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M H2SO4 (m + h2so4)
Selected AbstractsElectrocatalytic Reduction and Determination of Iodate and Periodate at Silicomolybdate-Incorporated-Glutaraldehyde- Cross-Linked Poly- L -lysine Film ElectrodesELECTROANALYSIS, Issue 10 2010Yu-Ching Pan Abstract The present work describes reduction of iodate (IO3,), and periodate (IO4,) at silicomolybdate-doped-glutaraldehyde-cross-linked poly- L -lysine (PLL-GA-SiMo) film coated glassy carbon electrode in 0.1,M H2SO4. In our previous study, we were able to prepare the PLL-GA-SiMo film modified electrode by means of electrostatically trapping SiMo12O404, mediator in the cationic film of PLL-GA, and the voltammetric investigation in pure supporting indicated that the charge transport through the film was fast. Here, the electrocatalytic activity of PLL-GA-SiMo film electrode towards iodate and periodate was tested and subsequently used for analytical determination of these analytes by amperometry. The two electron reduced species of SiMo12O404, anion was responsible for the electrocatalytic reduction of IO3, at PLL-GA-SiMo film electrode while two and six electron reduced species were showed electrocatalytic activity towards IO4, reduction. Under optimized experimental conditions of amperometry, the linear concentration range and sensitivity are 2.5×10,6 to 1.1×10,2,M and 18.47,,A mM,1 for iodate, and 5×10,6 to 1.43×10,4,M and 1014.7,,A mM,1 for periodate, respectively. [source] Performance of Impedimetric Biosensors Based on Anodically Formed Ti/TiO2 ElectrodesELECTROANALYSIS, Issue 20 2005Aikaterini Abstract The advantages and limitations of impedimetric sensors based on Ti/TiO2 architectures are described. Titanium dioxide (titania) was potentiostatically formed onto titanium electrodes of 2,mm diameter, at 10 and 30,V in 1,M H2SO4. The thickness of the titania layers was ellipsometrically determined to be 30 and 86,nm respectively and they are highly insulating with charge-transfer resistances in the M, range, as they were measured with electrochemical impedance spectroscopy under specific experimental conditions. Low voltage anodization (<10,V) results to amorphous TiO2, whereas at higher applied voltages (>25,V), anatase is the predominant form. SEM images are indicative of quite smooth, compact coatings without any severe cracks. [source] Catalytic Effect on Silver Electrodeposition of Gold Deposited on Carbon ElectrodesELECTROANALYSIS, Issue 19 2004Alfredo de, Escosura-Muñiz Abstract A new methodology, based on silver electrocatalytic deposition and designed to quantify gold deposited onto carbon paste electrode (CPE) and glassy carbon electrode (GCE), has been developed in this work. Silver (prepared in 1.0,M NH3) electrodeposition at ,0.13,V occurs only when gold is previously deposited at an adequate potential on the electrode surface for a fixed period of time. When a CPE is used as working electrode, an adequate oxidation of gold is necessary. This oxidation is carried out in both 0.1,M NaOH and 0.1,M H2SO4 at oxidation potentials. When a GCE is used as working electrode, the oxidation steps are not necessary. Moreover, a cleaning step in KCN, which removes gold from electrode surface, is included. To obtain reproducibility in the analytical signal, the surface of the electrodes must be suitably pretreated; this electrodic pretreatment depends on the kind of electrode used as working electrode. Low detection limits (5.0×10,10,M) for short gold deposition times (10,min for CPE and 5,min for GCE) were achieved with this novel methodology. Finally, sodium aurothiomalate can be quantified using silver electrocatalytic deposition and GCE as working electrode. Good linear relationship between silver anodic stripping peak and aurothiomalate concentration was found from 5.0×10,10,M to 1.0×10,8,M. [source] Electrochemical Overoxidation of Polyindole and Its Cation-Permselective BehaviorELECTROANALYSIS, Issue 12 2004Mihaela Ghita Abstract Polyindole films prepared by potentiostatic growth in dichloromethane solution were subjected to overoxidation studies in aqueous media. Overoxidation at potentials greater than 1.1,V (vs. SCE) in 0.1,M KNO3 or 0.1,M H2SO4 was possible. Overoxidation in 0.1,M NaOH resulted in mechanically unstable films which were not adherent to the electrode surface. The overoxidation process in 0.1,M KNO3 involved removal of one electron per four indole monomer moieties in the polymer film. Nucleophilic attack led to introduction of carboxylate functionality and to cation permselective behavior, as tested by cyclic voltammetry and hydrodynamic voltammetry of hexamminoruthenium(III) and hexacyanoferrate(III). Such films may be useful in various electrochemical sensor applications. [source] Evaluation of RuxWySez Catalyst as a Cathode Electrode in a Polymer Electrolyte Membrane Fuel CellFUEL CELLS, Issue 1 2010K. Suárez-Alcántara Abstract The oxygen reduction reaction (ORR) on RuxWySez is of great importance in the development of a novel cathode electrode in a polymer electrolyte membrane fuel cell (PEMFC) technology. The RuxWySez electrocatalyst was synthesised in an organic solvent for 3,h. The powder was characterised by transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). The electrocatalyst consisted of agglomerates of nanometric size (,50,150,nm) particles. In the electrochemical studies, rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) techniques were used to determine the oxygen reduction kinetics in 0.5,M H2SO4. The kinetic studies include the determination of Tafel slope (112,mV,dec,1), exchange current density at 25,°C (1.48,×,10,4,mA,cm,2) and the apparent activation energy of the oxygen reaction (52.1,,,0.4,kJ,mol,1). Analysis of the data shows a multi-electron charge transfer process to water formation, with 2% H2O2 production. A single PEMFC with the RuxWySez cathode catalysts generated a power density of 180,mW,cm,2. Performance achieved with a loading of 1.4,mg,cm,2 of a 40,wt% RuxWySez and 