Monodisperse Silver Nanoparticles Research Articles

Synthesis of silver nanoparticles in aqueous aminopolycarboxylic acid solutions via γ-irradiation and hydrogen reduction

Formation of silver nanoparticles in the presence of various aminipolycarboxylic acids (APCAs) such as iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), and N,N,N′,N″,N‴,N‴-triethylenetetraminehexaacetic acid (TTHA) was studied. Monodispersed silver nanoparticles capped by carboxylate groups of APCAs were prepared by the reduction of Ag+ ions induced by either γ-radiolytic or H2 reduction at room temperature. APCAs act as stabilizer to avoid the aggregation of silver nanoparticles. It has been shown that H2-induced reduction of Ag+ is possible at room temperature in the presence of APCAs. TTHA stabilized γ-reduced particles showed reactivity towards oxygen. The formed particles were characterized by UV–vis absorption, X-ray diffraction, zetasizer and transmission electron microscopy.

Preparation of crosslinked amphiphilic silver nanogel as thin film corrosion protective layer for steel.

Monodisperse silver nanoparticles were synthesized by a new developed method via reaction of AgNO3 and oleic acid with the addition of a trace amount of Fe3+ ions. Emulsion polymerization at room temperature was employed to prepare a core-shell silver nanoparticle with controllable particle size. N,N'-methylenebisacrylamide (MBA) and potassium peroxydisulfate (KPS) were used as a crosslinker, and as redox initiator system, respectively for crosslinking polymerization. The structure and morphology of the silver nanogels were characterized by Fourier transform infrared spectroscopy (FTIR), transmission and scanning electron microscopy (TEM and SEM). The effectiveness of the synthesized compounds as corrosion inhibitors for steel in 1 M HCl was investigated by various electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Monolayers of silver nanoparticle were self-assembled on the fresh active surface of the steel electrode and have been tested as a corrosion inhibitor for steel in 1 M HCl solution. The results of polarization measurements showed that nanogel particles act as a mixed type inhibitor.

A rapid method to estimate the concentration of citrate capped silver nanoparticles from UV-visible light spectra.

We present a generalized table of extinction coefficient data for silver nanoparticles from 8 to 100 nm. This table allows for easy and quick estimation of the concentration and size of modified and mono-dispersed silver nanoparticles from their optical spectra. We obtained data by determining the silver content of citrate-stabilised silver nanoparticles using sodium cyanide to dissolve the nanoparticles, and measuring solution conductivity with a pH meter and a cyanide-ion selective electrode. The quantification of the silver ion concentration enabled the calculation of extinction coefficients. Experimentally calculated extinction coefficients, in the current work, are in good agreement with collated literature values measured by different authors with non-standardized methodology and each for a limited range of particle size. They are also in good agreement with our theoretical calculations using Mie theory. Thus, we provide a highly standardized and comprehensive tabulated reference data-set.

Plasmon assisted enhanced nonlinear refraction of monodispersed silver nanoparticles and their tunability.

Nonlinear optical characterizations were performed on monodispersed silver (Ag) nanoparticles (NPs) of various sizes using a picosecond Z-scan technique with excitation wavelengths of 532 nm and 1064 nm. The Ag NPs were fabricated using a heterogeneous condensation technique in a gas medium. The nonlinear refraction values were higher for the monodispersed Ag NPs whose surface plasmon resonance (SPR) peak is closer to the excitation wavelength. The higher nonlinear optical response is explained in terms of an electric field enhancement near the SPR. Moreover, the fabrication method allows the tailoring of the nonlinear refraction index of the Ag NPs by tuning the SPR peak of the sample. A comparison of the nonlinear refraction index of the monodispersed and polydispersed Ag NPs showed that the nonlinear refractive index of the monodispersed Ag NPs is higher.

Facile size-regulated synthesis of silver nanoparticles using pectin

Monodispersed silver nanoparticles capped by pectin were prepared by the reaction of silver nitrate with alkali hydrolyzed pectin at 70°C for 30min. Spherical and size-regulated silver nanoparticles were prepared using alkali hydrolyzed pectin as a reducing and particle-stabilizing agent. This approach is facile, effective, rapid, and convenient for the large scale preparation of silver nanoparticles. UV–visible spectral analysis confirmed that the nanoparticles consisted of metallic silver. Transmission electron microscopy (TEM) was used to estimate particle size and size distribution of the produced silver nanoparticles. Transmission electron microscopy and size distribution analysis revealed the presence of spherical silver nanoparticles with a main diameter of 5–10nm and have a narrow size distribution. The concentration of reducing sugars was monitored by using dinitrosalicylic acid. A comprehensive schematic mechanism for the formation of silver nanoparticles using pectin is proposed.

