Electropolymerization and catalysis of well-dispersed polyaniline/carbon nanotube/gold composite

Polyaniline/multi-walled carbon nanotube/gold (PANI/MWNT/Au) composite film was synthesized via a two-step electrochemical process. First the mixture of aniline and MWNT was heated at refluxing and was electropolymerized. Then, the An nanoparticles were dispersed into the film of PANI/MWNT by electrochemical reduction of HAuCl4. The morphology of sample was analyzed by scanning electron microscopy (SEM). Raman measurement indicates a well electrochemical deposition of PANI on MWNT, and XPS result confirms the formation of Au-0 nanoparticles. Further, cyclic voltammograms show that the film exhibits a good electrochemical activity and electrocatalysis towards ascorbic acid. Based on these investigations, a formation mechanism of the PANI/MWNT composite film was proposed.

Biosynthesis of gold nanoparticles assisted by Escherichia coli DH5 alpha and its application on direct electrochemistry of hemoglobin

In this communication, biosynthesis of gold nanoparticles assisted by Escherichia coli DH5 alpha and its application on direct electrochemistry of hemoglobin are reported. The gold nanoparticles formed on the bacteria surface are mostly spherical. The direct electrochemistry of hemoglobin can be achieved by incorporated into the bio-nanocomposite films on a glassy carbon electrode.

A method to construct polyelectrolyte multilayers film containing gold nanoparticles

Gold nanoparticles in polyelectrolyte multilayers film can be easily prepared by repeating immersion of a substrate in poly(diallyl dimethylammonium) chloride (PDDA)-AuCl4- complexes solution followed by reduction Au3+ through heating. UV-vis spectroscopy, cyclic voltammetry (CV) and tapping-mode atomic force microscopy (AFM) are used to confirm the successful construction of the polyelectrolyte multilayers film and the formation of gold nanoparticles. The multilayers film shows electrocatalytic activity to dioxygen reduction.

Thionine-interlinked multi-walled carbon nanotube/gold nanoparticle composites

Multi-walled carbon nanotube (MWCNT)/thionine/gold nanoparticle composites were prepared by binding gold nanoparticles to the surfaces of thionine-coated carbon nanotubes. TEM images show gold nanoparticles distributed uniformly on nanotube walls and ends. UV-Vis, Raman, FT-IR, and zeta potential measurements were used to examine the properties of the resulting products. The composites demonstrate significant electrocatalytic activity for oxygen reduction. Although only gold nanoparticles were investigated here, the method could be easily extended to attach other metallic nanoparticles to the sidewalls of carbon nanotubes.

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.

Simple preparation method of Pd nanoparticles on an Au electrode and its catalysis for dioxygen reduction

A simple method for the fabrication of Pd nanoparticles is described. The three-dimensional Pd nanoparticle films are directly formed on a gold electrode surface by simple electrodeposition at -200 mV from a solution of 1 M H2SO4+0.01 mM K2PdCl4. X-Ray photoelectron spectroscopy verifies the constant composition of the Pd nanoparticle films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 45-60 nm. It is confirmed that the morphology of the Pd nanoparticle films are correlated with the electrodeposition time and the state of the Au substrate. The resulting Pd-nanoparticle-film-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen in 0.1 M KCl solution. Freshly prepared Pd nanoparticles can catalyze the reduction of O-2 by a 4-electron process at -200 mV in 0.1 M KCl, but this system is not very stable. The cathodic peaks corresponding to the reduction of O-2 gradually decrease with potential cycling and at last reach a steady state. Then two well-defined reduction peaks are observed at -390 and -600 mV vs. Ag/AgCl/KCl (sat.). Those two peaks correspond to a 2-step process for the 4-electron reduction pathway of O-2 in this neutral medium.

One-step synthesis and size control of dendrimer-protected gold nanoparticles: A heat-treatment-based strategy

Dendrimer-protected gold nanoparticles have been facilely obtained by heating an aqueous solution containing third generation poly(propyleneimine) dendrimers and HAuCl4 without the additional step of introducing other reducing agents. Transmission electron microscopy (TEM) and UV vis data indicate the size the nucleation and growth kinetics of gold nanoparticles thus formed which can be tuned by changing the initial molar ratio of dendrimer to gold.

Electrocatalytic mechanism for formaldehyde oxidation on the highly dispersed gold microparticles and the surface characteristics of the electrode

Electrocatalytic mechanism for the electrochemical oxidation of formaldehyde (HCHO) on the highly dispersed Au microparticles electrodeposited on the surface of the glass carbon (GC) electrode in the alkaline Na2CO3/NaHCO3 solution and the surface characteristics of the Au microparticle-modified glass carbon (Au/GC) electrode were studied with in situ FTIR spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the final products of HCHO oxidation is HCOO- at the Au/GC electrode and CO2 at the bulk Au electrode. The difference may be ascribed to the different surface characteristics between the Au/GC electrode and the bulk Au electrode. (C) 1999 Elsevier Science B.V. All rights reserved.

