Bismuth nanoparticles electrooxidation: theory and experiment

The article presents the findings of microscopic and electrochemical studies of electrooxidation of bismuth particle of varying sizes. Bismuth particles were immobilized on the surface of indifferent carbon containing screen-printed electrodes. The calculations and experimental studies demonstrated that the transition from macroparticles to nanoparticles caused a shift of the maximum current potential of bismuth oxidation into the area with more negative potentials. A positive correlation between experimental and calculated data confirms once again a relevant application of the earlier proposed mathematical model and the possible use of the shift of the maximum current potential of electrooxidation to describe electrochemical activity and energy properties of metal nanoparticles.

     

Bismuth nanoparticles electrooxidation: theory and experiment

The article presents the findings of microscopic and electrochemical studies of electrooxidation of bismuth particle of varying sizes. Bismuth particles were immobilized on the surface of indifferent carbon containing screen-printed electrodes. The calculations and experimental studies demonstrated that the transition from macroparticles to nanoparticles caused a shift of the maximum current potential of bismuth oxidation into the area with more negative potentials. A positive correlation between experimental and calculated data confirms once again a relevant application of the earlier proposed mathematical model and the possible use of the shift of the maximum current potential of electrooxidation to describe electrochemical activity and energy properties of metal nanoparticles.     

Silver nanoparticles electrooxidation: theory and experiment

This article presents the findings of microscopic and electrochemical studies of electrooxidation of silver nanoparticles of varying sizes in comparison with “bulk” silver. Silver particles were immobilized on the surface of indifferent carbon-containing screen-printed electrodes. Vacuum-deposited silver represented the “bulk” electrode. The calculations and experimental studies demonstrated that the transition from macro- to nanostructural electrodes is followed by a shift of the maximum current potential of metal oxidation into the area with more negative potentials. A positive correlation between experimental and calculated data confirms once again a relevant application of the earlier proposed mathematical model and the possible use of the shift of the maximum current potential of electrooxidation to describe the electrochemical activity and surface energy properties of metal nanoparticles.     

Electrochemistry of metal nanoparticles: the effect of substrate

It is shown that nanoparticles localized on a foreign solid electrode may display two opposite shifts of dissolution potential, namely, a shift toward either more positive or more negative values as compared with the equilibrium potential of M ⁿ⁺/M ⁰ or the potential of bulk metal electrooxidation. The observed phenomena are interpreted in view of three energy states of substance, which are realized depending on contribution of the surface Gibbs free energy (ΔG°) to the energy of the system. Literature data concerning different metal-substrate pairs and specially conducted experimental investigations of electrooxidation of gold nanoparticles (radius equal to 10 and 150?nm), which are localized on the surface of glassy carbon, bulk gold, and platinum electrodes are presented and discussed. A shift of maximum current potential of small nanoparticles oxidation toward more positive values is observed in this series. The oxidation potential of large nanoparticles is not affected by the nature of the substrate. In all cases, electrooxidation of gold nanoparticles occurs at the more negative potentials than those of the bulk gold electrooxidation. It is shown that depending on the nature of the substrate and nanoparticle size, the dominating effect is either interaction of nanoparticles with the substrate (ΔG°?<?0) and electrochemical potential shifts toward positive values or impact of surface Gibbs free energy of nanoparticles (ΔG°?>?0) into energy of the system and electrochemical potential shifts toward negative values. The validity of the proposed assumptions is confirmed by good correlation of literature and our experimental data with calculated ones.     

Synthesis of Silver and Gold Nanoparticles by a Novel Electrochemical Method

Spherical silver and gold nanoparticles with narrow size distributions were conveniently synthesized in aqueous solution by a novel electrochemical method. The technological keys to the electrochemical synthesis of monodispersed metallic nanoparticles lie in the choice of an ideal stabilizer for the metallic nanoclusters and the use of a rotating platinum cathode. Poly(N‐vinylpyrrolidone) (PVP) was chosen as the stabilizer for the silver and gold clusters. PVP not only protects metallic particles from agglomeration, but also promotes metal nucleation, which tends to produce small metal particles. Using a rotating platinum cathode effectively solves the technological difficulty of rapidly transferring the (electrochemically synthesized) metallic nanoparticles from the cathode vicinity to the bulk solution, avoiding the occurrence of flocculates in the vicinity of the cathode, and ensuring the monodispersity of the particles. The particle size and particle size distribution of the silver and gold nanoparticles were improved by adding sodium dodecyl benzene sulfonate (SDBS) to the electrolyte. The electrochemically synthesized nanoparticles were characterized by TEM and UV/Vis spectroscopy.     

