One-step synthesis and characterization of polyelectrolyte-protected gold nanoparticles through a thermal process

Polyelectrolyte-protected gold nanoparticles have been facilely obtained by heating an amine-containing polyelectrolyte/HAuCl₄ aqueous solution without the additional step of introducing other reducing agents. All experimental data indicate that different initial molar ratio of polyelectrolyte to gold can lead to the formation of dispersed nanoparticles, quasi one-dimensional aggregates of nanoparticles or bulk metal deposits. More importantly, the growth kinetics of gold particles thus formed can be tuned by changing the initial molar ratio of polyelectrolyte to gold.     

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.     

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.     

金纳米颗粒的微反应连续合成

金纳米颗粒具有特征性紫外-可见吸收光谱,在分析检测领域被广泛应用。为了突破间歇搅拌反应制备金纳米颗粒的技术局限,提出了一种连续流微反应方法。该方法在酸性条件下借助螺纹管实施HAuCl₄和Na₃Ct水溶液的快速均匀混合,引入惰性溶剂避免颗粒在反应器内沉积,利用膜分相装置完成油水在线相分离,实现了金纳米颗粒的连续稳定制备。探索了反应物摩尔比、浓度、停留时间、水油体积比、pH等因素对于颗粒粒径分布和吸收光谱的影响规律,成功制备了平均粒径20~24 nm、分散因子小于10%的窄分布金纳米颗粒。     

Reduced state carbon dots as both reductant and stabilizer for the synthesis of gold nanoparticles

The reduced state carbon dot (r-CD) is a new kind of carbon dot (CD) prepared by using sodium borohydride. Herein, we find that the r-CDs can directly reduce chloroauric acid to form gold nanoparticles (AuNPs) without adding other reducers or stabilizers. At the same time, we deduced that the hydroxyl groups (–OH) on the surfaces of r-CDs can act as both reducer and stabilizer for the synthesis of AuNPs. The AuNPs possess intrinsic catalytic activity, but compared with the AuNPs synthesized by citrate reduction, the AuNPs we prepared exhibit less excellent catalytic activity in the reduction of 4-nitrophenol (4-NP) with sodium borohydride. Conversely, for catalyzing oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by H₂O₂, the AuNPs we prepared show much higher catalytic activity than the AuNPs synthesized by citrate reduction. This work may open up a new route for the applications of CDs.     

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.     

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.     

Advanced synthesis for monodisperse polymer nanoparticles in aqueous media with sub-millimolar surfactants

Highly monodisperse polystyrene nanoparticles with mean diameters of less than 100 nm are synthesized via aqueous emulsion polymerization using an amphoteric initiator (VA-057) in the presence of sub-millimolar concentrations of anionic surfactant. Since the net charge on the initiator is almost zero at neutral pH, the resultant latex particle size is mainly determined by surfactant adsorption. Polymerizations were performed in the presence of a range of anionic surfactants with differing critical micelle concentrations (CMC) by varying the concentrations of surfactant, initiator and monomer, and also the ionic strength. Sodium dodecyl benzene sulfonate (SDBS), sodium hexadecyl sulfate (SHS), and sodium octadecyl sulfate (SOS) have relatively low CMCs and so enable formation of highly monodisperse nanoparticles at relatively low (sub-millimolar) surfactant concentrations, C_S (i.e. below the CMC in each case). Empirically, it was found that the particle number, N_p, and coefficient of variation of the particle size, C_V, were strongly dependent on the C_S/CMC ratio: N_p increased almost in proportion with the square of this ratio, while the C_V exhibited a minimum at approximately C_S/CMC = 0.20. Higher ionic strength reduced the particle size, which is consistent with the above relationship because the addition of salt lowers the CMCs of ionic surfactants. Polymer latex particles produced using such formulations form highly regular, close-packed colloidal arrays.     

Microwave irradiation synthesis and self-assembly of alkylamine-stabilized gold nanoparticles

The hydrophobic gold nanoparticles protected with octadecylamine, tetradecylamine and decylamine, respectively, were prepared by using ethanol reduction in reverse micelle through microwave dielectric heating. In this experiment, the commonly used toxic and highly volatile organic solvents such as chloroform, toluene and so on, which were an obstacle for preparing hydrophobic nanoparticles under microwave irradiation, were replaced by a safe organic mixed solvent n-heptane/ethanol used as an oil phase. The various alkylamine-stabilized gold nanoparticles obtained through this method were characterized and analyzed by ultraviolet visible spectroscopy (UV-vis), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and elemental analysis. When the molar ratio of alkylamine to HAuCl₄ was 40 : 1, the average diameters and standard deviations for octadecylamine-, tetradecylamine- and decylamine-capped gold nanoparticles were 4.53 ± 0.79, 5.22 ± 1.66, and 4.09 ± 1.22 nm, respectively. Furthermore, the composition of octadecylamine-stabilized gold nanoparticles was determined to be (C₁₈H₃₇NH₂)₂₆₅·Au₂₈₂₂, and the experimental result showed that both the monodispersity and stability of these gold nanoparticles were beneficial to forming large areas of ordered two-dimensional arrangement at the air/water interface.     

