Electrochemical chlorine sensor with multi-walled carbon nanotubes as electrocatalysts

It has been reported for the first time that an electrochemical gas sensor mdified with multi-walled carbon nanotubes (MWNTs) film as elctrocatalyst was fabricated for the determination of chlorine (Cl-2).Here, MWNTs and graphite were compared with each other in terms of their electrochemical properties using cyclic voltammetry. Cl-2 gas was allowed through the cathode surface of the sensor and the resulting galvanic effects were monitored. Results indicated that both of the MWNTs and graphite have the electrocatalytic activity for the reduction of Cl-2 while the MWNTs-modified electrode exhibited a higher accessible surface area in electrochemical reactions, excellent sensitivity, stable response, reproducibility and recovery for the determination of Cl-2.

Loosely packed self-assembled monolayer of N-hexadecyl-3,6-di(p-mercaptophenylacetylene)carbazole on gold and its application in biomimetic membrane research

Dithiols of N-hexadecyl-3,6-di(p-mercaptophenylacetylene)carbazole (HDMC) have been synthesized and employed to form self-assembled monolayers (SAMs) on gold. One characteristic of the HDMC molecule is its peculiar molecular structure consisting of a large and rigid headgroup and a small and flexible alkyl-chain tail. HDMC adsorbates can attach to gold substrates by a strong Au-S bond with weak van der Waals interactions between the alkyl-chain tails, leading to a loosely packed hydrophobic SAM. In this way we can couple hybrid bilayer membranes (HBMs) to gold surfaces with more likeness to a cell bilayer than the conventional HBMs based on densely packed long-chain alkanethiol SAMs. The insulating properties and stability of the HDMC monolayer as well as the HDMC/lipid bilayer on gold have been investigated by electrochemical techniques including cyclic voltammetry and impedance spectroscopy. To test whether the quality of the bilayer is sufficiently high for biomimetic research, we incorporated the pore-forming protein a-hemolysin) and the horseradish peroxidase into the bilayers, respectively.

Direct electron transfer between cytochrome c and a gold nanoparticles modified electrode

Quasi-reversible and direct electrochemistry of cytochrome c (cyt. c) has been obtained at a novel electrochemical interface constructed by self-assembling gold nanoparticles (GNPs) onto a three-dimensional silica gel network, without polishing or any modification of the surface. A cleaned gold electrode was first immersed in a hydrolyzed sol of the precursor (3-mercaptopropyl)-trimethoxysilane to assemble three-dimensional silica gel, then the GNPs were chemisorbed onto the thiol groups of the sol-gel network and modified the kinetic barrier of this self-assembled silicate film. Cyclic voltammetry and AC impendance spectroscopy were performed to evaluate electrochemical properties of the as prepared interface. These nanoparticle inhibits the adsorption of cyt. c onto bare electrode and acts as a bridge of electron transfer between protein and electrode.

Facilitated ion-transfer of sodium cation by (anthraquinone-1-yloxy) methane-15-crown-5 across the water/1,2-dichloroethane microinterface

The transfer of sodium cation facilitated by (anthraquinone-1-yloxy) methane-15-crown-5(L) has been investigated at the water/1,2-dichloroethane microinterface supported at the tip of a micropipette. The diffusion coefficient of (anthraquinone-1-yloxy) methane-15-crown-5 obtained was (3.42 +/- 0.20) x 10(-6) cm(2) s(-1). The steady-state voltammograms were observed for forward and backward scans due to sodium ion transfer facilitated by L with 1:1 stoichiometry. The mechanism corresponded to an interfacial complexation (TIC) and interfacial dissociation (TID) process. The association constant was calculated to be log beta(o) = 11.08 +/- 0.03 in the DCE phase. The association constant of other alkali metals (Li+, K+, Rb+) were also obtained.

Electrochemistry and electrogenerated chemiluminescence of SiO2 nanoparticles/tris(2,2 '-bipyridyl)ruthenium(II) multilayer films on indium tin oxide electrodes

In this paper, a simple method of preparing {SiO2/Ru-(bPY)(3)(2+)}(n) multilayer films was described. Positively charged tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) and negatively charged SiO2 nanoparticles were assembled on ITO electrodes by a layer-by-layer method. Electrochemical and electrogenerated chemiluminescence (ECL) behaviors of the {SiO2/Ru(bpy)(3)(2+)}(n) multilayer film-modified electrodes were studied. Cyclic voltammetry, UV-visible spectroscopy, quartz crystal microbalance, and ECL were adopted to monitor the regular growth of the multilayer films. The multilayer films containing Ru(bpy)(3)(2+) was used for ECL determination of TPA, and the sensitivity was more than 1 order of magnitude higher than that observed for previous reported immobilization methods for the determination of TPA. The multilayer films also showed better stability for one month at least. The high sensitivity and stability mainly resulted from the high surface area and special structure of the silica nanoparticles.