Electrochemical properties of carbon nanotube-supported metallic catalysts prepared by changing a sweep- or step-applied potential

The electrochemical deposition of Pt nanoparticles on carbon nanotube (CNTs) supports and their catalytic activities for an electro-oxidation were investigated. Pt catalysts of 4–12 nm average crystalline size were grown on supports by changing applied potential methods such as sweep-potential or step-potential. Electroplating of 24-min time by a step-applied potential was enough to obtain small crystalline-size 4.6-nm particles, resulting in good electrochemical activity. The catalysts’ loading contents could be controlled by increasing the deposition time. The crystalline sizes and structures of the Pt/support catalysts were analyzed using X-ray diffraction (XRD). The electrochemical properties of the Pt/support catalysts were studied according to their characteristic current–potential curves in a methanol solution. As a result, the electrochemical activity was increased by enlarging the plating time. The activity reached the maximum at 24 min and then decreased. The enhanced electroactivity for catalysts by step-potential methods could be explained by the changes of the crystalline size and crystalline structures of the catalysts.     

A disposable immunosensor based on gold colloid modified chitosan nanoparticles-entrapped carbon paste electrode

A new strategy is described to construct disposable electrochemical immunosensors for the assay of human immunoglobulin. It is based on a carbon paste electrode constructed from chitosan nanoparticles modified with colloidal gold. The stepwise assembly process of the immunosensor was characterized by means of cyclic voltammetry and electrochemical impedance spectroscopy. Assay conditions that were optimized included the amount of chitosan nanoparticles in the preparation of carbon paste electrode, antibody concentration, and the incubation time of the antibody immobilization. Using hexacyanoferrate as a mediator, the current change increased with the concentration of human immunoglobulin G. A linear relationship in the concentration range 0.3 to 120 ng mL^?1 was achieved, with a detection limit of 0.1 ng mL^?1 (S/N?=?3). The method combines the specificity of the immunological reaction with the sensitivity of the gold colloid amplified electrochemical detection, and it has potential application in clinical immunoassay.     

New method for preparation of polyoxometalate-capped gold nanoparticles, and their assembly on an indium-doped tin oxide electrode

Functionalized gold nanoparticles capped with polyoxometalates were prepared by a simple photoreduction technique where phosphododecamolybdates serve as reducing reagents, photocatalysts, and as stabilizers. TEM images of the resulting gold nanoparticles show the particles to have a relative narrow size distribution. Monolayer and multilayer structures of the negatively charged capped gold nanoparticles were deposited on a poly(vinyl pyridine)-derivatized indium-doped tin oxide (ITO) electrode via the layer-by-layer technique. The surface plasmon resonance band of the gold nanoparticles displays a blue shift on the surface of the ITO electrode. This is due to the substrate-induced charge redistribution in the gold nanoparticles and a change in the electromagnetic coupling between the assembled nanoparticles. The modified electrode exhibits the characteristic electrochemical behavior of surface-confined phosphododecamolybdate and excellent electrocatalytic activity. The catalysis of the modified electrode towards the model compound iodate was systematically studied. The heterogeneous catalytic rate constant for the electrochemical reduction of iodate was determined by chronoamperometry to be ca. 1.34?×?10⁵ mol^?1·L·s^?1. The amperometric method gave a linear range from 2.5?×?10^?6 to 1.5?×?10^?3 M and a detection limit of 1.0?×?10^?6 M. We believe that the functionalized gold nanoparticles prepared by this photoreduction technique are advantageous in terms of fabrication of sensitive and stable redox electrodes.

