Silk fibroin fibers supported with high density of gold nanoparticles: fabrication and application as catalyst

Silk fibroin (SF) fibers were modified with sulfonated polyaniline and, via an in situ redox technique, a high density of gold (Au) nanoparticles were supported directly on the surface of the fiber. The morphology, formation, and application of the as-prepared product, Au/SPANI-modified SF composite fiber, were investigated. By controlling the concentration of HAuCl₄, the density of Au nanoparticles on the composite fiber could be effectively adjusted. It is suggested that sulfonated polyaniline contributes to the generation of a high density of Au nanoparticles supported on the SF fibers. The composite fiber exhibited good activity when taking the reduction of p-nitrophenol as a model reaction.     

Spectral and adsorption characteristics of Au(III) and Au(0) composite materials

The adsorption of HAuCl₄ chloroauric acid on silica modified with γ-aminopropyltriethoxysilane (aminosilica) and on aluminum oxide is studied. Diffuse-scattering spectra of these Au(III) composite materials and their reduced Au(0) composites are recorded in the visible and infrared spectral ranges. Au(III) composites are selective with respect to the adsorption of phenylacetylene (PA) from octane due to the formation of π-complexes with Au(III). Au(III)-aluminum oxide composite material has a much larger capacity for PA adsorption than does aminosilica composite with the same gold content. The formation of coordination bonds between free aminopropyl groups of the silica carrier and gold atoms prevents PA adsorption. The formation of such bonds is manifested in a shift in λ_max of the spectral line from 408 to 522 and 546 nm with a decrease in [Au(III)] concentration from 400 to 120 and 60 μmol/g. The decrease in the intensity and the red shift of the absorption bands of NH₂ stretching vibrations in the infrared spectra of the specimen upon modification also confirms the supposition. There are absorption bands of free hydroxyl radicals, but no band of bound radicals in the infrared spectra of Au(0) composites. The electronic spectra (λ_max = 511, 504, and 512 nm) are close for all three specimens that differ in gold content, which means that the sizes of immobilized Au(0) nanoparticles are similar. Upon the sorption of HAuCl₄ on a Au(III)-aluminum oxide specimen, the absorption band of surface OH groups disappears, however, in Au(0) composite, it appears again near 3105 cm^?1.     

Enzyme electrodes stabilized by monolayer-modified nanoporous Au for biofuel cells

Open-cell nanoporous Au (np-Au) electrodes with pore size of approximately 40 nm were fabricated by dealloying of Au–Ag, and surfaces of the electrodes were modified with a self-assembled monolayer (SAM) of 4-aminothiophenol to enhance the electrocatalytic activities of immobilized laccase and glucose oxidase. Enzyme-immobilized SAM-modified np-Au working electrodes exhibited additional reduction–oxidation peak pairs in cyclic voltammograms in buffer solution (pH = 5.0). Thus, the SAM on the np-Au facilitated electron transfer between the electrode and reactants. First-principles calculations of perfect and defective Au (111) surfaces indicated that the atomic defects at nanoligament surface of np-Au are critically responsible for the electron transfer enhancement. For the utilization of these results, a glucose/O₂ biofuel cell composed of these enzyme-immobilized SAM-modified np-Au electrodes was preliminarily fabricated, and it exhibited a maximum power density of 52 μW/cm² at 20°C. Further optimization of nanoporous structures and kinds of SAM will improve the performance of biofuel cells.     

In-situ chemical synthesis route for a fiber shaped gold-polyaniline nanocomposite

A facile synthesis route is described for the preparation of a gold-polyaniline nanocomposite material by polymerization of aniline hydrochloride using HAuCl4 as the oxidant. It was found that the oxidative polymerization of aniline hydrochloride leads to the formation of polyaniline with a fiber-like morphology, while the concomitant reduction of HAuCl₄ results in the formation of gold nanoparticles of diameter 2–7 nm. The gold nanoparticles were highly dispersed and stabilized throughout the polyaniline fibers while being in intimate contact with the polymer. The combination formed a uniform metal-polymer composite material.     

