Preparation, characterization and photoelectrochemical study of mixed C60-Starburst PAMAM G0.0 dendrimer films anchored on the surface of nanocrystalline TiO2 semiconductor electrodes

Nanocrystalline TiO2 silanized electrodes were prepared and further modified in a sequential fashion with C60 and Starburst PAMAM G0.0 dendrimers, resulting in a novel photoelectrochemical sensitization film that showed particularly high photocurrent (IPCE) and global photoconversion efficiencies (eta).     

Electrosynthesis, characterization and electrocatalytic properties of Prussian Blue (PB) nanoparticles disposed on a template

In the present work, an arrangement of polystyrene (PS) spheres was employed as a pattern for the electrodeposition of nanostructured Prussian blue (PB). The pattern of PS spheres was formed on Indium tin oxide (ITO) glass substrate. The ITO substrate modified by the PS spheres was used as a working electrode for the electrosynthesis of PB. A macroporous PB film constituted by nanoparticles of the compound was obtained after the dissolution of the spheres and was characterized by voltammetric and atomic force microscopy techniques. The electrocatalytic properties of this material were tested in the electrooxidation of hydrazine.     

Assemblies of dendrimers and proteins on carbon and gold electrodes

Dendritic macromolecules of two adjacent (G3.5 and G4) generations have been used to modify gold or carbon electrodes. The structure and stability of deposited films have been explored by quartz crystal microbalance (QCM), Surface Plasma Resonance (SPR) and electrochemistry. Dendrimers have been shown to adsorb spontaneously on electrode materials as compressed macromolecular films. They are able to inhibit (G3.5) or promote (G4) electroactive anionic species such as Fe(CN)(6)(3-/4-) used as a probe system. Mixed protein/dendrimer assemblies have been constructed with proteins differing in charge, nature of the prosthetic groups and sizes such as lysozyme, cytochrome c, polyhemic cytochrome c(3) or glucose oxidase. Generally, the stability of adsorbed films seems to be limited to one dendrimer/protein bilayer. Owing to the satisfactory stability of composite cytochrome c(3)/G3.5 or glucose oxidase/G4 films, biosensing applications are described for metal bioremediation and glucose detection, respectively.     

An extraordinary electrocatalytic reduction of oxygen on gold nanoparticles-electrodeposited gold electrodes

The cathodic reduction of oxygen has been investigated at a gold nanoparticles-electrodeposited gold electrode in 0.5 M H₂SO₄ solution. Two well-defined reduction peaks were observed at +50 and −250 mV vs. Ag/AgCl/KCl (sat.). Those two peaks indicated a 2-step 4-electron reduction pathway of O₂ in this strong acidic medium. The former peak was ascribable to the 2-electron reduction of O₂ to H₂O₂, while the latter was assigned to the reduction of H₂O₂ to H₂O. The observed electrocatalysis for the reduction of O₂ is attributable to the extraordinary catalytic activity of the gold nanoparticles over the bulk gold electrode, at which the 2-electron reduction peak of O₂ to H₂O₂ was observed at −200 mV.     

普鲁士蓝纳米修饰电极的制备及表征

采用激光加热拉伸的方法制备铂纳米电极,并通过交流电刻蚀的方法制备纳米孔电极,在这两种电极上可通过电化学方法原位合成单颗普鲁士蓝微晶. 结果表明,普鲁士蓝微晶在纳米微孔电极上的机械附着强度增强. 这种方法可用于制备纳米修饰电极或研究功能微晶体材料的电化学性质.     

NiII1,4,8,11-tetraazacyclotetradecane electrocatalytic films prepared on top of surface anchored PAMAM dendrimer layers. A new type of electrocatalytic material for the electrochemical oxidation of methanol

Gold electrodes, previously prepared with surface anchored PAMAM dendrimers, were further modified with a Ni-containing tetraazamacrocycle resulting in a novel electrocatalytic material which proved to be particularly efficient for the electrochemical oxidation of methanol in basic aqueous medium.     