Seeded growth of monodisperse and spherical silver nanoparticles

Aiming at spherical and monodisperse silver nanoparticles with diameters up to 100nm, the potential of heterogeneous nucleation of silver particles was explored. Gold seed particles, mainly produced with a spark discharge generator, were carried by nitrogen through a three-zone tube furnace. Silver was evaporated at 1210°C in the first zone of the furnace and particle growth and shaping took place in the subsequent zones, heated to 730°C and 390°C, respectively. The generated aerosol was monitored by a scanning mobility particle sizer (SMPS), while parameters, such as furnace temperature, seed particle size and concentration and nitrogen carrier gas flow, were investigated. Off-line atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to characterize the morphology of the silver nanoparticles in addition to the SMPS scans. Spherical silver nanoparticles with a mobility diameter of more than 115nm and a geometric standard deviation of typically 1.09 or lower at concentrations as large as 5×105cm−3 could be produced. The mobility diameter of the monodisperse aerosol could be varied in the range of 50nm to 115nm by changing the furnace temperature or the gold seed particle size. Elemental analysis revealed that the gold from the seed particles formed a homogeneous alloy with the silver (≤3.5at.% of gold). The growth mechanism could not be identified unambiguously since the obtained silver particles could both originate from heterogeneous nucleation of silver vapour on the seed particles or from coagulation and coalescence of the seed particles with smaller, homogeneously nucleated silver particles. Moreover, the narrow size distribution opens the opportunity to obtain an exclusively singly charged, monodisperse calibration aerosol at sufficient concentrations after an additional mobility selection process.

Monodispersed Ag nanoparticles as catalyst: preparation based on crystalline supramolecular hybrid of decamethylcucurbit[5]uril and silver ions.

Monodispersed silver nanoparticles (Ag(0) NPs) have been first prepared on the basis of a postsynthesis via mild reduction from a new crystalline supramolecular hybrid solid assembled from Ag(+) ions and decamethylcucurbit[5]uril (Me10CB[5]). Uniform growth of nearly spherical Ag(0) NPs with an average size of ca. 4.4 nm was observed on the organic Me10CB[5] support to form Ag@Me10CB[5] composite material. The as-synthesized composite material was characterized by a range of physical measurements (PXRD, TGA, XPS, ICP, TEM, etc.) and was further exploited as a heterogeneous catalyst for the reduction of various nitrophenols in the presence of NaBH4. The kinetics of the reduction process was monitored under various experimental conditions. The Ag@Me10CB[5] composite material showed excellent catalytic performance over the reduction reactions and remained active after several consecutive cycles.

Synthesis of Highly Monodisperse Citrate-Stabilized Silver Nanoparticles of up to 200 nm: Kinetic Control and Catalytic Properties

Highly monodisperse sodium citrate-coated spherical silver nanoparticles (Ag NPs) with controlled sizes ranging from 10 to 200 nm have been synthesized by following a kinetically controlled seeded-growth approach via the reduction of silver nitrate by the combination of two chemical reducing agents: sodium citrate and tannic acid. The use of traces of tannic acid is fundamental in the synthesis of silver seeds, with an unprecedented (nanometric resolution) narrow size distribution that becomes even narrower, by size focusing, during the growth process. The homogeneous growth of Ag seeds is kinetically controlled by adjusting reaction parameters: concentrations of reducing agents, temperature, silver precursor to seed ratio, and pH. This method produces long-term stable aqueous colloidal dispersions of Ag NPs with narrow size distributions, relatively high concentrations (up to 6 × 1012 NPs/mL), and, more important, readily accessible surfaces. This was proved by studying the catalytic properties of as-synthesized Ag NPs using the reduction of Rhodamine B (RhB) by sodium borohydride as a model reaction system. As a result, we show the ability of citrate-stabilized Ag NPs to act as very efficient catalysts for the degradation of RhB while the coating with a polyvinylpyrrolidone (PVP) layer dramatically decreased the reaction rate.

