Poly(3-dodecylthiophenes) polymerized with different amounts of catalyst

The effect of the amount of the catalyst FeCl3, used during the direct oxidation polymerization, on the structure and properties of the obtained poly(3-dodecylthiophene) (P3DDT) was investigated in this paper. Such measurements as gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, thermal analysis, X-ray diffraction, infrared spectroscopy (FTIR) and ultraviolet-visible (W-vis) spectroscopy were applied. It is found that a suitable addition of FeCl3 can contribute to generate a P3DDT with greater percentage of head-to-tail head-to-tail (HT-HT) linkages, which are generally favored. The reduction of the other linkage defects helps to lengthen conjugation length, thus leading to more orderly chain packing. (C) 2000 Elsevier Science S.A. All rights reserved.

Renewable-surface amperometric nitrite sensor based on sol-gel-derived silicomolybdate-methylsilicate-graphite composite material

A new type of silicomolybdate-methylsilicate-graphite composite material was prepared by the sol-gel technique and used for the fabrication of an amperometric nitrite sensor. The silicomolybdic anion acts as a catalyst, the 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. Cyclic voltammetry, square-wave voltammetry and chronoamperometry were employed to characterize the sensor. The amperometric nitrite sensor exhibited a series of good properties: high sensitivity (1.771 mu A mmol(-1) dm(3)), a short response time (7 s), remarkable long-term stability and especially reproducibility of surface renewal in the event of electrode surface fouling.

Amperometric enzyme electrode for the determination of hydrogen peroxide based on sol-gel/hydrogel composite film

A new type of organic-inorganic composite material was prepared by sol-gel method, and a peroxidase biosensor was fabricated by simply dropping sor-gel-peroxidase mixture onto glassy carbon electrode surface. The sol-gel composite film and enzyme membrane were characterized by Fourier-transform infrared (FT-IR) spectroscopy and EQCM, the electrochemical behavior of the biosensor was studied with potassium hexacyanoferrate(II) as a mediator, and the effects of pH and operating potential were explored for optimum analytical performance by using amperometric method. The response time of the biosensor was about 10 s; the linear range was up to 3.4 mM with a detection limit of 5 x 10(-7) M. The sensor also exhibited high sensitivity (15 mu A mM(-1)) and good long-term stability. In addition, the performance of the biosensor was investigated using flow injection analysis (FIA), and the determination of hydrogen peroxide in real samples was discussed. (C)2000 Elsevier Science B.V. All rights reserved.

Confined crystallization behavior of PEO in silica networks

Poly(ethylene oxide) (PEO) and silica (SiO2) organic-inorganic hybrid materials have been synthesized by sol-gel approach. The crystallization behavior of PEO in silica networks has been investigated by differential scanning calorimeter (DSC) and scanning electron micrograph (SEM). The degree of PEO crystallinity in PEO/SiO2 hybrid networks reduces with the increase of SiO2. PEO is in amorphous state when the concentration of PEO is lower than 50 wt% in the hybrid materials. The melting points of PEO in the networks are lower than that of pure PEG, but the melting point of PEO in the networks almost has the same melting point. WAXD and SEM results show that the crystalline behavior of PEO in PEO/SiO2 hybrid system is sternly confined. (C) 1999 Elsevier Science Ltd. All rights reserved.

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 tyrosinase biosensor based on a sol-gel-derived titanium oxide-copolymer composite matrix for detection of phenolic compounds

A new type of tyrosinase biosensor was developed for the detection of phenolic compounds, based on the immobilization of tyrosinase in a sol-gel-derived composite matrix that is composed of titanium oxide sol and a grafting copolymer of poly(vinyl alcohol) with 4-vinylpyridine. Tyrosinase entrapped in the composite matrix can retain its activity to a large extent owing to the good biocompatibility of the matrix. The parameters of the fabrication process and the variables of the experimental conditions for the enzyme electrode were optimized. The resulting sensor exhibited a fast response (20 s), high sensitivity (145.5 muA mmol(-1) 1) and good storage stability. A detection limit of 0.5 muM catechol was obtained at a signal-to-noise ratio of 3.

Hydrogen peroxide biosensor with enzyme entrapped within electrodeposited polypyrrole based on mediated sol-gel derived composite carbon electrode

A novel amperometric biosensor for the detection of hydrogen peroxide was described. The biosensor was constructed by electrodepositing HRP/PPy membrane on the surface of ferrocenecarboxylic acid mediated sol-gel derived composite carbon electrode. The biosensor gave response to hydrogen peroxide in a few seconds with detection limit of 5.0 x 10(-5) M (based on signal:noise = 3). Linear range was upto 0.2 mM. The biosensor exhibited a good stability. (C) 2001 Elsevier Science B.V. All rights reserved.

Sol-gel synthesis and properties of Ce1-xGdxO2-x/2 solid solutions

A series of solid electrolytes Ce1-xGdxO2-x/2(x=0 similar to0.6) was prepared by sol-gel method. The structure, thermal expansion coefficient and electrical properties of the solid solutions were systematically studied. XRD data showed that a complete cubic fluorite structure was formed at 160 degreesC. The purity of the product prepared by the sol-gel method is higher, the grain size is uniformly smaller. They were easily sintered into highly dense ceramic pellets at 1 300 degreesC. The sintering temperature was significantly lower than that by traditionally high temperature solid phase reaction method. The thermal expansion coefficient of Ce0.8Gd0.2O1.9, determined from high- temperature XRD data, is 8. 125 X 10(-6) K-1. Impedance spectra analyses showed that the grain-boundary resistance of the solid electrolyte prepared by sol-gel method was reduced or even eliminated. The conductivity of Ce0.8Gd0.2O1.9 is 5.26 X 10(-3) S/cm at 600 degreesC. The activation energy (E-a) is 0.82 eV.

