Non-spherical Silver Research Articles

The Effect of Different Synthesis with Chemical and Biological Methods on Properties of Silver Oxide Nanoparticles

Silver oxide (Ag2O) nanoparticles have been successfully synthesized through several methods, namely sol-gel, sonochemical, and biological methods. X-ray diffraction studies revealed that the sonochemical method produces silver oxide with high phase purity, then the sol-gel method produces another phase, namely silver crystals, while the biological method produces Ag3PO4 phase from the precursor media. The research showed that the sol-gel method had the smallest crystallite and particle sizes of 9.5 and 232.7 nm, respectively, compared to sonochemical and biological methods. It is known that the specific surface area of the sol-gel method has the largest value, namely 60.09 m2/g, compared to the sonochemical and biosynthetic methods, which are 51.78 and 24.77 m2/g, respectively. Scanning electron microscopy study showed homogeneous spherical nanoparticles of silver oxide in the sol-gel and sonochemical methods, however, the biological method resulted in the formation of non-spherical silver oxide nanoparticles in the form like flakes. HIGHLIGHTS Synthesis of silver oxide by chemical method produces pure silver oxide crystals, smaller crystallite size, larger specific area, and more homogeneous particle size than biological methods The sol-gel method for the synthesis of silver oxide produces the smallest particle size than the sonochemical and biological methods The sonochemical method produces the highest crystallinity and size homogeneity compared to the sol-gel and biological methods GRAPHICAL ABSTRACT

Spontaneous Transformation of Biomedical Polymeric Silver Salt into a Nanocomposite: Physical-Chemical and Antimicrobial Properties Dramatically Depend on the Initial Preparation State.

An antimicrobial polyacrylic silver salt (freshly prepared, stored for one year and model-aged) was studied by physical–chemical techniques for nanoparticle detection. In all cases, this salt represents a composite of radical-enriched macromolecules and silver(0) nanoparticles. As time passed, the initial small spherical nanoparticles were converted into larger non-spherical silver nanoparticles. The initial highly water-soluble antimicrobial solid nanocomposite almost loses its solubility in water and cannot be used as an antimicrobial agent. Unlike insoluble solid silver polyacrylate, its freshly prepared aqueous solution retains a liquid-phase consistency after one year as well as pronounced antimicrobial properties. The mechanism of these spontaneous and model-simulated processes was proposed. These results have attracted attention for officinal biomedicinal silver salts as complex radical-enriched nanocomposite substances; they also indicate contrasting effects of silver polymeric salt storing in solid and solution forms that dramatically influence antimicrobial activity.

A Facile Route in Controlling the Optical Absorbance of Polyvinylpyrrolidone-Capped Silver Nanoparticles Via Chemical Reduction Technique

This work presents the synthesis of silver nanoparticles (AgNPs) capped with polyvinylpyrrolidone (PVP) via a simple chemical reduction approach. A route in controlling the optical absorbance of the AgNPs by varying the concentration of silver precursors, as reflected by the shifts and broadening of the UV-vis spectra of the AgNPs is also highlighted. Dynamic Light Scattering results revealed the narrow and small hydrodynamic size for AgNPs synthesized at low precursor concentration, while multiple hydrodynamic size peaks were observed for AgNPs produced at high precursor concentration. Likewise, Fourier transform-infrared spectroscopy confirmed the successful capping of PVP on the AgNPs through the O and N atoms as potential binding sites. Transmission electron micrographs revealed the formation of spherical PVP-capped AgNPs, having no apparent aggregation observed. A closer inspection of the micrograph showed the subsequent formation of rod-like growth template of the AgNPs, that might lead to the formation of non-spherical silver nanostructures.