Application of the paracrystal model to GISAXS analysis of the 3D self-assembled nanoparticle crystals

An original diffraction model for the evaluation of the grazing-incidence small-angle X-ray scattering (GISAXS) of the three-dimensional (3D) supported self-assembled nanoparticle crystals is presented. The model utilizes the formalism of traditional crystallography that is applied to nanoparticles as scattering entities. The infinite paracrystal concept was adopted in order to include cumulative disorder that is typical for the self-assembled nanoparticle structures. Azimuthal averaging around a chosen crystallographic direction allows incorporation of texture effects. A transformation of the SAXS paracrystal equations to comply with the GISAXS geometry was employed to describe the scattering process in the limit of the kinematical approximation which facilitates calculations. The model was developed for the face-centered cubic (FCC) symmetry, however, its extension to any other cubic symmetry is straightforward. The model was tested on a 3D nanoparticle assembly formed on silicon from a dried drop-cast colloidal solution of monodisperse silver nanoparticles of 5.8 ± 0.6 nm diameter. Presence of the FCC nanoparticle crystal with the [111] texture along the substrate normal was evidenced from evaluation of the synchrotron GISAXS data. The degree of paracrystal disorder is 2.5% and 3.6% parallel and perpendicular to the substrate, respectively, suggesting the anisotropic character of the self-assembling process. A SAXS measurement of the nanoparticle crystal formed from the same solution in a capillary revealed a randomly oriented FCC structure with a slightly larger paracrystal disorder of 4%. Obviously, different conditions of the nanoparticle crystal formation affect its azimuthal and translational disorder.

Facile and one-step synthesis of monodisperse silver nanoparticles using gum acacia in aqueous solution

A practical and convenient method for the synthesis of highly stable and small sized silver nanoparticles with a narrow distribution from 2nm to 20nm is reported. Silver nitrate was used as silver precursor and gum acacia was acted as a capping agent as well as a reducing agent. The formation of silver nanoparticles was observed by change of color from light yellow to black green. The silver nanoparticles were characterized by high resolution transmission electron microscopy (HRTEM), UV–visible spectroscopy (UV–vis), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra. The HRTEM images showed that the as-synthesized silver fine spherical particles were distributed uniformly. The XRD and HRTEM results demonstrated that the obtained metallic particles were single crystalline silver nanoparticles. FT-IR spectra data suggested that the silver nanoparticles were coated with gum acacia. The effects of the reaction time, the reaction temperature, the amount of gum acacia and the silver nitrate on the particle size were investigated. The silver nanoparticles are stable and hence can be found of practical use in medicine such as antimicrobial materials. The preparation process is simple and environmentally-friendly, which may be extended to other noble metal for other technological applications.

Preparation of mono-dispersed silver nanoparticles assisted by chitosan-g-poly(ɛ-caprolactone) micelles and their antimicrobial application

Amphiphilic chitosan-graft-poly(ɛ-caprolactone) (CS-g-PCLs) copolymers were synthesized by a homogeneous coupling method and characterized by 1H NMR, FTIR and ninhydrin assay. The graft copolymers were subsequently self-assembled into micelles, which were measured by DLS and TEM. The particle size of the micelles decreased as the segment grafting fraction was increased. Thereafter, silver nanoparticles were prepared in the presence of chitosan-based micelles under UV irradiation. The molar ratio and radiation time of silver to micelles were optimized with process monitored via UV–vis spectrophotometer. DLS and TEM were used to illustrate the particle structure and size while XRD patterns were applied to characterize the crystal structures of polymer-assisted silver nanoparticles. Films impregnated with silver nanoparticles were conducted with results of strong antimicrobial activities against Escherichia coli and Staphylococcus aureus as model Gram-negative and positive bacteria.

Silver Nanoparticles Encapsulated Polyacrylamide Nanospheres: An Efficient DNA Binding Nanomatrix

The present study describes the fabrication of silver nanoparticles/polyacrylamide nanospheres as a DNA binding matrix for various genomic applications. It was developed by nucleation of ascorbic acid-stabilized spherical mono dispersed silver nanoparticles (40nm) within polyacrylamide layer. The DNA binding nanomatrix was characterized for various physiochemical parameters and successfully validated for stable DNA binding efficiency. The silver nanoparticles/polyacrylamide nanospheres have shown a very good DNA conjugation yield of 1.8µg mg−1. The Ag nanoparticles/polyacrylamide nanospheres has also been proven as an efficient DNA carrier agent with a persistent DNA recovery of 80–85%, showing its potential in DNA based applications.

