilamônio e brometo de laurilisoquinolínio. Em função de suas interações com os solventes o corante é um indicador ácido-básico pouco sensível e em função de sua interação com surfatantes é um corante catiônico. 0s resultados experimentais apresentam importância teórica e prática considerando sistemas que envolvem armazenamento e transferência de energia, compostos porfirínicos, fotossíntese, fotocondutores, coletores solares, semi-condutores e processos de embelezamento e proteção de superficies de vários materiais.

Nanocatalysts for sustainable industrial processses

In Chapter 1, rhodium nanoparticles were supported on multiwalled carbon nanotubes (MWCNTs) and bound to the magnetic core-shell system Fe3O4@TiO2. The composite Fe3O4@TiO2-Rh-MWCNT and the intermediates were characterized by SEM, EDS and TEM. Their catalytic activity was studied using i) the hydrogenation transfer of nitroarenes and cyclohexene in the presence of hydrazine hydrate; ii) the reduction of 2-nitrophenol with NaBH4; and iii) the decoloration of pigments in the presence of hydrogen peroxide. The results were monitored by gas chromatography (i) and UV Visible (ii and iii). In the second chapter, the catalytic activity of six oxidovanadium(V) aroylhydrazone complexes, viz. [VOL1(OEt)][VOL1(OEt)(EtOH)] (1), [VOL2(OEt)] (2), [Et3NH][VO2L1] (3), [VO2(H2L2)]2·EtOH (4), [VOL1(µ -O)VOL1] (5) and [VOL2(µ -O)VOL2] (6) (H2L1 = 3,5-di-tert-butyl-2-hydroxybenzylidene)-2hydroxybenzohydrazide and H2L2 = 3,5-di-tert-butyl-2-hydroxybenzylidene)-2 aminobenzohydrazide), anchored on nanodiamonds with different treatments, was studied towards the microwave-assisted partial oxidation of 1-phenylethanol to acetophenone in the presence of tert-butyl hydroperoxide (TBHP) as oxidant. A high selectivity for acetophenone was achieved for the optimized conditions. The possibility of recycling and reuse the heterogeneous catalysts was also investigated. In chapter 3, the catalytic activity of gold nanoparticles supported at different metal oxides, such as Fe2O3, Al2O3 ZnO or TiO2, was studied for the above reaction. The effect of the support, quantity of the catalyst and temperature was investigated. The recyclability of the gold catalysts was also studied. In the last chapter, a new copper nanocomposite with functionalized mutiwalled carbon nanotubes (Cu-MWCNT) was synthesized using a microwave assisted polyol method. The characterization was performed using XRD and SEM. The catalytic activity of Cu-MWCNT was studied through the degradation of pigments, such as amaranth, brilliant blue, indigo, tartrazine and methylene blue.

Sensor array made with nanostructured films to detect a phenothiazine compound

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

Thermal and electrochemical study of solid-state reaction of mercury with Pt-20% Rh alloy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Microeletrodos: I. Construção e caracterização

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

Determination of selenium in nutritionally relevant foods by graphite furnace atomic absorption spectrometry using arsenic as internal standard

A method has been developed for the direct determination of Se in nutritionally relevant foods by graphite furnace atomic absorption spectrometry. Tungsten/rhodium carbide coating on the integrated platform of a transversely heated graphite atomizer or W coating with co-injection of Pd(NO3)(2) were used as a permanent modifiers. Samples and reference solutions were spiked with 500 mu g L-1 As and absorbance variations due to changes in experimental conditions were minimized. For 20 mu L aqueous analytical solutions delivered into the graphite tube, analytical curves in the 5.0-40 mu g L-1 with good linear correlation were established. Pyrolysis and atomization temperatures were evaluated using pyrolysis and atomization curves, respectively. The optimized heating program (temperature, ramp time, hold time) of the graphite tube of the Perkin-Elmer SIMAA 6000 atomic absorption spectrometer was: dry steps (110 degrees C, 5 s, 10 s; 130 degrees C, 15 s, 15 s); air-assisted pyrolysis step (600 degrees C, 20 s, 40 s; 20 degrees C, 1 s, 40 s); pyrolysis step (1300 degrees C, 10 s, 20 s); atomization step (2100 degrees C, 0 s, 4 s); clean step (2550 degrees C, 1 s, 5 s). The method was applied for Se determination in coconut water, coconut milk, soybean milk, cow milk, tomato juice, mango juice, grape juice and drinking water samples and four standard reference materials and results were in agreement at 95% confidence level. The lifetime of the tube was 500 firings and the relative standard deviations of measurements of typical samples containing 25 mu gL(-1) Se were 3.0% and 6.0% (n = 12) with and without internal standardization, respectively. The limits of detection were in the 0.35 mu g L-1-0.7 mu g Se L-1 range. The accuracy of the proposed method was evaluated by an addition-recovery experiment and all recovered values were in the 98-109% range. (c) 2004 Elsevier Ltd. All rights reserved.

