Monodisperse Silver Nanoparticles Research Articles

Novel Nanomaterials Synthesis by Laser-Liquid-Solid Interaction

A novel laser-liquid-solid interaction (LLSI) technique has been developed that is highly flexible and allows engineering nanomaterials in form of particles, rods, and tubes from liquid precursors. Synthesis reaction takes place in a molecular level and reaction rate is controlled by laser energy input, precursor solution chemistry, and other processing parameters including interaction time, and thermal conductivity of solid that is spinning in the solution. By the proper selection of liquid precursor, mono-dispersed silver nanoparticles were produced with average particle size 7–10 nm. Alloy composed Ag and Ni were produced in the form of nanoparticles and nanotubes with an average diameter of 40 nm. HRTEM of nanorod exhibited that Ag acted as seed for the synthesis of immiscible of Ag–Ni alloy. Laser writing of silver exhibited 50% lower electrical resistivity and eliminated many intermediate steps involved as compared to conventional silver patterning process.

Glycidyl-Methacrylate-Based Electrospun Mats and Catalytic Silver Nanoparticles

P(AN-GMA) and PGMA fibers coated with monodisperse silver nanoparticles have been prepared by a combination of electrospinning and electroless plating. The morphology of the electrospun fibers remains unchanged after surface hydrazination. Oxidation of hydrazine in an ammoniacal solution of AgNO3 reduces and deposits silver atoms along the fiber surface, which then coalesce to Ag particles. The size of the silver nanoparticles is varied between 20–60 nm. Since the density of the active sites for silver reduction is lower in P(AN-GMA), a smaller particle size could be obtained. The catalytic activity of the silver nanoparticles has been confirmed.

Preparation and characterization of stable monodisperse silver nanoparticles via photoreduction

Silver nanoparticles were synthesized by UV irradiation of [Ag(NH 3) 2] + aqueous solution using poly( N-vinyl-2-pyrrolidone) (PVP) as both reducing and stabilizing agents. The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima around 420 nm. It was found that the formation rate of silver nanoparticles from Ag 2O was much quicker than that from AgNO 3, and the absorption intensity increased with PVP concentration as well as irradiation time. The maximum absorption wavelength ( λ max) was blue shift with increasing PVP content until 8 times concentration of [Ag(NH 3) 2] + (wt%). The transmission electron microscopy (TEM) showed the resultant particles were 4–6 nm in size, monodisperse and uniform particle size distribution. X-ray diffraction (XRD) demonstrated that the colloidal nanoparticles were the pure silver. In addition, the silver nanoparticles prepared by the method were stable in aqueous solution over a period of 6 months at room temperature (∼25 °C).

Silver Nanoparticles Inhibit Hepatitis B virus Replication

Silver nanoparticles have been shown to exhibit promising cytoprotective activities towards HIV-infected T-cells; however, the effects of these nanoparticles towards other kinds of viruses remain largely unexplored. The aim of the present study was to investigate the effects of silver nanoparticles on hepatitis B virus (HBV). Monodisperse silver nanoparticles with mean particle diameters of approximately 10 nm (Ag10Ns) and approximately 50 nm (Ag50Ns) were prepared from AgNO3 in HEPES buffer. The in vitro anti-HBV activities of these particles were determined using the HepAD38 cell line as infection model. Ag10Ns and Ag50Ns were able to reduce the extracellular HBV DNA formation of HepAD38 cells by >50% compared with the vehicle control (that is, HepAD38 cells in the absence of silver nanoparticles). Silver nanoparticles had little effect on the amount of HBV covalently closed circular DNA (cccDNA), but could inhibit the formation of intracellular HBV RNA. Gel mobility shift assays indicated that Ag10Ns bound HBV double-stranded DNA at a DNA:silver molar ratio of 1:50; an absorption titration assay showed that the nanoparticles have good binding affinity for HBV DNA with a binding constant (Kb) of (8.8 +/- 1.0)x10(5) dm(3)mol(-1). As both the viral and Ag10Ns systems are in the nanometer size range, we found that Ag10Ns could directly interact with the HBV viral particles as revealed by transmission electronic microscopy. Silver nanoparticles could inhibit the in vitro production of HBV RNA and extracellular virions. We hypothesize that the direct interaction between these nanoparticles and HBV double-stranded DNA or viral particles is responsible for their antiviral mechanism.

Synthesis and characterisation of monodispersed silver nanoparticles with controlled size ranges

A method that enables reproducible synthesis of low aspect ratio, monodispersed and stable silver nanoparticle suspensions, uniform in its optical response and tunable over a range of diameters has been developed. The uniformity of the nanoparticles has been accurately determined using electron and atomic force microscopies for diameters down to 50 nm. These particles are highly suited to applications in optical nanotechnology.