A hydrogen peroxide biosensor combined HRP doped polypyrrole with ferrocene modified sol-gel derived composite carbon electrode

A novel amperometric biosensor for the detection of hydrogen peroxide is described. The biosensor was constructed by electrodepositing HRP/PPy membrane on the surface of ferrocenecarboxylic acid mediated sol-gel derived composite carbon electrode. The biosensor gives response to hydrogen peroxide in a few seconds with detection limit of 5x10(-7) mol (.) L-1 (based on signal : noise=3). Linear range is up to 0.2 mmol (.) L-1.

Fabrication of agar-gel microelectrodes and their application in the study of ion transfer across the agar-water 1,2-dichloroethane interface

In this paper, we describe a simple procedure to make agar-gel microelectrodes by filling micropipettes. These microelectrodes were used to study K+ transfer across the agar-water \ 1,2-dichloroethane interface facilitated by dibenzo-18-crown-6 (DB18C6), and the transfer of tetraethylammonium (TEA(+)). The results observed were similar to those obtained at micro-liquid \ liquid interfaces. The effect of various amounts of agar in the aqueous phase was optimized and 3% agar was chosen based on the potential window and solidification time. The different shapes of micro-agar-gel electrodes were prepared in a similar way. The fabricated agar-gel microelectrodes obey the classical micro-disk steady-state current equation, which is different from the behavior of a normal micropipette filled with aqueous solution without silanization. (C) 2001 Elsevier Science B.V. All rights reserved.

Preparation and optical characterization of an organoeuropium-doped sol-gel transparent luminescence thin film

Binary and ternary europium complexes with dibenzplymethane (DBM) and 1,10-phenanthroline (phen) were synthesized and doped into a sol-gel luminescence thin film and polyvinylbutyral (PVB) film. The luminescent spectra and lifetime of the films were measured. The final results showed that Eu(III) characteristic emission bands were observed in the spectra of all the doped films. Longer lifetimes and a higher photo-stability were observed in SiO2:Eu(III) complex luminescent thin films than in PVB:Eu(III) complex films that contained a corresponding amount of pure complexes. Heat-stability tests showed that SiO2:Eu(III) complex thin films still showed certain fluorescence after heat-treatment at a temperature of 130 degreesC, while little fluorescence could be observed in PVB:Eu(III) complex films under a UV lamp. (C) 2001 Elsevier Science B.V. All rights reserved.

Preparation and luminescence properties of lanthanide complexes and their silica-based composites

Binary complexes of europium and terbium with N-propyl-4-carboxyphthalimide (NP) were prepared and characterized. The luminescence behaviors of the lanthanide complexes as well as their doped silica-based composites were investigated by fluorescence spectra. The results indicated that the lanthanide complexes showed fewer emission lines and slightly lower intensities in silica matrix than that of corresponding pure complexes. The lifetimes of the lanthanide complexes became longer when they were incorporated in silica matrix. (C) 2001 Elsevier Science B.V. All rights reserved.

Synthesis and luminescence properties of organic-inorganic hybrid thin films doped with Eu(III)

In this study, silica-based transparent organic-inorganic hybrid films were prepared by the sol-gel method. Tetraethoxysilane and 3-(trimethoxysilyl)propyl methacrylate were used as the inorganic and organic compounds, respectively. Lanthanide complexes [Eu(phen)(2)]Cl-3 were incorporated into the organically modified silicates (ORMOSIL) and the luminescence properties of the resultant hybrid films (ORMOSIL:[Eu(phen)(2)]Cl-3) were characterized. The relative quantum efficiency was observed higher and the lifetimes were longer in hybrid films than those in pure silica films. Furthermore, thermal stability of hybrid films incorporating various concentration of Eu(III) complex was studied. (C) 2001 Elsevier Science B.V. All rights reserved.

Progress in luminescent films prepared by sol-gel process

In this paper, state of the art for luminescent films prepared by sol-gel process has been reviewed. The basic process and characteristics for the synthesis of luminescent films via sol-gel method, Characterization methods for the films and the current status for the development and application of luminescent films are discussed in the context, An elucidation has been made on the luminescent films classified by composition, including inorganic luminescent films and organic/inorganic hybrid luminescent films. The sol-gel derived luminescent films have found applications in the display devices for photoluminescence, electroluminescence, cathodoluminescence and field emission etc. Finally, the future development tendency for the luminescent films are forecasted.

Encapsulation of fluorescein into MCM-41 mesoporous molecular sieve by a sol-gel method

MCM-41-hosted fluorescein mesophase was prepared by addition of the dye into the sol-gel mixture for the synthesis of MCM-41 mesoporous molecular sieve under microwave radiation. The as-synthesized organo-silica-surfactant material possessed hexagonal mesostructure with short-range symmetry and a uniform nanosize of about 30 nm. Furthermore, fluorescence spectrum, increase in lifetime and lack of aggregation at high concentration were discussed in terms of the effect of the host-guest interaction on these properties. (C) 2001 Published by Elsevier Science B.V.