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Abstract: Highly dispersed gold–silver core–shell nanoparticles were synthesized in a two-step process. The stabilizer-free gold core particles with an average diameter of ∼30nm were first precipitated by rapid reduction of HAuCl4 with l-ascorbic acid. Thin continuous silver shells of variable thickness were subsequently obtained by reducing controlled amounts of silver nitrate added in the gold sol. The plasmon band of gold gradually blue-shifted and a peak characteristic for silver eventually emerged as the amount of deposited silver increased. A strong and well-defined silver absorption band was recorded when the Ag content exceeded 60wt.%. It is shown that the concentration of Cl− ions in the gold precursor solution plays a critical role in the stability of the bi-metallic sol and the structure of the deposited silver shell. [Copyright &y& Elsevier]

Abstract: Here, we report on the synthesis, characterization and catalytic evaluation of Cu, Ag and Au dendrimer encapsulated nanoparticles (DENs). Generations 4–6 of PAMAM-OH and PAMAM-NH2 were used as templating agents for the synthesis of Cu and Ag-DENs respectively. Generation 4 PAMAM-NH2 dendrimers were used for the synthesis of Au-DENs. These prepared DENs were characterized using UV visible (UV–vis) spectroscopy as well as a high resolution transmission electron microscopy (HRTEM). The catalytic activity of these DENs was evaluated on the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AMP) by sodium borohydride (NaBH4). The reaction was monitored by UV–vis spectroscopy at λ 400nm. These prepared DENs were found to exhibit good activity for this reduction reaction. [Copyright &y& Elsevier]

Abstract: We report a simple chemical reduction method for the synthesis of different colored silver nanoparticles, AgNP, using tyrosine as a reducing agent. Effects of cetyltrimethylammonium bromide, CTAB, and tyrosine concentrations are analyzed by UV–visible measurements and scanning electron microscopy (SEM) to evaluate the mode of AgNP aggregation. The position and shape of the surface resonance plasmon absorption bands strongly depend on the reaction conditions, i.e., [CTAB], [tyrosine], and reaction time. Sub-, post-, and dilution-micellar effects are accountable for the fast and slow nucleation and growth processes. Spectrophotometric measurement also shows that the average size and the polydispersity of AgNP increase with [CTAB] in the solution. CTAB acted as a shape-directing agent. [Copyright &y& Elsevier]

Abstract: Graphene oxide (GO) nanosheets impregnated with silver nanoparticles (Ag NPs) were fabricated by the in situ reduction of adsorbed Ag+ by hydroquinone (HQ) in a citrate buffer solution. Paper-like Ag NP/GO composite materials were fabricated owing to convenient structure characterization and antibacterial tests. The Ag NP/GO composites were characterized by UV–vis spectra, transmission electron microscope, electron diffraction, Raman spectroscopy, and field emission scanning electron microscope coupled with Energy Dispersive Spectrometer. Antibacterial activity was tested using Escherichia coli and Staphylococcus aureus as model strains of Gram negative and Gram positive bacteria, respectively. The as-prepared composites exhibit stronger antibacterial activity against both. The Ag NP/GO composites performed efficiently in bringing down the count of E. coli from 106 cfu/mL to zero with 45mg/L GO in water. The micron-scale GO nanosheets (lateral size) enable them to be easily deposited on porous ceramic membranes during water filtration; making them a promising biocidal material for water disinfection. [Copyright &y& Elsevier]

Abstract: We report a novel and simple hydrothermal method to synthesize silver nanowires using only silver nitrate and sodium citrate without any external seeds or templates. The effects of the molar ratio of silver ions to citrate, pH, and the reaction temperature were investigated. Silver nanowires and particles were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), and UV/vis absorption spectroscopy. A high yield of nanowires (average diameter 53±4nm, length up to 6μm) was obtained under optimized conditions with 1:1M ratio of Ag+ to citrate and pH 7.1 (no NaOH added) at 130°C. Increasing the citrate ratio, increasing the pH with NaOH, or decreasing the reaction temperature all resulted in samples with shorter lengths and fewer nanowires compared to nanospheres. At pH 10.1, monodispersed nanospheres with diameter of 58±9nm were produced. The nanowire and nanosphere synthetic methods are attractive because of their simplicity, the lack of capping agents besides citrate, and the uniformity of the particles produced. [ABSTRACT FROM AUTHOR]

Abstract: Novel hybrid material thin films based on polyvinyl alcohol (PVA)/tetraethyl orthosilicate (TEOS) with embedded silver nanoparticles (AgNps) were synthesized using sol–gel method. Two different strategies for the synthesis of silver nanoparticles in PVA/TEOS matrix were applied based on reduction of the silver ions by thermal annealing of the films or by preliminary preparation of silver nanoparticles using PVA as a reducing agent. The successful incorporation of silver nanoparticles ranging from 5 to 7nm in PVA/TEOS matrix was confirmed by TEM and EDX analysis, UV–Vis spectroscopy and XRD analysis. The antibacterial activity of the synthesized hybrid materials against etalon strains of three different groups of bacteria –Staphylococcus aureus (gram-positive bacteria), Escherichia coli (gram-negative bacteria), Pseudomonas aeruginosa (non-ferment gram-negative bacteria) has been studied as they are commonly found in hospital environment. The hybrid materials showed a strong bactericidal effect against E. coli, S. aureus and P. aeruginosa and therefore have potential applications in biotechnology and biomedical science. [Copyright &y& Elsevier]