In situ synthesis of highly monodispersed nonaqueous small-sized silver nano-colloids and silver/polymer nanocomposites by ultraviolet photopolymerization

Highly monodispersed nonaqueous small-sized (3.7±0.1nm) silver nano-colloids were successfully synthesized by in situ synthesis using silver dodecanoate as organic precursor, 3,3,5-trimethylcyclohexyl methacrylate (TMCHMA) as solvent, and triethylamine (Et3N) as promoter. The obtained silver nanoparticles were characterized by ultraviolet–visible (UV–vis) absorption spectrophotometer, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The results showed that the highly monodispersed silver nanoparticles with diameter in the range of 3.0nm to 4.2nm and have face centered cubic (FCC) crystal structure. The possible forming mechanism of the core–shell structured silver nanoparticles and silver/polymer nanocomposites was proposed. By thermogravimetric analysis (TG) and energy dispersive X-ray spectroscopy (EDX) spectrometer of silver nanoparticles, it was speculated that dodecanoic acid together with UV-curable monomer (i.e., TMCHMA) consisted of the shell of silver nanoparticles. The ratio of monomer and silver precursor, the dropping rate of Et3N and reaction temperature were the three key factors to determine particle size and size distribution. The photopolymerizable silver nano-colloids were able to disperse in nonaqueous solvent. Silver/polymer nanocomposites were prepared by addition of photo initiator and a short-term UV exposure on the silver nano-colloids.

Morphology tuning of mono-disperse silver nanoparticles by reaction temperature adjustment

Mono-disperse silver nanoparticles with tunable morphologies have been fabricated by reducing AgNO3 in the presence of N-dimethylformamide (DMF) and larger molecular weight poly (vinylpyrrolidone) (PVP). By adjusting the reaction temperature, the conversion of the morphology can be easily and effectively controlled. The crystal structures and growth mechanism of mono-disperse silver nanoparticles were studied by using TEM, HR-TEM, FFT, XRD and UV-Vis spectra data. The results show that the morphologies of nanoparticles with spherical shape can be adjusted to a truncated triangle/hexagon along with the change of reaction temperature from 80 to 120 °C. It is found that the shape transformation from sphere to truncated triangle is caused by the difference in surface energy and the selective adsorption of PVP on silver atom.

Synthesis of size tunable monodispersed silver nanoparticles and the effect of size on SERS enhancement

Spherical and monodispersed silver nanoparticles (AgNPs) are ideal for fundamental research as the contribution from size and shape can be accounted for in the experimental design. In this paper a seeded growth method is presented, whereby varying the concentration of sodium borohydride-reduced silver nanoparticle seeds, different sizes of stable spherical nanoparticles with a low polydispersity nanoparticles are produced using hydroquinone as a selective reducing agent. The surface-enhanced Raman scattering (SERS) enhancement factor for each nanoparticle size produced (17, 26, 50, and 65nm) was then assessed using three different analytes, rhodamine 6G (R6G), malachite green oxalate (MGO) and thiophenol (TP). The enhancement factor gives an indication of the Raman enhancement effect by the nanoparticle. Using non-aggregated conditions and two different laser excitation wavelength (633nm and 785nm) it is shown that an increase in particle size results in an increased enhancement for each analyte used.

Ultrafine silver nanoparticles obtained from ethylene glycol at room temperature: catalyzed by tungstate ions

Ethylene glycol (EG) has been widely utilized to fabricate silver nanoparticles with uniform size and morphology. However, the majority of the work reported to date using EG routinely require not only heating, but also a surfactant. In the present paper, we report a surfactant-free and facile method for the synthesis of fairly monodisperse smaller silver nanoparticles (~6 nm) through the reaction of silver ions with EG by using tungstates (such as potassium tungstate, sodium tungstate) as catalysts at room temperature. Particularly, in this method, tungstates as catalysts can dramatically speed up the reduction of silver ions, and EG acts as both a solvent and a reducing agent to reduce silver ions to Ag metal. Meantime, we have carried out a series of experiments to investigate the performance of the as-prepared silver nanoparticles. It was found that the silver nanoparticles show excellent catalytic activity for the reduction of 4-nitrophenol in the presence of NaBH4.

