One-step preparation and characterization of PDDA-protected gold nanoparticles

Poly(diallyl dimethylammonium) chloride (PDDA), an ordinary and watersoluble cationic polyelectrolyte, was investigated for its ability to generate and stabilize gold colloids from a chloroauric acid precursor. In this reaction, PDDA acted as both reducing and stabilizing agents for gold nanoparticles (AuNPs). More importantly, PDDA is a quaternary ammonium polyelectrolyte, which shows that the scope of the reducing and stabilizing agents for metal nanoparticles can be extended from the amine-containing molecules to quaternary ammonium polyelectrolytes or salts. UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and Fourier transform infrared (FTIR) were used to characterize the synthetic AuNPs. The PDDA-protected AuNPs obtained are very stable and have relative narrow size distribution.     

Catechin-capped gold nanoparticles: green synthesis,characterization, and catalytic activity toward 4-nitrophenol reduction

An eco-friendly approach is described for the green synthesis of gold nanoparticles using catechin as a reducing and capping agent. The reaction occurred at room temperature within 1 h without the use of any external energy and an excellent yield (99%) was obtained, as determined by inductively coupled plasma mass spectrometry. Various shapes of gold nanoparticles with an estimated diameter of 16.6 nm were green-synthesized. Notably, the capping of freshly synthesized gold nanoparticles by catechin was clearly visualized with the aid of microscopic techniques, including high-resolution transmission electron microscopy, atomic force microscopy, and field emission scanning electron microscopy. Strong peaks in the X-ray diffraction pattern of the as-prepared gold nanoparticles confirmed their crystalline nature. The catalytic activity of the as-prepared gold nanoparticles was observed in the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH₄. The results suggest that the newly prepared gold nanoparticles have potential uses in catalysis.     

Spontaneous synthesis of gold nanoparticles on gum arabic-modified iron oxide nanoparticles as a magnetically recoverable nanocatalyst

A novel magnetically recoverable Au nanocatalyst was fabricated by spontaneous green synthesis of Au nanoparticles on the surface of gum arabic-modified Fe₃O₄ nanoparticles. A layer of Au nanoparticles with thickness of about 2 nm was deposited on the surface of gum arabic-modified Fe₃O₄ nanoparticles, because gum arabic acted as a reducing agent and a stabilizing agent simultaneously. The resultant magnetically recoverable Au nanocatalyst exhibited good catalytic activity for the reduction of 4-nitrophenol with sodium borohydride. The rate constants evaluated in terms of pseudo-first-order kinetic model increased with increase in the amount of Au nanocatalyst or decrease in the initial concentration of 4-nitrophenol. The kinetic data suggested that this catalytic reaction was diffusion-controlled, owing to the presence of gum arabic layer. In addition, this nanocatalyst exhibited good stability. Its activity had no significant decrease after five recycles. This work is useful for the development and application of magnetically recoverable Au nanocatalyst on the basis of green chemistry principles.     

Electrochemical and morphological characterization of gold nanoparticles deposited on boron-doped diamond electrode

A novel two-step method was employed to synthesize gold nanoparticles dispersed on boron-doped diamond (BDD) electrode. It consisted of sputter deposition at ambient temperature of maximum 15 equivalent monolayers of gold, followed by a heat treatment in air at 600 °C. Gold nanoparticles with an average diameter between 7 and 30 nm could be prepared by this method on polycrystalline BDD film electrode. The obtained Au/BDD composite electrode appeared stable under conditions of electrochemical characterization performed using ferri-/ferrocyanide and benzoquinone/hydroquinone redox couples in acidic medium. The electrochemical behavior of Au/BDD was compared to that of bulk Au and BDD electrodes. Finally, the Au/BDD composite electrode was regarded as an array of Au microelectrodes dispersed on BDD substrate.     