About the relevance of particle shape and graphene oxide on the behavior of direct absorption solar collectors using metal based nanofluids under different radiation intensities

Nanofluids based on spherical gold, silver, and copper nanoparticles, nonspherical silver nanoparticles, layered graphene oxides (GO), and GO/silver hybrid structures, were synthesized to analyze their effect on the thermal behavior of direct absorption solar collectors. The thermal conductivities at room temperature of all the nanofluids were similar, with values 4% higher than pure water, meaning up to three orders of magnitude differences compared to the values expected from the Maxwell model. Photothermal conversion experiments under simulated solar radiation with 1 Sun (=1 kW/m2) of intensity showed that all the spherical metal nanofluids presented up to 5 K higher temperatures and 35% increase of the efficiencies than pure water after 3000 s of irradiation. A much larger effect was seen with nonspherical silver and GO/silver hybrid particles, as these nanofluids presented around 20% higher efficiencies than pure spherical silver nanofluids. The large effect of silver morphology and the addition of GO led to further tests of these nanofluids under natural solar radiation using a parabolic dish mirror with a concentration ratio of 60. Under this high radiation, nanofluids showed up to 50 K higher temperatures and 100% increase in the efficiencies than pure water. Indeed, a boiling process after just 200 s was seen in nanofluids, while in pure water this phase change did not occur. Non-spherical silver nanofluids and GO/silver hybrid structures produced steam faster than spherical silver nanofluids. Our results confirm the relevance of the nanoparticles on the thermal conversion of nanofluids, with nonspherical silver nanofluids and GO/silver hybrid nanofluids presenting the best behaviors under low and high solar radiation.

Demonstration of variation of the nonlinear optical absorption of non-spherical silver nanoparticles

We study the features of the nonlinear optical response of silver nanoparticles (Ag NPs) of the spherical and triangular shapes synthesized using a citrate-borohydride approach. The Z-scans were used to analyze the nonlinear optical absorption of Ag NPs of different morphology, particularly, the concurrence of saturable and reverse saturable absorption in the solution containing triangular Ag NP. We show the significant contribution to the increase in the normalized transmittance accomplished by photochemical degradation of the non-spherical Ag NPs (extinction maximum of 600 nm) and transformation into the spherical ones (extinction maximum of 400 nm). The nonlinear light scattering is analyzed as well, which showed the contribution to the variation of the sample transmission when it approaches the focal plane.

Nonlinear optical absorption of non-spherical silver nanoparticles and organic dyes mixtures

We study the features of the nonlinear optical response of silver nanoparticles (Ag NPs) of spherical and triangular shapes synthesized using a citrate-borohydride approach and their mixtures with methylene blue (MB+). The Z-scans at the wavelengths of 532 nm using 10 ns pulses were used to analyze the nonlinear optical absorption of MB+ solutions, Ag NPs of different morphology, particularly, the concurrence of saturable and reverse saturable absorption in the solution of triangular Ag NP and MB+. We show the significant contribution to the increasing in the normalized transmittance accomplished by photochemical degradation of the non-spherical Ag NPs (extinction maximum of 600 nm) and transformation into the spherical ones (extinction maximum of 400 nm). The nonlinear light scattering is also analyzed, which showed the contribution to the variation of the sample transmission when it approaches the focal plane. It is shown that the nonlinear optical response is not additive in the mixture of Ag NPs and MB+. The increasing of the nonlinear absorption is probably due to both a change in the population of the triplet states of the dye and the efficiency of photochemical degradation of NPs in the presence of MB+.

Shape and size of non-spherical silver nanoparticles: implications for calculating nanoparticle number concentrations.

The international drive to measure accurate number concentrations of nanoparticles is impeded by the typically heterogeneous populations of non-spherical nanoparticles. The irregular shape and size of "50 nm" silver nanoparticles is studied using Electron Tomography. It is evidenced that even for highly symmetrical particles the volume can be over 20% less than that of the circumscribed sphere; more irregularly shaped particles can have volumes of over 45% less. On this basis, criteria are provided to determine the particle sphericity from 2D projections obtained from Electron Microscopy, including an empirical method for particle volume estimation. The results allow the visualisation of irregularly shaped particles, revealing the presence of previously unseen voids in the nanoparticle structure. Comparison of tomographic data with other commonly used particle-sizing methods exposes the limitations of these methods in studying nanoparticle populations that exhibit heterogeneity.

