Spherical Metal Nanoparticles Research Articles

Nonlocal Hydrodynamic Models for the Optical Response of Plasmonic Nanostructures

In order to model the interaction between light and plasmonic structures at deep-nanometer scale, which is governed by non-classical effects, a nonlocal hydrodynamic approach has been extensively studied. Several hydrodynamic models have been proposed, solving the coupled equations: the linearized hydrodynamic equation of motion and the electrodynamic Maxwell’s equations, by employing additional boundary conditions. This work compares four hydrodynamic models: the hard wall hydrodynamic model (HW-HDM), the curl-free hydrodynamic model (CF-HDM), the shear forces hydrodynamic model (SF-HDM), and the quantum hydrodynamic model (Q-HDM). The analysis is conducted for a metallic spherical nanoparticle, as an example. The above hydrodynamic models are also compared with experiments available in literature. It is demonstrated that HW-HDM and QHDM outperform the other two hydrodynamic models.

Co, N co-doped porous carbons as high-performance oxygen reduction electrocatalysts

Although the Co and N co-doped carbon catalyst (Co-NC) has attracted much attention because of its low cost and the natural abundance of the dopants, it has a low oxygen reduction reaction (ORR) activity and a high selectivity for the two-electron (2e-) reduction of oxygen to H2O2, which affects its use in fuel cells. Co-NC catalysts were prepared by the pyrolysis of a mixture of cobalt chloride and chitosan pretreated with zinc chloride at 650, 750 and 850 oC, followed by washing with nitric acid and annealing at 900 oC. The results indicate that zinc chloride helps the complexing of chitosan with Co2+, which is also a chemical activator that generates pores, and annealing caused the evaporation of the spherical Zn metal nanoparticles formed by the carbothermal reduction of Zn ions, leading to a unique porous structure of the catalysts with spherical pores filled with spherical carbon nanoparticles formed by the growth of nitrogen-doped carbon as a result of the Co catalyst. The degree of graphitization is also improved by the Co catalyst. The Co-NC catalyst obtained at a pyrolysis temperature of 750 oCshows the same four-electron (4e-) reduction of oxygen as a commercial Pt/C catalyst, and a significantly higher ORR catalytic activity, longer-term stability and better methanol tolerance than a commercial Pt/C catalyst. These are due to its large specific surface area, high contents of pyridinic nitrogen and graphitic nitrogen that disperse the Co species and its excellent electrical conductivity.

Reverse Size-Dependent Electrooxidation of Gold Nanoparticles Coated with Alkanethiol Self-Assembled Monolayers

The oxidation potential of weakly stabilized, citrate-coated Au and other spherical metal nanoparticles (NPs) shifts negative by an amount proportional to 1/radius due to a size-dependent negative ...

Shape Transformation Mechanism of Gallium–Indium Alloyed Liquid Metal Nanoparticles

AbstractEutectic gallium indium (EGaIn) spherical liquid metal nanoparticles (NPs) can transform to gallium oxide hydroxide (GaOOH) microrods in water. Nevertheless, the mechanism of this process still remains unrevealed. In this work, the whole shape transformation process of EGaIn NPs is investigated via monitoring the change of NPs’ composition and morphology. Gallium (Ga) element in EGaIn NPs can be oxidized to form gallium oxide, which further reacts with water to generate micrometer‐sized GaOOH crystals. This chemical variation occurs gently at room temperature and is accelerated by heating. With continuous consumption of Ga element, indium condenses to form individual NPs. The dynamic temperature‐dependent dissolution and precipitation of GaOOH microrods in water are further demonstrated. Deep understanding of the mechanism of EGaIn NPs’ shape transformation would provide more approaches to control the surface and bulk properties of NPs for potential applications in various fields including soft robotics, wearable devices, and nanomedicine.