Electrosynthesis and characterization of gold nanoparticles for electronic capacitance sensing of pollutants

In the present study, gold/surfactant core/shell colloidal nanoparticles with a controlled morphology and chemical composition have been obtained via the so-called sacrificial anode technique, carried out in galvanostatic mode. As synthesized Au-NPs had an average core diameter comprised between 4 and 8 nm, as a function of the electrochemical process experimental conditions. The UV–Vis characterization of gold nanocolloids showed clear spectroscopic size effects, affecting both the position and width of the nanoparticle surface plasmon resonance peak.The nanomaterial surface spectroscopic characterization showed the presence of two chemical states, namely nanostructured Au(0) (its abundance being higher than 90%) and Au(I). Au-NPs were then deposited on the top of a capacitive field effect sensor and subjected to a mild thermal annealing aiming at removing the excess of stabilizing surfactant molecules. Au-NP sensors were tested towards some gases found in automotive gas exhausts. The sensing device showed the largest response towards NO_x, and much smaller – if any – responses towards interferent species such as NH₃, H₂, CO, and hydrocarbons.     

Dendrimer-encapsulated gold nanoparticles as building blocks for multilayer microshells

We report the effect of gold nanoparticles encapsulated into the shell-forming PAMAM dendrimers on the assembly and properties of multilayer microshells. We demonstrate that the PAMAM-encapsulated gold nanoparticles change dramatically the optical spectroscopic properties of microcapsule dispersions, without significantly affecting the stiffness of microcapsules. Our results indicate that the use of dendrimer-protected nanoparticles as building blocks opens numerous possibilities to vary the composition and diverse properties of microshells without changing their stiffness.     

Globotriose-functionalized gold nanoparticles as multivalent probes for Shiga-like toxin

Compared to monovalent carbohydrates, multivalent carbohydrate ligands exhibit significantly enhanced binding affinities to their interacting proteins. Here, we report globotriose (P(k) ligand)-functionalized gold nanoparticle (AuNP) probes for the investigation of multivalent interactions with the B(5) subunit of Shiga-like toxin I (B-Slt). Six P(k)-ligand-encapsulated AuNPs (P(k)-AuNPs) of varying particle size and linker length were synthesized and evaluated for their potential as multivalent affinity probes by using a surface plasmon resonance competition assay. The affinity of these probes for the interacting proteins was greatly affected by nanoparticle size, linker length, and ligand density on nanoparticle surface. For example, the 20-nm 20-P(k)-l-AuNP, which had a relatively long linker showed a >10(8)-fold increase in affinity compared with the mono P(k) ligand. This intrinsic high-affinity AuNP probe specifically captured the recombinant B-Slt from Escherichia coli lysate, and the resulting purity of the B-Slt was >95 %. We also developed a robust P(k)-AuNP-based detection method for Slt-I by combining the technique with silver enhancement.     

Terpolymers as precursors for CuO nanoparticles synthesis

This work describes the synthesis of terpolymers of aniline, diphenylamine, and o‐anthranilic acid (PANIDPAA) by 1 : 1 : 1 molar ratio of the respective monomers doped by different concentration of copper ions via in situ chemical terpolymerization. The results are justified by measuring spectral characteristics namely, UV‐vis absorption spectra, FTIR, and TGA. Calcining these PANIDPAA terpolymers doped by copper at temperatures in the range of 700°C led to the formation of CuO nanoparticles in the nanoscale by thermal decomposition in air directly. The stages of decompositions and the calcination temperature of the precursors have been determined from thermal analysis data sheet. The obtained CuO nanoparticles have been characterized by X‐ray diffraction and transmission electron microscope (TEM). TEM showed a particle size less than 40 nm. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41150.     