Synthesis of nonspherical nanoparticles by reducing silver neodecanoate extract with benzyl alcohol

A method for synthesizing nonspherical silver nanoparticles by reducing liquid extract of silver neodecanoate in benzyl alcohol has been developed. The method is simple and does not require the use of polyvinylpyrrolidone, sodium citrate or special methods using pre-synthesized seeds. The obtained particles have been investigated by the methods of electron microscopy, X-ray diffraction, and differential-thermogravimetric analysis. It has been found that triangular and hexagonal plates, as well as particles of pentagonal form and polyhedrons, are formed as a result of the reduction. The sizes of the obtained plates, depending on the synthesis conditions, vary from 80 nm to 2 μm. The method is promising for the industrial production of silver nano- and microplates.

Screening of nanoparticle properties in microfluidic syntheses

AbstractThe possible diversity of nanoparticles is extremely high. This variability corresponds to a huge potential of possible functions in future materials and nanotechnical devices. Apart from rational designs, there is an urgent need for screening strategies for specific nanoparticle properties. Miniaturized screening techniques are challenged for efficient screening procedures. The review gives an overview on the possibilities of tuning and screening of nanoparticle properties and focuses on the application of microfluidic techniques for nanoparticle synthesis. Furthermore, the variation of parameters during the generation of nanoparticles and its connection with the resulting nanoparticle properties are highlighted as well. Among other microfluidic techniques, microsegmented flow is particularly promising for the synthesis of different types of homogeneous nanoparticles and offers interesting approaches for the screening of process parameters and nanoparticle properties. The tuning of reactant concentrations in the micro-flow-through synthesis of nonspherical silver particles and gold/silver core/shell particles and their effects on the shape, size, and optical parameters of the formed nanoparticles are given as examples for the application of microsegmented flow in the screening of nanoparticle properties.

Surface plasmon assisted optical nonlinearities of uniformly oriented metal nano-ellipsoids in glass

The nonlinear optical properties of nanocomposites consisting of non-spherical silver nanoparticles in glass matrix have been studied using the femtosecond Z-scan technique. The spheroidal nanoparticles were uniformly oriented along a common direction. By polarization sensitive studies, longitudinal and transverse plasmon resonances can be addressed separately. A sign reversal in optical nonlinearity from negative to positive is observed while switching the light interaction from near to non-resonant regime, which can be done by simply rotating the light polarization by 90°. Studying samples with different aspect ratio, we obtained the dispersion of third-order nonlinearity in the near-resonant regime, showing an enhancement of the nonlinear processes by more than two orders of magnitude due to the electric field enhancement at the surface plasmon resonance.

Depolarized Light Scattering From Single Silver Nanoparticles

Depolarized scattering spectra from individual silver nanoparticles of different shapes and sizes were measured as a function of the incident polarization angle. The spectra were correlated to the nanoparticles’ shape, size, and orientation as determined by scanning electron microscopy. The intensity of depolarized scattered light from nonspherical silver nanoparticles strongly depends upon particle shape and orientation relative to the polarization vector. The intensity of depolarized scattered light also increases with the aspect ratio of the nanoparticles. The depolarized light scattering originated from the interference of the plasmon modes corresponding to the electron oscillations along different axes of the NPs.

Nano silver:antimony glass hybrid nanocomposites and their enhanced fluorescence application

A series of KBS antimony glass (K 2O–B2O3–Sb 2O 3) nanocomposites embedding non-spherical silver (Ag 0) nanoparticles have been synthesized by a single-step melt-quench in-situ thermochemical reduction technique without employing any external reducing agent. X-ray and selected area electron diffractions manifest growth of Ag 0 nanoparticles along the (111) and (200) crystallographic planes. The transmission electron microscopic image reveals rod-shaped (longitudinal lengths between 8 and 24 nm) as well as quasi-spherical particles. The quasi-spherical particles show bimodal size distribution. Small quasi-particles have sizes varying from 6 to 24 nm and large quasi-particles ranges from 45 to 105 nm. These complex distributions of particles are also revealed in the UV–Vis absorption spectra and the surface plasmon resonance bands show multiple peaks. These have been explained by electrodynamics theories. When co-doped with Er 2O 3 and excited at 798 nm, the two upconverted emission bands of Er 3+ centered at 536 (green) and 645 (red) nm undergo intensification by 3 and 8 fold respectively. It is due to local electric field enhancement effect of nanoparticles induced by Ag 0 SPR and energy transfer from Ag 0 to Er 3+ ion. These nanocomposites are the promising materials for solar cells, LEDs, display and laser applications.