Novel phase-transfer preparation of monodisperse silver and gold nanoparticles at room temperature

In a novel water-cyclohexane two-phase system, the aqueous formaldehyde is transferred to cyclohexane phase via reaction with dodecylamine to form reductive intermediates in cyclohexane; the intermediates are capable of reducing silver or gold ions in aqueous solution to form dodecylamine protected silver and gold nanoparticles in cyclohexane solution at room temperature. The prepared silver and gold nanoparticles are examined by transmission electron microscopy (TEM), UV–Visible spectroscopy (UV–vis), X-photon electron spectroscopy (XPS) and Fourier transfer infrared spectroscopy (FT-IR). It is found that these nanoparticles are monodisperse in size of less than 10 nm and have good stability in cyclohexane due to the adsorbed dodecylamine on nanoparticle surface. Moreover, the synthesis mechanism is revealed via gas chromatography (GC), gas chromatography-mass spectroscopy (GC-MS), nuclear magnetic resonance (NMR) analyses of the solutions during the preparation process.

A Theoretical Model for Digestive Ripening

Recently, gram quantities of monodisperse gold or silver nanoparticles were reported to be produced through a digestive ripening process, in which colloidal particles of size 2 to 40 nm are transformed to nearly monodisperse particles of 4 ~ 5 nm diameter. Digestive ripening, an example for an inverse Ostwald ripening process, is a puzzling phenomenon since it appears to go against the usual capillary effect, i.e., reduction of interfacial free energy. A theoretical model is presented, which accounts for the monodisperse state of such nanoparticles by considering the effect of charges on the particles and thus electrostatic energy during particle size evolution.

Laser-Induced Growth of Monodisperse Silver Nanoparticles with Tunable Surface Plasmon Resonance Properties and a Wavelength Self-Limiting Effect

We present a method for the tunable production of monodisperse silver nanoparticles. Using monochromatic light of different laser wavelengths to irradiate an initial solution of seed crystals, the size and shape of the products can be controlled. By monitoring the absorption spectrum during growth, it is found that initially the absorption maximum shifts to longer wavelengths and broadens, indicating an increase in particle size and size dispersion. Remarkably, this effect comes to a halt and reverses, displaying a shift to shorter wavelengths and simultaneously narrower bandwidths until, on completion, a final size and relatively narrow distribution are reached. The final size and shape is found to depend on laser wavelength and power. Both discs and triangular prisms as well as pyramidal and pentagonal prisms may be produced. A mechanism based on a wavelength-dependent self-limiting process governed by the surface plasmon resonance controlling the photochemical reduction of particles is suggested.

Environmentally friendly synthesis of organic-soluble silver nanoparticles for printedelectronics

In this study, we attempted to synthesize organic-soluble silver nanoparticles inthe concentrated organic phase with an environmentally friendly method. Thefully organic phase system contains silver acetate as a silver precursor, oleic acidas both a medium and a capping molecule, and tin acetate as a reducingagent. Monodisperse silver nanoparticles with average diameters of ca. 5 nmcan be easily synthesized at large scale. Only a small usage of tin acetate(<0.05 eq.mol) resulted in ahigh synthesis yield (>90%). Also, it was investigated that the residual tin atom does not exist in the synthesizedsilver nanoparticles. This implied that tin acetate acts as a reducing catalyst.

A theoretical model for digestive ripening

Recently, gram quantities of monodisperse gold or silver nanoparticles were reported to be produced through a digestive ripening process, in which colloidal particles of size from 2 to 40 nm are transformed to nearly monodisperse particles of 4–5 nm diameter. Digestive ripening, an example for inverse Ostwald ripening, is a puzzling phenomenon since it appears to avoid the usual capillary consequence, i.e., reduction of interfacial free energy. This paper presents a theoretical model which accounts for the self-assembled monodisperse state of such nanoparticles by considering the effect of charges, and therefore electrostatic energy, in the coarsening behavior of the particles. An appropriate Gibbs–Thomson equation is first derived, and then particle growth rates are calculated. The results show that success of a monodisperse state depends on, among other things, the initial particle distribution, and the size distribution at equilibrium follows some of the thermodynamic principles observed in binary phase diagrams of alloy systems.

Synthesis of Spherical Silver Nanoparticles with Controllable Sizes in Aqueous Solutions

A new method that combines the seed technique with laser treatment of a synthesized colloid was used to prepare spherical, almost monodisperse silver nanoparticles ranging in diameter from 10 to 80 nm (±10%). Particles in the 10−40 nm size range can easily be produced in a one-step synthesis. Preparation of particles in the 40−60 nm range requires a multistep synthesis that involves laser treatment of the synthesized colloid. Particles larger than 60 nm were produced using a multistep synthesis with laser treatment of intermediate products. Appropriate “soft” conditions were developed for the laser treatment, where “soft” laser fluence was defined as the maximum possible fluence that heats and melts but does not evaporate the spherical particles and, therefore, does not change their sizes. The numerical values for this fluence were calculated for different particle diameters using the particle heating−melting−evaporation model.35,21 The criteria for application of this model are discussed.

