Fast ultrasound-assisted treatment of urine samples for chronopotentiometric stripping determination of mercury at gold film electrodes

This work describes an efficient, fast, and reliable analytical methodology for mercury determination in urine samples using stripping chronopotentiometry at gold film electrodes. The samples were sonicated in the presence of concentrated HCl and H2O2 for 15 min in order to disrupt the organic ligands and release the mercury. Thirty samples can be treated over the optimized region of the ultrasonic bath. This sample preparation was enough to allow the accurate stripping chronopotentiometric determination of mercury in the treated samples. No background currents and no passivation of the gold film electrode due to the sample matrix were verified. The samples were also analyzed by cold vapour atomic absorption spectrometry (CV-AAS) and good agreement between the results was verified. The analysis of NIST SRM 2670 (Toxic Metals in Freeze-Dried Urine) also validated the proposed electroanalytical method. Finally, this method was applied for mercury evaluation in urine of workers exposed to hospital waste incinerators. (c) 2006 Elsevier B.V. All rights reserved.

Chemical vapor deposition of multi-walled carbon nanotubes from nickel/yttria-stabilized zirconia catalysts

Multi-walled carbon nanotubes (MWNT) were produced by chemical vapor deposition using yttria-stabilized zirconia/nickel (YSZ/Ni) catalysts. The catalysts were obtained by a liquid mixture technique that resulted in fine dispersed nanoparticles of NiO supported in the YSZ matrix. High quality MWNT having smooth walls, few defects, and low amounts of by-products such as amorphous carbon were obtained, even from catalysts with large Ni concentrations (> 50 wt.%). By adjusting the experimental parameters, such as flux of the carbon precursor (ethylene) and Ni concentration, both the MWNT morphology and the process yield could be controlled. The resulting YSZ/Ni/MWNT composites can be interesting due to their mixed ionic-electronic transport properties, which could be useful in electrochemical applications.

Ferroelectric and piezoelectric properties of bismuth titanate thin films grown on different bottom electrodes by soft chemical solution and microwave annealing

Bismuth titanate (Bi4Ti3O12, BIT) films were evaluated for use as lead-free piezoelectric thin films in micro-electromechanical systems. The films were grown by the polymeric precursor method on LaNiO3/SiO2/Si (1 0 0) (LNO), RuO2/SiO2/Si (1 0 0) (RuO2) and Pt/Ti/SiO2/Si (1 0 0) (Pt) bottom electrodes in a microwave furnace at 700 degrees C for 10 min. The domain structure was investigated by piezoresponse force microscopy (PFM). Although the converse piezoelectric coefficient, d(33), regardless of bottom electrode is around (similar to 40 pm/V), those over RuO2 and LNO exhibit better ferroelectric properties, higher remanent polarization (15 and 10 mu C/cm(2)), lower drive voltages (2.6 and 1.3 V) and are fatigue-free. The experimental results demonstrated that the combination of the polymeric precursor method assisted with a microwave furnace is a promising technique to obtain films with good qualities for applications in ferroelectric and piezoelectric devices. (c) 2006 Elsevier Ltd. All rights reserved.

Electrochemical stability of anodic titanium oxide films grown at potentials higher than 3 V in a simulated physiological solution

The cathodic behaviour of oxides formed on titanium electrodes in physiological solutions at potentials between 3 and 5 V (vs. SCE) was studied by cyclic voltammetry. In case of anodic polarization at potentials higher than 3 V (vs. SCE), a cathodic peak at similar to 0.4 V (vs. SCE) appears in the cathodic scan, which could be due to the reduction of unstable peroxides. The results show that this peak depends on the anodic potential and the oxidation time. This behaviour supposedly is due to the formation of unstable titanium peroxides like TiO3 during anodization. Based on repetitive oxidation-reduction processes can be concluded that the created amount of TiO3 inside of the TiO2 surface layer seems to be constant. (c) 2006 Elsevier Ltd. All rights reserved.

Electrochemical oxidation of an acid dye by active chlorine generated using Ti/Sn(1-x)Ir O-x(2) electrodes

The generation of active chlorine on Ti/Sn(1-x)Ir (x) O-2 anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of chloride ions (0.05 mol L-1) and a low current density (5 mA cm(-2)) it was possible to produce up to 60 mg L-1 of active chlorine on a Ti/Sn0.99Ir0.01O2 anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated with in situ electrogenerated active chlorine on Ti/Sn(1-x)Ir (x) O-2 anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4, 25 mA cm(-2) and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus time reveal a zero order reaction at dye concentrations up to 1.0 x 10(-4) mol L-1. Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed.

