Sol-gel-derived ceramic carbon composite electrode containing isopolymolybdic anions

A new class of polyoxomelalate (POM)-modified electrodes is fabricated by the sol-gel technique and demonstrated for nitrite sensing. The electrode material comprises an interconnected dispersion of graphite powder and a uniform dispersion of isopolymolybdic anions (Mo8O26) in a porous methylsilicate matrix. The chemically modified electrodes showed well-defined cyclic voltammograms with three reversible redox couples in acidic aqueous solutions because of the good physicochemical compatibility of Mo8O26 and the carbon ceramic matrix. The Mo8O26-modified electrodes show good stability and reproducibility, especially the renewal repeatability by simple polishing in the event of surface fouling. (C) 2000 Elsevier Science Ltd. All rights reserved.

PMo12-doped carbon ceramic composite electrode based on sol-gel chemistry and its electrocatalytic reduction of bromate

A conductive carbon ceramic composite electrode (CCE) comprised of cc-type 1:12 phosphomolybdic acid (PMo12) and carbon powder in an organically modified silicate matrix was fabricated using a sol-gel method and characterized by scanning electron microscopy, cyclic voltammetry, and Osteryoung square-wave voltammetry. Osteryoung square-wave voltammograms of the modified electrode immersed in different acidic aqueous solutions present the dependence of current and redox potential on pH. The PMo12-doped CCE shows more reversible reaction kinetics, good stability and reproducibility, especially the renewal repeatability by simple polishing in the event of surface fouling or dopant leaching. Moreover, the modified electrode shows good catalytic activity for the electrochemical reduction of bromate.

Ion channel behavior of supported bilayer lipid membranes on a glassy carbon electrode

A new kind of solid substrate, a glassy carbon (GC) electrode, was selected to support lipid layer membranes. On the surface of the GC electrode, we made layers of didodecyldimethylammonium bromide (a synthetic lipid). From electrochemical impedance experiments, we demonstrated that the lipid layers on the GC electrode were bilayer lipid membranes. We studied the ion channel behavior of the supported bilayer lipid membrane. In the presence of perchlorate anions as the stimulus and ruthenium(II) complex cations as the marker ions, the lipid membrane channel was open and exhibited distinct channel current. The channel was in a closed state in the absence of perchlorate anions.

Renewable three-dimensional Prussian blue modified carbon ceramic electrode

Prussian blue (PB) supported on graphite powder was prepared by the chemical deposition technique and subsequently dispersed into methyltrimethoxysilane-derived gels to yield a conductive graphite organosilicate composite. The composite was used as the electrode material to fabricate a three-dimensional PB-modified electrode. PB acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. The chemically modified electrode can electrocatalyze the oxidation of hydrazine, and exhibits a distinct advantage of polishing in the event of surface fouling, as well as simple preparation, good chemical and mechanical stability and good repeatability of surface-renewal. Hydrodynamic voltammetric experiments were performed to characterize the electrode as an amperometric sensor for the determination of hydrazine. (C) 2000 Elsevier Science B.V. All rights reserved.

Organic-phase enzyme electrode for phenolic determination based on a functionalized sol-gel composite

An amperometric biosensor for monitoring phenols in the organic phase was constructed by the silica sol-gel immobilization of tyrosinase on a glassy carbon electrode. The organic-inorganic hybrid materials with different sol-gel precursors and polymers were optimized, and the experimental conditions, such as the effect of the solvent, operational potential and enzyme loading were explored for the optimum analytical performance of the enzyme electrode. The biosensor can reach 95% of steady-state current in about 18 s, and the trend in the sensitivity of different phenols is as follows: catechol > phenol >p-cresol. In addition, the apparent Michaelis-Menten constants (K-m(app)) and the stability of the enzyme electrode were discussed. (C) 2000 Elsevier Science S.A. All rights reserved.