Activity enhancement of a screen-printed carbon electrode by modification with gold nanoparticles for glucose determination

We have successfully developed a highly sensitive electrochemical sensor strip for a home blood-sugar monitoring device by a single-step straightforward procedure. The strip consists of a pair of screen-printed carbon electrodes, which work as counter and working electrodes in the chronoamperometric mode. To remedy the poor electrochemical activity of the printed carbon electrode, a small amount of gold nanoparticles was immobilized on the electrode. In the presence of glucose oxidase, the electrode modified with 2-nm particles showed about a five times higher sensitivity for glucose oxidation than the bare printed carbon electrode, and there was a significant dependence of the current on the particle diameter. Based on these observations, we have elucidated the glucose oxidation mechanism, which is comprised of two key factors, i.e. (1) electron transfer between the gold particles, and (2) electronic coupling between the gold particles and glucose oxidase.     

Electrodeposition of gold nanoparticles from ionic liquid microemulsion

Gold nanoparticles were electrodeposited directly for the first time from a new electrolyte system: water-in-ionic liquid (W/IL) microemulsion. The electrochemical behavior of Au(Ш) in W/IL microemulsion was investigated. The cyclic voltammetry (CV) result of Au(Ш) shows a pair of redox peak. The effect of precursor apparent concentration on the reduction peak current density is similar to that in homogeneous solution such as aqueous solution. The effect of scan rate on the reduction peak current density is different from that in homogeneous solution. Linear-sweep voltammograms result for a rotating disk electrode in the W/IL microemulsion suggests that the reduction is kinetically limited and not transport limited. And also the activation energy of the reaction was calculated to be 26.7 KJ mol^?1. The gold electrodeposits were characterized by scanning electron microscopy and X-ray diffraction. It is found that the gold electrodeposits are face-centered cubic and nanosized. Furthermore, the potential mechanism for the electrode reaction was proposed. In addition, the electrochemical properties of the gold nanoparticles were researched through the electro-oxidation of glycerol. The CV and electrochemical impedance spectroscopy studies demonstrate that the gold nanoparticles electrodeposited from W/IL microemulsion have much higher electro-catalytic activities than bare gold for glycerol oxidation.     

Electrochemical Fabrication of Nanostructured Surfaces for Enhanced Response

The objective of this work is to explore approaches to enhance electrochemical signals through sequential deposition and capping of gold particles. Gold nanoparticles are electrodeposited from KAuCl₄ solution under potentiostatic conditions on glassy carbon substrates. The number density of the nanoparticles is increased by multiple deposition steps. To prevent secondary nucleation processes, the nanoparticles are isolated after each potentiostatic deposition step by self‐assembled monolayers (SAMs) of decanethiol or mercaptoethanol. The increasing number of particles during five deposition/protection rounds is monitored by assembling electroactive SAMs using a ferrocene‐labeled alkanethiol. A precise estimation of the surface area of the gold nanoparticles by formation of an oxide layer on gold is difficult due to oxidation of the glassy carbon surface. As an alternative approach, the charge flow of the electroactive SAM is used for surface measurement of the gold surface area. A sixfold increase in the redox signal in comparison to a bulk gold surface is observed, and this increase in redox signal is particularly notable given that the surface area of the deposited nanoparticles is only a fraction of the bulk gold surface. After five rounds of deposition there is a gold loading of 1.94 μg cm^?2 of the deposited nanoparticles as compared to 23.68 μg cm^?2 for the bulk gold surface. Remarkably, however, the surface coverage of the ferrocene alkanethiol on the bulk material is only 10 % of that achieved on the deposited nanoparticles. This enhancement in signal of the nanoparticle‐modified surface in comparison to bulk gold is thus demonstrated not to be attributable to an increase in surface area, but rather to the inherent properties of the surface atoms of the nanoparticles, which are more reactive than the surface atoms of the bulk material.     

Voltammetric determination of cysteine at a graphite electrode modified with gold nanoparticles

The electrochemical behaviour of cysteine (Cys) at a graphite electrode modified with gold nanoparticles (G-Au_nano electrode) was studied by cyclic voltammetry. It was found that the graphite electrode-Au nanoparticles show an electrocatalytic activity towards the oxidation of Cys in 0.1?M NaOH. At 0.05?V, there is an “inverse” maximum in the cathodic voltammogram of Cys. Using a G-Au_nano electrode, the dependence of the peak current of the “inverse” maximum on Cys concentration was linear in the range from 1 to 14?pM, and the detection limit was 0.6?pM. The proposed analytical method is simple, rapid and sensitive.     