Hydrogel of ketoconazole and PAMAM dendrimers: formulation and antifungal activity

Ketoconazole (KET), an imidazole derivative with well-known antifungal properties, is lipophilic and practically insoluble in water, therefore its clinical use has some practical disadvantages. The aim of the present study was to investigate the influence of PAMAM-NH(2) and PAMAM-OH dendrimers generation 2 and generation 3 on the solubility and antifungal activity of KET and to design and evaluate KET hydrogel with PAMAM dendrimers. It was shown that the surface charge of PAMAM dendrimers strongly affects their influence on the improvement of solubility and antifungal activity of KET. The MIC and MFC values obtained by broth dilution method indicate that PAMAM-NH(2) dendrimers significantly (up to 16-fold) increased the antifungal activity of KET against Candida strains (e.g., in culture Candida albicans 1103059/11 MIC value was 0.008 μg/mL and 0.064 μg/mL, and MFC was 2 μg/mL and 32 μg/mL for KET in 10 mg/mL solution of PAMAM-NH(2) G2 and pure KET, respectively). Antifungal activity of designed KET hydrogel with PAMAM-NH(2) dendrimers measured by the plate diffusion method was definitely higher than pure KET hydrogel and than commercial available product. It was shown that the improvement of solubility and in the consequence the higher KET release from hydrogels seems to be a very significant factor affecting antifungal activity of KET in hydrogels containing PAMAM dendrimers.     

Stability of Prussian Blue films on ITO electrodes: effect of different anions

Transformation of insoluble newly deposited Prussian Blue (PB) into the soluble structure stabilizes the film and allows its total oxidation to Prussian Yellow. The stability of PB films in electrochemical processes in successive potential cycling experiments and under long-term chemical attack by an electrolyte depends not only on the cation that takes part but also on the nature of the anion present. In aqueous media, the sulphate ion clearly destabilizes the crystalline structure whereas the nitrate ion favours stabilization. Initial changes in the voltammograms recorded immediately after the spectroscopic tests have been detected in all media. During the immersion period water molecules and ions enter the film and affect the redox processes. With time the ions arrange themselves in the heart of the lattice and the water molecules are lost, and the blocking of the redox processes disappears.     

Synthesis of ferrocenethiols containing oligo(phenylenevinylene) bridges and their characterization on gold electrodes

Ferrocene-terminated oligo(phenylenevinylene) (OPV) methyl thiols have been prepared by orthogonal coupling of phenylene monomers. Ethoxy substituents on the phenyl rings improve the solubility of OPV, enabling the synthesis of longer oligomers. Self-assembled monolayers containing a mixture of a ferrocene OPV methyl thiol and a diluent alkanethiol were deposited on gold. A cyclic voltammetric study of monolayers containing oligomers of the same length with and without ethoxy solubilizing groups reveals that both solubilized and unsolubilized oligomers form well-packed self-assembled monolayers. Changing the position of the solubilizing groups on an oligomer chain does not preclude packing of the oligomer in the monolayer. Conventional chronoamperometry, which can be used to measure rate constants up to approximately 10(4) s(-1), is too slow to measure the electron-transfer rate through these oligomers over distances up to 35 A. OPV bridges are expected to be highly conjugated unlike oligo(phenyleneethynylene) bridges, which may be only partially conjugated because of rotation of the phenyl rings about the ethynylene bonds. Because of its high conjugation, OPV may prove useful as a molecular wire.     

Role of acidity on the electrochemistry of Prussian Blue at plain and Nation filmcoated electrodes

Prussian Blue (PB) coated on plain platinum (Pt) shows a redox wave at 0.44V vs SCE in addition to the two usual redox waves at 0.82 and 0.12 V vs SCE when the electrodes were dipped in acidic KC1 solution. PB incorporated into Nation film-coated on Pt electrode exhibited the same behaviour even in the presence of neutral KG solution. In acidic KC1, the additional redox wave observed for PB incorporated into Nation film shifted positively to 0.39V vs SCE and the peak separation was reduced to 30mV. The observed additional redox wave for PB coated on plain Pt electrode and incorporated into Nafion film-coated Pt electrodes was assigned to the partial reduction of PB occurring due to the insertion of protons into the film. The effect of various cations on the electrochemistry of PB incorporated into Nafion film-coated electrode was also studied.     

