Electrochemical studies of a lanthanide heteropoly tungstate/molybdate complex in polypyrrole film electrode and its electrocatalytic reduction of bromate

An electrode modified with a polybasic lanthanide heteropoly tungstate/molybdate complex K10H3[Nd(SiMo7W4O39)(2)] entrapped into polypyrrole (PPy) film, denoted as Nd(SiMo7W4)(2)-PPy, exhibits three couples of two-electron redox waves in pH 1-5 buffer solutions. The redox waves are surface-controlled at lower scan rates and diffusion-controlled at higher scan rates. The effects of pH on the electrochemical behavior of Nd(SiMo7W4)(2) in PPy film were investigated in detail and compared with that of Nd(SiMo7W4)(2) in aqueous solution. The various charge states of PPy during its redox process have peculiar effects on the relationship between pH and formal potentials of Nd(SiMo7W4)(2)-PPy at different acidities. The Nd(SiMo7W4)(2)-PPy cme can remarkably catalyze the electrochemical reduction of bromate with good stability. (C) 1997 Elsevier Science Ltd.

Electrocatalytic oxidation and flow amperometric detection of hydrazine at an electropolymerized 4-vinylpyridine/palladium film electrode

A poly(4-vinyl)pyridine (PVP)/Pd film electrode was constructed for the electrocatalytic detection of hydrazine. The preparation of the PVP/GC electrode was performed by electropolymerization of the monomer 4-vinylpyridine onto the surface of a glassy carbon electrode. Subsequently, palladium is electrodeposited onto the polymer modified electrode surface. The ion-exchange function of PVP polymer is helpful to this process in view of the tetrachlorapalladate anion. Compared with the Pd/GC electrode, the modified electrode displays a better mechanical stability in a flowing stream. The PVP/Pd film electrode exhibits higher sensitivity when detecting hydrazine with a detection limit of 0.026 ng (S/N=3).

Study on the modified electrode of conducting polymers .3. Electron spin resonance characteristic of polypyrrole film electrode doped with heteropolyanions

The ESR of PPy films doped with Co (W2O7)(6)(10-) and CuW12O406- ions were reported and discussed. Results show that heteropolyanions not only play the role of neutralizing electricity in the PPy film, but also interact with the PPy molecular chain to form some adducts. The adducts affect the electronic structure of the PPy film and are unstable at more positive or more negative potentials. Dysonian ESR lineshape was recorded for the dry PPy film with CuW12O406- for the first time.

PREPARATION AND CHARACTERIZATION OF ISOPOLYMOLYBDIC ANIONS DOPED POLYPYRROLE (IPOMO/PPY) FILM ELECTRODE

Isopolymolybdic anion doped polypyrrole film electrode was prepared by electrochemical polymerization of pyrrole in 0.5 mol.L-1 H2SO4 aqueous solution containing isopolymolybdic anions. The film thus prepared has good stability upon potential cycling in s

Characterization of 1:12 Phosphomolybdic Anions Doped Polypyrrole (PMo12/PPy) Film Electrode

1:12 phosphomolybdic anion doped polypyrrole film electrode was characterized by in-situ UV-vis spectroelectrochemistry, X-ray photoelectron spectroscopy(XPS), scan electronic microscopy(SEM) and electron spin resonance(ESR) spectroscopy.

STUDY OF A 1/12 PHOSPHOMOLYBDIC ANION DOPED POLYPYRROLE FILM ELECTRODE AND ITS CATALYSIS

A phosphomolybdic anion doped polypyrrole (PMo12O403- + PPy) film electrode has been prepared by electrochemical polymerization of pyrrole in an aqueous solution of 0.5 mol l-1 H2SO4 or 0.5 mol l-1 KNO3 containing PMo12O403- anions, and characterized by scanning electron microscopy and in-situ UV-visible spectroelectrochemical methods. The film electrode obtained is very stable upon potential cycling in acidic solution, but not in neutral solution. The catalytic effect of the film electrode on the reduction of ClO3- and BrO3- was studied.

ELECTROCATALYSIS AND DETERMINATION OF HYDRAZINE COMPOUNDS IN LIQUID-CHROMATOGRAPHY AT A MIXED-VALENT COBALT OXIDE CYANOCOBALTATE FILM ELECTRODE

A glassy carbon electrode coated with an electrodeposited film of mixed-valent cobalt oxide/cyanocobaltate (Co-O/CN-Co) enabled hydrazine compounds to be catalytically oxidized at the greatly reduced overpotential and in a wide operational pH range (pH 2.0-7.0). Electrocatalytic activity at the Co-O/CN-Co modified electrode was evaluated with respect to solution pH, film thickness, supporting electrolyte ions, potential scan rate, operating potential, concentration dependence and other variables. The Co-O/CN-Co film electrode was completely compatible with a conventional reversed-phase liquid chromatographic (RP-LC) system. Practical RP-LC amperometric detection (RP-LCEC) of hydrazines was performed. A dynamic linear response range over three orders of magnitude and a detection limit at the pmol level were readily obtained. The Co-O/CN-CO film electrode exhibited excellent electrocatalytic stability in the flowing streams.