Structural and surface properties of thermally prepared Ti/RhxTi(1-x)Oy electrodes: I - influence of preparation parameters

Electrodes of RhxTi(1-x) O-y nominal composition were prepared by thermal decomposition of the chloride or nitrate precursor salts dissolved in strongly acidic medium and applied by brush to both sides of a Tidegrees support. A systematic study of the influence of calcination temperature and time as well as oxygen flux was conducted. The coatings were characterised by SEM, EDAX, XRD, open circuit potential measurements and cyclic voltammetry (CV). Visible-ultraviolet spectrophotometry was employed to identify the chemical form of the precursor in solution while thermogravimetric analysis (TGA) was used to assess the decomposition temperature ranges. Optimisation of the coating preparation parameters showed coatings obtained from [Rh(H2O)(6)](NO3)(3) precursor dissolved in HNO3 1:2 (v/v) and fired at 430 degreesC for 2 h in a 5 1 min (-1) oxygen stream-furnished stable electrodes having the highest electrochemically active surface area. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Evaluation of a highly sensitive amperometric biosensor with low cholinesterase charge immobilized on a chemically modified carbon paste electrode for trace determination of carbamates in fruit, vegetable and water samples

A highly sensitive amperometric biosensor for determination of carbamate pesticides directly in water, fruit and vegetable samples has been evaluated, electrochemically characterized and optimized. The biosensor strip was fabricated in screen printed technique on a ceramic support using silver-based paste for reference electrode, and platinum-based paste for working and auxiliary electrodes. The working electrode was modified by a layer of carbon paste mixed with cobalt(II) phthalocyanine and acetylcellulose. Cholinesterase (ChE) enzymes with low enzymatic charge were immobilized on this layer. The operational simplicity of the biosensor consists in that a small drop (similar to 50 mu l) of substrate or sample is deposited on a horizontally positioned biosensor strip representing the microelectrochemical cell. The working potential of the biosensor was 370 mV versus Ag/AgI on a ship reference electrode preventing the interference of electroactive species which are oxidable at more positive potentials. The biosensor was applied to investigate the degradation of two reference ChE inhibitors in freeze dried water under different storage conditions and for direct determination of some N-methylcarbamates (NMCs) in fruit and vegetable samples at ppb concentration levels without any sample pretreatment. A comparison of the obtained results for the total carbamate concentration was done against those obtained using HPLC measurements. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Direct determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by simultaneous GFAAS using integrated platforms pretreated with W-Rh permanent modifier together with Pd plus Mg modifier

