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.

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.

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.

Sol-gel-derived carbon ceramic composite electrodes bulk-modified with 1 : 12-silicomolybdic acid

1:12-Silicomolybdic acid (SiMo12) doped carbon ceramic composite electrodes were fabricated by incorporating SiMo12 and graphite powder in a methyltrimethoxysilane-based gel and characterized by cyclic and square-wave voltammetry, It was demonstrated that the chemically modified electrodes were suitable for electrocatalytic reduction of bromate, The electrodes had the remarkable advantage of surface renewal owing to bulk modification, as web as simple preparation, good mechanical and chemical stability and reproducibility.

Sol-gel deposition of calcium silicate red-emitting luminescent films doped with Eu3+

Eu3+-activated calcium silicate (CaO-SiO2:Eu3+) luminescent films were prepared by the sol-gel method. The structural evolution of the film was studied by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), and the luminescence properties of the phosphor films were investigated as a function of heat treatment temperature. The XRD study indicates that a kilchoanite phase forms in the film sintered at 800 degreesC, which is different from that in gel powder treated under the same conditions. The SEM results show that the film thickness decreases and the particles in the film become smaller with increasing heat treatment temperature. The CaO-SiO2:Eu film shows the characteristic emission of Eu3+ under UV excitation, with the Eu3+ D-5(0)-->F-7(2) band (616 nm) being the most prominent. A large difference in the Eu3+ lifetime is observed between the film samples treated at 500 and 700 degreesC (or above). Concentration quenching occurs when the Eu3+ doping concentration is above 6 mol% of Ca2+ in the film.

Ceramic carbon/polypyrrole materials for the construction of bienzymatic amperometric biosensor for glucose

A novel amperometric glucose biosensor was constructed by electrochemical formation of a polypyrrole (PPy) membrane in the presence of glucose oxidase (GOD) on the surface of a horseradish peroxidase (HRP) modified ferrocenecarboxylic acid (FCA) mediated sol-gel derived ceramic carbon electrode. The amperometric detection of glucose was carried out at +0.16 V (vs. SCE) in 0.1 mol/L phosphate buffer solution (pH 6.9) with a linear response range between 8.0x10(-5) and 1.3x10(-3) mol/L of glucose. The biosensor showed a good suppression of interference and a negligible deviation in the amperometric detection.

Sol-gel-derived carbon ceramic electrode containing 9,10-phenanthrenequinone, and its electrocatalytic activity toward iodate

9,10-Phenanthrenequinone (PQ) supported on graphite powder by adsorption was dispersed in propyltrimethoxysilane-derived gels to yield a conductive composite which was used as electrode material to fabricate a PQ-modified carbon ceramic electrode. In this configuration, PQ acts as a catalyst, graphite powder guarantees conductivity by percolation, the silicate provides a rigid porous backbone, and the propyl groups endow hydrophobicity and thus limit the wetting region of the modified electrode. Square-wave voltammetry was exploited to investigate the pH-dependent electrochemical behavior of the composite electrode and an almost Nernstian response was obtained from pH 0.42 to 6.84. Because the chemically modified electrode can electrocatalyze the reduction of iodate in acidic aqueous solution (pH 2.45), it was used as an amperometric sensor for the determination of iodate in table salt. The advantages of the electrode are that it can be polished in the event of surface fouling, it is simple to prepare, has excellent chemical and mechanical stability, and the reproducibility of surface-renewal is good.

Amperometric determination of thiosulfate at a surface-renewable nickel(II) hexacyanoferrate-modified carbon ceramic electrode

Graphite powder-supported nickel(II) hexacyanoferrate (NiHCF) was prepared by the in situ chemical deposition method and then dispersed into methyltrimethoxysilane-derived gels to form a conductive composite. The composite was used as electrode material to construct a surface-renewable three-dimensional NiHCF-modified carbon ceramic electrode. Electrochemical behavior of the chemically modified electrode was well characterized using cyclic and square-wave voltammetry. The electrode presented a good electrocatalytic activity toward the oxidization of thiosulfate and thus was used as an amperometric sensor for thiosulfate in the photographic waste effluent. In addition, the electrode exhibited a distinct advantage of surface-renewal by simple mechanical polishing, as well as simple preparation, good chemical and mechanical stability. (C) 2001 Elsevier Science B.V. All rights reserved.

