Synthesis and optical properties of silver nanoparticles and arrays.

This Minireview systematically examines optical properties of silver nanoparticles as a function of size. Extinction, scattering, and absorption cross-sections and distance dependence of the local electromagnetic field, as well as the quadrupolar coupling of 2D assemblies of such particles are experimentally measured for a wide range of particle sizes. Such measurements were possible because of the development of a novel synthetic method for the size-controlled synthesis of chemically clean, highly crystalline silver nanoparticles of narrow size distribution. The method and its unique advantages are compared to other methods for synthesis of metal nanoparticles. Synthesis and properties of nanocomposite materials using these and other nanoparticles are also described. Important highlights in the history of the field of metal nanoparticles as well as an examination of the basic principles of plasmon resonances are included.     

Influence of polysaccharide matrices of silver nanocomposites on their optical properties

Russian Chemical Bulletin - The specific features of the optical characteristics of spherical silver nanoparticles stabilized by polysaccharide matrices of galactomannan and carrageenan with a...     

Magnetite nanoparticles with tunable gold or silver shell

Fe3O4 nanoparticles with size approximately 13 nm have been prepared successfully in aqueous micellar medium at approximately 80 degrees C. To make Fe3O4 nanoparticles resistant to surface poisoning a new route is developed for coating Fe3O4 nanoparticles with noble metals such as gold or silver as shell. The shell thickness of the core-shell particles becomes tunable through the adjustment of the ratio of the constituents. Thus, the route yields well-defined core-shell structures of size from 18 to 30 nm with varying proportion of Fe3O4 to the noble metal precursor salts. These magnetic nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), FTIR, differential scanning calorimetry (DSC), Raman and temperature-dependent magnetic studies.     

Hemoprotein bioconjugates of gold and silver nanoparticles and gold nanorods: structure-function correlations

Bioconjugates of the hemoproteins, myoglobin, and hemoglobin have been synthesized by their adsorption on spherical gold and silver nanoparticles and gold nanorods. The adsorption of hemoproteins on the nanoparticle surface was confirmed by their molecular ion signatures in matrix assisted laser desorption ionization mass spectrometry and specific Raman features of the prosthetic heme b units. High-resolution transmission electron microscopy (HRTEM) and UV-visible spectroscopy showed that the particles retain their morphology and show aggregation only in the case of silver. The binding of azide ion to the Fe(III) center of the prosthetic heme b moiety caused a red shift of the Soret band, both in the case of the bioconjugates and in free hemoproteins. This was further confirmed by the characteristic signature at 2050 cm-1 in the Fourier-transform infrared spectra, which corresponds to the asymmetric stretching of the Fe(III) bound azide. The retention of the chemical behavior of the prosthetic heme group after adsorption on the nanoparticle is interesting due to its implications in nanoparticle supported enzyme catalysis. The absence of morphology changes after the reaction of bioconjugates with azide ion observed in HRTEM studies implies the stability of nanoparticles under the reaction conditions. All these studies indicate the retention of protein structure after adsorption on the nanoparticle surface.     

Study on thermal properties of organic ester phase-change material embedded with silver nanoparticles

This study investigates the thermal properties of new silver nano-based organic ester (SNOE) phase-change material (PCM) in terms of latent heat capacity, thermal conductivity and heat storage and release capabilities experimentally. Spherical-shaped surface-functionalized crystalline silver nanoparticles (AgNP) prepared were embedded in mass proportions of 0.1 through 5.0 wt% into the pure (base) PCM. Experimental results reveal that dispersion of AgNP into PCM was effective, only physical and no chemical interaction between AgNP and PCM has been exhibited; thereby phase-change temperature of SNOE PCMs were acceptable. These are essential characteristics for SNOE PCMs which signified their thermal and chemical stability on long term. Test results suggest that while compared to pure PCM, degree of supercooling was reduced by 11.7–6.8 % for aforesaid mass proportions of AgNP, whereas latent heat capacities decreased by 7.88 % in freezing and 8.91 % in melting. The interdependencies between thermophysical properties in improving nucleation and growth rate of stable SNOE PCM crystals were signified and discussed. Thermal conductivity of SNOE PCMs were enhanced from 0.284 to 0.765 W m^?1 K^?1 which was expected to be a 10–67 % increase for the above mass loading of AgNP. Furthermore, for SNOE PCMs enhancement span in freezing and melting cycles was improved by 41 and 45.6 %, respectively. Similarly, cooling and melting times were reduced by 30.8 and 11.3 %, respectively. Embedded AgNP helps to achieve improved thermophysical and heat storage characteristics for SNOE PCMs, which in turn can be considered as a potential candidate for cool thermal energy storage applications.     