Optical properties of a Maxwell–Garnett composite medium with nonspherical silver inclusions

Using the Maxwell-Garnett model, a complex effective index of refraction of a matrix metal-dielectric composite medium with silver inclusions of spheroidal shape is investigated. A possibility of observing the unit refractive index in the visible spectral region is shown, with the effective absorption coefficient being less than 0.1. The results of analytical calculations based on the electrodynamic Maxwell-Garnett model are compared with those obtained by an exact electrodynamic calculation.

Optical Properties of Shaped Silver Nanoparticles

The influence of shape and dielectric property of surrounding media on surface plasmon absorption band of silver nanoparticles was studied. Spherical silver nanoparticles (d = 5.6 nm) synthesized in water using NaBH4 as a reducing agent are transferred in non-polar solvent (chloroform) with phase-transfer reagent oleylamine. The absorption spectrum of oleylamine-capped silver nanoparticles dispersed in chloroform shows a strong surface plasmon resonance band that is 19 nm red-shifted compared to unmodified particles in water. The values for peak position and corresponding half widths are compared with theoretical calculations based on Mie theory. Prismatic and plate-like silver nanoparticles were synthesized in water using trisodium citrate as a reducing agent and cetyltrimethylammonium bromide as stabilizer. Due to structural anisotropy of prismatic and plate-like silver nanoparticles three surface plasmon resonance bands were observed in absorption spectrum. Nanocomposites consisting of non-spherical silver nanoparticles and polyvinyl alcohol exhibit different optical properties compared to water colloid. Instead of three surface plasmon bands, nanocomposite film has only one peak at 460 nm. Reason for appearance of single surface plasmon resonance band in nanocomposite film was discussed according to Maxwell-Garnet theory.

Modeling the optical response of nanoparticle-based surface plasmon resonance sensors

We model the optical response of surface plasmon resonance (SPR) sensors based on colloidal metal nanoparticles using extended Mie theory. The theoretical description includes the particle adsorption layer, the surrounding medium as well as particle–particle and particle–substrate electromagnetic coupling effects. We obtain quantitative agreement with recently reported experimental results on gold nanoparticle SPR sensors, indicating the possibility to perform accurate a priori estimates of detector sensitivity for different particle sizes and compositions in a variety of electromagnetic environments. The possibility to increase sensitivity by using non-spherical silver particles as SPR sensors is discussed.

Optical response of thin plasma-polymer films with non-spherical silver nanoparticles

The size and shape of silver nanoparticles which are embedded in a plasma-polymer matrix were obtained by transmission electron microscopy and analyzed with optical image processing. We used a sample in which silver particles were present before and after reshaping caused by thermal annealing in adjacent regions. As most of the particles appeared as elongated rotational ellipsoids, the major and minor half axis were determined for each particle. We adopted the model of Gans in the Rayleigh approximation to calculate for each investigated particle the extinction spectra from 4000 cm-1 to 35000 cm-1 using the data from the image processing. The various spectra for 368 silver particles were added to get total extinction spectra for the sample as deposited and after reshaping, respectively. We found good agreement with the experimental spectra. The blue shift of the plasma-resonance absorption, which occurs due to the reshaping of the silver particles during thermal annealing, was also confirmed by using only changes in the particle sizes and shapes.

Optical properties of nonspherical silver nanoparticles embedded in a plasma polymer thin film matrix

ABSTRACTSilver nanoparticles which are embedded in a plasma polymer matrix were obtained by transmission electron microscopy. Their sizes and shapes were analyzed with optical image processing. As most of the particles appeared as elongated rotational ellipsoids, the major and minor half axes were determined for each particle. The model of Gans in the Rayleigh approximation was used to calculate the extinction spectra for each investigated particle using the data from the image processing. Various spectra for 1049 silver particles were added to get a total extinction spectrum which was in good agreement with the experimental spectrum.