Morphology Of Au Nanoparticles Research Articles

Unexpectedly high thermal stability of Au nanotriangle@mSiO2 yolk-shell nanoparticles.

The shape of Au nanoparticles (NPs) plays a crucial role for applications in, amongst others, catalysis, electronic devices, biomedicine, and sensing. Typically, the deformation of the morphology of Au NPs is the most significant cause of loss of functionality. Here, we systematically investigate the thermal stability of Au nanotriangles (NTs) coated with (mesoporous) silica shells with different morphologies (core-shell (CS): Au NT@mSiO2/yolk-shell (YS): Au NT@mSiO2) and compare these to 'bare' nanoparticles (Au NTs), by a combination of in situ and/or ex situ TEM techniques and spectroscopy methods. Au NTs with a mesoporous silica (mSiO2) coating were found to show much higher thermal stability than those without a mSiO2 coating, as the mSiO2 shell restricts the (self-)diffusion of surface atoms. For the Au NT@mSiO2 CS and YS NPs, a thicker mSiO2 shell provides better protection than uncoated Au NTs. Surprisingly, the Au NT@mSiO2 YS NPs were found to be as stable as Au NT@mSiO2 CS NPs with a core-shell morphology. We hypothesize that the only explanation for this unexpected finding was the thicker and higher density SiO2 shell of YS NPs that prevents diffusion of Au surface atoms to more thermodynamically favorable positions.

Serially diluting centrifugal microfluidics for high-throughput gold nanoparticle synthesis using an automated and portable workstation

We report a novel high-throughput (HTP) synthetic platform for gold (Au) nanoparticles (NPs), consisting of a HTP centrifugal microfluidic device and a portable automatic workstation. The proposed platform is capable of performing 60 different reactions, and can produce a variety of Au NP types on a single device in one run without any human interference. In the microdevice, a zigzag aliquoting microchannel was designed to facilitate the loading of each reactant in a single injection shot. Besides, we developed serially diluting microfluidic structures by pairing the ascorbic acid (AA) solution-loaded microchannel with the water-loaded microchannel, and gradually varying the depths of the two microchannels in reverse, thereby generating the serially diluted concentration-gradient of the AA solution. The morphology of the Au NPs in the triplicate experiments changed from spherical to triangle/ quadrangular/ polyhedron to star shapes in the end, as the concentration of the reducing agent AA increased. Among them, the hexapod star morphology of Au NP was the most effective substrate for surface-enhanced Raman spectroscopy (SERS). In addition, we constructed a portable automatic workstation, which enables on-demand injection of the designated solution onto a microfluidic centrifugal device, the programmed chip rotation, and the multiplex NP synthesis on a chip in a completely automatic manner. Therefore, we could obtain the desired nanomaterials using a HTP automatic screening platform that is cost-, time-, and labor-effective.

Controlled Synthesis of Au Nanoparticles by Modified Polyol Methods: Determination of Their Size, Shape, and Crystal Structure

We successfully prepared Au nanoparticles using the modified polyol methods and design of experiments. The desirable crystal structure and particle size of Au nanoparticles with various kinds of polyhedral and spherical shapes as well as various kinds of their morphologies or complete and rough spherical crystal surfaces were experimentally predicted in TEM and XRD measurements according to the theoretical calculation and data. The fine crystal formation of Au nanostructures by modified polyol methods with EG, PVP, and NaBH4 is of great importance to their practical applications. Our research shows that the critical nucleation, growth, and formation of sizes, shapes, and morphologies of Au nanoparticles were experimentally discussed in modified polyol methods and design of experiments. In this context, our particle size calculation can hold the greatest attraction for researchers in the field of nanoparticles.

Plasmonic Au‐Metal Oxide Nanocomposites for High‐Temperature and Harsh Environment Sensing Applications

Noble metal nanoparticles like Au have long been admired for their brilliant colour, significantly influenced by plasmon resonance. When embedded in metal oxides, they exhibit unique properties which make them an excellent choice for sensing in high-temperature and harsh environment atmospheres. In this review, the various morphologies of Au nanoparticles (AuNPs) used in combination with metal oxides for sensing gases at temperatures greater than 300 °C are discussed. Theoretical discussions on the plasmon resonance properties of AuNPs as well as computational techniques like finite difference time domain (FDTD), are often used for understanding and correlating their extinction spectra and are briefed initially. The sensing properties of AuNPs embedded on a metal oxide matrix (such as TiO2 , SiO2 , NiO etc) for quantifying multiple analytes are then elucidated. The effect of high temperature as well as gas environments including corrosive atmospheres on such nanocomposites, and the different approaches to comprehend them are presented. Finally, techniques and methods to improve on the challenges associated with the realization and integration such Au-metal oxide plasmonic nanostructures for applications such as combustion monitoring, fuel cells, and other applications are discussed.

