Nanoparticles Of Different Shapes Research Articles

Shape dependent catalytic activity of unsupported gold nanostructures for the fast reduction of 4-nitroaniline

A one step seed mediated strategy is adopted here for synthesizing spherical, dog bone and rod shaped gold nanoparticles. Usually noble metals decorated by supporting materials are used for chemical catalysis. Here, a variety of unsupported gold nanoparticles (spherical, dog bone and rod shaped) originating from the same growth procedure are used for the catalytic reduction of para-nitroaniline (4-NA). The product obtained, para-phenylenediamine, is an important material, especially in the field of dye industry. The reaction kinetic values were analyzed based on to the Langmuir–Hinshelwood (LH) mechanism. A comparison of the rate constants obtained for gold nanoparticles of different shapes with almost similar volume pointy that gold nanorods are superior to that of spherical and dog bone like nanoparticles. The turnover frequency obtained here is high compared to other reported results and is found to be sensitive to the shape of the nanoparticles.

Nanoparticle shape effects on thermal-hydraulic performance of boehmite alumina nanofluid in a horizontal double-pipe minichannel heat exchanger

The aim of the present study is an investigation of the impact of nanoparticle shape on the hydrothermal characteristics of boehmite alumina nanofluid flowing through a horizontal double-pipe minichannel heat exchanger. Boehmite alumina (γ-AlOOH) nanoparticles of different shapes (i.e. cylindrical, brick, blade, platelet, and spherical) are dispersed in a mixture of water/ethylene glycol as the nanofluid. The effects of the Reynolds number and nanoparticle concentration on the heat transfer rate, overall heat transfer coefficient, effectiveness, pressure drop, pumping power, and performance index are numerically analyzed for different nanoparticle shapes. The results reveal that the nanofluids containing cylindrical and platelet shaped nanoparticles have the highest and lowest thermal conductivity, respectively. Additionally, it is found that the highest and lowest viscosity belong to the nanofluids with platelet shaped and spherical nanoparticles, respectively. Furthermore, it is depicted that, among the considered nanoparticle shapes, platelet shaped demonstrates better heat transfer characteristics, while performance index of the heat exchanger for nanofluid containing spherical nanoparticles is higher. Finally, it is inferred from the obtained results that the increase of Reynolds number and nanoparticle concentration result in a higher heat transfer rate, overall heat transfer coefficient, pressure drop, and pumping power and a lower performance index.

Plasmon sensing and enhancement of laser prepared silver colloidal nanoplates

Sensing properties of noble metal colloids are strongly dependent on their size, shape, composition and distribution so that the individuation of suitable strategies for synthesis and modification is one of the facts in experimental designing. In this paper we show that silver nanoplates can be obtained through a simple two-step process, involving the formation of seeds generated by laser ablation of a metal target in an aqueous solution, followed by addition of H2O2 under light irradiation without additional silver ions. These experiments open up the possibility to obtain metal nanoparticles of different shapes directly in a colloidal state without the action of polluting agents. Nanoplates show excellent plasmon sensitivity and SERS enhancement factor.

Gold nanoparticles of different shape for bicolor lateral flow test

Spherical gold nanoparticles are the most commonly used marker in lateral flow assays. However, the widespread practice of using identical coloration for the test and control zones of test strips can lead to erroneous interpretations of the assay's results. We propose an immunochromatographic test strip with lines of different colors. For this purpose, gold nanoparticles of different shapes were used, namely blue nanoflowers in the test zone and red gold nanospheres in the control zone. A detailed synthesis procedure for nanoparticles and their conjugates is considered and design parameters for optimal results are described. For the first time, nanoparticles of different shapes have been combined in the test strip with indirect labeling of specific antibodies (via their interaction with labeled secondary antibodies). Using the T-2 toxin (T2T) as an example, an instrumental detection limit of 30 pg/ml and a working range 0.06–0.9 ng/mL were achieved in an analysis of water-organic corn extracts.