The direct electrochemistry of cytochrome c at the nanometer-sized rare earth element oxide particle-modified gold electrodes

The direct electrochemistry of cytochrome c was studied at nanometer-sized rare earth element dioxide particle-modified gold electrodes. It was demonstrated that rare earth element oxides can accelerate the electrochemical reaction of cytochrome c and the reversibility of the electrochemical reaction of cytochrome c was related to the size of rare earth element oxide particles.

PROMOTER EFFECT OF POLY(4-VINYLPYRIDINE) ON THE DIRECT ELECTRON-TRANSFER BETWEEN CYTOCHROME-C AND GOLD ELECTRODE

The electrochemistry of cytochrome c was studied at the PVP-modified gold electrode. It was found that the promoter effect is related to the amount of PVP at the gold electrode. From our results, it can be seen that the nitrogen element in the polymer is important for accelerating the electron transfer of cytochrome c.

ELECTROOXIDATION OF ASCORBIC-ACID AT THE BIS(4-PYRIDYL) DISULFIDE MODIFIED GOLD ELECTRODE

The electrooxidation of ascorbic acid (AA) at the bis(4-pyridyl)disulfide (PySSPy) modified gold electrode was studied. The results showed that the oxidation process was pH-dependent. It was mainly due to the static interaction between AA and the modified

Study of the Adsorption of Fibrinogen on Gold-Coated Silicon Wafer by an Impedance Method

In 0.1 mol/l KH2PO4–Na2HPO4 (pH 7.80) buffer solution, the potential of zero charge (PZC) and the open circuit potential of gold-coated silicon were determined to be about −0.6 and +0.10 V (vs SCE), respectively. The open circuit potential was higher than the PZC, which indicated that the surface of the gold-coated electrode had a positive charge. The ellipsometry experiment showed that the adsorption of fibrinogen onto the gold-coated silicon wafer surface arrived at a saturated state when the adsorption time exceeded 50 min. The percentage of surface without adsorbed protein, θ, was about 63%. This means that the proportion of surface actually occupied by fibrinogen was only about 37% after the adsorption arrived at saturation. The solution/protein capacitance value was determined in an impulse state around −0.59 V (vs SCE) and was stable (4.2×10−5 F) at other potentials.

Influence of Electrostatic Interaction on Fibrinogen Adsorption on Gold Studied by Imaging Ellipsometry Combined with Electrochemical Methods

Imaging ellipsometry was combined with electrochemical methods for studying electrostatic interactions of protein and solid surfaces. The potential of zero charge for gold-coated silicon wafer/solution interfaces wad determined by AC impedance method. The potential of the gold-coated silicon wafer was controlled at the potential of zero charge, and the adsorption of fibrinogen on the potential-controlled and non-controlled surfaces was measured in real time at the same time by imaging ellipsometry The effect of electrostatic interaction was studied by comparing the difference between the potential of controlled adsorption and the Potential of noncontrolled adsorption. It was shown that the rate of fibrinogen adsorption on the potentiostatic surface was faster than that on the nonpotentiostatic surface. The electrostatic influence on fibrinogen adsorption on the gold-coated silicon wafer was weak, so the hydrophobic interaction should be the major affinity.

Adsorption of human serum albumin onto gold: a combined electrochemical and ellipsometric study

Human serum albumin adsorption onto gold surfaces was investigated by electrochemical and ellipsometric methods. Albumin adsorption onto gold was confirmed by the change of the open circuit potential of gold and by the ellipsometric parameter variation during albumin immobilization. In both experiments the parameters reached stable values within 10-15 min. The albumin adsorption layer thickness measured with the ellipsometer was about 1.5 nm. The adsorption of albumin Under applied potential was also investigated and it was found that both positive and negative applied potential promote albumin adsorption. Changes in the optical parameters of bare gold and albumin adsorbed onto gold surface under applied potential were investigated with in Situ ellipsometry. The similarity and reversibility of the optical changes showed that adsorbed albumin was stable on the gold surface Under the applied potential range (-200-600 mV). The cyclic voltammograms of K3Fe(CN)(6) on the modified gold surface showed that albumin Could partly block the oxidation and reduction reaction. (C) 2004 Elsevier Inc. All rights reserved.

Femtosecond laser-induced breakdown of multilayers and gold film

unavailable<br>H. Sun's e-mail address is shy780327@siom.ac.cn.