水浴法制备钯纳米颗粒及其修饰电极的电催化性能

利用Keggin结构的12-硅钨酸作为模板,采用水浴法还原硝酸钯制备了纳米钯.用透射电子显微镜(TEM)和X射线衍射(XRD)等手段对制备的钯纳米颗粒的形貌、粒径大小和结构进行了表征.利用滴涂法将Pd纳米颗粒修饰到Au电极表面,通过循环伏安法,研究了纳米Pd对肼的电催化性质.结果显示,制备的纳米钯为3～4 nm的类球形颗粒,为面心立方结构.纳米Pd修饰电极对肼具有良好的电催化氧化作用.在pH=6时,氧化峰电流(lpa)与肼的浓度呈现良好的线性关系.     

Novel plating solution for electroless deposition of gold film onto glass surface

In this paper, a simple and environmentally friendly electroless plating solution of chloroauric acid (HAuCl₄) and hydrogen peroxide (H₂O₂) for depositing gold film onto (3-aminopropyl)-trimethoxysilane (APTMS) -coated glass surface has been developed. APTMS as an adhesive reagent was used to attach the gold nanoparticles (AuNPs) onto the glass substrate. These AuNPs could be regarded as the preferential nucleation or catalytic sites for gold electroless reduction, which accelerated the reduction of Au³⁺ on the glass surface and effectively prevented the formation of gold metal in the bulk solution. During the gold plating process, H₂O₂ as the reducing agent was thermodynamically capable of reducing Au³⁺ ions from the HAuCl₄ precursor to gold atoms, which deposited onto the glass surface and finally formed the continuous gold film. The resulting gold film was characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atomic force microscope (AFM), respectively.     

Preparation of nano- and microstructured gold surfaces by application of a square wave potential regime

Gold nanometallic structures have been prepared by application of square wave potential regime to a platinum electrode in a 1.0 × 10^?3 M HAuCl₄ + 0.5 M H₂SO₄ solution. Formation of gold particles onto the platinum surface has been followed by cyclic voltammetry, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The results indicate that the size, shape, uniformity of distribution of the particles are affected by the selected parameters of the applied square wave potential regime. Parameters of the square wave include the frequency, the lower and the upper limits of the square wave and the time of application of the square wave potential regime. The concentration of HAuCl₄ in the solution is another important factor. The results of the present work indicated that the 100 Hz frequency is the optimal frequency for obtaining gold nanoparticles on platinum surface. Deposition time has been also found to play a critical role in affecting the size, shape and homogeneity of gold nanostructures at the surface. The surface coverage with nanoparticles as calculated from the decrease in the charge of hydrogen adsorption/desorption peaks is found to be directly proportional to the time of application of the square wave. Testing the nanostructured gold/Pt electrode for oxidation of formic acid shows its higher catalytic activity than that of platinum and gold plain electrodes.     

Growing and stability of gold nanoparticles and their functionalization by cysteine

Gold nanoparticles in aqueous dispersion were prepared using the trisodium citrate reduction method to control the size of particles by changing the concentration of HAuCl₄. The average particle size measured by DLS is higher than that obtained by TEM at a zeta potential of -40 mV. When trisodium citrate concentration is kept constant, the particle size increases with gold concentration. The kinetics of growth was studied and apparent kinetic rate constants were determined at various gold/citrate ratios. Gold nanoparticles were attached to silanized glass surfaces; Au rods were grown (ca. 200 nm) by adding more precursors and the rods’ growth rate was monitored by UV-Vis spectroscopy as well as by AFM. Surface functionalization of gold surface was influenced by cysteine. The surface modification by cysteine at pH=6.0 results in aggregation and the red shift of absorption maximum is nearly 200 nm. When glutathione molecules are bound onto the cysteinelinked Au rods on the glass surface, the spectral shift reaches only an amount of 5–10 nm, because the surface attachment hinders the tendency to aggregate.     