A Theoretical Insight into Enhanced Catalytic Activity of Au by Multiple Twin Nanoparticles

Recently, it has been reported that the morphology of Au nanoparticles (NPs) affects the catalytic activity of CO oxidation; twin crystal NPs show higher activity for CO oxidation than single-crystal NPs. In this study, density functional calculations have been carried out to investigate the morphology effect of Au NPs using CO as a probe molecule. In the case of Au NPs with a size of more than 2 nm, CO adsorption energy on the Au NPs is mainly determined by a coordination number (CN) of adsorption sites. CO binding to a multiple twin NP with a size of about 1 nm is stronger than that on a single-crystal NP with the same size. A simple CN explanation cannot be applied to the enhancement of CO binding to the small multiple twin NP. This enhancement is related to a deformation of the NP structure before and after CO adsorption. It is suggested that the multiple twin NP with a size of less than 1 nm, which shows the deformation upon CO adsorption, contributes to the higher activity for CO oxidation.

“Green” seed-mediated synthesis and morphology of Au nanoparticles using β-cyclodextrin

Gold nanoparticles (NPs) with dendritic morphology were synthesized by a “green” seed-mediated approach in the presence of β-cyclodextrin (β-CD) as stabilizing biocompatible capping agent. First, 50 mL of an aqueous solution containing 5 mM of β-CD were prepared, to which a variable amount of HAuCl4 was added. The β-CD/Au molar ratio was monitored from 20 to 200. Optical properties, including Surface-Enhanced Raman Scattering (SERS) activity, of the synthesized structures were characterized by Raman and UV-vis spectroscopies. Morphology was studied by transmission electron microscopy (TEM). Samples prepared using this procedure presents an increase of their SERS signal with respect to samples without peak-rich morphology. Optimized nanodendrites were obtained at a β-CD/Au molar ratio of 100. Moreover, a growth mechanism is proposed to describe the β-cyclodextrin role in the synthesis of Au nanodendrites. The “green” seed-mediated synthesis technique used herein produces Au NPs with good biocompatibility pointing them out for biomedical applications.

Simple Method to Fabricate Au Nanoparticle-Decorated TiO2 Nanotube Arrays for Enhanced Visible Light Photocurrent**Supported by the National Natural Science Foundation of China under Grant Nos 11474215 and 21204058, and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

Au nanoparticle-decorated TiO2 nanotube arrays are prepared by a simple method, which is a thermal annealing thin gold film deposited on anodic oxidized TiO2 nanotube arrays. These electron microscope images present that Au nanoparticles are well dispersed within the wall and on the surface of the TiO2 nanotubes. Meanwhile, the morphologies of Au nanoparticles can be controlled by changing the thickness of the deposited gold film. Associated with the excitation of localized surface plasmon resonances, the prepared Au nanoparticle-decorated TiO2 nanotube arrays could work as visible light responsive photocatalysts to produce a greatly enhanced photocurrent density. By varying the initial gold film thickness, such Au nanoparticle-decorated TiO2 nanotube arrays could be optimized to obtain the highest photocurrent generation efficiency in the visible and UV light regions.

Systematic Control of Self-Assembled Au Nanoparticles and Nanostructures Through the Variation of Deposition Amount, Annealing Duration, and Temperature on Si (111).

The size, density, and configurations of Au nanoparticles (NPs) can play important roles in controlling the electron mobility, light absorption, and localized surface plasmon resonance, and further in the Au NP-assisted nanostructure fabrications. In this study, we present a systematical investigation on the evolution of Au NPs and nanostructures on Si (111) by controlling the deposition amount (DA), annealing temperature (AT), and dwelling time (DT). Under an identical growth condition, the morphologies of Au NPs and nanostructures drastically evolve when the DA is only slightly varied, based on the Volmer-Weber and coalescence models: i.e. I: mini NPs, II: mid-sized round dome-shaped Au NPs, III: large Au NPs, and IV: coalesced nanostructures. With the AT control, three distinctive ranges are observed: i.e., NP nucleation, Au NPs maturation and melting. The gradual dimensional expansion of Au NPs is always compensated with the density reduction, which is explained with the thermodynamic theory. The DT effect is relatively minor on Au NPs, a sharp contrast to other metallic NPs, which is discussed based on the Ostwald-ripening.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1084-z) contains supplementary material, which is available to authorized users.