Transport and Kinetic Effects on the Morphology of Silver Nanoparticles in a Millifluidic System

This work investigates the synthesis of silver nanoparticles of different shapes using silver nitrate as a precursor and ascorbic acid as a reducing agent in different reactors. The main focus of this work is to study the effect of capping agent concentrations and ratios of reducing agent to precursor concentrations (reactant ratios) on the shape and size of the nanoparticles synthesized. Three reactor configurations, namely, batch, straight millichannel, and spiral millichannel, are considered to study the transport effect on the morphology of silver nanoparticles synthesized. The kinetic effect on the particle morphology is studied by changing the capping agent concentrations and reactant ratios. It is shown that these variables play an important role in determining the nanoparticle shape and size. In this work, spherical nanoparticles (30–60 nm), triangular plates (80–200 nm), nanorods (130–150 nm), and bent wires (130–150 nm) morphologies are synthesized by controlling thermodynamic and kinetic parame...

Shaped Fe2O3 nanoparticles – Synthesis and enhanced photocatalytic degradation towards RhB

Iron oxide nanoparticles of different shape were synthesized via an ion-mediated hydrothermal route. The addition of Zn2+ and Al3+ to the reaction system is no doubt the reason for the formation of hematite with cubic and disc structures, respectively. The growth mechanism of iron oxides is proposed. The morphology of the obtained nanostructures was analyzed by SEM and HR-TEM. The phase identification was performed by XRD and FTIR spectroscopy. Nanopowders were characterized by optical and zeta potential PZ measurements. The overall density of hydroxyl groups depends on the crystal structure and crystal faces. Placing oxides in the Rhodamine B RhB solution reduces the potential value PZ. The observed changes are the most pronounced for discs (ΔPZ = 16.2 mV) and the least pronounced for cubes (ΔPZ = 5.5 mV). A significant degree of adsorption of the dye on the surface of the discs, which confirms the presence of a significant number of hydroxyl groups responsible for surface activity. The photocatalytic activity of the obtained nanostructures investigated by photodecomposing RhB can be improved by applying H2O2 as an electron trap. Cyclic photodegradation experiments show that iron oxides with variously exposed planes can be used multiple times without losing their photocatalytic properties. Discs exhibited the most desirable photocatalytic behavior. Based on the performed addition of hydrogen peroxide, it seems that the shape of the particles affects the diffusion of H2O2 at the surface.

Grain refinement, texture, and mechanical properties of a magnesium alloy after radial-shear rolling

Microstructure (including its uniformity), texture, and mechanical properties of Mg-Al-Zn-Mn alloy billets after radial-shear rolling (RSR) were investigated. RSR with the temperature in the interval 420–140 °C and true strain up to 2.63 was shown to lead to grain refinement down to 1.5–3.5 μm (as determined by optical microscopy). The microstructure was found to be reasonably uniform over the transversal cross-sections of the billets. The transmission electron microscopy analysis also revealed submicron sized grains and the formation of two types of particles: Mg17Al12 particles 300–500 nm in size and MgAl nanoparticles of different shapes 20–40 nm in size. Increments in strain and step-wise decrease in deformation temperature with the number of RSR passes was found to lead to a transformation of the initial basal texture to the prismatic texture. The RSR of the Mg-Al-Zn-Mn magnesium alloy was demonstrated to result in significant strength and good ductility owing to a fortunate interplay between fine grain structure and favorable texture promoting activity of non-basal slip systems.

Metastable vortex-like polarization textures in ferroelectric nanoparticles of different shapes and sizes

The dependence of the polarization texture topology in ferroelectric PbTiO3 nanoparticles, embedded in a dielectric matrix, on the particle shape and size was investigated with a time-dependent Landau-Ginzburg-Devonshire approach combined with coupled-physics finite-element-method based simulations. Particle shapes belonging to the superellipsoidal family were probed, including octahedral, cubic, and intermediate geometries. For each shape, a parametric sweep of particle sizes ranging from 2 to 40 nm was conducted, revealing a general trend for the texture transformations from a monodomain, through a vortex-like, to a multidomain state, as the size increases. Critical particle sizes for the texture instabilities were found to be strongly dependent on the particle shape, with octahedral particles undergoing transitions at much larger volumes, compared to the cubic particles. Furthermore, for each of the considered non-spherical shapes of appropriate size, it was possible to obtain multiple vortex-like textures whose paraelectric cores are aligned with every rotational axis of the particle point symmetry group. The shape-dependent metastability of the vortex-like textures opens up new avenues for controlling polarization at the nanoscale in a variety of technological applications.

