Evolution Of Silver Nanoparticles Research Articles

Evolution of Silver Nanoparticles Synthesized In Situ in a Glass-Like Epoxy Matrix

The evolution of silver nanoparticles (NPs) synthesized in situ in an epoxy matrix is investigated. The change in the stability of epoxy nanocomposites as a result of secondary processes of the transformation of NPs in a glass-like epoxy matrix when stored under natural light and in darkness is shown by means of absorption spectroscopy. The first order of the reaction and the dependence of the rate constant on the concentration of the precursor are found. Possible mechanisms for the conversion of silver NPs (e.g., digestive ripening and the formation of anisotropic structures) are discussed. It is concluded that the glass-like state of the polymer matrix is not a sufficient condition for the stabilization of NPs or the stability of the properties of the nanocomposite. This must be considered in the study and practical application of polymer nanocomposites (NCs) based on metal nanoparticles.

Effect of the Al2O3 addition on the formation of silver nanoparticles in heat treated soda-lime silicate glasses

We investigate the formation and evolution of silver nanoparticles in the non-irradiated thermally treated glass system Ag:(37–x)Na2O–10CaO–xAl2O3–53SiO2mol%, where x=0.0, 0.5, 1, 2 and 5, doped with 0.2mol% AgNO3. Using optical absorption and transmission electron microscopy we studied the effect of the gradual addition of Al2O3 to the chemical composition of the soda aluminosilicate glasses. A quantitative method for the evaluation of the relative nanoparticles concentration, proportional to the optical absorption intensity of the silver Surface Plasmon Resonance band, was developed and applied to the study of the behavior of the number of particles precipitated in samples thermally treated at temperatures of 400, 500, and 600°C. Three mechanisms were found, as consequence of the substitution of SiO4 by AlO4 glass forming local tetrahedral structural units, resulting in the gradual suppression of the negatively charged NBOs−, which are the only reducing sources available in the present non-irradiated glass system. The effects produced by the glass chemical and structural changes on the Ag nanoparticles production are discussed.

A hierarchical view on material formation during pulsed-laser synthesis of nanoparticles in liquid.

Pulsed-laser assisted nanoparticle synthesis in liquids (PLAL) is a versatile tool for nanoparticle synthesis. However, fundamental aspects of structure formation during PLAL are presently poorly understood. We analyse the spatio-temporal kinetics during PLAL by means of fast X-ray radiography (XR) and scanning small-angle X-ray scattering (SAXS), which permits us to probe the process on length scales from nanometers to millimeters with microsecond temporal resolution. We find that the global structural evolution, such as the dynamics of the vapor bubble can be correlated to the locus and evolution of silver nanoparticles. The bubble plays an important role in particle formation, as it confines the primary particles and redeposits them to the substrate. Agglomeration takes place for the confined particles in the second bubble. Additionally, upon the collapse of the second bubble a jet of confined material is ejected perpendicularly to the surface. We hypothesize that these kinetics influence the final particle size distribution and determine the quality of the resulting colloids, such as polydispersity and modality through the interplay between particle cloud compression and particle release into the liquid.

Evolution of silver nanoparticles in the rat lung investigated by X-ray absorption spectroscopy.

Following a 6-h inhalation exposure to aerosolized 20 and 110 nm diameter silver nanoparticles, lung tissues from rats were investigated with X-ray absorption spectroscopy, which can identify the chemical state of silver species. Lung tissues were processed immediately after sacrifice of the animals at 0, 1, 3, and 7 days post exposure and the samples were stored in an inert and low-temperature environment until measured. We found that it is critical to follow a proper processing, storage and measurement protocol; otherwise only silver oxides are detected after inhalation even for the larger nanoparticles. The results of X-ray absorption spectroscopy measurements taken in air at 85 K suggest that the dominating silver species in all the postexposure lung tissues were metallic silver, not silver oxide, or solvated silver cations. The results further indicate that the silver nanoparticles in the tissues were transformed from the original nanoparticles to other forms of metallic silver nanomaterials and the rate of this transformation depended on the size of the original nanoparticles. We found that 20 nm diameter silver nanoparticles were significantly modified after aerosolization and 6-h inhalation/deposition, whereas larger, 110 nm diameter nanoparticles were largely unchanged. Over the seven-day postexposure period the smaller 20 nm silver nanoparticles underwent less change in the lung tissue than the larger 110 nm silver nanoparticles. In contrast, silica-coated gold nanoparticles did not undergo any modification processes and remained as the initial nanoparticles throughout the 7-day study period.