Enhanced chemocatalytic reduction of aromatic nitro compounds by biosynthesized gold nanoparticles

A novel and eco-friendly green procedure was developed for the synthesis of Au nanoparticles using stem extract of Salvadora persica. This plant stem extract provides a favorable environment for the formation of small size and well dispersed Au nanoparticles within 15–30 nm diameter. The Au nanoparticles were characterized by UV–vis spectroscopy, XRD, HRTEM, SEM, EDX and FT-IR. The particle size and morphology of Au nanoparticles were also investigated at different stem extract concentrations. The results showed that lesser the concentration of stem extract, spherical and small will be the size of Au nanoparticles. The present research indicated that the green synthesized Au nanoparticles can be used as an effective catalyst for the chemocatalytic reduction of 4-NP to 4-AP. Various factors i.e. catalyst amounts and particle size and shape that affect the chemocatalytic reduction of 4-NP to 4-AP were also studied. The results showed that Au nanoparticles synthesized at 15 vol.% extract's concentration have strong chemocatalytic activity and reduced 4-NP only within 3 min. It may be due to the single spherical shape and small size of Au nanoparticles.

Localized Surface Plasmon Resonance in Au Nanoparticles Embedded dc Sputtered ZnO Thin Films.

The plasmonic behavior of metallic nanoparticles is explicitly dependent on their shape, size and the surrounding dielectric space. This study encompasses the influence of ZnO matrix, morphology of Au nanoparticles (AuNPs) and their organization on the optical behavior of ZnO/AuNPs-ZnO/ZnO/GP structures (GP: glass plate). These structures have been grown by a multiple-step physical process, which includes dc sputtering, thermal evaporation and thermal annealing. Different analytical techniques such as scanning electron microscopy, glancing angle X-ray diffraction, Rutherford backscattering spectrometry and optical absorption have been used to study the structures. In-situ rapid thermal treatment during dc sputtering of ZnO film has been found to induce subtle changes in the morphology of AuNPs, thereby altering the profile of the plasmon band in the absorption spectra. The results have been contrasted with a recent study on the spectral response of dc magnetron sputtered ZnO films embedded with AuNPs. Initial simulation results indicate that AuNPs-ZnO/Au/GP structure reflects/absorbs UV and infrared radiations, and therefore can serve as window coatings.

Impacts of Organic Stabilizers on Catalysis of Au Nanoparticles from Colloidal Preparation

Metal nanoparticles (NPs) from colloidal synthesis are advantageous in fundamental catalysis research because of their precisely controlled size and morphology but unfortunately are usually contaminated with residues from the organic stabilizer essentially required in the synthesis. These residues could modify the surface property and disturb the catalysis intrinsic to “clean” NPs. Herein, polyvinylpyrrolidone (PVP)-stabilized Au NPs (4.7 ± 1.0 nm) from colloidal synthesis were immobilized on SiO2 support and subjected to ultraviolet-ozone (UVO) treatment to remove the residues. Hydrogenation reactions of p-chloronitrobenzene (p-CNB) and cinnamaldehyde (CAL) were conducted to probe consequences of the stabilizer removal on the catalytic properties of Au NPs. Measurements by FTIR and XPS revealed a controlled removal and degradation of PVP according to the UVO-treatment duration. Careful HRTEM analysis disclosed that both the size and morphology of Au NPs remained unchanged after the UVO-treatment. Residua...

Preparation and spectral analysis of gold nanoparticles using magnetron sputtering and thermal annealing

Gold (Au) nanoparticles were prepared on Au-film-coated K9 glass and silicon substrates by direct current (DC) magnetron sputtering and thermal annealing treatment. The effects of substrate material, annealing temperature, and time on morphologies of Au nanoparticles were investigated, and the formation mechanism of Au nanoparticles was discussed. The experimental results indicate that silicon substrate is more suitable for the formation of Au nanoparticles. On a silicon substrate, Au nanoparticles formed with good spherical shapes at temperature over 700 °C. It was also found by spectral analysis that the field enhancement factor of the island-shaped Au particles was smaller than that of the granular Au particles; the better the spherical shape as well as the smaller the size and spacing of Au particles, the higher the light absorption rate; the absorption peak had a red shift with increasing particle size and spacing.