Preparation and characterization of polyurethane–gold nanocomposites prepared using encapsulated gold nanoparticles

Gold nanoparticles (GNPs) have been widely studied due to their unique properties. Although many research groups have developed the synthesis of GNPs using various polymers as stabilizing or reducing agents, the effects of GNPs on the structures and properties of polymer matrices have been less reported. We propose a new design for the preparation of polyurethane–gold (PU–Au) nanocomposites. 11‐Mercapto‐1‐undecanol‐coated GNPs acted as the chain extenders and reacted with isocyanates to form covalent bonds between PU and GNPs. PU–Au nanocomposites were successfully synthesized, and the effects of multifunctional GNPs on the structures, morphology and properties of poly(ester urethane) were investigated. Scanning electron microscopy images suggested the GNPs can be dispersed uniformly in the PU matrix. Maltese‐cross of spherical crystals was observed in the PU–Au nanocomposites, and the size of the crystals decreased with an increase in gold content. As the gold content increased, the thermal decomposition temperature and the temperature of the maximum decomposition rate increased. The glass transition temperature, crystal melting temperature and melting enthalpy of the soft segment also increased progressively. The results showed that multifunctional GNPs concentrated hard segments and resulted in an increase of heterogeneous nucleation, phase separation and elasticity. Copyright © 2010 Society of Chemical Industry     

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.     

Microwave-assisted synthesis of gold nanoparticles self-assembled into self-supported superstructures

Passivated gold nanoparticles were synthesized through a microwave-assisted process in a two-phase system, in the presence of 1-dodecanethiol. An average particle size of 1.8 nm of the gold nanoparticles obtained and 0.35 S.D. was determined through HRTEM and STEM analysis. It was observed that these nanoparticles spontaneously self-assemble into self-supported superstructures of 1 μm in diameter avg and 400 nm thickness, yielding an off-white powder which can be handled as a simple powder. XRD analysis indicates that n-alkanethiol molecules used as a passivating compound, besides protecting against crystal growth, interact to form cubic ordered arrays between the nanoparticles. This interaction leads to the superstructure formation, with an average distance between nanoparticles in the array, of 3.56 nm. Theoretical calculations and molecular dynamics simulations were performed to analyze the resulting structure.     

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.     

1,3,5-Triazine-based polymer: synthesis,characterization and application for immobilization of silver nanoparticles

Six s-triazine-based polymers were prepared through the nucleophilic reaction of 2,4-dichloro-6-substituted s-triazine derivatives with 1,4-diaminobutane employing conventional heating and microwave irradiation. The prepared polymers were characterized by using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The microwave irradiation provides the target polymers in less reaction time with higher yields and purities; the results from the TGA revealed that microwave technique enhanced the thermal behavior of the prepared polymers. The effect of substituent on the thermal stability of polymers has the main factor, where incorporation of the aromatic ring on the triazine core in the prepared polymers increased their thermal stability. As a model for immobilization of silver nanoparticles (AgNPs), p-methoxy-s-triazine- 1,4-butadiamine (BDPMA) copolymer was used as an example in the presence and absence of hydrazine-hydrate. AgNPs were characterized by zeta potential, scanning electron microscope (SEM), X-ray powder diffraction analysis (XRD) and transmission electron microscope (TEM). Best results in term of particle size was obtained by using BDPMA in the absence of hydrazine hydrate, where the particle size of AgNPs was less than 20 nm as observed from TEM.

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Mixed monolayer protected gold atom-oxide cluster synthesis and characterization

Small atomic gold clusters in solution, Au(n), stabilized by cetyl trimethylammonium bromide (CTAB) and cysteine, have been synthesized potentiodynamically in quiescent aqueous solutions. The electrodissolution of gold to gold ions during an anodic scan and subsequent cluster formation during a cathodic scan in underpotential (UPDD) and overpotential dissolution-deposition (OPDD) regions were studied. The experimental potentiodynamic I-E profiles and chronoamperometric i-t transients are fit into reported theoretical models of adsorption and electrocrystallization. The plausible application of clusters/cluster film to cysteine sensing based on fluorescence quenching and square wave stripping voltammetry is demonstrated.     

Bridging the gap between homogeneous and heterogeneous gold catalysis: supported gold nanoparticles as heterogeneous catalysts for the benzannulation reaction

Gold nanoparticles supported on metal oxides and activated carbon are able to catalyze the benzannulation reaction of o-(phenylethynyl)benzaldehyde and phenylacetylene to 1-benzoyl-2-phenylnaphtalene with high selectivity at 99% conversion. Benzannulation of ortho-alkynyl benzaldehydes is a reaction typically catalyzed by soluble AuCl₃ and, now, we have found that it can also be catalyzed by heterogeneous gold supported catalysts. The heterogeneous catalytic system can be reused several times without loss of activity or selectivities.