Spherical Silver Particles Research Articles

Influence of several factors on the growth of selenium nanowires induced by silver nanoparticles

This paper presents a study on the crystallization and growth mechanism of selenium nanowires induced by silver nanoparticles at ambient conditions with special reference to the effects of factors such as the shapes and size of silver nanoparticles, the induced reaction time, and the molar ratio of Ag0 to SeO 3 2− ions. The synthesis approach is conducted with no need of any stabilizers, and with no sonochemical process and/or templates. It is found that whether silver spherical particles or colloids can lead to the formation of nanowires with average diameter of 25 nm and lengths up to a few micrometers, and silver nanoplates lead to the formation of flat Se nanostructures. In particular, Au, Cu, Pt, and Pd particles cannot induce the growth of selenium nanowires in aqueous solution at room temperature. The results indicate that silver particles play a critical role in determining the growth of selenium nanowires. The lattice match between hexagonal-Se and orthorhombic- or trigonal-Ag2Se particles is the major driving force in the growth of such nanostructures. The findings would be useful for design and construction of heterogeneous nanostructures with similar lattice parameter(s).

Optical properties of metallic nanoparticle arrays on a thin metallic film

We consider the optical properties of a periodic array of silver spherical particles with diameters of a few hundred nanometers on top of a thin Ag film. Maxwell's equations are solved using a multiple-scattering formalism which combines high accuracy with efficiency. We study the interaction between flat-surface and localized particle plasmons. Interestingly, the presence of a periodic array can lead to an enhanced transmission through the metallic film due to leakage of the surface plasmon-polaritons in the substrate.

The preparation of hydrophobic silver nanoparticles via solvent exchange method

We have prepared hydrophobic silver nanoparticles capped by oleic acid via solvent exchange method. AgNO3 was reduced by NaBH4 to produce Ag nanoparticles in aqueous solution with various pH conditions and oleic acid as stabilizer. By the addition of H3PO4, the carboxylate group was converted to carboxylic acid, and this induced the reorientation of oleic acid, and provided hydrophobic silver nanoparticles. The oleic acid-capped silver nanoparticles were characterized by UV–vis spectrophotometer and Fourier transfer infrared spectrometer (FTIR). Spherical silver particles with uniform size of 8nm were obtained from silver nitrate under basic aqueous solution.

Self-supported silver nanoparticles containing bacterial cellulose membranes

Hydrated bacterial cellulose (BC) membranes obtained from cultures of Acetobacter xylinum were used in the preparation of silver nanoparticles containing cellulose membranes. In situ preparation of Ag nanoparticles was achieved from the hydrolytic decomposition of silver triethanolamine (TEA) complexes. Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns both lead to the observation of spherical metallic silver particles with mean diameter of 8 nm well adsorbed onto the BC fibriles.

Silver microflowers and large spherical particles: Controlled preparation and their wetting properties

In this article, we report a simple wet-chemical method to prepare silver microflowers and large spherical particles. The formation of the two different microstructures of silver is based on the reduction of AgNO 3 by para-phenylenediamine in aqueous medium at room temperature. The controlling of the silver microstructures can be achieved only by adjusting the concentration of the reactants. It is found that the two different silver microstructures display opposite wetting properties. Large spherical silver particles exhibit superhydrophilic properties with a contact angle (CA) of close to 0°, microflower-like silver particles exhibit highly hydrophobic properties with CA about 132°. X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and UV–vis spectra are used to characterize the chemical structure of the obtained products.

Preparation of spherical silver particles for solar cell electronic paste with gelatin protection

Spherical silver particles used in electronic paste for solar cell were prepared using the chemical reduction method with ammonia as a complex agent, hydrazine hydrate as a reducing agent, and gelatin as a protective agent. The gelatin protective mechanism in the preparing process of spherical silver particles was studied. Observations of SEM and results of laser particle size analysis and ultraviolet absorption spectra demonstrate the formation of the coordinative complex of silver ions with gelatin in aqueous solution which accelerated the reduction of silver ions. Moreover, gelatin can promote the nucleation of the metallic silver particles, thus beneficiating availability of the monodisperse spherical silver particles.