Colloidal dispersion of metal nanoparticles electrosterically stabilized with Carrageenan type κ and its application as hydrogel.

ABSTRACTIn this work Carrageenan type κ was used as electrosteric stabilizer in order to prepare a biocompatible colloidal dispersion of novel metal nanoparticles. Gold and silver nanoparticles were synthesized by reducing the metal precursor using sodium borohydride in presence of Carrageenan type κ. The growth mechanism of metal nanoparticles and stabilization behavior by Carrageenan type κ was analyzed by UV-Vis spectroscopy and transmission electron microscopy. The morphology and particle size distribution were also studied as a function of reaction parameters and the particle size was dependent of the pH of the reaction media. The Ag nanoparticles with sphere-like morphology and average size of 10 nm were obtained. The morphology of Au nanoparticles was strongly affected by the pH value resulting in particles with snake-like morphology at alkaline conditions. The UV-Vis spectra showed that Ag nanoparticles were highly stable at alkaline conditions and for long period of time. Au nanoparticles dispersion showed a better stability for long period of time at acidic conditions. The nanoparticles dispersion electrosterically stabilized were used to prepare hydrogels by poured into a plastic mold and frozen with liquid nitrogen and then lyophilized. The morphology and thermal stability of resulting composites were analyzed by using scanning electronic microscopy and differential scanning calorimetry respectively. The degradation temperature of Carrageenan type κ was increased due to the presence of metal nanoparticles.

Spectral response of nanocrystalline ZnO films embedded with Au nanoparticles

The optical response of a two-phase composite consisting of Au nanoparticles (AuNPs) in a nanocrystalline ZnO thin film matrix has been systematically studied and analyzed by the Bergman–Milton spectral density formalism. The real and imaginary parts of the effective dielectric function exhibited anomalous dispersion and absorption, respectively, at the characteristic localized surface plasmon resonance (LSPR) wavelength. A multilayer structure consisting of two AuNP–ZnO composite films separated by a thin ZnO film displayed a twofold increase in the absorption at LSPR (with negligible change in FWHM), which is attributed to the increase in the number density of the AuNPs resulting from the nanocrystalline nature of the ZnO film. The results have been used to correlate the spectral density function to the morphology of AuNPs in a ZnO matrix.

Electrochemical Behavior of Gold Nanoparticles Modified Nitrogen Incorporated Tetrahedral Amorphous Carbon and Its Application in Glucose Sensing

Gold nanoparticles (NPs) with 10-50 nm in diameter were synthesized on nitrogen incorporated tetrahedral amorphous carbon (ta-C:N) thin film electrode by electrodeposition. The deposition and nucleation processes of Au on ta-C:N surface were investigated by cyclic voltammetry and chronoamperometry. The morphology of Au NPs was characterized by scanned electron microscopy. The electrochemical properties of Au NPs modified ta-C:N (ta-C:N/Au) electrode and its ability to sense glucose were investigated by voltammetric and amperometric measurements. The potentiostatic current-time transients showed a progressive nucleation process and diffusion growth of Au on the surface of ta-C:N film according to the Scharifker-Hills model. The Au NPs acted as microelectrodes improved the electron transfer and electrocatalytic oxidation of glucose on ta-C:N electrode. The ta-C:N/Au electrode exhibited fast current response, a linear detection range of glucose from 0.5 to 25 mM and a detection limit of 120 microM, which hinted its potential application as a glucose biosensor.

Gold nanoparticles resist deformation by swift heavy ion irradiation when embedded in a crystalline matrix

We have attempted to deform, by swift heavy ion irradiation, gold nanoparticles embedded in crystalline AlAs which resists amorphization. AlAs was first implanted with 1.3 MeV Au ions at room temperature to a fluence of 2 × 10 16 cm −2. Rapid thermal annealing (RTA) at 600 °C for 1 or 2 min was used to grow Au nanoparticles in the matrix. Deformation was attempted by 30 MeV Cu 5+ irradiation at liquid nitrogen temperature. Crystal damage of the matrix was studied using Rutherford backscattering spectrometry in channeling configuration and Raman spectrometry. The morphology of Au nanoparticles was investigated by Transmission Electron Microscopy. It was found that, in spite of some crystal damage, the AlAs remained crystalline throughout the experiment and spherical Au nanoparticles with size distribution between 2 and 12 nm were observed with no indication of elongation. Thus, high energy heavy ion irradiation does not deform spherical Au nanoparticles embedded in AlAs. This supports the suggestion that the deformation of the gold nanoparticles which has been observed for particles embedded in amorphous materials is a consequence of the hammering deformation of the matrix surrounding the nanoparticles.