Particle Shape Effects in the Extinction Spectra of Gold and Silver Nanoparticles

Particle shape effects in the absorption and scattering spectra of gold and silver nanoparticles are studied for optical-range radiation. Numerical calculations of extinction cross section are performed using the FDTD approach for particles of three shapes: disks, triangular prisms, and triradial-base prisms. It is established that the spectra of nanoparticles of different shapes differ qualitatively even if they are of the same characteristic dimensions. The obtained results can be used to develop a spectroscopic procedure for determining the shape of metallic nanoparticles and producing quantitative estimates of their characteristic dimensions.

Synthesis and pH-dependent assembly of isotropic and anisotropic gold nanoparticles functionalized with hydroxyl-bearing amino acids

In recent years, the synthesis of gold nanostructures of controllable shapes and dimensions has become a subject of intensive and interesting studies. Especially, anisotropic gold nanostructures such as nanoplates, nanoribbons, nanoprisms and nanorods have attracted much attention due to their striking optical properties and promising applications in electronics, photonics, sensing and biomedicine. Keeping this in mind, in the present report, an unprecedented, facile and one pot synthesis of isotropic (spherical) and anisotropic (triangular, pentagonal, hexagonal, rod shaped) gold nanomaterials via pH controlled shape modulation using hydroxyl moeity containing α-amino acids (Serine, Threonine, Tyrosine) as both reducing and capping agents is reported. The synthesized nanostructures have been further characterized by UV–Vis spectroscopy and transmission electron microscopy. It was deduced from these studies that pH played a key role in the anisotropic growth of gold nanostructures. These gold nanoparticles can be further used for applications in biosensing, plasmonics, and electrocatalysis and others involving surface enhanced raman scattering. This study is therefore, important from the point of view of using amino acids for the synthesis of gold nanoparticles of different shapes and sizes leading towards the development of inventive biosensors and biocompatible nanoconstructs.

Inkjet-Printed Multiwavelength Thermoplasmonic Images for Anticounterfeiting Applications.

Inkjet printing of thermoplasmonic nanoparticles enables instantaneous, large-area heat pattern generation upon light illumination from distance. By printing multiple metal nanoparticles of different shapes overlaid, we can fabricate multiwavelength thermoplasmonic images, which generate different heat patterns from a single printed image depending on the wavelength choice of light. In this work, we propose a novel multiwavelength thermoplasmonic image printing process that can be used for anticounterfeit technology. With this technology, "printed thermoplasmonic labels" allow fully secured anticounterfeit inspection procedure. Input stimulus of near-infrared or infrared light illumination and output signal reading of thermal patterns can be both completely invisible. Wavelength selective photothermal effect also enables the encryption of the contained information, which adds more complexity and thus higher security.

Room temperature synthesis of polyvinyl alcohol stabilized palladium nanoparticles: Solvent effect on shape and electro-catalytic activity

Palladium nanoparticles have been synthesized at room temperature, 25±.5°C by the reduction of K2PdCl4 using biocompatible polymer polyvinyl alcohol (PVA) as reducing and stabilizing agent in water and aqueous dimethyl formamide (DMF) media with varying composition of DMF. The effect of variation of composition of aqueous DMF on growth, morphology and size of palladium nanocrystals is explained. Different aqueous DMF mixtures furnish palladium nanoparticles of different shapes like triangular plates, cuboids, hexagon with different average edge length between (3–30 nm) indicating preferential interaction and blocking of DMF to some specific planes of nanocrystals leading to various shapes. The synthesized nanoparticles have been characterized by different spectroscopic, microscopic and electro-analytical studies like cyclic voltammetry (CV), chronopotentiometry (CP) and chronoamperometry (CA). The increase in electro-catalytic activity is found to decrease with the increased size of the embedded crystallites deposited on the support constituting the electrodes and hence on the precursor medium. The same order of the studied electrodes is found from mole normalized peak current density values (Amol−1Pd) in CV, transition time in CP and steady current density values in CA, on increasing the content of DMF in the aqueous DMF solvent system as expected. The outcomes are explained on the basis of the crystallite size, morphology of the surface, unequal development of certain planes and purity of the products as guided by the rate of nucleation and growth of the particles formed in different media.