Preparation and characterization of silver colloids with different morphologies under ultrasonic field

In the ultrasonic field, stable silver colloids were produced by the reduction of AgNO3 with the protection of PVP using KBH4 or N2H4·H2O as reductant. The main factors affecting the morphology of silver nanoparticles, such as distribution of the ultrasonic field, ultrasonic time, ultrasonic power, and the species of reductant, were studied. The silver colloids were identified by TEM and spectrophotometry. The results indicate that the factors such as distribution of the ultrasonic field, ultrasonic time, ultrasonic power, and the species of reductant have a great impact on the morphology of the silver nanoparticles. The size of the silver nanoparticles decreases with the ultrasonic power and ultrasonic time increasing. Ag nanoparticles prepared in standing wave field preferentially grow in a certain direction, which is propitious for forming hexagonal-and spherical-like silver nanoparticles. Monodispersed spherical silver nanoparticles are easily synthesized in the diffusion field. The stability of silver colloid becomes improved by ultrasonic treatment. For example, precipitate is not found after several weeks for the silver colloid prepared with an ultrasonic treatment time of 180 min. The silver nanoparticles prepared without ultrasonic treatment are large spherical-like and hexagonal. Well-dispersed spherical silver particles with a mean size of about 20 nm have been prepared under ultrasonic treatment. Spherical, spherical-like, and hexagonal silver nanoparticles can be obtained by changing the reductants.

Silver nanoparticle doped dendrimer/DNA nanogel- A novel approach of getting assembled metal nanoparticle in solution

The synthesis and characterization of poly (amido amine) dendrimer/DNA nanogel containing silver nanoparticle have been reported. Initially dendrimer protected-nanoscale silver particles have been synthesized in aqueous medium. UV-Vis spectra and transmission electron micrograph indicate almost spherical silver particles with an average diameter 6 ± 2 nm were formed. The preformed dendrimer protected silver nanoparticle solution was mixed with DNA solution to fabricate the dendrimer/DNA complex. At the dendrimer/DNA-mixing ratio (number ratio of NH 2 groups in dendrimer vs phosphate groups in DNA) 0.3, aggregates (nanogel) were formed. Transmission micrograph revealed the presence of silver nanoparticles inside that gel matrix. Binding of dendrimer molecule with DNA chain occurs through electrostatic interaction. This kind of approach promises the development of polyelectrolyte-based soluble conductive nanowires and three dimensionally self-assembled complex nanostructure.

Properties of Nanosilver Coatings on Polymethyl Methacrylate

Elemental silver particles were prepared by the reduction of silver nitrate in ethanol in the presence of poly(N‐vinyl‐2‐pyrrolidone), poly(N‐vinyl‐2‐pyrrolidone)‐co‐polyvinyl acetate or poly(N‐vinyl‐2‐pyrrolidone)‐co‐polyvinyl alcohol as stabilizing agent. Transmission electron microscopy (TEM) investigations reveal that in all cases spherical silver particles are obtained. Using poly(N‐vinyl‐2‐pyrrolidone) or poly(N‐vinyl‐2‐pyrrolidone)‐co‐polyvinyl alcohol as stabilizer, the average diameter of the silver particles is around 20 nm, and the degree of aggregation is low. That means these polymers are good stabilizers for silver particles. In contrast to that, in the presence of poly(N‐vinyl‐2‐pyrrolidone)‐co‐polyvinyl acetate, heavily aggregated silver particles are formed. The good film‐forming properties of the stabilizers were exploited to prepare coatings onto polymethylmethacrylate sheets using the silver dispersions. The optical as well as the silver ion release properties of the silver coatings were investigated. As expected, the wavelength of the surface plasmon resonance absorption shows a bathochromic shift with increasing mean diameter of the silver particles. The amount of silver ions released from these coatings as well as the kinetics of silver ion release depend on the polymer used as stabilizer for the silver particles. Silver ion diffusion processes govern the silver ion release kinetics from coatings consisting of silver nanoparticles and poly(N‐vinyl‐2‐pyrrolidone) or poly(N‐vinyl‐2‐pyrrolidone)‐co‐polyvinyl alcohol.

Assessment of spectroscopic properties of erbium ions in a soda-lime silicate glass after silver–sodium exchange

Spectroscopic properties of Ag/Er co-doped thin plates of silicate glass were investigated with the aim of assessing the effective role of silver as a sensitizer for erbium. Additive heat treatments in air at different temperatures were performed on both a silver-exchanged and a silver-free plate in order to promote the formation of silver nanoparticles in the former and to refer to the later in the spectroscopic characterization. Absorption as well as photoluminescence and lifetime measurements in the region of the 4I13/2 → 4I15/2 transition of the Er3+ ion were performed; excitation wavelengths in the range from 360 to 750 nm were used. Enhancement of the Er3+ luminescence at 1.53 μm was observed when the excitation wavelength was in the blue region. This spectral range typically coincides with the excitation energy of the surface plasmon resonance of nanometer-sized spherical silver particles.