In Ukrainian

In recent years, interest in studying the optical properties of metallic nanostructures has grown. This interest is primarily related to the possibility of practical application of such nanostructures in quantum optical computers, micro- and nanosensors. These applications are based on the fundamental optical effect of surface plasmon excitation. The consequence of this phenomenon is surface plasmon resonance (SPR) - an increase in the cross section of energy absorption by a metal nanoparticle as the frequency of incident light (laser radiation) approaches the SPR frequency of the nanoparticle. Plasmon structures are used to improve the efficiency of thin-film SC. In such structures, metal nanoparticles can primarily act as additional scattering elements for the long-wavelength component of sunlight illuminating SC. As a collective phenomenon, SPR can be described using kinetic approaches, ie using the Boltzmann kinetic equation for the conduction electrons of metal nanoparticles. In this work, the theory of SPR based on the kinetic equation for the conduction electrons of nanoparticles is constructed. to the well-known results derived from the Drude-Sommerfeld theory. Second, the kinetic method makes it possible to study metal nanoparticles with sizes larger or ptical conductivity tensor for spheroidal metal nanoparticles. It is shown that the effect of nanoparticle asymmetry on the ratio of the components of the optical conductivity tensor differs not only smaller than the average electron free path length. The developed theory is used to calculate the oquantitatively but also qualitatively in high-frequency and low-frequency surface scattering. It was found that in metal nanoparticles in a dielectric matrix, under SPR conditions, the full width of the SPR line in a spherical metal nanoparticle depends on both the radius of the particle and the frequency of the electromagnetic (laser) radiation exciting this SPR. It is shown that oscillations of the SPR line width with a change in the dielectric constant of the medium in which they are located can be observed in metal nanoparticles. The magnitude of these oscillations is greater the smaller the size of the nanoparticle and increases significantly with increase. As the radius of the spherical nanoparticle increases, the width of the SPR line decreases significantly and prevails around a certain constant value in media with a higher value of dielectric constant.

A novel highly dispersed tetra-metal nano heterogeneous ozone catalyst derived from microbial adsorption and in situ pyrolysis

In recent years, the pyrolysis of microbial biomasses that adsorb various metal ions has enabled the preparation of carbon-based polymetallic nanomaterials with excellent electrocatalytic and electrical energy storage properties. However, the preparation of ozone catalysts by this technique and the corresponding catalytic oxidation mechanism are still unclear. In this study, an Escherichia coli strain (BL21) was used for tetra-metal (Cu, Fe, Mn and Al) absorption and the obtained microbial biomass was pyrolyzed under the protection of a nitrogen flow at 700 °C and activated at 900 °C to prepare a microbial-char-based tetra-metal ozone catalyst (MCOC). This was used to degrade phenol and coking wastewater and exhibited a strong catalytic capability for coking wastewater, whose chemical oxygen demand removal efficiency of 70.86% is 16.7% higher than that of pure ozone and 14.67%, 7.21% and 3.58% higher than that of three commercial catalysts, respectively. It also improved the efficiency of ozonation for phenol by 33%. The MCOC was characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy–energy-dispersive spectroscopy, transmission electron microscopy and other methods. The results demonstrated that the spherical metal nanoparticles had sizes ranging from 3 nm to 7 nm and that crystals of Fe2O3 and Fe3P were observed. The study showed that the MCOC promoted the production of more hydroxyl radicals and superoxides from ozone, which attack organics. The oxygen vacancies of the catalyst were also investigated. It was proved that the Lewis acid sites on the surface of metal oxides are the active centers of ozone decomposition. Therefore, this work provides a new method for the synthesis of multi-metal nanocomposites and expands the application of biosynthetic nanomaterials.

Novel Ni–Al nanosheet catalyst with homogeneously embedded nickel nanoparticles for hydrogen-rich syngas production from biomass pyrolysis

In this work, an innovative porous Ni–Al nanosheet catalyst synthesized by a homogeneous precipitation method via urea hydrolysis is proposed for enhanced hydrogen-rich syngas production from catalytic pyrolysis of rice husk in a two-stage reactor system. The role of synthesis temperature in modulating the crystalline composition, particle size, metal dispersion as well as porous structure of resulting Ni–Al nanocomposite has been delineated. The results indicate that fine spherical NiO and metallic Ni0 nanoparticles are homogeneously embedded in amorphous Al2O3 matrix for all Ni–Al catalysts, which also have developed bimodal micro/mesoporous structure with high surface areas (513–948 m2/g). Catalytic tests show that these highly active catalysts exhibit almost ten times higher hydrogen production rate (7.74–17.39 mmol/g biomass) and H2/CO molar ratio (1.96–2.74) than that in the absence of catalyst (0.56–1.64 mmol/g, 0.11–0.24) by tuning catalytic temperatures. The Ni–Al catalysts that with the presence of metallic Ni0 and developed porous structure exhibit higher catalytic activity and suppression of coke deposition through providing more active sites for catalytic cracking and reforming reactions, and rapid diffusion of intermediate products.