Study on adsorption and oxidation of calf thymus DNA at glassy carbon electrode

The oxidation and adsorption of the temperature-denatured DNA at GC electrode are studied by differential pulse voltammetry and in situ FTIR spectroelectrochemistry. The temperature-denatured DNA is adsorbed and formed a DNA multilayer at electrode surface. The temperature-denatured DNA showing partly reversible process was first observed based on the reduction peaks appearing at negative scans and the reversible spectral change. The oxidation product of the temperature-denatured DNA can not diffuse away from the electrode surface easily due to the impediment of the DNA multilayer, so it can be partly reduced.

Surface renewable graphite organosilicate composite electrode containing indium(III) hexacyanoferrate(II/III)

Indium(III) hexacyanoferrate(II/III) (InHCF) supported on graphite powder was prepared using the in situ chemical deposition procedure and subsequently dispersed into methyltrimethoxysilane-derived gels to yield a conductive graphite organosilicate composite. The composite was used as the electrode material to fabricate a three-dimensional InHCF-modified electrode. InHCF acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. The chemically modified electrode can electrocatalyze the oxidation of thiosulfate, and exhibits a good repeatability of surface-renewal by simple mechanical polishing, as well as simple preparation, good chemical and mechanical stability.

Fabrication and electrochemical behavior of a sol-gel-derived carbon ceramic composite electrode entrapping 2 : 18-molybdodiphosphate

A new type of inorganic-organic hybrid material incorporating carbon powder and alpha -type 2:18-molybdodiphosphate (P2Mo18) in a methyltrimethoxysilane (MTMOS) based gel has been produced by a sol-gel process and used to fabricate a chemically modified electrode. The P2Mo18-doped carbon ceramic composite electrode was characterized using SEM and cyclic voltammetry. Square-wave voltammetry with an excellent sensitivity was exploited to conveniently investigate the dependence of current and half-wave potential (E-1/2) on pH. The chemically modified electrode has some advantages over the modified film electrodes constructed by the conventional methods, such as long-term stability, reproducibility, and especially repeatability of surface-renewal by simple polishing in the event of surface fouling or dopant leaching. In addition, the modified electrode shows a good catalytic activity for the electrochemical reduction of bromate in an acidic aqueous solution. (C) 2000 Elsevier Science B.V. All rights reserved.

Electrocatalytic oxidation of NADH by rutin in biomembrane-like films on glassy carbon electrode

Stable lipid film was made by casting dipalmitoylphosphatidylcholine (DPPC) and rutin onto the surface of a glassy carbon (GC) electrode. The electrochemical behavior of rutin in the DPPC film was studied. The modified electrode coated with rutin gave quasi-reversible reduction-oxidation peak on cyclic voltammogram in the phosphate buffer (pH 7.4). The peak current did not decrease apparently after stored at 4 degreesC for 8 hours in refrigerator. This model of biological membrane was used to investigate the oxidation of dihydronicotinamide adenine dinucleotide (NADH) by rutin. Rutin in the film acts as a mediator. The modified electrode shows a great enhancement and the anodic peak potential was reduced by about 220 mV in the oxidation of 5 X 10(-3) mol L-1 NADN compared with that obtained at a bare glassy carbon electrode. (C) 2000 Elsevier Science S.A. All rights reserved.

Electrochemiluminescent detection of chlorpromazine by selective preconcentration at a lauric acid-modified carbon paste electrode using tris(2,2 '-bipyridine)ruthenium(II)

A new detection scheme for the determination of adsorbable coreactants of Ru(bpy)(3)(2+) electrochemiluminescent reaction is presented. It is based on selective preconcentration of coreactant onto an electrode, followed by Ru(bpy)(3)(2+) electrochemiluminescent detection. The coreactant employed is chlorpromazine. It was sensitively detected after 5-min preconcentration onto a lauric acid-modified carbon paste electrode. The linear concentration range was found to occur from 1 x 10(-8) to 3 x 10(-6) mol L-1 with a detection limit of 3.1 x 10(-9) mol L-1. The total analysis time is less than 10 min. As a result of selective preconcentration and medium exchange, such remarkable selectivity is achieved that reproducible quantitation of chlorpromazine in urine is possible.