Electrochemical design of ultrathin platinum-coated gold nanoparticle monolayer films as a novel nanostructured electrocatalyst for oxygen reduction

The deliberate tailoring of nanostructured metallic catalysts at the monolayer-level is an ongoing challenge and could lead to new electronic and catalytic properties, since surface-catalyzed reactions are extremely sensitive to the atomic-level details of the catalytic surface. In this article, we present a novel electrochemical strategy to nanoparticle-based catalyst design using the recently developed underpotential deposition (UPD) redox replacement technique. A single UPD Cu replacement with Pt2+ yielded a uniform Pt layer on colloid gold surfaces. The ultrathin (nominally monolayer-level) Pt coating of the novel nanostructured particles was confirmed by cyclic voltammetry and X-ray photoelectron spectra (XPS). The present results demonstrate that ultrathin Pt coating effects efficiently and behaves as the nanostructured monometallic Pt for electrocatalytic oxygen reduction, and also shows size-dependent, tunable electrocatalytic ability. The as-prepared ultrathin Pt-coated Au nanoparticle monolayer electrodes reduce O-2 predominantly by four electrons to H2O, as confirmed by the rotating ring-disk electrode (RRDE) technique.

Nanocomposite multilayer film of preyssler-type polyoxometalates with fine tunable electrocatalytic activities

Through layer-by-layer (LBL) assembly technique, iron oxide (Fe3O4) nanoparticles coated by poly (diallyldimethylammonium chloride) (PDDA) and Preyssler-type polyoxometalates (NH4)(14)NaP5W30O110.31H(2)O (P5W30) were alternately deposited on quartz and ITO substrates, and 4-aminobenzoic acid modified glassy carbon electrodes. Thus-prepared multilayer films were characterized by UV-visible spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. It was proved that the multilayer films are uniform and stable. And the electrocatalytic activities of the multilayer films can be fine-tuned by adjusting the assembly conditions in the LBL assembly process, such as the pH of the assembly solution. The multilayer films fabricated from P5W30 solutions dissolved in 0.1 M H2SO4 exhibit high electrocatalytic response and sensitivity toward the reduction of two substrates of important analytical interests, HNO2 and IO3- whereas the films assembled with P5W30 solutions dissolved in 1.0 M H2SO4 show remarkable electrocatalytic activity for the hydrogen evolution reaction (HER). Furthermore, the electrocatalytic properties of the HER of the latter film can be obtained from the former film upon exposure to 1.0 M H2SO4 for several hours.

Surface charge influence on the surface plasmon absorbance of electroactive thiol-protected gold nanoparticles

Gold nanoparticles (3.1-5.0 nm in size) surface-derivatized with both electroactive and nonelectroactive self-assembled monolayers were synthesized. The surface-derivatized electroactive particles can be easily oxidized/reduced at an electrode surface based on the diffusion-controlled current-voltage curve observed in cyclic voltammetry measurements. Spectroelectrochemical investigation demonstrated that the maximum absorbance of the nanoparticles in their oxidized state red-shifted compared with their reduced state to a different extent according to their size distribution. In the case of the particles surface-derivatized with nonelectroactive monolayers, much less shift was observed. This study showed that surface plasmon absorbance of gold nanoparticles was not only related to core charge states but was also influenced by surface charge states as well.

Single-wall carbon nanotube-based voltammetric sensor and biosensor

The pH-sensitive property of the single-wall carbon nanotube modified electrode based oil the electroactive group on the single-wall carbon nanotube was explored by differential pulse voltammetry technique. In pH range 1-13 investigated in Britton-Robinson (B-R) buffer, the anodic peak shifted negatively along with the increase of pH exhibiting a reversible Nernstian response. Experiments were carried out to investigate the response of the single-wall carbon nanotube (SWNT) modified electrode to analytes associated with pH change. The response behavior of the modified electrode to ammonia was studied as an example. The potential response could reach equilibrium within 5 min. The modified electrode had good operational stability. Voltammetric urease and acetylcholinesterase biosensors were constructed by immobilizing the enzymes with sol-get hybrid material. The maximum potential shift could reach 0.130 and 0.220V for urea and acetylthiocholine, respectively. The methods for preparing sensor and biosensor were simple and reproducible and the range of analytes could be extended to substrates of other hydrolyases and esterases.

Electrochemical and electrogenerated chemiluminescence of clay nanoparticles/Ru(bpy)(3)(2+) multilayer films on ITO electrodes

The electrochemical and electrogenerated chemiluminescence of Ru(bpy)(3)(2+) immobilized in {clay/Ru(bpy)(3)(2+)}(n) multilayer films by layer-by-layer assembly were investigated. The stable multilayer films of clay and Ru(bpy)(3)(2+) were assembled by alternate adsorption of negatively charged clay platelets and positively charged Ru(bpy)(3)(2+) from their aqueous dispersions. UV-vis spectroscopy, quartz crystal microbalance (QCM), cyclic voltammetry, and electrogenerated chemiluminescence (ECL) were used to monitor the immobilization of Ru( bpy)(3)(2+) and the regular growth of the {clay/Ru( bpy)(3)(2+)}(n) multilayer films. The multilayer films modified electrode was used for the ECL detection of tripropylamine ( TPA) and oxalate. The proposed novel immobilized method exhibited good stability, reproducibility and high sensitivity for the determination of TPA and oxalate, which mainly resulted from the contributing of clay nanoparticles with appreciable surface area, special structural features and unusual intercalation properties.