Tuning the Shape and Size of Gold Nanoparticles with Triblock Polymer Micelle Structure Transitions and Environments

Three block polymers, viz., L31, L64, and P123, were used as reducing agents for the synthesis of gold (Au) nanoparticles (NPs) to determine the effect of their micelle size, structure transitions, and environments on the mechanism of the reduction process leading to the overall morphology of Au NPs. Aqueous phase reduction was monitored with time at constant temperature and under the effect of temperature variation from 20 to 70 °C by simultaneous measurement of UV–visible spectra. The ligand to metal charge transfer (LMCT) band around 300 nm, due to a charge transfer complex formation between the micelle surface cavities and AuCl4– ions, and Au NP absorbance around 550 nm, due to the surface plasmon resonance, were simultaneously measured to understand the mechanism of the reduction process and its dependence on the micelle structure transitions and environment of TBPs micelles. L64 micelles showed dramatic shift in the LMCT band from lower to higher wavelength due to an increase in the reduction potential of surface cavities induced by the structure transitions under the effect of temperature variations. This effect was not observed for micelles of either L31 or P123 and is explained on the basis of a difference in their micelle environments. The morphology of Au NPs thus evolved from the reduction process was studied with the help of TEM and SEM studies. Smaller micelle size with few surface cavities, as in L31, produced small NPs in comparison to large micelles with several surface cavities as in P123. Structure transitions of L64 demonstrated direct influence on the final morphology of NPs, and stronger transitions produced fused and deformed NPs in comparison to weaker transitions. The results showed that efficient reduction by the surface cavities and uninterrupted nucleation without structure transitions lead to well-defined morphologies in the presence of P123 micelles.

A facile approach to synthesize poly(4-vinylpyridine)/multi-walled carbon nanotubes nanocomposites: highly water-dispersible carbon nanotubes decorated with gold nanoparticles

A facile approach to attach high-density and uniform gold nanoparticles on individual multi-walled carbon nanotubes (MWNTs) is achieved. By simple grinding, water-soluble linear polymers poly(4-vinylpyridine) (PVP)-wrapped around nanotubes and thus rendered them reversibly soluble in water, ethanol, and DMF. Individual tubes are clearly observed after PVP-wrapped nanotubes were spin-coated onto a silicon wafer. Subsequently, Au nanoparticles were densely decorated on the individual MWNTs by in situ reduction of HAuCl4 in the homogeneous aqueous solution of MWNTs–PVP to form stable water-dispersible Au/PVP/MWNTs hybrid. Morphology of Au nanoparticles was determined by scanning electron microscope and atomic force microscope. The diameter of the Au nanoparticles is controlled in the range of 3.5 to 13.5 nm. The presence of gold nanoparticles with decreased particle size was also detected by UV–Vis spectroscopy.

Shape Dependence of Gold Nanoparticles on In Vivo Acute Toxicological Effects and Biodistribution

The toxicity and biodistribution in vivo of various morphologies of Au nanoparticles (AuNPs) were studied by using KM mice. The quantitative analysis of Au in each tissue of mice was done by using the Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Sphere-shaped AuNPs displayed the best biocompatibility, compared with rod- and cube-shaped of AuNPs, and rod-shaped AuNPs was more toxic than cube-shaped AuNPs. In vivo biodistribution study revealed all AuNPs were preferentially accumulated in organ of liver and spleen. The findings from this study thus revealed that the toxicity and biodistribution in vivo of AuNPs are shape dependent.

Dendritic-shaped, fractal nanogold aggregates based on surfactant/polymer complex template

Dendritic-shaped, Au nanoparticles (AuNPs) aggregates with the fractal feature could be formed by using a complex template of surfactant/polymer films. Hexadecyltrimethylammonium bromide (CTAB)/modified partially hydrolyzed polyacrylamide (MHPAM) complexes deposited on mica substrate were observed to form the dendritic aggregates (e.g. tree-like ramified structures) through the salt-induced self-assembly. Then this structure was used as “soft template” for the self-assembly of the AuNPs. The effects of the surface pressure and AuNPs concentrations in subphase on the morphology of AuNPs self-assembly were studied. The resulting morphology and structure have been observed and characterized by atomic force microscopy.