Facile synthesis of monodisperse silver nanoparticles by bio-template of squama inner coat of onion

This paper describes a facile sy]nthetic method for preparing monodisperse silver nanoparticles by bio-template of the squama inner coat of onion. The method is able to make silver nanoparticles with average diameters in the range of 4.6–7.9 nm with narrow size distribution. The important factors in the synthesis of monodisperse silver nanoparticles were discussed. The nanoparticles were characterized by transmission electron microscope, Powder X-ray diffraction and UV-Vis spectroscopy. A possible formation mechanism was also proposed. Because of its simple apparatus, high yield, convenient operation and mild conditions, this synthetic method will have potential application in preparing nanoparticles.

Silver Nanoparticles Capped by Oleylamine: Formation, Growth, and Self-Organization

Nearly monodisperse silver nanoparticles have been prepared in a simple oleylamine-liquid paraffin system. Intensive study has found that the formation process of silver nanoparticles could be divided into three stages: growth, incubation, and Ostwald ripening stages. Ultraviolet-visible spectroscopy, transmission electron microscopy (TEM), and high-resolution TEM have all demonstrated the occurrence of Ostwald ripening, which could result in better control over the size and size distribution of silver nanoparticles. SAXS (small-angle X-ray scattering) results show that the as-obtained silver nanoparticles can self-assemble into ordered arrays. The possible reduction mechanism of silver ions by oleylamine is related to the Ag+-mediated conversion of primary amines to nitriles.

Synthesis and Growth Mechanisms of Ag Metallo-Organic Nanoparticles in Different Morphologies by Using Polymer-Mediated Polyol Process

Mono-dispersed silver nanoparticles with various morphologies were synthesized in large quantities by reducing silver nitrate with ethylene glycol in the presence of poly(vinylpyrrolidone) (PVP). The effects of the concentration of AgNO3, temperature, adding rates of PVP and AgNO3 injected into ethylene glycol as well as molar ratio between the repeating unit of PVP and AgNO3 were discussed. By varying the temperature and reaction time, silver nanocubes, nnoprisms and nanospheres were obtained. It is indicated that at elevated temperatures, the ethylene glycol can reduce Ag+ ion into Ag atoms, and thereby inducing the nucleation and growth of silver nanostructures in the solution phase. In the polymer-mediated polyol process, PVP plays a critical role in producing silver nanostructures with good stability and size/shape uniformity. As a result, both the crystallinity of a seed and extent of PVP coverage on the seed were instrumental in controlling the morphology of Ag nanoparticles.

A facile and novel way for the synthesis of nearly monodisperse silver nanoparticles

A facile and novel way was reported for the preparation of nearly monodisperse silver nanoparticles with controlled hydrophilic or hydrophobic surface, using trioctylphosphine as the surfactant and stabilizer. The synthesized nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and UV–vis spectroscopy. The monodisperse silver nanoparticles showed a strong surface plasmon resonance band at 402 nm from the UV–vis spectrum.

Preparation and Antiwear Property of Monodisperse Silver Nanoparticles in Microemulsion

Monodisperse Ag nanoparticles were prepared in quaternary W/O microemulsions containing Span 80-Tween 80,liquid paraffin and 1-butanol.It was found that mass ration of Span 80 and Tween 80 had an obvious effect on the morphology and size distribution of the Ag nanoparticles.Morphologies,structure and thermal properties of the silver nanoparticles were characterized by means of X-ray diffraction(XRD),transmission electron microscopy(TEM),Fourier transform infrared(FT-IR),thermogravimetry(TG)and differential thermal analysis(DTA).The results show that the Ag nanoparticles have cube crystal structure;exhibit uniform size distribution and have an average size of 6 nm at the mass ratio of Span 80∶Tween 80=7∶3;and are coated with long chain fatty acid through carboxyl.H2O and 1-butanol in microemulsions were removed through vacuum distillation,and Ag nanoparticles were dispersed stably in liquid paraffin.The tribological properties of liquid paraffin containing Ag nanoparticles were evaluated on a four-ball test machine.Results showed that the Ag nanoparticles in liquid paraffin exhibited good antiwear property and could improve load carrying capacity of base oil remarkably.