Ultrarapid catalytic reduction of some dyes by reusable novel erythromycin-derived silver nanoparticles

A novel green approach for the synthesis of silver nanoparticles using erythromycin as a reducing/capping agent is presented. Erythromycin-derived silver nanoparticles were characterized by ultraviolet-visible spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. Monodispersed silver nanoparticles showed excellent and promising catalytic activity for reduction of 3 differently charged dyes (eosin B, methylene blue, and rose bengal) in the presence of NaBH4. The study revealed that 100% reduction of these dyes can be achieved efficiently in just 150--250 s. They were easily recovered from the reaction medium and were reused 5 times, showing enhanced catalytic potential each time. Glass-supported Ag(0) NPs (0.15 mg) were removed by washing sequentially and reused 5 times for catalytic reduction of these dyes at 10 m M. All dyes were successfully reduced by erythromycin-derived silver nanoparticles up to 7%. Based upon these results, it was concluded that erythromycin-derived silver nanoparticles are a novel, rapid, and highly economical alternative for environmental protection against pollution caused by dyes and can be extended for the control of other reducible contaminants.

Fabrication of Monodispersed Silver Nanoparticles and their Collective Sharp Plasmonic Response

Monodispersed silver (Ag) nanoparticles (NPs) were obtained by applying an electric field on unipolar-charged Ag NPs fabricated using a heterogeneous condensation technique in gas media. Well defined and charged Ag NPs were separated based on their sizes and were collected on quartz substrates. Thin films consisting of monodispersed Ag NPs with size ranging from 35 to 120 nm were prepared by varying an applied electric field during the fabrication process. Scanning electron microscope results showed that the samples have uniform size distribution. Coherent oscillations of conduction band electrons in gas medium induced by electromagnetic field and coupling of all similar plasmon resonances due to uniform Ag NPs size produced unique and interesting optical properties. Narrow extinction widths (∼41 to ∼69 nm) were observed compared to the width of polydispersed Ag sample. The ability to prepare samples in gas media and tune the plasmon resonance by merely varying an electric field during fabrication makes the method simple, fast, and highly economical.

The Anti-Fasciolasis Properties of Silver Nanoparticles Produced by Trichoderma harzianum and Their Improvement of the Anti-Fasciolasis Drug Triclabendazole

Recently, new strains of Fasciola demonstrated drug resistance, which increased the need for new drugs or improvement of the present drugs. Nanotechnology is expected to open some new opportunities to fight and prevent diseases using an atomic scale tailoring of materials. The ability to uncover the structure and function of biosystems at the nanoscale, stimulates research leading to improvement in biology, biotechnology, medicine and healthcare. The size of nanomaterials is similar to that of most biological molecules and structures; therefore, nanomaterials can be useful for both in vivo and in vitro biomedical research and applications. Therefore, this work aimed to isolate fungal strains from Taif soil samples, which have the ability to synthesize silver nanoparticles. The fungus Trichoderma harzianum, when challenged with silver nitrate solution, accumulated silver nanoparticles (AgNBs) on the surface of its cell wall in 72 h. These nanoparticles, dislodged by ultrasonication, showed an absorption peak at 420 nm in a UV-visible spectrum, corresponding to the plasmon resonance of silver nanoparticles. The transmission electron micrographs of dislodged nanoparticles in aqueous solution showed the production of reasonably monodisperse silver nanoparticles (average particle size: 4.66 nm) by the fungus. The percentage of non hatching eggs treated with the Triclabendazole drug was 69.67%, while this percentage increased to 89.67% in combination with drug and AgNPs.

Size and mass determination of silver nanoparticles in an aqueous matrix using asymmetric flow field flow fractionation coupled to inductively coupled plasma mass spectrometer and ultraviolet–visible detectors

The powerful antibacterial properties of engineered silver nanoparticles (AgNPs) have, in recent years, led to a great increase in their use in consumer products such as textiles and personal care products offers. This widespread and often indiscriminate use of nano-silver is inevitably increasing the probability that such materials be accidentally or deliberately lost into the environment. Once present in the environment the normally useful antibacterial properties of the silver may instead become a potential hazard to both man and the environment. In the face of such concerns it therefore desirable to develop easy, reliable and sensitive analytical methods for the determination of nano-sized silver in various matrices. This paper describes a method for the simultaneous determination of particles-size and mass-concentration of citrate-stabilized silver nano-particles in aqueous matrices by asymmetric flow field flow fractionation coupled to an ICP-mass spectrometer and UV/vis detector. In particular, this work has evaluated the use of pre-channel injections of mono-dispersed silver nano-particles as a means of accurate size and mass-calibration. The suitability of the method as a means to generate accurate and reliable results was verified by determination of parameters such as precision under repeatability conditions, linearity, accuracy, recovery and analytical sensitivity.