Magnetite nanoparticles: Electrochemical synthesis and characterization

Magnetite (Fe₃O₄) nanoparticles (NP) with sizes between 20 and 30 nm have been obtained by Fe electrooxidation in the presence of an amine surfactant, which acted as a supporting electrolyte and coating agent, controlling particle size and aggregation during the synthesis. The effect of different parameters on the nature and size of the particles as well as the mechanism of formation of the particles have been studied by different techniques. It was concluded that, under the electrochemical conditions used in this work, the NP mean size was found to be constant at around 20 nm when the electrooxidation current density is increased from 10 to 200 mA cm⁻². However, when the potential is over 6 V, particle size decreases from 30 to 20 nm and metallic iron appears as an impurity. The mechanism of particles formation has being clarified and the critical effect of the distance between electrodes for obtaining magnetic iron oxide nanoparticles has been understood. Finally, the presence of an electrostatic adsorbed surfactant coating the particles allows the functionalization of the particles easily by exchange reaction with biomolecules of interest, which makes this material very promising for future application in biotechnology.     

Glucomannan-mediated facile synthesis of gold nanoparticles for catalytic reduction of 4-nitrophenol

A facile one-pot approach for synthesis of gold nanoparticles with narrow size distribution and good stability was presented by reducing chloroauric acid with a polysaccharide, konjac glucomannan (KGM) in alkaline solution, which is green and economically viable. Here, KGM served both as reducing agent and stabilizer. The effects of KGM on the formation and stabilization of as-synthesized gold nanoparticles were studied systematically by a combination of UV-visible (UV-vis) absorption spectroscopy, transmission electron microscopy, X-ray diffraction, dynamic light scattering, and Fourier transform infrared spectroscopy. Furthermore, the gold nanoparticles exhibited a notable catalytic activity toward the reduction of 4-nitrophenol to 4-aminophenol.     

Size-dependent antimicrobial properties of sugar-encapsulated gold nanoparticles synthesized by a green method

The antimicrobial properties of dextrose-encapsulated gold nanoparticles (dGNPs) with average diameters of 25, 60, and 120 nm (± 5) and synthesized by green chemistry principles were investigated against both Gram-negative and Gram-positive bacteria. Studies were performed involving the effect of dGNPs on the growth, morphology, and ultrastructural properties of bacteria. dGNPs were found to have significant dose-dependent antibacterial activity which was also proportional to their size. Experiments revealed the dGNPs to be bacteriostatic as well as bactericidal. The dGNPs exhibited their bactericidal action by disrupting the bacterial cell membrane which leads to the leakage of cytoplasmic content. The overall outcome of this study suggests that green-synthesized dGNPs hold promise as a potent antibacterial agent against a wide range of disease-causing bacteria by preventing and controlling possible infections or diseases.     

Earthworm extracts utilized in the green synthesis of gold nanoparticles capable of reinforcing the anticoagulant activities of heparin

Gold nanoparticles were obtained using a green synthesis approach with aqueous earthworm extracts without any additional reducing or capping agents. The gold nanoparticles were characterized using UV-visible spectrophotometry, high-resolution transmission electron microscopy, atomic force microscopy, field emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and inductively coupled plasma mass spectrometry. The anticoagulant activity of the gold nanoparticles was assessed using the activated partial thromboplastin time and was mildly enhanced by combining the gold nanoparticles with heparin. In addition to the generation of spherical nanoparticles with an average diameter of 6.13 ± 2.13 nm, cubic and block-shaped nanoparticles with an average aspect ratio, defined as the length divided by width, of 1.47 were also observed.     

Plant‐mediated synthesis of silver and gold nanoparticles and their applications

Nanobiotechnology deals with the synthesis of nanostructures using living organisms. Among the use of living organisms for nanoparticle synthesis, plants have found application particularly in metal nanoparticle synthesis. Use of plants for synthesis of nanoparticles could be advantageous over other environmentally benign biological processes as this eliminates the elaborate process of maintaining cell cultures. Biosynthetic processes for nanoparticles would be more useful if nanoparticles were produced extracellularly using plants or their extracts and in a controlled manner according to their size, dispersity and shape. Plant use can also be suitably scaled up for large‐scale synthesis of nanoparticles. In view of this, we have reviewed here the use of plants or their extracts in the synthesis of silver and gold nanoparticles for various human applications. Copyright © 2008 Society of Chemical Industry     