INDIGO-CARMINE-MODIFIED POLYPYRROLE FILM ELECTRODE

Functionalized polypyrrole films were prepared electrochemically in the presence of indigo-carmine from aqueous solution. The film shows a couple of reversible redox peaks superimposed on a large background of polypyrrole. The redox reaction is pH dependent. The film has good stability in air and can be cycled between -0.1 and 0.4 V (Ag/AgCl) for several hours without any significant changes in the voltammograms. UV-visible spectra indicate the incorporation of indigo-carmine into the polymer matrix.

STUDY OF THE ELECTRODE PROCESS OF HEMOGLOBIN AT A POLYMERIZED AZURE A FILM ELECTRODE

The electrochemically polymerized azure A film electrode is reported. The resulting film on a platinum electrode surface was analyzed with electron spectroscopy for chemical analysis (ESCA). The heterogeneous electron transfer processes of hemoglobin at the polymerized azure A film electrode have been investigated using in situ UV-visible spectroelectrochemistry. The formal potential (E-degrees') and electron transfer number (n) of hemoglobin were calculated as E = 0.088 V versus NHE (standard deviation +/- 0.5, N = 4) and n = 1.8 (standard deviation +/- 0.5, N = 4). Exhaustive reduction and oxidation electrolysis are achieved in 80 and 380 seconds, respectively, during a potential step between -0.3 and +0.3 V. A formal heterogeneous electron-transfer rate constant (k(sh)) of 3.54(+/- 0.12) X 10(-6) cm/s and a transfer coefficient (alpha) of 0.28(+/- 0.01) were obtained by cyclic voltabsorptometry, which indicated that the poly-azure A film electrode is able to catalyze the direct reduction and oxidation of hemoglobin.

STUDIES ON INTERFACIAL PHENOMENA OF POLYCRYSTALLINE HG1-XCDXTE THIN-FILM ELECTRODE POLYSULFIDE REDOX SOLUTION

Electrode capacitance and photocurrent spectra of electrodeposited polycrystalline Hg1-xCdxTe thin films of varying (1-x) were measured in polysulfide redox solution, hence the flatband potentional PHI(fb) and the bandgap E(g) of Hg1-xCdxTe thin films obtained. It was of interest to find out that only the location of conduction band E(c) shifts negatively with increasing (1-x) while the valence band E(v), is almost constant. The experimental open circuit photovoltage V0 is smaller than theoretical value V(max) calculated through flatband potential PHI(fb), therefore there is a possibility of promoting the experimental open circuit photovoltage.

STUDY ON ELECTRODE PROCESS OF MYOGLOBIN AT A POLYMERIZED AZURE A FILM ELECTRODE

The electrochemically polymerized azure A film electrode was firstly reported in this paper. A quasi-reversible electrode processes of myoglobin with the formal heterogeneous electron transfer rate constant (k(sh)) of 1.73 x 10(-4) cm.s-1 at the polymerized azure A modified electrode have been achieved using in-situ UV-visible spectroelectrochemistry. The adsorption of myoglobin on the polymerized azure A film electrode surface was confirmed by XPS. With simultaneously studying of cyclic voltammetry and in-situ cyclic voltabsorptometry, the attribution of the voltammetry responses of myoglobin at the film electrode has been studied. The mechanism for the heterogeneous electron transfer of myoglobin at the polymerized azure A film modified electrode has been proposed as well.

An electrochemical sensor for (L)-dopa based on oxovanadium-salen thin film electrode applied flow injection system

An oxovanadium-salen complex (NAP-ethylene-bis(salicylidenciminato) oxovanadium) thin film deposited on a graphite-polyurethane electrode was investigated with regard to its potential use for detection of L-dopa in flow injection system. The oxovanadium(IV)/oxovanadium(V) redox couple of the modified electrode was found to mediate the L-dopa oxidation before its use in the FIA system. Experimental parameters, such as pH of the carrier solution, flow rate, sample volume injection and probable interferents were investigated. Under the optimized FIA conditions, the amperometric signal was linearly dependent on the L-dopa concentration over the range 1.0 x 10(-1) to 1.0 x 10(-4) mol L-1 (I-anodic, mu A) = 0.01 + 0.25 [L-dopa mu mol L-1]) with a detection limit (S/N = 3) of 8.0 x 10(-7) mol L-1 and a sampling frequency of 90 h(-1) was achieved. For a concentration of 1.0 x 10(-5) mol L-1 L-dopa, the R.S.D. of nine consecutive measurements was 3.7%. (c) 2006 Elsevier B.V. All rights reserved.

Photoelectrocatalytic treatment of p-nitrophenol using Ti/TiO2 thin-film electrode

The photoelectrochemical degradation of p-nitrophenol (PNP) was investigated using titanium dioxide thin-film photoelectrode. The effects of different supporting electrolytes, pH, applied potential and PNP concentration were examined and discussed. Complete photodegradation was obtained in perchlorate medium at pH 2 when the photoanode was biased at +1.0 V (versus SCE) during a 3-h experiment. Under these conditions, carbon removal of approximately 60% was achieved. (C) 2005 Elsevier B.V. All rights reserved.

Nanoporous of W/WO3 Thin Film Electrode Grown by Electrochemical Anodization Applied in the Photoelectrocatalytic Oxidation of the Basic Red 51 used in Hair Dye

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