Electrochemical synthesis of a graphene sheet and gold nanoparticle-based nanocomposite, and its application to amperometric sensing of dopamine

We describe a simple, green and controllable approach for electrochemical synthesis of a nanocomposite made up from electrochemically reduced graphene oxide (ERGO) and gold nanoparticles. This material possesses the specific features of both gold nanoparticles and graphene. Its morphology was characterized by scanning electron microscopy which reveals a homogeneous distribution of gold nanoparticles on the graphene sheets. Cyclic voltammetry was used to evaluate the electrochemical properties of this nanocomposite towards dopamine by modification of it on surface of glassy carbon electrode (GCE). Compared to the bare GCE, the electrode modified with gold nanoparticles, and the electrode modified with ERGO, the one modified with the nanocomposite displays better electrocatalytic activity. Its oxidation peak current is linearly proportional to the concentration of dopamine (DA) in the range from 0.1 to 10?μM, with a detection limit of 0.04?μM (at S/N?=?3). The modified electrode also displays good storage stability, reproducibility, and selectivity.

Fabrication of gold nanoparticles/polypyrrole composite-modified electrode for sensitive hydroxylamine sensor design

A highly sensitive hydroxylamine (HA) electrochemical sensor is developed based on electrodeposition of gold nanoparticles with diameter of 8 nm on the pre-synthesized polypyrrole matrix and formed gold nanoparticles/polypyrrole (GNPs/PPy) composite on glassy carbon electrode. The electrochemical behavior and electrocatalytic activity of the composite-modified electrode are investigated. The GNPs/PPy composite exhibits a distinctly higher electrocatalytic activity for the oxidation of HA than GNPs with twofold enhancement of peak current. The enhanced electrocatalytic activity is attributed to the synergic effect of the highly dispersed gold metal particles and PPy matrix. The overall numbers of electrons involved in HA oxidation, the electron transfer coefficient, catalytic rate constant, and diffusion coefficient are investigated by chronoamperometry. The sensor presents two wide linear ranges of 4.5 × 10⁻⁷–1.2 × 10⁻³ M and 1.2 × 10⁻³–19 × 10⁻³ M with the detection limit of 4.5 × 10⁻⁸ M (s/n = 3). In addition, the proposed electrode shows excellent sensitivity, selectivity, reproducibility, and stability properties.     

Ni hollow spheres as catalysts for methanol and ethanol electrooxidation

In this paper, we successfully synthesized Ni hollow spheres consisting of needle-like nickel particles by using silica spheres as template with gold nanoparticles seeding method. The Ni hollow spheres are applied to methanol and ethanol electrooxidation in alkaline media. The results show that the Ni hollow spheres give a very high activity for alcohol electrooxidation at a very low nickel loading of 0.10 mg cm⁻². The current on Ni hollow spheres is much higher than that on Ni particles. The onset potential and peak potential on Ni hollow spheres are more negative than that on Ni particles for methanol and ethanol electrooxidation. The Ni hollow spheres may be of great potential in alcohol sensor and direct alcohol fuel cells.     

Characterization of gold nanoparticles electrochemically deposited on amine-functioned mesoporous silica films and electrocatalytic oxidation of glucose

This study reports the preparation and characterization of gold nanoparticles deposited on amine-functioned hexagonal mesoporous silica (NH₂–HSM) films and the electrocatalytic oxidation of glucose. Gold nanoparticles are fabricated by electrochemically reducing chloroauric acid on the surface of NH₂–HSM film, using potential step technology. The gold nanoparticles deposited have an average diameter of 80 nm and show high electroactivity. Prussian blue film can form easily on them while cycling the potential between −0.2 and 0.6 V (vs saturated calomel electrode) in single ferricyanide solution. The gold nanoparticles loading NH₂–HSM-film-coated glassy carbon electrode (Au–NH₂–HSM/GCE) shows strong catalysis to the oxidation of glucose, and according to the cathodic oxidation peak at about 0.16 V, the catalytic current is about 2.5 μA mM⁻¹. Under optimized conditions, the peak current of the cathodic oxidation peak is linear to the concentration of glucose in the range of 0.2 to 70 mM. The detection limit is estimated to be 0.1 mM. In addition, some electrochemical parameters about glucose oxidation are estimated.     

