Polyol-mediated synthesis of polyhedral silver clusters

Besides the spheres, polyhedral silver nanoclusters were prepared by the polyol process with 3-aminopropyl triethoxysilane (APTES). In the process, APTES acts as not only the stabilizer but also the template.

Surface plasmon resonance studies on the electrochemical doping/dedoping processes of anions on polyaniline-modified electrode

The combination of in situ surface plasmon resonance (SPR) with electrochemistry was used to investigate the electrochemical doping/dedoping processes of anions on a polyaniline (PAn)-modified electrode. Electrochemical SPR characteristics of the PAn film before and after doping/dedoping were revealed. The redox transformation between the insulating leucoemeraldine, and the conductive emeraldine, corresponding to the doping/dedoping of anion, can lead to very distinct changes in both the resonance minimum angle and the shape of SPR curve. This is ascribed to the swelling/shrinking effect, and the change of the PAn film in the imaginary part of the dielectric constant resulted from the transition of the film conductivity. In situ recording the time evolution of reflectance change at a fixed angle permits the continuous monitoring of the kinetic processes of doping/dedoping anions. The size and the charge of anions, the film thickness, as well as the concentration of anions are shown to strongly influence the rate of ingress/egress of anions. The time differential of SPR kinetic curves can be well applied in the detecting electroinactive anion by flow injection analysis. The approach has higher sensitivity and reproducibility compared with other kinetic measurements, such as those obtained by amperometry.

Formation of a supported hybrid bilayer membrane on gold: A sterically enhanced hydrophobic effect

Adsorption of a monolayer of didecanoyl-L-alpha-phosphatidylcholine (DDPC) from dispersions of small unilamellar vesicles onto hydrophobic surfaces was investigated by mean of cyclic voltammetry and impedance spectroscopy. The hydrophobic surfaces were self-assembled monolayers of 2-mereapto-3-n-octylthiophene (MOT) on gold. One characteristic of the MOT monolayer is its permeability to organic molecules in aqueous solution, thus providing a more energetically favorable hydrophobic surface for the addition of phospholipid vesicles. The kinetics of the lipid monolayer formation were followed by measuring the time-dependent interfacial capacitance. Unusual values of thickness and capacitance of the MOT/ DDPC bilayers were observed. An interdigitating conformation of the bilayer structure was proposed to interpret the experimental results, The horseradish peroxidase reconstituted into the bilayer demonstrated the expected protein activity, showing practical use in research and in biosensor application.

Preparation and characterization of poly(ethyl acrylate)/bentonite nanocomposites by in situ emulsion polymerization

Transparent poly(ethyl acrylate) (PEA)/bentonite nanocomposites containing intercalated-exfoliated combinatory structures of clay were synthesized by in situ emulsion polymerizations in aqueous dispersions containing bentonite. The samples for characterization were prepared through direct-forming films of the resulting emulsions without coagulation and separation. An examination with X-ray diffraction and transmission electron microscopy showed that intercalated and exfoliated structures of clay coexisted in the PEA/bentonite nanocomposites. The measurements of mechanical properties showed that PEA properties were greatly improved, with the tensile strength and modulus increasing from 0.65 and 0.24 to 11.16 and 88.41 MPa, respectively. Dynamic mechanical analysis revealed a very marked improvement of the storage modulus above the glass-transition temperature. In addition, because of the uniform dispersion of silicate layers in the PEA matrix, the barrier properties of the materials were dramatically improved. The permeability coefficient of water vapor decreased from 30.8 x 10(-6) to 8.3 x 10(-6) g cm/cm(2)s cmHg. (C) 2002 Wiley Periodicals, Inc.

Morphological study on water-borne conducting polyaniline-poly(ethylene oxide) blends

Conducting polyaniline-poly(ethylene oxide) blends were prepared from their aqueous solutions. The blends displayed an electrical conductivity percolation threshold as low as 1.83 wt % of polyaniline loading. As demonstrated by scanning electron microscopy, polarized optical microscopy, and wide-angle X-ray diffraction studies, the conducting polyaniline took a fibrillar morphology in the blend, and it existed only in the amorphous phase of poly(ethylene oxide). A three-phase model combining morphological factors instead of a two-phase model was proposed to explain the low-conductivity percolation threshold.