Compact disks, a new source for gold electrodes. Application to the quantification of copper by PSA

In this work we describe a versatile and very sensitive way for copper quantification by potentiometric stripping analysis using gold electrodes obtained from recordable compact disks (CDs). This new source of electrodes (CDtrodes) shown similar performance to the commercial gold electrodes with superior versatility and lower cost. Recordable CDs contains a highly pure gold film with thickness between 50 and 100 nm and superficial area of ca. 100 cm(2). The working electrode developed was used successfully in stationary cell and many experimental parameters have been optimized. For copper, the detection limit attained was 30 ng L-1 (600 s deposition time) with remarkable precision (standard deviation of 1.8 % for 20 repetitive measurements using 25 mu gL(-1) of copper with 60 s of deposition time). The gold electrode developed was used for analysis of copper in sugar cane spirits and tap water samples. The results were compared with those obtained by atomic absorption spectroscopy.

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.

Amperometric differential determination of ascorbic acid in beverages and vitamin C tablets using a flow cell containing an array of gold microelectrodes modified with palladium

A simple and attractive method for quantification of ascorbic acid (AA) in beers, soda, natural juices and commercial vitamin C tablets was achieved by combining Bow injection analysis and amperometric detection. An array of gold microelectrodes electrochemically modified by deposition of palladium was employed as working electrode which was almost unaffected by fouling effects. Ascorbic acid was quantified in beverages and vitamin tablets using amperometric differential measurements. This method is based on three steps involving the flow injection of: 1) the sample plus a standard addition of AA, 2) the pure sample, and 3) the enzymatically-treated sample. The enzymatic treatment was carried out with Cucumis sativus tissue, which is a rich source of ascorbate oxidase, at pH 7. The calibration plots for freshly prepared ascorbic acid standards were very linear in the concentration range of 0.18-1.8 mg L-1 with a relative standard deviation (RSD) < 1%, while for real samples the deviations were between 2.7% to 8.9%.

Improvement of the Mo/TiO2-Al2O3 catalyst by the control of the sol-gel synthesis

Traditional hydrotreating catalysts are constituted by molybdenum deposited on Al2O3 promoted by nickel and phosphorous. Several studies have shown that TiO2-Al2O3 mixed oxides are excellent supports for the active phases. Results concerning the preparation, characterization and testing of molybdenum catalyst supported on titania-alumina are presented. The support was prepared by sol-gel route using titanium and aluminum isopropoxides, the titanium one chelated with acetylacetone (acac) to promote similar hydrolysis ratio for both the alcoxides. The effect of nominal molar ratio [Ti]/[Ti+Al] on the microstructural features of nanometric particles was analyzed by X-Ray Diffraction, N-2 Adsorption Isotherms and Transmission Electron Microscopy. The catalytic activity of Mo impregnated supports was evaluated using the thiophene hydrodesulfurization at different temperatures and atmospheric pressure. The pores size distribution curve moves from the micropores to the mesopores by increasing the Ti contents, allowing the fine tuning of average size from 2.5 to 6 nm. Maximal (367 m(2).g(-1)) and minimal (127 m(2).g(-1)) surface area were found for support containing [Ti]/[Ti+Al] ratio equal to 0.1 and 1, respectively. The good mesopore texture of alumina-titania support with [Ti]/[Ti+Al] molar ratio between 0.3 and 0.5 was found particularly valuable for the preparation of well dispersed MoS2 active phase, leading to HDS catalyst with somewhat higher activity than that prepared using a commercial alumina support.

Tailoring of heterostructures in a SnO2/TiO2 system by the oriented attachment mechanism

In order to verify the possibility of forming a heterostructure-i.e., a nanoparticle tailored by the junction of two or more different materials-through the oriented attachment (OA) mechanism, experiments with rutile TiO2 and cassiterite SnO2 as candidate materials were done, since they have similar crystallographic parameters. The experiments were carried out in hydrothermal conditions and in an in situ observation at the high resolution transmission electron microscopy. The results showed the formation of TiO2/SnO2 heterostructures, confirming the coexistence of rotation-alignment and oriented collision mechanisms, hypothesis of OA behavior proposed in previous theoretical works.