Investigation of stress state of silver nanoparticles in silicate glasses by means of EXAFS

Nanosized spherical silver particles were formed in silicate glass by sodium/silver ion exchange and subsequent annealing in air or hydrogen atmosphere at elevated temperatures. Furthermore, the sol-gel procedure was used to prepare embedded Ag particles. Structural characterisation of these composite materials by temperature dependent EXAFS-spectroscopy with transmission and fluorescence experiments revealed distinct differences of the particle/matrix interaction across the interface. The Ag-O and Ag-Ag correlations could be separated by fit procedures. The Ag-Ag bond length of the crystalline particles sensitively reflects their state of stress depending on the formation conditions. It was found an increase as well as a decrease of the Ag-Ag distance, i. e. tensile and compressive stress states were formed, for ion-exchanged glasses as a result of different cooling procedures and after hydrogen treatments, respectively, and for sol-gel samples. The combination with high-resolution electron microscopy (HREM) experiments yields the confirmation of such effects. Furthermore, the size-dependent parameters of nanoparticles could be determined. The results can be interpreted by the size effect of nanoscaled particles and the influence of the surrounding matrix.

The formation of monodisperse spherical silver particles

The process of formation of monodisperse spherical silver particles in gelatin-stabilized ammonia-tartrate electroless deposition solution has been investigated. The production of monodisperse spherical silver particles, 150–420 nm in size, was shown to be feasible, the particle diameter depending on pH of the solution. The spherical silver particles, as evidenced by TEM, optical spectroscopy and X-ray diffraction data, were comprised of 10–15 nm sized particles, and hence, were formed by the colloidal aggregation mechanism. The optical spectra of the sols largely composed of monodisperse silver particles over 300 nm in size demonstrate the absorption band in the region of silver plasmon absorption ( λ max = 420 nm), which is characteristic of colloidal particles.

Self-organization of silver nanoparticles forming on chemical reduction to give monodisperse spheres

It was found possible to produce monodisperse spherical silver particles using K–Na-tartrate as the reductant for Ag + in the presence of gelatin. It was shown that the silver spheres form in the process of spontaneous self-organization of 10–15 nm-sized primary particles. The conditions making it possible to control the sizes of the monodisperse spheres in the range from 150 nm to 1.5 μm were specified.

Structural Characteristics of Metal Nanoparticles in Glass Upon Irradiation-Assisted Processing

Irradiation-assisted processing, i.e. ion, electron and laser irradiation, have been applied to fabricate metal/glass nanocomposites. The particle configurations are studied by transmission electron microscopy to get some insight into the rather complex formation mechanisms. Special attention is given to spheroidally shaped particles surrounded by smaller secondary particles observed upon ion beam mixing of silica/silver/silica layer compounds as well as irradiating femtosecond laser pulses on sodium silicate glass containing spherical silver particles. Another unique type of structure are cavities observed in silver particles formed by high fluence ion implantation into silica as well as upon laser pulse irradiation of silver particles in glass. The experimental findings are discussed in terms of irradiation-induced defect formation and radiation-enhanced diffusion.

Enhanced activity of silver modified thin‐film TiO2 photocatalysts

Novel, composite silver/titania immobilized on glass substrates were prepared, characterized and their photocatalytic activity was evaluated. The undoped original material consists of rough, high surface area nanocrystalline titanium dioxide (TiO2) thin films. To increase their efficiency, the TiO2 films were modified by silver cations deposition and subsequent UV‐C irradiation. SEM pictures confirmed the existence of an open porous network of interconnected titania particles on the semiconductor surface. AFM analysis proved the presence of spherical silver particles on the catalyst surface and provided quantitative surface parameters as fractal dimension, surface roughness and mean particle diameter. Spectroreflectometry showed the presence of an increase in optical absorbance attributed to plasmon resonance absorption of the silver clusters. The photocatalytic properties of the surface modified materials were investigated through photodegradation of Methyl Orange. The silver deposition conditions were optimized for maximum photocatalytic efficiency and crucial parameters such as dipping period, UV irradiation time, and concentration of the dipping solution were determined. The optimum silver nitrate concentration of the dipping solution was found to be 10-3 M. This silver doped photocatalyst decomposes the azo‐dye pollutant 3‐times faster than the un‐doped Degussa P25 TiO2 film. A concentration increase results in a decrease of the films photocatalytic performance. Strength and reproducibility tests proved that the photocatalytic activity of the silver doped titania was perfectly reproducible.