Effect of the compatibilization of linear low-density polyethylene-g-acrylic acid on the morphology and mechanical properties of poly(butylene terephthalate)/linear low-density polyethylene blends

A poly(butylene terephthalate) (PBT)/linear low-density polyethylene (LLDPE) alloy was prepared with a reactive extrusion method, For improved compatibility of the blending system, LLDPE grafted with acrylic acid (LLDPE-g-AA) by radiation was adopted in place of plain LLDPE. The toughness and extensibility of the PBT/LLDPE-g-AA blends, as characterized by the impact strengths and elongations at break, were much improved in comparison with the toughness and extensibility of the PBT/LLDPE blends at the same compositions. However, there was not much difference in their tensile (or flexural) strengths and moduli. Scanning electron microscopy photographs showed that the domains of PBT/LLDPE-g-AA were much smaller and their dispersions were more homogeneous than the domains and dispersions of the PBT/ T,T PE blends. Compared with the related values of the PBT/LLDPE blends, the contents and melting temperatures of the usual spherulites of PBT in PBT/LLDPE-g-AA decreased.

Sol-gel-derived alpha(2)-K7P2W17VO62/graphite/organoceramic composite as the electrode material for a renewable amperometric hydrogen peroxide sensor

The conductive alpha (2)-K7P2W17VO62/graphite/organoceramic composite was prepared by dispersing alpha (2)-K7P2W17VO62 and graphite powder in a propyltrimethoxysilane-based sol-gel solution; it was used as the electrode material for an amperometric hydrogen peroxide sensor. The modified electrode had a homogeneous mirror-like surface and showed well defined cyclic voltammograms. Square-wave voltammetry was employed to study the pH-dependent electrochemical behavior of c alpha (2)-K7P2W17VO62 doped in the graphite organoceramic matrix, and the experiment showed that both protons and sodium cations participated in the odor process. A hydrodynamic voltammetric experiment was performed to characterize the electrode as an amperometric sensor for the determination of hydrogen peroxide. The sensor can be renewed easily in a repeatable manner by a mechanical polishing step and has a long operational lifetime. (C) 2000 Elsevier Science B.V. All rights reserved.

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.

Preparation, structures, and electrochemistry of a new polyoxometalate-based organic/inorganic film on carbon surfaces

The preparation, structure, and electrochemical and electrocatalytical properties of a new polyoxometalate-based organic/inorganic film, composed of cetyl pyridinum 11-molybdovanadoarsenate (CPMVA) molecules, have been studied. Cyclic potential scanning in acetone solution led to a stable CPMVA film formed on a highly oriented pyrolytic graphite (HOPG) surface. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used for characterizing the structure and properties of the CPMVA film. These studies indicated that self-aggregated clusters were formed on a freshly cleaved HOPG surface, while a self-organized monolayer was formed on the precathodized HOPG electrode. The CPMVA film exhibited reversible redox kinetics both in acidic aqueous and in acetone solution, which showed that it could be used as a catalyst even in organic phase. The CPMVA film remained stable even at pH > 7.0, and the pH dependence of the film was much smaller than that of its inorganic film (H4AsMo11VO40) in aqueous solution. The CPMVA film showed strong electrocatalysis on the reduction of bromate, and the catalytic currents were proportional to the square of the concentration of bromate. The new kind of polyoxometalate with good stability may have extensive promise in catalysis.

Construction of a heteropolyanion-modified electrode by a two-step sol-gel method and its electro catalytic applications

The sol-gel technique was used here to construct heteropolyanion-containing modified electrodes. This involves two steps, i.e. the first forming a functionalized sol-gel thin film on the surface of the glassy carbon electrode and then immersing the electrode into a heteropolyanion solution to incorporate the heteropolyanion into the sol-gel film. Here a Dawson-type heteropolyanion, K6P2W18O62 (P2W18), was used as a representative to illuminate the behavior of the as-prepared composite film. The electrochemical performance of the P2W18-modified electrode was studied with respect to the pH effect and long-term stability. The modified electrode exhibited a high electrocatalytic response for the reduction of BrO3- and NO2-. Steady-state amperometry was applied to characterize the electrode as an amperometric sensor for the determination of NO2-. The sensor had a linear range from 0.02 to 34 mM and a detection limit of 5 x 10(-6) M. (C) 2001 Elsevier Science B.V. All rights reserved.