Bright red organic electroluminescent devices based on a soluble rare earth complex Eu(TTA)(3) Phen

An Electroluminescent device with PVK film doped with Eu(TTA)(3) Phen and PBD was fabricated. The device structure of glass substrate/indium-tin-oxide/PPV/PVK : Eu(TTA)3 Phen : PBD/Alq(3)/Al was employed. A sharply red electroluminescence with a maximum luminance of 56. 8 cd/m(2) at 48 V was achieved.

Bright red electroluminescent devices based on a soluble lanthanide complex Eu(DBM)(3)(phen)

Electroluminescent devices with PVK film doped with Eu(DBM)(3)(phen) and PBD were fabricated. The device structure of glass substrate/indium-tin-oxide/PPV/PVK:Eu(DBM)(3)-(phen):PBD/Alq(3)/Al was employed. The emissive layer was formed by spin-casting method. A sharply red electroluminescence with a maximum luminance of 114.4 cd/m(2) was achieved at 42 V.

Scanning tunnelling microscopy observation of cytochrome-c denaturation induced by bromopyrogal red on highly oriented pyrolytic graphite

The denaturation of cytochrome-e (cyt-c) induced by bromopyrogal red (BPR) was studied by scanning tunnelling microscopy (STM) on the electrochemically pretreated highly oriented pyrolytic graphite (HOPG) surface. STM images reveal that denatured cyt-c molecules exist in variable states including aggregates, globular compact, partially unfolded and combined with BPR molecule. The apparently low image contrast of denatured cyt-c observed in this experiment comparing to that of native cyt-c molecules, and the relative low image contrast of the unfolded part comparing with the compact globular part, are ascribed to the unfavourable tunnelling paths for the conformational variations of denatured cyt-c molecules. (C) 1997 Elsevier Science B.V.

Red color filter in an organo-soluble polyamide matrix for liquid crystal displays

A red color filter was laminated from a solution of red color pigment and an organo-soluble polyamide, based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and 2,2'-dimethyl-4,4'-methylene dianiline (DMMDA). The red color filter in a polyamide matrix with negative birefringence plays an important role in twisted nematic liquid crystal displays (TN-LCDs). The red color filter, and also compensation films, extend the viewing angle of LCDs. (C) 1997 Elsevier Science S.A.

Dynamic spectroelectrochemical measurement for the conformational transition of cytochrome c induced by bromopyrogal red

The conformational transition of horse heart cytochrome c induced by bromopyrogal red (BPR) in very low concentration has been firstly investigated by dynamic spectroelectrochemical technique, both at the BPR adsorbed platinum gauze electrode and at a bare platinum gauze electrode in a solution containing BPR. The effect of BPR on the structure of cytochrome c was studied by UV-visible and Fourier transform IR spectroscopy. The unfolded cytochrome c behaves simply as an electron transfer protein with a formal potential of -142 mV vs. a normal hydrogen electrode. The difference between the formal potentials of the native and unfolded cytochrome c is coupled to a difference in conformational energy of the two states of about 40 kJ mol(-1), which agrees well with the result reported. The stability and slow refolding of the unfolded cytochrome c are discussed.

DETERMINATION OF PARAMETERS OF FAST CHEMICAL REACTION OF ALIZARIN RED S BY SPECTROELECTROCHEMICAL METHOD WITH LOPTLC

The rate constant of very fast chemical reaction generally can be measured by electrochemical methods, but can not by the thin layer electrochemical methods because of the influence of diffusion effect. Long optical path length thin layer cell (LOPTLC) with large ratio of electrode area to solution volume can be used to monitor the fist chemical reaction in situ with high sensitivity and accuracy. It enable the adsorption spectra to be measured without the influence of diffusion effect. In the present paper, a fast chemical reaction of Alizarin Red S (ARS) with its oxidative state has been studied. The reaction equilibrium constant (K) under different potentials can be determined by single step potential-absorption spectra in LOPTLC. An equilibrium constant of 7.94 x 10(5) l.mol(-1) for the chemical reaction has been obtained from the plot of lgK vs. (E - E-1(0)'). Rate constant (k) under different potentials can be measured by single step potential-chronoabsorptiometry. A rate constant of 426.6 l.mol(-1).s(-1) for the chemical reaction has been obtained from the plot of lgK vs. (E - E-1(0)') with (E - E-1(0)') = 0.