60,wt% carbon Vulcan (i.e. 0.56,mg,cm,2 of pure RuxWySez). Single PEMFC working was obtained with hydrogen and oxygen at 80,°C with 30,psi. [source] Chemical synthesis and electric properties of the conducting copolymer of aniline and o -aminophenolJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007Jing Zhang Abstract A copolymer, poly(aniline- co-o -aminophenol), was prepared chemically by using ammonium peroxydisulfate as an oxidant. The monomer concentration ratio of o -aminophenol to aniline strongly influences the copolymerization rate and properties of the copolymer. The optimum composition of a mixture for the chemical copolymerization consisted of 0.3 M aniline, 0.021 M o -aminophenol, 0.42 M ammonium peroxydisulfate, and 2 M H2SO4. The result of cyclic voltammograms in a potential region of ,0.20 to 0.80 V (vs.SCE) indicates that the electrochemical activity of the copolymer prepared under the optimum condition is similar to that of polyaniline in more acid solutions. However, the copolymer still holds the good electrochemical activity until pH 11.0. Therefore, the pH dependence of the electrochemical property of the copolymer is improved, compared with poly(aniline- co-o -aminophenol) prepared electrochemically, and is much better than that of polyaniline. The spectra of IR and 1H NMR confirm that o -aminophenol units are included in the copolymer chain, which play a key role in extending the usable pH region of the copolymer. The visible spectra of the copolymers show that a high concentration ratio of o -aminophenol to aniline in a mixture inhibits the chain growth. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5573,5582, 2007 [source] Modelling and parameter comparison of equivalent circuits on the basis of impedance measurements of stainless steelsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 4 2006M. Slemnik Abstract In our former work [1] we have discussed the impedance of differently heat treated steels X20Cr13 in 0.1 M H2SO4, undergoing an active passive transition. Impedance spectra were interpreted in terms of a model by Armstrong [2, 3], describing the electrochemical reaction at interfaces with adsorbed intermediates. The present work was performed in order to study this phenomenon in more detail, with computer simulations of a new created and more convenient equivalent circuit in comparison with the former model. Computer simulations of equivalent circuits were also made in the region of passivity which was also continuation of our earlier work [4]. In this sense the entire study for these steels was completed by collating distinctive parameter values, demonstrating electrochemical characteristics of steel X20Cr13, undergoing different heat treatments in the active-passive and passive region. [source] Facile High-Yield Synthesis of Polyaniline Nanosticks with Intrinsic Stability and Electrical ConductivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2008Xin-Gui Li Prof. Abstract Chemical oxidative polymerization at 15,°C was used for the simple and productive synthesis of polyaniline (PAN) nanosticks. The effect of polymerization media on the yield, size, stability, and electrical conductivity of the PAN nanosticks was studied by changing the concentration and nature of the acid medium and oxidant and by introducing organic solvent. Molecular and supramolecular structure, size, and size distribution of the PAN nanosticks were characterized by UV/Vis and IR spectroscopy, X-ray diffraction, laser particle-size analysis, and transmission electron microscopy. Introduction of organic solvent is advantageous for enhancing the yield of PAN nanosticks but disadvantageous for formation of PAN nanosticks with small size and high conductivity. The concentration and nature of the acid medium have a major influence on the polymerization yield and conductivity of the nanosized PAN. The average diameter and length of PAN nanosticks produced with 2,M HNO3 and 0.5,M H2SO4 as acid media are about 40 and 300,nm, respectively. The PAN nanosticks obtained in an optimal medium (i.e., 2,M HNO3) exhibit the highest conductivity of 2.23,S,cm,1 and the highest yield of 80.7,%. A mechanism of formation of nanosticks instead of nanoparticles is proposed. Nanocomposite films of the PAN nanosticks with poly(vinyl alcohol) show a low percolation threshold of 0.2,wt,%, at which the film retains almost the same transparency and strength as pure poly(vinyl alcohol) but 262,000 times the conductivity of pure poly(vinyl alcohol) film. The present synthesis of PAN nanosticks requires no external stabilizer and provides a facile and direct route for fabrication of PAN nanosticks with high yield, controllable size, intrinsic self-stability, strong redispersibility, high purity, and optimizable conductivity. [source] Determination of the uronic acid composition of seaweed dietary ,bre by HPLCBIOMEDICAL CHROMATOGRAPHY, Issue 2 2004D. I. Sánchez-Machado Abstract A high-performance liquid chromatographic (HPLC) method is described for determination of the ratio of , - d -mannuronic acid to , - l -guluronic acid (M/G ratio) in dietary ,bre of edible seaweeds. Total dietary ,bre (TDF) content was determined gravimetrically. The TDF fraction was hydrolysed with 12 m and 1 m H2SO4, then neutralized with AG 4 × 4 resin. The uronic acids were separated in a Tracer Extrasil SAX 5 µm column (25 cm × 4 mm) at 35°C, with 2 mm KH2PO4 containing 5% methanol as mobile phase at a ,ow rate of 1.5 mL/min. The detection wavelength was UV 210 nm. The chromatographic identi,cations of , - d -mannuronic acid and , - l -guluronic acid were con,rmed by liquid chromatography,mass spectrometry (LC-MS). The method precision was 1.4% for , - d -mannuronic acid and 3.5% for , - l -guluronic acid. The method was used to determine M/G ratio in canned seaweeds (Saccorhiza polyschides and Himanthalia elongata) and in dried seaweeds (H. elongata, Laminaria ochroleuca, Undaria pinnati,da, Palmaria sp. and Porphyra sp.). Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||