Poly(phenylene sulfide-tetraaniline): The soluble conducting polyaniline analogue with well-defined structures

A novel conducting polymer poly(phenylene sulfide-tetraaniline) (PPSTEA), with tetraaniline (TA) and phenylene sulfide (PS) segments in its repeat unit, has been synthesized through an acid-induced polycondensation reaction of 4-methylsulfinylphenyl-capped tetraaniline. The new polymer, which represents the first soluble conducting polyaniline analogue with well-defined structure, has high molecular weight, good solubility in common solvents, and good film-forming properties. Its electrical property is analogous to polyaniline. The conductivity of preliminarily, protonic-doping PPSTEA is up to 10 degrees S/cm. This synthetic strategy appears to be general for developing novel well-defined polyaniline analogue containing much longer fixed conjugation length.

Multilayer assemblies of tungstodiphosphate anions on 1,7-diaminoheptane modified glassy carbon electrode and the electrocatalytic reduction to iodate

1,7-Diaminoheptane (DAH) had been covalently grafted on glassy carbon electrode by amino cation radical formation, which resulted in a stable cationic monolayer under proper pH conditions. Dawson-type tungstodiphosphate anion, P2W18O626- and small molecule, Ru(NH3)(6)(3+) were alternately assembled on the DAH modified electrode through layer-by-layer electrostatic interaction. Thus-prepared multilayer film had been characterized by cyclic voltammetry and X-ray photoelectron spectroscopy. The P2W18O626- multilayers exhibit high electrocatalytic response and sensitivity towards the reduction of iodate. With the increase of the number of P2W18O626- the catalytic current was enhanced and the catalytic potential shifted positively. Iodate in table salt was determined at the modified electrode containing three layers of P2W18O626- with satisfactory results. The multilayer electrode is promising as an electrochemical sensor for the detection of trace iodate.

Cobalt(II)hexacyanoferrate film modified glassy carbon electrode for construction of a glucose biosensor

An amperometric glucose biosensor was constructed based on a glassy carbon electrode modified with a Cobalt(II)hexacyanoferrate film which catalyzes electroreduction of hydrogen peroxide. Gelatin was used as immobilization matrix. Interference could be effectively eliminated by the combination of low detection potential with a Nafion coating. A low applied potential can avoid oxidation of interferences such as ascorbic acid, uric acid, p-acetyl-aminophenol, etc.. Nafion coating prevents interferences from access to the electrode surface by electrostatic repulsion. A wide linear range of detection was obtained. Analytical performance parameters are given and kinetic analysis discussed.

Electrochemical preparation and characterization of silicotungstic heteropolyanion monolayer electrostatically linked aminophenyl on carbon electrode surface

In this paper, an organic-inorganic composite film of heteropolyanion was Formed by attaching a Keggin-type heteropolyanion, SiW12O404-, on carbon electrode surface derivatized by 4-aminophenyl monolayer. The composite film thus grafted on carbon electrode surface has good stability because of the ionic bonding character between SiW12O404- and surface aminophenyl groups. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used to characterize the composite film. Compared with SiW12O404- electrodeposited on a bare glassy carbon electrode (GCE), the composite film gives three more sharp and well-defined redox couples attributed to two one- and two-electron processes, and the analyses of the voltammograms of SiW12O404- anion in the composite film modified on GCE shows that its surface coverage is close to a closest packing monolayer. STM characterization shows that a two-dimensional order heteropolyanion monolayer was formed on HOPG substrate. The composite film provides a favorable environment for electron and proton transfer between SiW12O404- ion and electrode surface, which may make it suitable for various applications in sensors and microelectronics devices.