Dispersion state phase diagram of citrate-coated metallic nanoparticles in saline solutions

The fundamental interactions underlying citrate-mediated chemical stability of metal nanoparticles, and their surface characteristics dictating particle dispersion/aggregation in aqueous solutions, are largely unclear. Here, we developed a theoretical model to estimate the stoichiometry of small, charged ligands (like citrate) chemisorbed onto spherical metallic nanoparticles and coupled it with atomistic molecular dynamics simulations to define the uncovered solvent-accessible surface area of the nanoparticle. Then, we integrated coarse-grained molecular dynamics simulations and two-body free energy calculations to define dispersion state phase diagrams for charged metal nanoparticles in a range of medium’s ionic strength, a known trigger for aggregation. Ultraviolet-visible spectroscopy experiments of citrate-capped nanocolloids validated our predictions and extended our results to nanoparticles up to 35 nm. Altogether, our results disclose a complex interplay between the particle size, its surface charge density, and the ionic strength of the medium, which ultimately clarifies how these variables impact colloidal stability.

Influence of a planar metal nanoparticle assembly on the optical response of a quantum emitter

We develop an analytical framework to study the influence of a weakly intercoupled inplane spherical metal nanoparticle (MNP) assembly on a coherently illuminated quantum emitter (QE). We reduce the analytical expressions derived for the aforementioned generic planar setup into simple and concise expressions representing a QE mediated by a symmetric MNP constellation, by exploiting the symmetry. We use the recently introduced generalized nonlocal optical response (GNOR) theory that has successfully explained plasmonic experiments to model the MNPs in our system. Due to the use of GNOR theory, and our analytical approach, the procedure we suggest is extremely computationally efficient. Using the derived model, we analyse the absorption rate, resultant Rabi frequency, effective excitonic energy shift and dephasing rate shift spectra of an exciton bearing QE at the centre of a symmetric MNP setup. We observe that the QE experiences plasmon induced absorption rate spectral linewidth variations that increase in magnitude with decreasing MNP-QE centre separation and increasing number of MNPs. Our results also suggest that, parameter regions where the QE exhibits trends of decreasing linewidth against decreasing MNP-QE centre separation are likely to be associated with plasmon induced excitonic energy redshifts. Similarly, regions where the QE absorption rate linewidth tends to increase against decreasing MNP QE centre separation are likely to be accompanied by plasmon induced excitonic energy blueshifts. In both these cases, the magnitude of the observed red/blueshift was seen to increase with the number of MNPs in the constellation, due to enhancement of the plasmonic influence.

Endophytic Streptomyces laurentii Mediated Green Synthesis of Ag-NPs with Antibacterial and Anticancer Properties for Developing Functional Textile Fabric Properties.

Improvement of the medical textile industry has received more attention recently, especially with widespread of microbial and viral infections. Medical textiles with new properties, such as bacterial pathogens self-cleaning, have been explored with nanotechnology. In this study, an endophytic actinomycetes strain of Streptomyces laurentii R-1 was isolated from the roots of the medicinal plant Achillea fragrantissima. This is used as a catalyst for the mediated biosynthesis of silver nanoparticles (Ag-NPs) for applications in the textile industry. The biosynthesized Ag-NPs were characterized using UV-vis spectroscopy, Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), and X-ray Diffraction (XRD), which confirmed the successful formation of crystalline, spherical metal nanoparticles. The biosynthesized Ag-NPs exhibited broad-spectrum antibacterial activity. Our data elucidated that the biosynthesized Ag-NPs had a highly cytotoxic effect against the cancerous caco-2 cell line. The selected safe dose of Ag-NPs for loading on cotton fabrics was 100 ppm, regarding their antibacterial activity and safe cytotoxic efficacy. Interestingly, scanning electron microscope connected with energy dispersive X-ray spectroscopy (SEM-EDX) of loaded cotton fabrics demonstrated the smooth distribution of Ag-NPs on treated fabrics. The obtained results highlighted the broad-spectrum activity of nano-finished fabrics against pathogenic bacteria, even after 5 and 10 washing cycles. This study contributes a suitable guide for the performance of green synthesized NPs for utilization in different biotechnological sectors.