One-step ball-milling synthesis of cesium tungsten bronze nanoparticles and near-infrared shielding performance

Tungsten bronze (M_xWO₃) materials have been widely used as thermal insulation for architectural glass because of their higher near-infrared (NIR) light shielding capacity. To solve the problems encountered in solvothermal preparation with high costs and low yields, this study has developed a facile, eco-friendly, effective, but low-cost method, with no need for any annealing process, for promoting the large-scale fabrication of cesium tungsten bronze (Cs_xWO₃, x = 0.32) nanomaterials for potential thermal insulation windows applications. In the proposed ball-milling process, the tungstic acid material could be reduced to hydro tungsten bronze (H_xWO₃) by cellulose, while the cesium ions (Cs⁺) could be gradually incorporated into the interspace until the formation of Cs_0.32WO₃ (Cs/W atomic ratio = 0.32), with an average particle size of ∼33 nm after a 15 h ball-milling process. The reaction mechanism has been investigated in detail via particle structural analysis and optical performance characterization. The obtained Cs_0.32WO₃ nanoparticles are dispersed in a solution composed of surfactant (s) and polymer (s) which can form a thin film with a thickness of about 2 μm on a glass substrate, by a spinning coating or casting method, to exhibit high visible (Vis) light transmittance (T_566nm = 72.6%), and excellent NIR-shielding capability (T_1388nm = 5.3%), reflected by good heat-insulating performance in practice use. This work will pave a new path for large-scale production of Cs_0.32WO₃ nanomaterials with low costs and high performance, beneficial for practical applications in energy-saving glass coatings.     

Polyaniline–polyelectrolyte–gold(0) ternary nanocomposites: Synthesis and electrochemical properties

Ternary composites based on polyaniline (PAni), a polyelectrolyte-namely poly(diallyldimethylammoniumchloride) (PDDMAC) and gold (Au(0)) nanoparticles have been formulated and synthesized where the high concentration of PDDMAC acted as medium of reaction. The nanocomposites are characterized by FT-IR, UV–vis, XRD, XPS, SEM, AFM and TEM techniques. XRD showed the presence of all three viz., polyaniline, PDDMAC and Au(0) components in the ternary system. The composites exhibited higher conductivities in the range 26 × 10⁻⁶ to 217 × 10⁻⁶ S/cm compared with the binary composite of PAni–PDDMAC. The ternary composites were adsorbed on a GC electrode and used for sensing dopamine. The composites are useful in sensing as low as 0.05 mM concentration of dopamine at lower potential values compared to some binary PAni–Au nanocomposites.     

Enhanced electrocatalytic activity of a polyoxometalates-based film decorated by gold nanoparticles

A K₆P₂MoW₁₇O₆₂-based film decorated by gold nanoparticles was prepared by layer-by-layer self-assembly method. It was fabricated on quartz, silicon and ITO substrates in a progressive and uniform manner monitored by UV–vis spectroscopy, and characterized by atomic force microscopy (AFM), cyclic voltammograms (CVs) and electrochemical impedance spectra (EIS). A set of experimental results revealed that the incorporation of Au nanoparticles into K₆P₂MoW₁₇O₆₂-based film enhanced the conductivity of the film, leading to several or more than tenfold increase in electrocatalytic efficiency of this film for reduction of H₂O₂, IO₃⁻, NO₂⁻ compared to the no use of Au nanoparticles. It also has been found that presence of Au nanoparticles endowed the film electrocatlytic activity towards oxidation of ascorbic acid and the photo-luminescence property arising from inter electron transitions between occupied 5d bands to 6sp conduction bands of AuNPs.     