Synthesis of skeletal silver from rapidly solidified Al–Ag precursor

Skeletal silver was synthesized by applying an alkaline leaching process to rapidly solidified Al–Ag granular precursors. The structure of the leached materials was examined by scanning electron microscopy, EPMA, X-ray diffraction and differential scanning calorimetry. Most of the aluminum was leached out and only a few percent aluminum remained in the as-leached state. The crystallographic structure of the leached material was face centered cubic and it was formed by rearrangement of silver atoms dissolved in the α-Al solid solution during leaching. The Ag 2Al phase was too stable for the alkaline solution so that it did not contribute to the formation of skeletal silver. The formation ratio of skeletal silver to the total silver in the precursor depended on the amount of dissolved silver in the α phase. Rapid solidification of Al–Ag alloys was quite effective for obtaining the super-saturated α phase. More than 80% of the silver in the precursor turned into skeletal silver using the rapidly solidified precursor. The specific surface area of the skeletal silver was about 9 m 2/g. The mean diameter of the skeletal silver was about 20 nm as derived using the X-ray line broadening method. This value was 1.2–1.5 times smaller than that evaluated from the specific surface area assuming spherical silver particles. The difference may result from shape degeneration.

Novel ionic polymer–metal composites equipped with physically loaded particulate electrodes as biomimetic sensors, actuators and artificial muscles

Described is a novel fabrication process of manufacturing ionic polymer–metal composites (IPMCs) equipped with physically loaded electrodes as biomimetic sensors, actuators and artificial muscles. The underlying principle of processing this novel IPMCs is to first physically load a conductive primary powder layer into the polymer (ionomeric) network forming a dispersed particulate layer. This primary layer functions as a major conductive medium in the composite. Subsequently, this primary layer of dispersed particles of a conductive material is further secured within the polymer network with smaller secondary particles via chemical plating, which uses reducing agents to load another phase of conductive particles within the first layer. In turn, both primary and secondary particles can be secured within the polymer network and reduce the potential intrinsic contact resistance between large primary particles. Furthermore, electroplating can be applied to integrate the entire primary and secondary conductive phases and serve as another effective electrode. In this paper, we describe the details of this newly developed technique to efficiently produce an IPMC loaded with spherical silver particles (D10<0.8 μm, D50<1.5 μm, D90<2.5 μm; Asur<6 m2/g) and subsequently secured by palladium (Dp∼50 nm, via a chemical reducing process). It has been established that such an IPMC is quite comparable in force and displacement performance with the traditional platinum loaded and gold electroplated IPMCs but can be manufactured at about 1/10th of the cost. Yet it produces a low surface resistivity (less than 1 Ω per square), which is highly desirable in creating more uniform deformation.

Nanocrystalline silver particulate films by liquid–liquid interface reaction technique (LLIRT)

A process to deposit nanocrystalline silver particulate film by adjusting the physical/chemical parameters at liquid–liquid interface was developed. The film was transferred on a suitable substrate by Langmuir–Blodgett (LB) technique. The film was characterized by transmission electron microscopy (TEM), electron diffraction (ED) and atomic force microscopy (AFM). TEM revealed that the as-prepared film consists of partly aggregated spherical silver particles and their sizes were in the range 5–20 nm. ED shows a spot pattern, characteristic of partly aggregated material with very small crystallite size. The optical absorption of vergin and annealed films is studied. The effect of annealing is attributed to Ostwald ripening of some particles and simultaneous breaking of aggregates to smaller particles.

A novel laser-liquid-solid interaction technique for synthesis of silver, nickel and immiscible silver-nickel alloys from liquid precursors

Silver, nickel, nickel oxide and silver-nickel alloys have been produced from their inexpensive liquid precursors using CO2 and Nd-YAG lasers. Ethylene glycol, diethylene glycol and 2-ethoxyethanol were used as reductants in the synthesis reactions. Spherical and faceted silver particles of high purity were formed by laser interaction between the precursor solution and a rotating substrate, while porous dual phase nickel and nickel oxide particles were produced when nickel nitrate was used as a precursor. The composition and morphology of the alloy particles was dependent on laser parameters and chemical composition of the precursor solution. The product composition was dependent only upon the chemistry of the precursors used. The mean particle size was dependent upon the temperature generated by irradition and the duration of exposure to the laser beam. The synthesis of nano-particles and metastable alloys is proposed to occur primarily at the laser-liquid-solid interface by a nucleation and growth mechanism.

Adhesion of silver particles on aluminum beads

The kinetics of deposition of monodispersed spherical silver particles stabilized by a surfactant, Daxad 19, on aluminum beads was studied as a function of the pH and ionic strength using the packed column technique. At low pH values, the attachment proceeded from mono- to multilayer with increased ionic strength, while at high pH the adsorbed surfactant was found to play a significant role in the attachment process, resulting in multilayer deposition only. The kinetics of removal was followed by rinsing the column loaded with silver with a solution of the same composition as that of the suspension used in the deposition process. The results suggest a possible bond formation between the beads and the stabilizer adsorbed on the particles. In order to interpret the adhesion data, a uniform dispersion of silver, 60±5 nm in particle diameter, was synthesized and its stability towards different electrolytes was determined. Furthermore, the surface charge characteristics of silver particles and aluminum beads were evaluated over a broad pH range at different ionic strength.