Enhanced thermal and mechanical properties and biostability of polyurethane containing silver nanoparticles

A polyether-type polyurethane (PU) containing silver (Ag) nanoparticles (4-7 nm, 1.51 × 10⁻³-1.13 × 10⁻² wt-%) was prepared by mixing the waterborne PU with the nanoparticle suspension, casting and drying at 60 °C. The Ag nanoparticles were found to be well dispersed in PU. A significant increase in the thermal stability and mechanical properties of the polymer was demonstrated in the nanocomposite PU films, which was believed a result of induced crystallization in the presence of Ag nanoparticles. The biostability was tested in a rat subcutaneous model. After 19 days of implantation, the PU containing Ag showed enhanced biostability and lowered foreign body reaction. The effect of Ag on the stability of the PU polymer was even more remarkable over a wider range of particle contents than that of the gold nanoparticles previously studied.     

Synthesis and properties of silver and gold nanocomposites in poly-1-vinyl-1,2,4-triazole matrix

Novel multifunctional hybrid nanocomposites with silver and gold nanoparticles stabilized by original polymer matrix based on poly-1-vinyl-1,2,4-triazole were synthesized and studied using UV and IR spectroscopy, X-ray diffraction analysis and transmission electron microscopy. The obtained nanocomposites comprise silver or gold nanoparticles of spherical and elliptical shape with size 3–20 nm and 1–10 nm, respectively.     

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.     

Polymer colloids and silver nanoparticles hybrid materials

The present study presents two different methods to obtain hybrid material formed by the poly [styrene (ST)–poly(ethylene glycol) methyl ether methacrylate (PEGMA) 1100] and silver (Ag⁰). The aim has been to cover the polymeric particles with Ag⁰ shell. The first method consisted of mixing Ag⁰ nanoparticles dispersion with poly (ST-PEGMA 1100) dispersion, while in the second method, the Ag⁰ nanoparticles have been generated in situ. The hybrid materials have been characterized by MO, dynamic light scattering, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray energy dispersive spectrometry, and ultraviolet–visible spectrophotometry. The results confirm the obtaining of two types of morphologies. In the first case, the nanoparticles have been arranged in the interspatial zones of the polymer particles, while in the second method, the Ag⁰ nanoparticles have covered the polymer particles. Thus, the film obtained using the second method is more suitable for the practical application, as a separation membrane, using the antiseptic properties of Ag⁰.     

Preparation and optical properties of composite materials based on polybenzimidazole and silver nanoparticles

Rigid-chain heat resistant polymers (with poly-2,2'-p-oxydiphenylene-5,5′-bisbenzimidazole as example) were impregnated for the first time with a silver-containing precursor in formic acid and in supercritical carbon dioxide. A procedure allowing the precursor reduction to silver nanoparticles both throughout the volume by thermal annealing of the films in the temperature interval 100–150°С and in the targeted mode using lasers operating at 405 and 532 nm was developed. It opens prospects for developing a process for production of heatresistant optical gratings and light guides. The reduces nanoparticles and their agglomerates have the size in the interval 50–200 nm and give a plasmon band in the range 450–460 nm.     