Reductant-free synthesis of magnetoplasmonic iron oxide-gold nanoparticles

Stable suspensions of spherical 10–15 nm superparamagnetic iron oxide nanoparticles (SPIONs) have been synthetized by co-precipitation, stabilized with citric acid, surface functionalized with aminopropyltriethoxysilane (APTES) and finally decorated with ultra-small gold nanoparticles (GNPs) by in situ reduction of a soluble gold salt (HAuCl₄), obtaining well dispersed SPIONs-GNPs colloids.The morphology, size and stability of the SPIONs-GNPs suspensions have been controlled by adjusting the molar ratio of the reagents (Fe/HAuCl₄ and Fe/APTES). The synthesis route differs from that typically found in literature, using tunable chelating layer modifications (such as citric acid and –NH₂ groups) of the magnetic core, depositing GNPs on the amine-functionalized iron oxide surface without the use of a specific reducing agent, and tuning the process pH and temperature. An explanation of how the different chemical species involved in the synthesis route could be responsible for the reducing action has been provided. The SPIONs-GNPs colloids have been characterized after each synthesis step by Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM), energy-dispersive X-ray spectroscopy (EDXS), Fourier transform infrared spectroscopy (FTIR), ζ Potential measurements, magnetic measurements with a vibrating-sample magnetometer (VSM) and UV–VIS spectroscopy. The SPIONs-GNPs colloids showed magnetoplasmonic behaviors since they maintained the plasmonic properties of GNPs and the superparamagnetic response of iron oxide NPs.     

Photo-initiated miniemulsion polymerization as a route to the synthesis of gold nanoparticle encapsulated latexes

We report the first use of photo-initiated miniemulsion polymerization for the synthesis of well defined poly(methyl methacrylate) (PMMA) latexes. Furthermore, the application of photo-initiation is employed to the incorporation of decanethiol-capped gold nanoparticles (AuNPs). The procedure provides a low temperature polymerization for an oil-in-water miniemulsion with temperatures not exceeding 40 °C and polymerization times of only one hour. Using these mild reaction conditions allows the use of miniemulsion polymerization for the encapsulation of temperature sensitive species within the latex. Furthermore, we demonstrate the applicability of this method for the incorporation of decanethiol-capped AuNPs. Particle size distribution and morphology was studied using dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). PMMA latexes ranged between 100 and 200 nm in diameter showing good particle size distribution and tendencies to form semi-ordered domains. We show that variations in surfactant, hydrophobe and initiator concentrations behave in the same manner as miniemulsions initiated through conventional thermal methods. TEM observations revealed that the latexes with encapsulated AuNPs displayed even distributions of AuNPs throughout the PMMA latex with no aggregation witnessed.     

Clay mineral-supported gold nanoparticles

Supported gold nanoparticles were prepared on clay minerals from the smectite and sepiolite–palygorskite groups (particularly montmorillonite and sepiolite) by cation adsorption from the cationic gold precursor Au(en)₂Cl₃ (en = ethylenediamine). Thermal gravimetric analysis, X-ray diffraction, transmission electron microscopy (TEM), high resolution TEM (HRTEM) and energy dispersive X-ray spectroscopy (EDS) were used to characterize these potential gold catalysts. The results show that the mean diameters of gold particles supported both on sepiolite and on montmorillonite are below 5 nm after calcination at 350–450 °C when the gold loading is lower than 2 wt.%. An increase of the amount of the gold precursor results in agglomeration of gold nanoparticles. An organosilane functionalized sepiolite was also used as support to obtain highly dispersed gold nanoparticles on the modified mineral surfaces, with narrow size distribution and an average size of 2.7 nm.     