The structure of coordination precursors as an effective tool for governing of size and morphology of ZnS and ZnO nanoparticles

The zinc sulphide and zinc oxide micro- and nanoparticles of different shapes were synthesized from the five zinc coordination precursors, via controlled thermal decomposition process. The precursors were synthesized from zinc thiocyanate and N-donor ligands (2-aminopyrimidine, 1H-1,2,4-triazole and hexamethylenetetraamine), and they possessed different molecular and crystal structures (confirmed by X-ray crystallographic and spectroscopic studies). The proper set of parameters of precursors conversion process allows producing of ZnS in cubic (sphalerite) and hexagonal (wurtzite) form, as well as ZnO in hexagonal form. The relationship between the particles geometry (size and morphology) and the precursor structure, as well as the parameters of thermal conversion process was investigated.

Absorption and Scattering of Light by Silver and Gold Nanodisks and Nanoprisms

We study the influence of the shape of silver and gold nanoparticles on the spectra of absorption and scattering of the optical-range electromagnetic radiation. We perform numerical calculations of the cross sections of absorption and scattering of light on the basis of the FDTD method for the particles having the shape of a disk and a triangular prism. We establish that the positions of plasmon resonance peaks and the spectral distributions of intensities differ significantly for nanoparticles of different shapes even when the characteristic sizes of the particles are equal. The calculations carried out thus demonstrate that, along with the size and material of the plasmonic particle, its shape is yet another factor that essentially determines its optical features. The results of the study can be utilized in the development of the spectroscopic method of determining the shape of the metal nanoparticles and the quantitative estimate of their characteristic sizes.

Dynamic morphogenesis of dendritic structures formation in hen egg white lysozyme fibrils doped with magnetic nanoparticles

In this research, the dynamic process of aggregation that forms microflower morphology in solution of lysozyme amyloid fibrils doped with spherical or spindle-like magnetic nanoparticles during the process of drying as well as their final microstructures were investigated. The prepared lysozyme amyloid fibrils as well as their mixtures with in-lab synthesized magnetic particles, which were prepared by adding the nanoparticles to the fibrils solution after the process of fibrillation was done, were characterized using brightfield trans-illumination-mode optical microscope, atomic force microscopy (AFM) and scanning electron microscope (SEM). Brightfield optical imaging bases upon photoabsorptive property of the fibrils-nanoparticle composites clearly reveals the morphological features in microscale, and additionally, for the in vivo, live action of the time-dependent process of self-assembly of such composites composed of fibrillary structure incorporated with magnetic particles was optically elucidated at ambient temperature. Moreover, while results of AFM reveal delicate and peculiar association of fibrils with magnetic nanoparticles of different shapes, SEM images illustrate a stark difference in fine detailed final morphology of microstructures associated with spherical and spindle-like nanoparticles. Our results indicated that the interaction between fibrils solution and the nanoparticles commence right after mixing, the dynamic process of forming dendritic structure resembling microflower morphology is on the order of minutes, and its final structure is highly dependent on the shape of magnetic nanoparticles.

Synthesis of anisotropic silver nanoparticles using silk fibroin: characterization and antimicrobial properties

In the present investigation, anisotropic silver nanoparticles (AgNPs) were synthesized using silk fibroin (SF) obtained from Bombyx mori silk without any reducing agent under UV-B environment. The UV-visible (UV-vis) spectra of the SF-AgNPs colloids showed strong localized surface plasmon resonance (LSPR) in the range of 441–451 nm along with additional peaks at different wavelengths confirming the formation of anisotropic AgNPs. The X-ray diffraction (XRD) study revealed metal silver with face-centered cubic (FCC) crystal structure. The transmission electron microscopy (TEM) images proved that the biogenic synthesis route is suitable to produce silver nanoparticles of different shapes. These biogenic anisotropic AgNPs showed enhanced antibacterial activity against tested human pathogens compared with spherical shaped AgNPs.

Shape effects of nanoparticles on the squeezed flow between two Riga plates in the presence of thermal radiation

This paper aims to explore the flow of water saturated with copper nanoparticles of different shapes between parallel Riga plates. The plates are placed horizontally in the coordinate axis. Influence of the linear thermal radiation is also taken into account. The equations governing the flow have been transformed into a nondimensional form by employing a set of similarity transformations. The obtained system is solved analytically (variation-of-parameters method) and numerically (Runge-Kutta scheme). Under certain conditions, a special case of the model is also explored. Furthermore, influences of the physical quantities on velocity and thermal fields are discussed with the graphical aid over the domain of interest. The quantities of engineering and practical interest (skin friction coefficient and local rate of heat transfer) are also explored graphically.