Chemical modification of electrochemically oxidized and partially rereduced carbon fibre electrodes

Carbon fibre electrodes (residual graphite oxide fibres) electrochemically oxidized and partially rereduced in concentrated H₂SO₄ have excellent cation-exchanging properties. Chemically modified carbon fibre electrodes have been prepared by Na⁺-exchange of residual graphite oxide fibres and subsequent action of chlorocompounds in methanolic solutions (the Williamson reaction).The attachment of the various reagents on to the carbon fibres is reflected through the corresponding cyclic voltammograms obtained in aqueous buffer solutions. When modified with iron phthalocyanine, carbon fibre electrodes show a significant catalytic effect on the electrochemical reduction of oxygen in aqueous and methanolic solutions.     

AuCu双金属纳米颗粒的制备、表征及性能探究

采用水热法制备AuCu双金属纳米颗粒,并用X射线衍射(XRD)、透射电镜(TEM)和紫外可见光谱(UV-Vis)进行表征,初步研究了其对4-硝基苯酚(4-NP)还原的催化性能和光热效应。结果表明,制备时不同的AuCl_4~-/Cu~(2+)摩尔比(r_(Au))可以调控AuCu双金属纳米颗粒的组分和形貌,XRD和吸收光谱特征随r_(Au)的增加表现出更明显的金的特征,r_(Au)0.5时得到的颗粒具有典型的核-壳结构;核-壳结构的AuCu双金属纳米颗粒对4-NP还原表现出更好的催化活性,受光热效应影响,532 nm激光照射能够加强催化活性;在激光辐射作用下,不同AuCu双金属纳米颗粒具有相似的光热效应。     

金银复合纳米微粒的光学吸收特性

以NaHB4做还原剂,利用一步共还原氯金酸(HAuCl4)和硝酸银(AgNO3)制备了金银复合结构的纳米颗粒。用透射电子显微镜对所制备的金银复合纳米微粒的形貌和尺寸进行了表征。紫外可见光学吸收光谱的研究表明:通过一步共还原法所制备的金银复合纳米微粒的光学吸收谱具有单峰的等离子体吸收特征,其吸收峰介于纯金和纯银纳米颗粒特征吸收峰之间,且随着反应液中金离子和银离子的摩尔比的增加而向长波方向移动。Mie散射理论的定量计算结果同样说明了实验所观察到的金银复合纳米微粒的光学吸收的组分可剪裁性。     

Di-(2-ethylhexyl) dithiophosphoric acid surface protected gold nanoparticles: micellar synthesis, stabilization, isolation, and properties

Gold nanoparticles (AuNPs) were synthesized in the organic solution by means of the reduction of HAuCl₄ by hydrazine in reverse micelles of oxyethylated surfactant Triton N-42, with decane as the dispersion medium. To isolate the powder of particles, the micelles were destroyed with chloroform in the presence of di-(2-ethylhexyl) dithiophosphoric acid as a surface protecting agent. According to the results of several experiments, the yield is within the limits of 90–98%, calculated for gold. The obtained preparations are dark blue hydrophobic powders containing aggregated but not agglomerated gold nanoparticles, as well as microcrystals (∼0.08–0.2 μm) of NaCl. The powders get re-dispersed in weakly polar organic solvents with the formation of colloidal solutions. The shape of the nanoparticles is spherical. Their nuclei are gold single crystals with a narrow size distribution; their diameter (d _Au) is about two times as large as the diameter of the aqueous nucleus (d _c) of initial micelles: d _Au = 7.7 ± 1.4 nm (d _c = 3.6 nm) and 8.8 ± 1.5 nm (4.6 nm). The preparations were studied by means of dynamic light scattering, atomic force microscopy, transmission electron microscopy, UV–vis spectroscopy, IR spectroscopy, X-ray powder diffraction, and thermogravimetric and elemental analyses. In the case of the particles with d _Au = 8.8 nm, the product is a mixture of AuNPs and the salt with the molar ratio Au/NaCl ≈ 1:4.54, while the gross composition of AuNPs per one gold atom is estimated as Au(C₁₆H₃₄O₂PS₂Na∙2N₂H₄)_0.16 with the number of gold atoms in one particle ∼21,000.     