油酸辅助水热合成纳米钛酸锶的性能调控与表征

采用油酸辅助一步水热法,以廉价易得的锐钛矿型TiO2为钛源、Sr(OH)2?8H2O为锶源合成SrTiO3纳米颗粒,通过XRD, TEM和SEM研究了SrTiO3纳米颗粒的形貌,考察了反应时间、Sr/Ti摩尔比和油酸浓度对SrTiO3纳米颗粒性能的影响,以所制SrTiO3为催化剂降解亚甲基蓝考察其光催化性能。结果表明,钙钛矿型立方相SrTiO3纳米颗粒具有均匀的尺寸和规则的形貌。实验范围内,随反应时间和Sr/Ti摩尔比增加,SrTiO3纳米粒子的晶粒尺寸呈增加趋势;随油酸浓度增加,SrTiO3颗粒粒度呈下降趋势。添加油酸可调控制备出具有规则形貌的钙钛矿型立方相结构的SrTiO3纳米颗粒;Sr/Ti摩尔比为0.75时,产品纯度高、结晶度好。油酸、反应时间和Sr/Ti摩尔比对SrTiO3纳米粒子微观结构的影响可分别用颗粒间作用力、奥斯特瓦尔德熟化和晶体成核理论解释。     

One-step hydrothermal microwave-assisted synthesis of LaFeO3 nanoparticles

Lanthanum orthoferrite (LaFeO₃) powders were synthesized via a highly efficient one-step hydrothermal microwave-assisted synthesis at relatively low temperatures of 240 °C and pressure of 60 bar. The use of microwave irradiation for heating during the synthesis intensifies the LaFeO₃ crystallization process leading to reduced synthesis duration at least 16 times as compared with conventional heating (3 versus 48 h).     

Network films of conducting polymer-linked polyoxometalate-modified gold nanoparticles: Preparation and electrochemical characterization

The ability of Keggin-type phosphododecamolybdate (PMo₁₂O₄₀³⁻, PMo₁₂) to undergo chemisorption on solid surfaces (including gold) is explored here to convert (by ligand place-exchange and phase transfer to aqueous solution) the alkanothiolate-modified Au nanoparticles of controlled size (prepared in toluene) into a stable colloidal solution of PMo₁₂-protected gold nanoparticles, PMo₁₂-AuNPs, the sizes of which are ca. 4-5 nm as determined by transmission electron microscopy. By dip-coating, PMo₁₂-AuNPs were assembled on carbon electrode substrates. The step-by-step assembly, by which alternate exposures to the solutions of PMo₁₂-AuNPs and either anilinium cations or pyrrole monomers, was utilized to grow in controlled manner hybrid network films in which the negatively charged PMo₁₂-AuNP deposits were linked, or electrostatically attracted, by ultra-thin, positively charged conducting polymer (polyaniline or polypyrrole) structures. The three-dimensionally distributed PMo₁₂-AuNPs immobilized within the polypyrrole-based composite film exhibited some electrocatalytic reactivity towards reduction of hydrogen peroxide.     

Selective hydrogenation of citral over gold nanoparticles on alumina

Gold nanoparticles have been supported on alumina by wet impregnation in the presence of sodium citrate and polyvinyl alcohol. The catalytic performance of these catalysts for the selective hydrogenation of 3,7-dimethyl-2,6-octadienal (citral) in the liquid phase has been evaluated. The presence of polyvinyl alcohol significantly improved the selectivity to cis-3,7-dimethyl-2,6-octadien-1-ol (nerol).     

In situ synthesis of iron oxide nanoparticles on poly(ethylene oxide) nanofibers through an electrospinning process

Iron oxide nanoparticle coated poly(ethylene oxide) nanofibers as organic–inorganic hybrids with 200–400‐nm diameters were prepared by the in situ synthesis of iron oxide nanoparticles on poly(ethylene oxide) nanofibers through the electrospinning of a poly(ethylene oxide) solution having Fe²⁺ and Fe³⁺ ions in a gaseous ammonia atmosphere. Transmission electron microscopy analysis proved the presence of iron oxide nanoparticles on the polymer nanofibers. The thermal properties of the nanofiber mat were also studied with differential scanning calorimetry and thermogravimetric analysis techniques. X‐ray diffraction showed that the formed iron oxide nanoparticles were maghemite nanoparticles. The results were compared with those of the electrospinning of a poly(ethylene oxide) solution having Fe²⁺ and Fe³⁺ ions and a pure poly(ethylene oxide) solution in an air atmosphere. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007