Surface Engineered Nanoparticles: Considerations for Biomedical Applications

The development of reproducible methods for the fabrication of nanoparticles in the 21st century is a major scientific achievement. Currently, there are many well‐established methods for the production of nanoparticles of different shapes, sizes, and compositions. Along with these advancements in nanotechnology, nanoparticles have emerged as excellent tools for a diverse range of applications and have become a focus of research globally. With fundamental research being established, efforts are now being directed toward intelligently designed nanoparticles in which the properties of the nanomaterial are finely tuned depending on the application of interest. Usually, this involves the functionalization of the nanoparticle surface with a ligand. In this review, the impact of nanoparticle surface chemistry is discussed as it applies to biological systems.

Thermo-responsive PNIPAM-metal hybrids: An efficient nanocatalyst for the reduction of 4-nitrophenol

Micron size thermoresponsive cross-linked polymeric microgels of poly(N-isopropylacrylamide) (PNIPAM) are used as “microreactor” for embedding metal nanoparticles of different shapes. Using a simple and robust method, we have synthesized various polymer–metal hybrid nanostructures incorporated with Au nanorods (AuNR), Au nanospheres (AuNS) and Ag nanospheres (AgNS). These hybrid nanostructures have been characterized by transmission electron microscope (TEM), UV–vis spectroscopy, dynamic light scattering (DLS) and static light scattering (SLS) followed by their catalytic activity. TEM studies directly confirmed the mondispersity of synthesized hybrid microgels and stability of the embedded metal nanoparticles within the microgels. Optical studies confirmed the presence of respective absorption bands that correspond to AuNS, AgNS and AuNR respectively. Extensive DLS studies demonstrated that although these hybrid microgels preserve their thermoresponsive properties, i.e their hydrodynamic radius decreased with increasing temperature, their thermosensitivity were comparatively lesser than pure PNIPAM microgels. Combining with studies using static light scattering, we further found that AuNS and AgNS were inhomogeneously distributed within microgels where the majority of the nanoparticles present within the loosely cross-linked shell. On the other hand AuNR were distributed more homogeneously within the microgels. Catalytic performance of various nanostructures loaded onto PNIPAM microgel beads were evaluated by studying the catalytic reduction of 4-nitrophenol. Complete catalytic conversion using AgNS occurred in ∼30min with a first-order rate constant of 0.159min−1 having a 7min induction period. On the other hand no induction period was observed for AuNS and AuNR and the reaction completed in 3–4min with a first-order rate constant of 1.607min−1 and 1.627min−1 respectively. Further, PNIPAM-AuNS and PNIPAM-AuNR possess better catalytic activity as well as recyclability compared to that of PNIPAM-AgNS.

A facile synthesis of broad plasmon wavelength tunable silver nanoparticles in citrate aqueous solutions by laser ablation and light irradiation

A complete light based synthesis of silver nanoparticles of different shapes exhibiting strong and broad band plasmon resonances is demonstrated in aqueous solutions of single reagent tri-sodium citrate (TSC). This method involves synthesis of almost spherical nanoparticles using liquid phase pulsed laser ablation (LPPLA) followed by their photo-mediated shape transformation into triangular nanoplates by visible light irradiation. UV–vis spectroscopy and Mie theory based analytical calculations show that this method can produce high concentrations of nanoparticles at optimum TSC concentration. LPPLA method is shown to be potential for producing relatively smaller size, isolated spherical silver nanoparticles at optimum TSC concentration without aid of strong reducing agents like borohydrides. This method has also resulted interconnected nanoparticle networks in pure water or at very low TSC concentrations. These isolated spherical nanoparticles were further shown to act as seed particles for high yield synthesis of nanoplates. The concentration of TSC played a vital role in producing both highly stable spherical nanoparticles and their photo-mediated shape transformation into triangular nanoplates. At the optimum TSC concentration of about 10mM, pH about 7.5 and visible light irradiation of about 24h, the produced triangular nanoplates have shown strong plasmon absorption in visible to near NIR region, useful for solar light harvesting applications. Further during the light irradiation, presence of additional silver ions in the nanoparticle solution initially increased the growth of spherical nanoparticles which finally resulted in high yield formation of triangular nanoplates.