Degradation of Acid Blue 40 dye solution and dye house wastewater from textile industry by photo-assisted electrochemical process

In this paper, electrochemical and photo-assisted electrochemical processes are used for color, total organic carbon (TOC) and chemical oxygen demand (COD) degradation of one of the most abundant and strongly colored industrial wastewaters, which results from the dyeing of fibers and fabrics in the textile industry. The experiments were carried out in an 18L pilot-scale tubular low reactor with 70% TiO2/30% RuO2 DSA. A synthetic acid blue 40 solution and real dye house wastewater, containing the same dye, were used for the experiments. By using current density of 80 mA cm(-2) electrochemical process has the capability to remove 80% of color, 46% of TOC and 69% of COD. When used the photochemical process with 4.6 mW cm(-2) of 254nm UV-C radiation to assist the electrolysis, has been obtained 90% of color, 64% of TOC and 60% of COD removal in 90 minutes of processing; furthermore, 70% of initial color was degraded within the first 15 minutes. Experimental runs using dye house wastewater resulted in 78% of color, 26% of TOC and 49% of COD in electrolysis at 80 mA cm(-2) and 90 min; additionally, when photo-assisted, electrolysis resulted in removals of 85% of color, 42% of TOC and 58% of COD. For the operational conditions used in this study, color, TOC and COD showed pseudo-first-order decaying profiles. Apparent rate constants for degradation of TOC and COD were improved by one order of magnitude when the photo-electrochemical process was used.

Electrochemical study of perchlorate reduction at tin electrodes

The electrochemical behaviour of tin in de-aerated sodium perchlorate was studied using potentiodynamic and potentiostatic techniques. Tin behaviour in sodium perchlorate has been complicated unexpectedly by the reduction of the perchlorate anion. It is shown that the reduction process takes place within a potential region comprising the negative side of the double layer region and the positive side of the hydrogen region (-0.7 less than or equal to E less than or equal to -1.3 V). The presence of oxide on the electrode surface favours the reduction reaction, which may occur in two steps: the formation of basic tin(II) chloride followed by its reduction, producing chloride.

Electrodeposited thin mercury films on Pt-Ir alloy electrodes

Mercury thin films prepared by electrochemical deposition on Pt-Ir alloy and after partial removing of mercury at different temperatures were studied by means of an interferometric surface mapping microscope and by X-ray photoelectronic spectroscopy. Mercury film samples having mercury partially removed by anodic stripping at a potential more positive than the corresponding peak in the voltammogram were also studied using the same techniques. For blank samples the surface topographic studies showed well defined grain boundaries. Mercury film samples when heated up to different temperatures showed as material is removed and that the surface roughness decreases as the temperature increases. For samples heated up to 800 degrees C the surface roughness is approximately the same that for the blank. A model for the interphase of volumetric mercury electrodeposited on a Pt-Ir alloy has been proposed using samples both electrochemically and thermally removed of their Hg coatings. The model includes a layered three-region structure, containing at least two Pt-Hg intermetallics: PtHg4 and PtHg2. A substrate modified region, iridium rich, has also been detected. (C) 1999 Elsevier B.V. S.A. All rights reserved.

Anisotropic growth of oxide nanocrystals: Insights into the rutile TiO2 phase

In this work, we report the synthesis of titanium oxide nanocrystals, especially the rutile TiO2 phase with nanorod morphology, by a method based on peroxotitanium complex decomposition. The results indicate that the anisotropic morphology reported for rutile TiO2 nanocrystals is related to the oriented attachment process. Despite the predominance of rutile nanocrystals at longer treatment times, the nanocrystals were obtained also in the anatase type, according to the degradation time adopted. XANES results evidenced the absence of structural correlation between the peroxytitanium complex and phase evolution, and the coexistence of the two phases strongly suggests a correlation of the oriented attachment mechanism and the rutile phase stabilization.

Model for electrodes' filaments of hot cathode fluorescent lamps, during preheating with constant rms current

This paper presents a new model for the representation of electrodes' filaments of hot-cathode fluorescent lamps, during preheating processes based on the injection of currents with constant root mean square (rms) values. The main improvement obtained with this model is the prediction of the R-h/R-c ratio during the preheating process, as a function of the preheating time and of the rms current injected in the electrodes. Using the proposed model, it is possible to obtain an estimate of the time interval and the current that should be provided by the electronic ballast, in order to ensure a suitable preheating process. is estimate of time and current can be used as input data in the design of electronic ballasts with programmed lamp start, permitting the prediction of the R-h/R-c ratio during the initial steps of the design (theoretical analysis and digital simulation). Therefore, the use of the proposed model permits to reduce the necessity of several empirical adjustments in the prototype, in order to set the operation of electronic ballasts during the preheating process. This fact reduces time and costs associated to the global design procedure of electronic ballasts.