Low-temperature metallic alloying of copper and silver nanoparticles with gold nanoparticles through digestive ripening

We describe a remarkable and simple alloying procedure in which noble metal intermetallic nanoparticles are produced in gram quantities via digestive ripening. This process involves mixing of separately prepared colloids of pure Au and pure Ag or Cu particles and then heating in the presence of an alkanethiol under reflux. The result after 1 h is alloy nanoparticles. Particles synthesized according to this procedure were characterized by UV-vis spectroscopy, EDX analysis, and high-resolution electron microscopy, the results of which confirm the formation of alloy particles. The particles of 5.6+/-0.5 nm diameter for Au/Ag and 4.8+/-1.0 nm diameter for Cu/Au undergo facile self-assembly to form 3-D superlattice ordering. It appears that during this digestive ripening process, the organic ligands display an extraordinary chemistry in which atom transfer between atomically pure copper, silver, and gold metal nanoparticles yields monodisperse alloy nanoparticles.     

Reactions of alkyl-radicals with gold and silver nanoparticles in aqueous solutions

Silver and gold nanoparticles are very efficient catalysts for the dimerization of methyl-radicals in aqueous solutions. The rate constants for the reaction of methyl-radicals with the gold and silver nanoparticles were measured and found to be 3.7 x 10(8) M(-1) s(-1) and 1.4 x 10(9) M(-1) s(-1), respectively. The results thus suggest that alkyl-radicals, also not reducing ones, are scavenged by these nanoparticles. This might explain the role, if such a role exists, of these nanoparticles in medical applications.     

Macromolecular systems and nanocomposites based on N-succinylchitosan and silver nanoparticles

Russian Chemical Bulletin - A water-soluble chitosan derivative, namely, N-succinylchitosan (NS-Chit), was used as a matrix for the formation of silver nanoparticles (AgNP) by metal ion re duction...     

Synthesis and optical properties of poly(N-isopropylacrylamide) nanogel containing silver nanoparticles

Composite nanoparticles representing silver nanoparticle-containing polymer gels have been synthesized. The synthesis comprises two main stages. Initially, monodisperse hydrogel particles with a controlled diameter of approximately 500 nm are obtained by N-isopropylacrylamide polymerization. Then, silver ions are reduced on the surface of the polymer network. Variations in the concentration ratio between reductants and silver nitrate make it possible to produce silver nanoparticles with sizes in a range of 10–30 nm and different packing densities on the gel particle surface. The resultant nanocomposites have been studied by transmission electron microscopy, spectrophotometry, and dynamic light scattering. Depending on the size and packing density of the silver nanoparticles on the polymer particle surface, the plasmon resonance of the nanocomposites varies in a range of 420–750 nm, which determines variations in the color of the colloid from yellow, orange, and red to blue and blue-green. After the inclusion of silver nanoparticles, nanogels of poly(N-isopropylacrylamide) retain their capability for thermosensitive phase transition with a lower critical mixing temperature of 31°C.     

Obtaining of hybrid nanocomposites by simultaneous photopolymerization of some urethane monomers and photoinduced formation of gold nanoparticles

Urethane–urea dimethacrylates were synthesized and used in the preparation of nanocomposites containing gold nanoparticles (Au NPs) in situ photogenerated during the UV‐curing process in the absence of reducing agent. A study of the photopolymerization kinetics showed that the photoreactivity of the monomers alone or in combination with a dual urethane benzophenone (BP) macromer is dependent on the nature of photoinitiator (Irgacure819, BP/amine) and the formulation composition. It was found that the addition of 1 wt % AuBr₃ in monomers slightly improved the polymerization rate and the degree of conversion. The formation of Au NPs into the network was confirmed through UV–vis, XRD, EDX, SAXS, and TEM analyses, the last indicating the existence of NPs with size around 8.5 nm and spherical/triangle shapes. On addition of 10 wt % 2[N‐methacryloyloxyethyl‐(N'‐2‐thioethyl)] (urea) in formulation, the Au NPs (200 nm) became predominantly cubic/hexagonal in shape. The composite films emit fluorescence at 575 nm, and this property could be exploited in the field of fluorescent bio/sensors. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 728–738