Sol-gel-derived, polishable, 1 : 12-phosphomolybdic acid-modified ceramic-carbon electrode and its electrocatalytic oxidation of ascorbic acid

Novel ceramic-carbon electrodes (CCEs) containing 1:12-phosphomolybdic acid (PMo12) were constructed by homogeneously dispersing PMo12 and graphite powder into methyltrimethoxysilane-derived gel. Peak currents for the PMo12-doped CCE were surface-controlled at lower scan rates but diffusion-controlled at higher scan rates and peak potentials shifted to the negative potential direction with increasing pH. In addition, the electrode exhibited electrocatalytic activity toward the oxidation of ascorbic acid. The PMo12-modified CCE presented good chemical and mechanical stability and good surface renewability (ten successive polishing resulted in less than 5% relative standard deviation). (C) 2000 Elsevier Science B.V. All rights reserved.

Anodic voltammetric behavior of medecamycin at a glassy carbon electrode

The anodic voltammetric behavior of medecamycin (MD) in the presence of various electrolytes was studied by linearsweep voltammetry, differential-pulse voltammetry and cyclic voltammetry at a glassy carbon electrode. In phosphate buffer solutions (pH = 9.4), MD is oxidized irreversibly. The peak potential is at about +0.75 V (vs.Ag/AgCl). The height of the peak is linearly increased with the concentration of MD over the range of 5 x 10(-5) similar to 1 x 10(-1) g/L. The method has been used for the direct determination of MD in tablets. The relative standard deviation (n = 10) is 1.8%. The recoveries of MD in urine samples are in the range of 95% similar to 115%.

Studies on electrocatalytic performance of titanium oxide electrode modified with Pt toward the oxidation of methanol

Electrocatalytic performance of the Pr-TiOx/Ti electrode prepared with electrochemical reduction-oxidation method toward the oxidation of methanol has been studied, The experimental results showed that the Pt-TiOx/Ti electrode has a high electrocatalytic activity and good stability for the electrocatalytic oxidation of methanol, By means of electrochemical, XPS, STM and in-situ FTIR techniques, it was found that one reason for the electrode to exhibit an excellent performance is attributed to the high dispersion between nanosized Pt and TiOx particles, The low adsorption ability of the intermediate derived from methanol, such as linearly adsorbed CO species on the electrode surface due to the interaction between Pt and TiOx, also results in the excellent performance.

Layer-by-layer assembly of multilayer films consisting of silicotungstate and a cationic redox polymer on 4-aminobenzoic acid modified glassy carbon electrode and their electrocatalytic effects

A novel 4-aminobenzoic acid (4-ABA) monolayer film is formed on glassy carbon electrode (GCE) by amino cation radical method. Silicotungstic heteropolyanion (SiW12O404-, denoted as SiW12)-containing multilayer films have been fabricated on the 4-ABA modified GCE surface by alternate deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/+) (denoted as QPVP-Os). Cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XR) have been used to characterise the as-prepared multilayer films. It is proved that the multilayer films are uniform and stable. The average thickness for a bilayer of QPVP-Os/SiW12 in the multilayer film is 30.2 Angstrom. The electrocatalytic activities of the multilayer films have been investigated on the reduction of three substrates of important analytical interests, HNO2, BrO3- and H2O2. Especially, the influence of layer number of the multilayer films on the electrocatalytic reduction of HNO2 has been investigated in detail. (C) 2000 Elsevier Science B.V. All rights reserved.

Digital simulation in a thin layer spectroelectrochemical cell with minigrid platinum electrode by microregion approximation explicit finite difference method

The microregion approximation explicit finite difference method is used to simulate cyclic voltammetry of an electrochemical reversible system in a three-dimensional thin layer cell with minigrid platinum electrode. The simulated CV curve and potential scan-absorbance curve were in very good accordance with the experimental results, which differed from those at a plate electrode. The influences of sweep rate, thickness of the thin layer, and mesh size on the peak current and peak separation were also studied by numerical analysis, which give some instruction for choosing experimental conditions or designing a thin layer cell. The critical ratio (1.33) of the diffusion path inside the mesh hole and across the thin layer was also obtained. If the ratio is greater than 1.33 by means of reducing the thickness of a thin layer, the electrochemical property will be far away from the thin layer property.