Toward Monodispersed Silver Nanoparticles with Unusual Thermal Stability

A novel in situ autoreduction route has been developed, by which monodispersed silver nanoparticles with tunable sizes could be easily fabricated on silica-based materials, especially inside the channels of mesoporous silica (MPS). 13C CP/MAS NMR spectroscopy was employed to monitor the whole assembly process. It was demonstrated that the amino groups of APTS (aminopropyltriethoxyl silane)-modified MPS can be used to anchor formaldehyde to form novel reducing species (NHCH2OH), on which Ag(NH3)2NO3 could be in situ reduced. Monodispersed silver nanoparticles were thus obtained. In situ XRD and in situ TEM experiments were used to investigate and compare the thermal stabilities of silver nanoparticles on the external surface of silica gels (unconfined) and those located inside the channels of SBA-15 (confined). It was observed that unconfined silver nanoparticles tended to agglomerate at low temperatures (i.e., lower than 773 K). The aggregation of silver nanoparticles became more serious at 773 K. However, for those confined silver nanoparticles, no coarsening process was observed at 773 K, much higher than its Tammann temperature (i.e., 617 K). Only when the treating temperature was higher than 873 K could the agglomeration of those confined silver nanoparticles happen with time-varying via the Ostwald ripening process. The confinement of mesopores played a key role in improving the thermal stabilities of silver nanoparticles (stable up to 773 K without any observable coarsening), which is essential to the further investigations on their chemical (e.g., catalytic) properties.

Photocatalytic Deposition of Silver Nanoparticles onto Organic/Inorganic Composite Nanofibers

AbstractSummary: In this work, silver nanoparticles were embedded in electrospun organic/inorganic composite nanofibers consisting of PAN and TiO2 through photocatalytic reduction of the silver ions in silver nitrate solutions under UV irradiation. The morphology and diameter of PAN/TiO2 composite nanofibers could be controlled by varying the initial contents of TiO2 in the spinning solution. From TEM images and UV‐Vis spectra, it has been confirmed that monodisperse silver nanoparticles with a diameter of ≈2 nm were deposited selectively upon the titania of the as prepared composite nanofibers. The amount of Ag nanoparticles embedded on composite nanofibers was greatly influenced by the amount of TiO2 in composite nanofibers, reflecting the role of titania as the inorganic stabilizer and photocatalyst.Morphology of silver nanoparticles embedded on PAN/TiO2 composite nanofibers.magnified imageMorphology of silver nanoparticles embedded on PAN/TiO2 composite nanofibers.

Mechanism of nanoparticle manipulation by scanning tunnelling microscopy

Scanning tunnelling microscopy (STM) imaging was performed on gold surfaces with alarge coverage of monodispersed silver nanoparticles soft-landed on the surfacefrom the gas phase. In both ambient and ultra-high vacuum conditions, STMscanning was found to displace the particles out of the scanning area, due toweak adhesion of the particles to the substrate surface. Calculations based oncontact mechanics and electrostatics show that the particles can overcome the forceof adhesion to the surface and jump onto the STM tip beyond the tunnellingdistance. The observation provides the possibility for patterning or arrangingnanoparticles on a surface, which is demonstrated, and offers the potential for amultiplexed approach to create very precise surface patterns and particle arrangements.

Size-Controlled Synthesis of Monodispersed Silver Nanoparticles Capped by Long-Chain Alkyl Carboxylates from Silver Carboxylate and Tertiary Amine

Monodispersed silver nanoparticles capped by long-chain alkyl carboxylates were prepared by the reaction of silver carboxylate with tertiary amine at 80 degrees C for 2 h. This approach is a unique, size-controlled synthetic method for the large-scale preparation of silver nanoparticles. Long-chain alkyl carboxylate derived from a precursor acts as a stabilizer to avoid the aggregation of silver nanoparticles and to control particle size. In addition, amine plays an important role both as a reagent to form a thermally unstable, amine-coordinated intermediate, bis(amine)silver(I) carboxylate, and as a mild reducing agent for the intermediate to produce nanoparticles at a low temperature. The silver core and carboxylate-capping ligand of silver nanoparticles were characterized by various techniques such as transmission electron microscopy, optical absorption spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, gas chromatograph mass spectroscopy, and thermogravimetric and differential thermal analysis. The diameter of the nanoparticles can be strongly influenced by the alkyl chain length and the structure of the carboxylate. The average diameters of the silver nanoparticles were controlled to less than 5 nm in the case of silver carboxylate with a single alkyl chain length of 13 or 17 carbon atoms. On the contrary, the average diameters of silver nanoparticles became large and polydisperse in the case of silver carboxylate with a chain length of 7 carbon atoms or a branched chain. In comparing triethylamine with trioctylamine, there was no obvious effect to regulate the size distribution of the nanoparticles because they could not function as a capping ligand of the nanoparticles due to their weak coordination to silver. In addition, the heat treatment of silver nanoparticles in solution rather than in the solid state was effective for the growth of particles while maintaining narrow size distributions.