Preparation of a phosphopolyoxomolybdate P2Mo18O626- doped polypyrrole modified electrode and its catalytic properties

A phosphopolyoxomolybdate (P2Mo18) doped polypyrrole (PPy) modified electrode was prepared in aqueous solution by a one-step method. During the polymerization of PPy, P2Mo18 acted as both catalyst and dopant. The electrochemical behavior of the PPy/P2Mo18 modified electrode before and after the overoxidation of PPy was investigated. Both of these showed a catalytic effect toward bromate. The PPy/P2Mo18 composite film was characterized by chronoamperometry, cyclic voltammetry, the rotating disk electrode technique, X-ray photoelectron spectroscopy and Raman spectroscopy.

The electrocatalytic oxidation of ascorbic acid on polyaniline film synthesized in the presence of camphorsulfonic acid

Polyaniline-camphorsulfonic acid (PAN-CSA) composite film on platinum electrode surface has been synthesized via the electrochemical polymerization of aniline in the presence of camphorsulfonic acid (CSA). It was found that the doping of polyaniline (PAN) with CSA extends the electroactivity of PAN in neutral and even in alkaline media. The PAN-CSA composite film coated platinum electrodes are shown to be good electrocatalytic surfaces for the oxidation of ascorbic acid (AA) in phosphate buffer solution (PBS) of pH 7.0. The anodic peak potential of AA shifts from 0.63 V at the bare platinum electrode to 0.34 V at the PAN-CSA composite modified platinum electrode with a greatly enhanced current response. A linear calibration graph is obtained over the AA concentration range of 5-50 mM using cyclic voltammetry. The kinetics of the catalytic reaction are investigated using rotating disk electrode voltammetry and chronoamperometry. The results are explained using the theory of electrocatalytic reactions at chemically modified electrodes. The PAN-CSA composite on the electrode surface shows good reproducibility and stability.

Polyaniline-coated carbon particles and their electrode behavior in organic carbonate electrolyte

In an attempt to increase the interface stability of carbon used in Li-ion batteries, a thin conducting polyaniline (PANI) film was fabricated on the surface of carbon by in situ chemical polymerization. The chemical and electrochemical properties of the composite material were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscope, cyclic voltammetry, and electrochemical impedance spectroscopy. It was confirmed that the PANI film has an obvious effect on the morphology and the electrochemical performance of carbon. The results could be attributed to the electronic and electrochemical activity of the conducting PANI films.

Poly(vinylidene fluoride-hexafluoropropylene)/organo-montmorillonite clays nanocomposite lithium polymer electrolytes

Polymer-clay nanocomposite (PCN) materials were prepared by intercalation of an alkyl-ammonium ion spacing/coupling agent and a polymer between the planar layers of a swellable-layered material, such as montmorillonite (MMT). The nanocomposite lithium polymer electrolytes comprising such PCN materials and/or a dielectric solution (propylene carbonate) were prepared and discussed. The chemical composition of the nanocomposite materials was determined with X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, which revealed that the alkyl-ammonium ion successfully intercalated the layer of MMT clay, and thus copolymer poly(vinylidene fluoride-hexafluoropropylene) entered the galleries of montmorillonite clay. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of the lithium polymer electrolyte. Equivalent circuits were proposed to fit the EIS data successfully, and the significant contribution from MMT was thus identified. The resulting polymer electrolytes show high ionic conductivity up to 10(-3) S cm(-1) after felling with propylene carbonate.

Simultaneous determination of dopamine and ascorbic acid at an in-site functionalized self-assembled monolayer on gold electrode

The in-site functionalization of 4-aminothiophenol (4-ATP) self-assembled monolayer on gold electrode at physiological pH yields a redox active monolayer of 4'-mercapto-N-phenylquinone diimine (MNPD). The functionalized electrode exhibits excellent electrocatalytic responses towards dopamine (DA) and ascorbic acid (AA), reducing the overpotentials by about 0.22 V and 0.34 V, respectively, with greatly enhanced current responses. Due to its different catalytic activities toward DA and AA, the modified electrode resolves the overlapping voltammetric responses of DA and AA into two well-defined voltammetric peaks by differential pulse voltammetry (DPV), which can be used for the simultaneous determination of these species in a mixture. The catalytic peak current obtained from DPV was linearly related to DA and AA concentration in the ranges of 5.0 x 10-6 - 1.25 x 10-4 M and 8.0 x 10-6 - 1.3 x 10-4 M with correlation coefficient of 0.999 and 0.998, respectively. The detective limits (3sigma) for DA and AA were found to be 1.2 x 10-6 M and 2.4 x 10-6 M, respectively.