铁基普鲁士蓝正极的制备及电化学储钠性能

通过引入抗氧化剂(抗坏血酸)和配位剂(柠檬酸钠),采用共沉淀法在室温下制备出了高钠含量、低缺陷的铁基普鲁士蓝材料。由于高的钠含量和低的晶体缺陷,该材料在0.1C时容量可达110.0 mAh·g^-1。除了普鲁士蓝材料独特的开放框架结构,其多边界结构和低的缺陷,使该材料表现出优异的倍率性能和循环稳定性。在10C大电流下,容量仍有86.6 mAh·g^-1,1C电流下经过1300次循环,容量保持在90.1 mAh·g^-1,容量保持率达到86.9%。     

Strong blue photoluminescence and ECL from OH-terminated PAMAM dendrimers in the absence of gold nanoparticles

A product showing strong blue photoluminescence was obtained by oxidation of OH-terminated PAMAM dendrimers, such as G4-OH, G2-OH, and G0-OH, with HAuCl4 or (NH4)2S2O8. The fluorescence emission spectrum peaked at 450 nm, while the excitation maximum was at 380 nm, independent of the generation of dendrimer. The product also shows two weak electrogenerated chemiluminescence (ECL) signals upon cycling the potential between about 1.2 and -1.7 V.     

Electrodeposited Pt-Ir electrodes: characterization and electrocatalytic activity for the reduction of the nitrate ion

The activity of Pt-Ir deposits on titanium for the reduction of the nitrate ion in 0.5 M perchloric acid was studied. The electrodes were characterized by SEM-EDAX, XPS and cyclic voltammetry. The activity of the electrodes for the nitrate reduction depended on the Pt-Ir ratio. Repetitive cyclic voltammograms produced an enrichment of the electrode surface with Ir and a decrease of the catalytic activity. A synergistic effect in the electrodes with low iridium content is discussed. Received: 2 June 1997 / Accepted: 28 August 1997     

Preparation and characterization of V-shaped PS-b-PEO brushes anchored on planar gold substrate through the trithiocarbonate junction group

Trithiocarbonate group was introduced into the polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymers as the junction of the blocks through RAFT polymerization. Mixed PS and PEO brushes with a V-shape were prepared by anchoring the trithiocarbonate group on the planar gold substrate. The morphology of the V-shaped brushes was characterized by atomic force microscopy (AFM) and the surface composition responsive to solvent treatment was detected by X-ray photoelectron spectroscopy (XPS). Different morphologies were observed for the V-shaped PS-b-PEO brushes, depending on the chain structure and solvent treatment. The highly selective solvent for PEO, ethanol, can intensify or induce microphase separation of the V-shaped brushes, leading to vertical microphase separation. When the V-shaped brushes are treated with the co-solvent, THF, miscible morphology, lateral microphase separation, and vertical microphase separation are observed as the PS block length increases. After treatment with the non-selective poor solvent, cyclohexane, the V-shaped PS(106)-b-PEO(113) brush, exhibits a laterally microphase-separated morphology, but the V-shaped PS(52)-b-PEO(113) and PS(253)-b-PEO(113) brushes are vertically microphase-separated.     