Evolution of Silver Nanoparticles within an Aqueous Dispersion of Nanosized Zeolite Y: Mechanism and Applications

Stable aqueous dispersion of silver ion-exchanged nanozeolite Y was reacted with the three common dihydroxyphenols, hydroquinone, catechol, and resorcinol. With hydroquinone and catechol, there was rapid reduction of the intrazeolitic silver to form metallic silver with complete destruction of the zeolite framework. Resorcinol, the weakest reducing agent among the group, behaved differently. The formation of metallic silver was considerably slower, and the zeolite framework was mostly intact. This made it possible to examine the evolution of silver cluster formation with optical spectroscopy and transmission electron microscopy. In the first 135 min of reaction, extinction/fluorescence spectroscopy indicates the formation of Agn 4 clusters. The smaller clusters disappear more rapidly with time. For the 1 h reduced sample, transmission electron microscopy showed uniform distribution of 1.4 nm Ag particles throughout the zeolite. After 2 h of reduction, the average size of the particles was 2.5 nm...

Morphological Evolution of Silver Nanoparticles and Its Effect on Metal-Induced Chemical Etching of Silicon

In this report, we have demonstrated the morphological evolution of the silver nanoparticles (AgNPs) by controlling the growth conditions and its effect on morphology of silicon (Si) during metal-induced electroless etching (MICE). Self-organized AgNPs with peculiarly shape were synthesized by an electroless plating method in a conventional aqueous hydrofluoric acid (HF) and silver nitrate (AgNO3) solution. AgNP nuclei were densely created on Si wafer surface, and they had a strong tendency to merge and form continuous metal films with increasing AgNO3 concentrations. Also, we have demonstrated that the fabrication of aligned Si nanowire (SiNW) arrays in large area of p-Si (111) substrates by MICE in a mixture of HF and hydrogen peroxide (H2O2) solution. We have found that the morphology of the initial AgNPs and oxidant concentration (H2O2) greatly influence on the shape of the SiNW etching profile. The morphological results showed that AgNP shapes were closely related to the etching direction of SiNWs, that is, the spherical AgNPs preferred to move vertical to the Si substrate, whereas non-spherical AgNPs changed their movement to the [100] directions. In addition, as the etching activity was increased at higher H2O2 concentrations, AgNPs had a tendency to move from the original [111] direction to the energetically preferred [100] direction.

Solgel synthesis and structural characterization of silver-silica nanocomposites

The solgel process has been successfully used to prepare silver/silica nanocomposites. After drying in air at 50°C for 30 min, samples were heat treated in air, at 100, 200, 400 and 500°C for the formation of silver nanoparticles. Evolution of silver nano-particles in the amorphous SiO2 matrix as a function of annealing temperature has been studied. Characterizations were made by X-ray diffraction, ultraviolet-visible, and infrared spectroscopy. Mechanisms of silver clusters formation in the densified silica matrix with respect to thermal treatment are discussed.

Effect of annealing temperature on Ag nano-composite synthesized by sol–gel

Composite silicate thin films containing silver nano-particles were prepared on the glass substrate by sol–gel method to investigate the effect of annealing temperature. The sol coated samples were annealed in the oxidative air environment and subsequently reduced in pure hydrogen environment at 400, 500 and 600 °C for the formation of silver nano-particles. Evolution of silver nano-particles in the amorphous SiO 2 matrix as a function of annealing temperature has been studied. Coating structure, morphology and optical properties of nano-particle formation in the matrix were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis Spectrophotometery. Spherical, isolated and well dispersed Ag nano-particles with size between 12 and 25 nm were produced. The theoretical model based on diffusion and coalescence predicts the particle sizes close to the experimental values.

Studies on the Evolution of Silver Nanoparticles in Micelle by UV-Photoactivation

Ultraviolet (UV) photoirradiation of Ag(I) compounds in the presence of an aqueous Triton X-100 solution has been exploited for the first time to prepare reproducible yellow silver hydrosol. The evolution of nanosized silver particles has been examined critically under the influence of different anions/ligands. Hence, time dependent evolution of silver hydrosol from different silver compounds in micelle via photochemical reduction is observed. Anions/ligands of precursor salts have been found to show profound influence (due to electron scavenging property, solubility, stability etc.) on the evolution route and efficiency of photochemical reduction of Ag(I) to Ag(O) in micelle and thereby classification of silver compounds becomes possible. Kinetic results reveal that the formation of silver particles proceeds via autocatalytic growth mechanism. The observed variation in rate constant values for the evolution of nanoparticles from different silver compounds have been explained in terms of available thermodynamic and kinetic parameters. Nucleophile induced dissolution and reversible photogeneration of zerovalent silver particles have been investigated under ambient condition.