Width of the surface plasmon resonance line in spherical metal nanoparticles

Width of the surface plasmon resonance line in spherical metal nanoparticles

Plasmons in two-dimensional lattices of near-field coupled nanoparticles

We consider plasmonic metasurfaces constituted by an arbitrary periodic arrangement of spherical metallic nanoparticles. Each nanoparticle supports three degenerate dipolar localized surface plasmon (LSP) resonances. In the regime where the interparticle distance is much smaller than the optical or near-infrared wavelength associated with the LSPs, the latter couple through the dipole-dipole interaction and form collective plasmonic modes which extend over the whole metasurface. Within a Hamiltonian model which we solve exactly, we derive general expressions which enable us to extract analytically the quasistatic plasmonic dispersion for collective modes polarized within the plane and perpendicular to the plane of the metasurface. Importantly, our approach allows us not only to consider arbitrary Bravais lattices, but also non-Bravais two-dimensional metacrystals featuring nontrivial topological properties, such as, e.g., the honeycomb or Lieb lattices. Additionally, using an open quantum system approach, we consider perturbatively the coupling of the collective plasmons to both photonic and particle-hole environments, which lead, respectively, to radiative and nonradiative frequency shifts and damping rates, for which we provide closed-form expressions. The radiative frequency shift, when added to the quasistatic dispersion relation, provides an approximate analytical description of the fully retarded band structure of the collective plasmons. While it is tempting to make a direct analogy between the various systems which we consider and their electronic tight-binding equivalents, we critically examine how the long-range retarded and anisotropic nature of the dipole-dipole interaction may quantitatively and qualitatively modify the underlying band structures and discuss their experimental observability.

The thermal lens effect on laser heating of a metal nano-sphere particle immersed in oil

In this work, we revise the model describing laser heating of a spherical metallic nanoparticle (NP) immersed in transparent oil. We study the generated temperature non-uniformity of the ambient medium and its effect on the propagation of the laser beam. Thus, the model describes the influence of thermal non-uniformity on scattering and absorption of light by the heated particle. Recently, different aspects of the heating of NPs by a laser beam have been actively researched. Some experimental works demonstrated an enigmatic dependence of the effective scattering cross-section of the heated particle on the intensity of the laser beam, illuminating it. The authors of these works labeled the observed effects as “saturation,” and “reverse saturation.” In this paper, we show that the propagation of the incident laser beam in a non-uniform oil can by itself be the source of both “saturation” and “reverse saturation” els effects.

Silver Nanoparticle Trypsin Corona Formation and the Impacts on Enzymatic Potency

Herein, the protein corona formation on the spherical metal nanoparticles was studied to investigate the possible effects of silver nanoparticles (AgNPs) on the protein activity and conformation. The digestion capability of trypsin was monitored on the human serum albumin (HSA) at standard enzymatic hydrolysis conditions in the absence and presence of different concentrations of AgNPs. So the ratio of enzyme:HSA, the duration and the temperature of nanoparticle treatment were evaluated. The activity of treated trypsin molecules, in the form of hard (HC) and soft corona (SC) were studied using sodium dodecyl sulfate poly acrylamide gel electrophoresis (SDS-PAGE), and nano liquid chromatography electrospray (ion trap) mass spectrometry (nano LC-ESI/MS, LC-ESI/MS). In addition the characteristics of silver nanoparticles and the formation of HSA corona on the nanoparticle surface were monitored using ultra-violet/visible spectroscopy (UV-Vis), Dynamic light scattering (DLS) and fluorescence spectrophotometry. The results demonstrated that not only the corona formation but also the AgNPs/Trypsin interaction, decreases the hydrolysis potency of trypsin. Furthermore, the encountering of the AgNPs/HSA could influence both nanoparticles and HSA molecule features. Accompanied with fluorescence study, that the HSA secondary structure. Also LC-ESI/MS data revealed the most affected HSA triptics have α-helix structure.

Protein Assisted Fabrication of Metallic Nanorings and Spherical Nanoparticles for Electrocatalytic and Organocatalytic Applications

Inspiration from nature has driven the development and application of greener nanomaterials prepared using biotemplates in the field of nanoscience. Compared to traditional chemical routes, bioinspired nanomaterial synthesis has the advantage of mild synthetic conditions such as aqueous environment, ambient temperature, and no requirement for organic capping agent. In addition, the structures of some biomolecules make it possible to fabricate nanomaterials with complex and interesting morphology that are difficult to achieve through chemical methods. In this study, tobacco mosaic virus coat protein (TMV cp) was investigated as a versatile template to mediate the synthesis of nanorings and spherical nanoparticles under neutral and alkaline conditions, respectively. While the prepared silver nanorings displayed superior selectivity (95% Faradaic Efficiency) and stability of catalyzing CO2 electroreduction (CO2 RR) compared to free silver nanoparticles prepared by chemical methods, the platinum nanorings showed excellent electrocatalytic activity for hydrogen evolution reaction (HER). Spherical nanoparticles synthesized under alkaline conditions (Pt, Pd and Au NPs) were also investigated for their catalytic behavior towards organic transformations such as 4-nitrophenol reduction and alkyne hydrogenation.