Abstract: Monodisperse silver particles were synthesized according to the method of Creighton et al. by reduction of AgNO3 solutions with NaBH4 in the presence of polyvinyl alcohol as the stabilizing agent. Bulk characteristics of silver nanoparticles in aqueous solutions were carried out by measuring their extinction spectrum, fluorescence, diffusion coefficients using the PCS method and the electrophoretic mobilities. The average hydrodynamic diameter of PVA covered silver particles was 44nm, being fairly independent of ionic strength and pH in the range of 3–9. It was also shown that the hydrodynamic radius did not change within prolonged storage of suspensions (up to 75days), indicating that the sols were quite stable. A similar value of 45±8nm was determined from SEM measurements. The electrophoretic mobility measurements showed that the zeta potential of silver nanoparticles was insensitive to pH and decreased with the ionic strength, attaining −45mV for I =10−5 M and −25mV for I =10−2 M. Additionally, the kinetics of silver particle deposition on mica modified by adsorption of a saturated layer of poly(ethylene imine) (PEI) was studied. Surface concentration was determined directly by counting the number of particles over various surface areas using the atomic force microscopy working in the semicontact mode. The maximum surface concentration for I =10−3 M was 102μm−2, which corresponds to the coverage degree of 16%. The kinetic run and the maximum coverage value was in a good agreement with theoretical predictions stemming from the random sequential adsorption (RSA) model. This kinetic run allowed one to determine the size of Ag core, which was 20nm and the thickness of the PVA layer, equal to 12nm. [Copyright &y& Elsevier]

Abstract: Synthesis of silver nanoparticles in homogeneous aqueous solutions of the precursors silver nitrate and three saccharides (two mono saccharides i.e. glucose and fructose and one disaccharide such as sucrose) has been performed. These Ag-nanoparticles can be derivatized by other surface treatments, as required. The anionic surfactant SDS was tested to investigate its effect on the dependence of size, growth rate, photoluminescence (PL) emission and polydispersity of the nanoparticles. The time evolution of UV–vis absorbance suggested that nucleation and growth rate markedly vary in a first order fashion w.r.t. Ag+ salt concentration. The differences in the reducing ability of the saccharides were discussed with reference to their structure dependent adsorption behavior onto the particles. Changes in UV–vis, PL and FT-IR spectra during nucleation and growth of the nanoparticles were used to establish plausible mechanisms for the adsorption of surfactant on the particle surface, so as to restrict the growth. The results revealed a simple and easy strategy for synthesizing metal nanoparticles with well controlled shapes, sizes and structures. [Copyright &y& Elsevier]

Abstract: Colloidal dispersions of silver (Ag) particles were prepared by the photoreduction of silver perchlorate (AgClO4) in water/AOT/benzene water-in-oil (w/o) microemulsions consisting of sodium bis(2-ethylhexyl) sulfosuccinate (AOT), water and benzene. Formation mechanisms of Ag particles prepared in the presence of benzoin by photoreduction from Ag+-containing w/o microemulsions were investigated by UV–vis, transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS) and small-angle X-ray scattering (SAXS) measurements. By a combination of TEM and EXAFS results, Ag particles show a metallic nature after the photoreduction and the diameter of Ag particles ranges between 5 and 30nm. In situ time-resolved SAXS measurements show that the integrated rate equation can be applied in the reduction process of Ag+ ions to Ag0 atoms, and the autocatalytic Ag particle growth proceeds in the association process of Ag0 atoms during the photoreduction of Ag+-containing w/o microemulsions. The nanometer-sized water droplets microemulsified by AOT in benzene continuous-phase regulated the size of Ag particles, and the size and shape of water droplets were retained during the Ag particle formation. [Copyright &y& Elsevier]

Abstract: We describe the preparation and characterisation of inorganic–organic hybrid block copolymer silver nanoparticles via the preparation of spherical multi-responsive polymeric micelles of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP38-b-PEO211 and poly(acrylic acid)-block-poly(isopropyl acrylamide), PAA55-b-PNIPAAm88 in the presence of AgNO3. Hence, the P2MVP and PAA segments were employed to fix Ag+ ions within the micellar core (25°C) or shell (60°C), while the PEO segments ensured spontaneous reduction of Ag+ ions into metallic Ag, as well as colloidal stabilisation. Spherical and elongated composite core–shell(–corona) nanoparticles (CNPs) were formed containing several small, spherical silver nanoparticles within the micellar core or shell. As the co-assembly of the oppositely charged copolymers into micelles is electrostatically driven, the CNPs can be destabilised by, for example, addition of simple salts, i.e., the CNPs are stimuli responsive. CNP size and morphology control can be achieved via the preparation protocol. For example, heating to 60°C, i.e., above the PNIPAAm LCST, results in core–shell–corona CNPs with the Ag-NPs situated in the aggregate shell. [Copyright &y& Elsevier]