Electrochemical behavior of bisphenol A at glassy carbon electrode modified with gold nanoparticles, silk fibroin, and PAMAM dendrimers

A glassy carbon electrode was modified with a composite made from gold nanoparticles and silk fibroin whose surface was further modified with amino-terminated G4 poly(amidoamine) dendrimer. This electrode shows distinct electrochemical response to bisphenol A (BPA). Electrochemical impedance spectroscopy was used to characterize the surface. The electrode displayed improved adsorption capacity and an increased response to BPA, compared to a surface without modification. Under the optimal detection conditions, the respeonse is linear in the concentration range from 1 nM to 1.3 μM, the correlation coefficient is 0.9991, and the detection limit is 0.5 nM (at an S/N of 3). The method was applied to the determination of BPA in water samples, and the recovery was in the range from 97% to 105%.     

Platinum-coated gold nanoporous film surface: electrodeposition and enhanced electrocatalytic activity for methanol oxidation

This report describes the preparation of Pt-nanoparticle-coated gold-nanoporous film (PGNF) on a gold substrate via a simple "green" approach. The gold electrode that has been anodized under a high potential of 5 V is reduced by freshly prepared ascorbic acid (AA) solution to obtain gold nanoporous film electrode. Then the Pt nanoparticle is grown on the electrode by cyclic voltammetry (CV). The resulting PGNF electrode has highly ordered arrangement and large surface area, as verified by scanning electron microscopy (SEM) and CV, suggesting that the nanoporous gold film electrode provides a good matrix for obtaining PGNF with high surface area. Furthermore, the as-prepared PGNF electrode exhibited high electrocatalytic activity toward methanol oxidation in a 0.5 M H 2SO 4 solution containing 1.5 M methanol. The present novel strategy is expected to reduce the cost of the Pt catalyst remarkably.     

Amperometric Detection of H2O2 Using Gold Electrodes Modified with Starburst PAMAM Dendrimers and Prussian Blue

Gold‐bead electrodes were modified by covalent bonding or physical adsorption of several Starburst PAMAM dendrimers (generations 2.0, 3.0 and 4.0) followed by absorption of Prussian Blue (PB). The covalent dendrimer‐PB‐modified electrodes can be used as amperometric sensors of H₂O₂ in aqueous solution. They offer enhanced sensitivity with correspondingly lower detection and quantification limits compared to similar amperometric detectors.     

Effect of aging on the electrocatalytic activity of gold nanoparticles

The electrocatalytic activities of freshly prepared nanomaterials do not represent normal activities, if they change with aging. We report the dependence of the electrocatalytic activity of gold nanoparticles (AuNPs) upon aging. The activities of AuNPs prepared by four different methods (electrodeposition; reduction of Au ions with NaBH₄, citrate, and ascorbate, respectively) slowly decrease with aging in the electrooxidation of H₂O₂ or formic acid, both in air and in solution. The possible origin of this effect is discussed.     

Waveguide surface plasmon resonance studies of surface reactions on gold electrodes

We describe the fabrication and characterisation of gold-coated graded index channel waveguide sensors designed for simultaneous electrochemical and surface plasmon resonance studies. The active sensing electrode area is a thin gold film between 0.5 and 5 mm in length and 200 microm wide deposited on top of a 3 microm wide waveguide which forms one arm of a Y-junction while the other arm of the Y-junction serves as a reference. Using these devices we have measured simultaneously the changes in transmittance through the device whilst carrying out cyclic voltammetry in either sulfuric or perchloric acid solution or during the deposition of an UPD layer of copper at the gold surface. In all cases we obtain stable and reproducible results which demonstrate the very high sensitivity of the devices to sub-monolayer changes occurring at the gold electrode surface. The response of these integrated optoelectrochemical devices is discussed in terms of a numerical model for the propagation of light within the waveguide structure.     

铁基普鲁士蓝正极材料的宏量制备及电化学储钠性能

以柠檬酸钠作为配位剂,采用共沉淀法,在室温下制备了铁基普鲁士蓝材料(FePB).当使用20 L容积的反应釜,并将前驱体亚铁氰化钠(Na4[Fe(CN)6])的浓度提高至0.5 mol·L-1时,制备一次可实现高达500 g的产量.电化学测试显示,所得FePB材料具有较高的容量、优异的倍率性能和良好的循环寿命.在0.1C...