PHOTODEPOSITION SYNTHESIS AND CHARACTERIZATION OF Ag/ZnO NANOCOMPOSITES FOR PHOTODEGRADATION OF METHYLENE BLUE AND METHYL ORANGE

In this work, Ag nanoparticles were deposited on hierarchical ZnO nanostructure flowers by photodeposition method. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) coupled with energy dispersive spectrometer (EDS), Fourier transform infrared (FTIR) spectrometry and X-ray photoelectron spectroscopy (XPS). Photocatalytic performance of the asprepared ZnO and Ag/ZnO nanocomposites was investigated through photodegradation of methylene blue (MB) and methyl orange (MO) as cationic and anionic dye models under UV light irradiation. The analytical results showed that the spherical metallic Ag nanoparticles with 10–12 nm diameter were deposited on nanosheets as petals of hierarchical ZnO nanostructure flowers. The photodegradation efficiencies of MB and MO by Ag/ZnO nanocomposites were higher than that by pure ZnO sample because of the electronic transfer through Ag/ZnO heterojunctions.

The influence of gold nanoparticles on reduction of [Co(NH3)5Br](NO3)2 by iron(II)

Variable size (50–220 nm), intrinsically mono-dispersed, single shaped gold (Au) nanomaterials was made showing man-made replica of nature’s flower like structures associated with vast kinetic activity. 220 nm Au nanopopcorns and nanoflowers have been synthesized simply by controlling the concentration of the reducing agent and reaction time. Other spherical metal nanoparticles made of platinum (Pt), Au and palladium (Pd) also show catalytic effect on the rate of the reduction of [Co(NH3)5Br](NO3)2 by iron(II), which was taken as a model reaction. Their activity increases with increased loading. Catalytic activity follows the order: Pt > Au > Pd, which has been compared with that of the various Au nano-formations (popcorns and flowers). The larger Au nanopopcorns and nanoflowers induce appreciable reduction in the rate of the reaction compared to the effects of similar concentrations of the spherical nanoparticles. Catalytic activity follows the order: Pt > Au > Pd, which has been compared with that of the various gold nano-formations (popcorns and flowers). The larger gold nanopopcorns and nanoflowers induce appreciable reduction in the reaction rate compared to the effects of similar concentrations of the spherical nanoparticles.

Biocompatible nanoparticles production by pulsed laser ablation in liquids

The preparation of spherical metallic nanoparticles (NPs), in the range of 10–100 nm, using pulsed laser ablation in water has particular interest in many scientific fields. The fast released laser energy to the solid metal in water produces plasma at the solid-liquid interface generating NPs in solution. The size distribution and the solution concentration depend by many parameters concerning the laser source (wavelength, pulse energy, pulse duration), the irradiation conditions (target depth in water, focal spot, repetition rate, irradiation time), and the medium where the ablation occurs (water, solution concentration, presence of surfactants). Optimal conditions can be found to control the average particle size, the size distribution, and the coalescence effect. A study of the NPs dependence from the ns pulsed Nd:YAG laser, irradiating metals in water is presented, discussing also the physical characterization of the produced NPs employing microscopy and optical analyses.

Second-Harmonic Generation from a Quantum Emitter Coupled to a Metallic Nanoantenna

We use time-dependent density functional theory and a semiclassical model to study second-harmonic generation in a system comprising a quantum emitter and a spherical metallic nanoparticle, where t...

Photoluminescence of molecules near metal nanoparticles with a dielectric shell

The article discusses the issues of modifying the photoluminescence intensity of quantum dipole emitters (molecules, quantum dots (nanocryslalls)) located near metal spherical nanoparticles with a dielectric shell. It is shown that by specifying the optimal configuration of a nanoparticle with a shell and the position of the emitter, it is possible to create the conditions, under which an increase in the photoluminescence intensity can be greater than in the case of the same nanoparticle without a shell.