Electrodeposition of Ag nanoparticles onto carbon coated TEM grids: A direct approach to study early stages of nucleation

An innovative experimental approach to study the electrodeposition of small nanoparticles and the early stages of electrochemical nucleation and growth is presented. Carbon coated gold TEM grids are used as substrates for the electrodeposition of silver nanoparticles so that electrochemical data, FESEM, HAADF–STEM and HRTEM data can be acquired from the same sample without the need to remove the particles from the substrate. It is shown that the real distribution of nanoparticles cannot be resolved by FESEM whereas HAADF–STEM analysis confirms that a distribution of ‘small’ nanoparticles (d ≈ 1–2 nm) coexist with ‘large’ nanoparticles corresponding to a bimodal size distribution. Besides, particles grown under the same conditions have been found to present different structures such as monocrystals, polycrystals or aggregates of smaller particles.     

室温离子液体自组装金纳米粒子模板化制备内消旋多孔材料增强细胞色素c直接电化学（英文）

室温离子液体作为一种软模板用来组装内消旋多孔材料,这种材料是由表面覆盖有半胱氨酸的自组装巨型金纳米粒子构成的. 首先,由于静电相互作用或者配体外部末端的羧基和氨基基团之间的缩合反应,覆盖有半胱氨酸的金纳米粒子能够自组装形成纳米线和亚微米球形粒子. 其次,球形自组装粒子在和疏水性室温离子液体1-辛基-3-甲基咪唑鎓六氟磷酸盐相互摩擦时能形成一种准固态凝胶. 最后,将复合凝胶涂在玻碳电极上,然后在PH = 7.4的磷酸缓冲溶液中用循环伏安法进行极化,由于多余的室温离子液体分散在溶胶中从而形成了一种内消旋多孔结构. 该材料具有良好的导电性和生物大分子亲和性. 由于大的外部表面积和内部的“薄层”效应,细胞色素c的感应显著增强. 实验结果表明,这种内消旋多孔材料在包括生物传感器和生物燃料电池在内的电化学设备方面具有潜在的应用前景.     

Microsensor Chip Integrated with Gold Nanoparticles‐Modified Ultramicroelectrode Array for Improved Electroanalytical Measurement of Copper Ions

This paper presents a microsensor chip integrated with a gold nanoparticles‐modified ultramicroelectrode array (UMEA) as the working electrode for the detection of copper ions in water. The microsensor chip was fabricated with Micro‐Electromechanical System technique. Gold nanoparticles were electrodeposited onto the surface of UMEA at a constant potential of ?0.3 V. The ratio d/R_b of interelectrode spacing (d) over the individual electrode’s radius (R_b) was investigated to improve the electrochemical performance. The UMEA with a d/R_b of 20 showed the best hemispherical diffusion mode, resulted in fast response time and high current response. The gold nanoparticles increased the active surface area of UMEA by not changing the geometries of UMEA, and the current response was increased further. Incorporating the optimized characteristic of UMEA and gold nanoparticles, the microsensor showed a good linear range from 0.5 to 200 µg L^?1 of copper ions in the acetate buffer solutions with the method of square wave stripping voltammetry. Compared with the gold nanoparticles‐modified disk electrode, the gold nanoparticles‐modified UMEA showed higher sensitivity (0.024 µA mm^?2 µg^?1 L) and lower limit of detection (0.2 µg L^?1). Water samples from river water and tap water were analyzed by the microsensor chip with recovery ranging from 100.7 % to 107.8 %.     

Regioselective Bridging Calix[6]arenes: Synthesis and X-ray Structure of Trisbridged Calix[6]arene

The preparation and characterization of gold nanoparticles (～6 nm in diameter) modified with mono-6-thio-β-cyclodextrin (II) is described. The resulting monolayer-protected gold nanoparticles are water-soluble and more stable. The concentration of II plays a crucial role for the distribution of the modified nanoparticles. When the ratio of concentration of II to HAuCl₄,[II]/[HAuCl₄] ≥ 0.93, a stable gold nanoparticle with uniform distribution and diameter of 6.0 ± 0.9 nm will be obtained. The recognition of modified gold nanoparticles to organic guest molecule is researched. The modified gold nanoparticles can make the electrochemical reduction current of nitrobenzene decrease and can be self-assembled in three-dimensional to form spherical clusters with ligand of methylene green.