A method is proposed for the simultaneous determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by electrothermal atomic absorption spectrometry (ETAAS) using W-Rh permanent modifier together with Pd(NO3)(2) + Mg(NO3)(2) conventional modifier. The integrated platform of a transversely heated graphite atomizer (THGA) was treated with tungsten, followed by rhodium, forming a deposit containing 250 mug W + 200 mug Rh. A 500-muL, volume of fuel ethanol was diluted with 500 muL, of 0.14 mol L-1 HNO3 in an autosampler cup of the spectrometer. Then, 20 muL, of the diluted ethanol was introduced into the pretreated graphite platform followed by the introduction of 5 mug Pd(NO3)(2) + 3 mug Mg(NO3)(2). The injection of this modifier was required to improve arsenic and iron recoveries in fuel ethanol. Calibrations were carried out using multi-element reference solutions prepared in diluted ethanol (1 + 1, v/v) acidified to 0. 14 mol L-1 HNO3. The pyrolysis and atomization temperatures of the heating program were 1200degreesC and 2200degreesC, respectively, which were obtained with multielement reference solutions in acidic diluted ethanol (1 + 1, v/v; 0. 14 mol L-1 HNO3). The characteristic masses for the simultaneous determination in ethanol fuel were 78 pg Al, 33 pg As, 10 pg Cu, 14 pg Fe, 7 pg Mn, and 24 pg Ni. The lifetime of the pretreated tube was about 700 firings. The detection limits (D.L.) were 1.9 mug L-1 Al, 2.9 mug L-1 As, 0.57 mug L-1.Cu, 1.3 mug L-1 Fe, 0.40 mug L-1 Mn, and 1.3 mug L-1 Ni. The relative standard deviations (n = 12) were 4%, 4%, 3%, 1.5%, 1.2%, and 2.2% for Al, As, Cu, Fe, Mn, and Ni, respectively. The recoveries of Al, As, Cu, Fe, Mn, and Ni added to the fuel ethanol samples varied from 81% to 95%, 80% to 98%, 97% to 109%, 85% to 107%, 98% to 106% and 97% to 103%, respectively. Accuracy was checked for the Al, As, Cu, Fe, Mn, and Ni determination in 10 samples purchased at a local gas station in Araraquara-SP City, Brazil. A paired t-test showed that at the 95% confidence level the results were in agreement with those obtained by single-element ETAAS.

A Simple Method Based on ICP-MS for Estimation of Background Levels of Arsenic, Cadmium, Copper, Manganese, Nickel, Lead, and Selenium in Blood of the Brazilian Population

Throughout the world, biomonitoring has become the standard for assessing exposure of individuals to toxic elements as well as for responding to serious environmental public health problems. However, extensive biomonitoring surveys require rapid and simple analytical methods. Thus, a simple and high-throughput method is proposed for the determination of arsenic (As), cadmium (Cd), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and selenium (Se) in blood samples by using inductively coupled plasma-mass spectrometry (ICP-MS). Prior to analysis, 200 l of blood samples was mixed with 500 l of 10% v/v tetramethylammonium hydroxide (TMAH) solution, incubated for 10 min, and subsequently diluted to 10 ml with a solution containing 0.05% w/v ethylenediamine tetraacetic acid (EDTA) + 0.005% v/v Triton X-100. After that, samples were directly analyzed by ICP-MS (ELAN DRC II). Rhodium was selected as an internal standard with matrix-matching calibration. Method detection limits were 0.08, 0.04, 0.5, 0.09, 0.12, 0.04, and 0.1 g//L for As, Cd, Cu, Mn, Ni, Pb, and Se, respectively. Validation data are provided based on the analysis of blood samples from the trace elements inter-\comparison program operated by the Institut National de Sante Publique du Quebec, Canada. Additional validation was provided by the analysis of human blood samples by the proposed method and by using electrothermal atomic absorption spectrometry (ETAAS). The method was subsequently applied for the estimation of background metal blood values in the Brazilian population. In general, the mean concentrations of As, Cd, Cu, Mn, Ni, Pb, and Se in blood were 1.1, 0.4, 890, 9.6, 2.1, 65.4, and 89.3 g/L, respectively, and are in agreement with other global populations. Influences of age, gender, smoking habits, alcohol consumption, and geographical variation on the values were also considered. Smoking habits influenced the levels of Cd in blood. The levels of Cu, Mn, and Pb were significantly correlated with gender, whereas Cu and Pb were significantly correlated with age. There were also interesting differences in Mn and Se levels in the population living in the north of Brazil compared to the south.

Metal-Organic Semiconductor Nanostructures for Surface-Enhanced Raman Scattering

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

Detection of catechol using mixed Langmuir-Blodgett films of a phospholipid and phthalocyanines as voltammetric sensors

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