Sensing behavior of silica-coated Au nanoparticles towards nitrobenzene

In the present work, we report silica-stabilized gold nanoparticles (SiO₂/Au NPs) as a wide-range sensitive sensing material towards nitrobenzene (NB). Surface hydroxyl groups of silica selectively form Meisenheimer complex with electron-deficient aromatic ring of NB and facilitate its immobilization and subsequent catalytic reduction by Au cores. Silica-coated Au NPs were synthesized and characterized for their chemical, morphological, structural, and optical properties. SiO₂/Au NPs-modified electrodes were characterized with impedometric and cyclic voltammetric electrochemical techniques. SiO₂/Au NPs are found to have a higher optical detection window of range, 0.1 M to 1 μM and a lower electrochemical detection window of range, 10⁻⁴ to 2.5 × 10⁻² mM with a detection limit of 12.3 ppb. A significant enhancement in cathodic peak current, C ₁, and sensitivity (102 μA/mM) was observed with modified electrode relative to bare and silica-modified electrodes. The I _P was found to be linearly co-related to NB concentration (R ² = 0.985). The interference of cationic and anionic species on sensor sensitivity was also studied. Selectivity in the present sensing system may be further improved by modifying silica with specific functional moieties.     

Fabrication of modified-poly(divinylbenzene)/Au core–shell structure

A novel PDVB/Au core–shell structure was prepared by the chemical reduction of a gold–phenanthroline complex on the surface of a poly(divinylbenzene) (PDVB) cores (2–4 μm). The PDVB cores were synthesized by precipitation polymerization, and the surface was modified by introducing thiol and sulfonic acid groups. The modified surface structure was examined by FT-IR, XPS and EDS and the degree of sulfonation was measured according to its ion exchange capacity (IEC, 5.72 meq/g). The modified PDVB cores were immersed in a solution of a gold–phenanthroline complex and subsequently reduced to form gold nanoseeds. These were further grown in a solution of HAuCl₄ and NH₂OH to form gold nanoshells. The effects of the functional groups on the PDVB cores on fabrication of the core–shell structure were carefully examined. SEM and XPS were used to characterize the gold nanoshells. The presence of the functional groups could be of great assistance for the gold shell formation.     

Effects of Au nanoparticles on TiO2 in the photocatalytic degradation of an azo dye

The photocatalytic activity of Au modified titanium dioxide was evaluated in the photodegradation of the azo dye Acid Red 1 (AR1) under 254 nm irradiation. Noble metal nanoparticles were deposited on TiO₂ either through depositionprecipitation (DP), or by immobilisation of preformed metallic sols (polyvinylalcohol (PVA)/NaBH₄ or tetrakis(hydroxymethyl)phosphonium chloride (THPC)/NaOH systems). Gold nanoparticles on the photocatalyst surface had dimensions of around 3–4 nm in diameter, as determined by HRTEM analysis, and exhibited visible light plasmon absorption. THPC Au/TiO₂ appears to be the most photoactive amongst the photocatalysts with a 1 wt.% Au loading, while among THPC samples with different Au loadings (0.5–20.0 wt.%) the maximum photoactivity was attained with 5 wt.% Au/TiO₂. The higher AR1 photodegradation rate observed on Au/TiO₂ at basic pH can be related to the higher concentration of hydroxyl anions at the interface: these are able to effectively scavenge photoproduced valence band holes, possibly in competition with Au⁰ oxidation to Au⁺.     

Formation of nanometer-sized Au particles on USY zeolites under hydrogen atmosphere

Gold was deposited on ultrastable Y (USY) zeolite using a newly developed method: just mixing an aqueous solution of HAuCl₄ and zeolite at 353 K in which the NH₄⁺ cation reacted with the Cl⁻ in HAuCl₄. Treatment of the Au-loaded USY zeolite in the atmosphere of hydrogen resulted in the formation of Au⁰ nanoclusters with 1.8 nm diameter at 773 K. The size of Au particle was dependent on the type of zeolite support, composition of gas atmosphere, and temperature of calcination, which was correlated with catalytic performance. This study demonstrated the potential use of zeolites with strong Br?nsted acid character as gold supports.     

Electrochemical synthesis of adherent polypyrrole films on zinc electrodes in acidic and neutral organic media

The electrodeposition of polypyrrole on zinc electrodes has been performed by anodic oxidation of pyrrole in acetonitrile, nitrobenzene and propylene carbonate media in the presence of para-toluene sulfonate counter-ions. When the zinc electrode has preferably undergone a chemical treatment by aqueous sodium sulfide solution, homogeneous and adherent PPy films are obtained. While, no PPy film grows (in the case of C₆H₅NO₂ and PC) or a non-homogeneous and poorly adherent PPy–zinc oxide composite forms (in the case of CH₃CN) when the zinc surface is simply polished. Among the electrochemical techniques used in these experiments, the galvanostatic mode was proved to be better adapted to perform the electropolymerization of pyrrole on the pretreated zinc electrodes using low applied current densities. The polypyrrole films synthesized by this technique has been characterized by several microscopic and spectroscopic techniques. In particular, SEM, XPS, FT-IR and Raman analyses showed that the obtained coatings have the same structure and morphological properties as those electrodeposited on Pt electrodes.     

Carbon nanotubes-supported PtAu-alloy nanoparticles for electro-oxidation of formic acid with remarkable activity

PtAu-alloy nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) were successfully prepared by simultaneous reduction of H₂PtCl₆·6H₂O and HAuCl₄·3H₂O with sodium borohydride as a reducing reagent and sodium citrate as a stabilizing reagent. The morphology and composition of the composite catalyst were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The results show that the PtAu alloy nanoparticles with an average diameter of about 3.5 nm and narrow size distribution are supported on MWCNTs. Electrocatalytic oxidation of formic acid at the PtAu/MWCNTs nanocomposite electrode was investigated in a solution containing 0.50 M H₂SO₄ as a supporting electrolyte and 0.50 M formic acid by cyclic voltammogram and chronoamperometry. The results demonstrate that the PtAu/MWCNTs catalyst exhibits higher activity and stability for electro-oxidation of formic acid than the commercial Pt/C catalyst, reflecting by its lower onset potential (−0.05 V), oxidation mainly occurring in low potential range of −0.05 ± 0.65 V and higher peak current density of 3.12 mA cm⁻². The result of CO stripping voltammetry discloses that gold in the PtAu/MWCNTs nanocomposite enhances the catalytic activity and stability.     

Electrodeposition of composite films consisting of polypyrrole and mesoporous silica

Electrochemical formation of composite films consisting of polypyrrole (PPy) and MCM particles has been presented, in which pyrrole is electrochemically oxidized in an aqueous solution with suspension of purely siliceous or aluminum-containing MCM-41. The composite films were characterized by scanning electron microscopy, X-ray diffraction and infrared reflection spectroscopy, and the electrochemical response of the PPy/MCM-deposited electrode to Fe(CN)₆³⁻ investigated. From IR spectra, it is indicated that the polymerization of pyrrole takes place on the internal wall of MCM particles where the cationic PPy is charge-balanced by the negatively charged MCM. A PPy/SiMCM composite electrode prepared in the presence of higher concentration of pyrrole (≧0.5 M) shows a reproducible electrochemical response for Fe(CN)₆³⁻. The CV curve on this electrode is comparable to that on pure PPy-modified electrode, and it is suggested that the negative charge on the mesopore surface is almost completely neutralized by the positive charge of PPy.     

Preparation and tribological studies of nanocomposite films fabricated using spin-assisted layer-by-layer assembly

Uniform and smooth composite multilayer films composed of gold nanoparticles and polyelectrolytes ([Au/(PAH-PSS)_nPAH]_m) multilayers were fabricated on a silicon substrate using a time-and cost-efficient spin-assisted layer-by-layer (SA-LbL) self-assembly technique. The microstructure and morphology of the multilayer films were characterized by means of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The tribological behavior of the composite multilayer films was evaluated using a ball-on-plate tribometer. It was found that the density of the monolayer of gold nanoparticles on the silicon substrate was dependent on the deposition time, but the coverage of the Si substrate by the gold nanoparticle kept almost unchanged at a deposition duration above 30 min. The antiwear life and load-carrying capacity of the [Au/(PAH-PSS)_nPAH]_m composite film substantially increased with increasing number of the polymer bilayers and gold nanoparticles monolayer, which could be attributed to the robust organic-inorganic nanocomposite structure and PAH and PSS fragments transferred onto the counterpart surface.