Morphology Of Gold Nanoparticles Research Articles

Shape control technology during electrochemical synthesis of gold nanoparticles

Gold nanoparticles with different shapes and sizes were prepared by adding gold precursor (HAuCl4) to an electrolyzed aqueous solution of poly(N-vinylpyrrolidone) (PVP) and KNO3, which indicates the good reducing capacity of the PVP-containing solution after being treated by electrolysis. Using a catholyte and an anolyte as the reducing agents for HAuCl4, respectively, most gold nanoparticles were spherical particles in the former case but plate-like particles in the latter case. The change in the pH value of electrolytes caused by the electrolysis of water would be the origin of the differences in shape and morphology of gold nanoparticles. A hypothesis of the H+ or OH− catalyzed PVP degradation mechanism was proposed to interpret why the pH value played a key role in determining the shape or morphology of gold nanoparticles. These experiments open up a new method for effectively controlling the shape and morphology of metal nanoparticles by using electrochemical methods.

Block Copolymer Micelles as Nanoreactors for Self-Assembled Morphologies of Gold Nanoparticles

Self-assembled gold (Au) nanoparticles (NPs) were synthesized in micelle surface cavities of a L121 block polymer in the presence of zwitterionic (viz. DPS, TPS, and HPS) and sugar surfactants (OG and DDM) in aqueous phase at 70 °C by using the surface cavities of L121 as reducing sites for converting Au(III) into Au(0). All reactions were monitored simultaneously by UV-visible spectroscopy to determine the growth kinetics in gold nucleating centers on the basis of surface plasmon resonance that also helped in tracing the structure micelle transitions over a wide temperature range of 10-70 °C. The surfactant/L121 mole ratio was changed systematically from 0.5 to 2.5 by keeping L121 and HAuCl4 concentrations constant at 10 and 0.25 mM, respectively, to determine the shape and size of the micelles and their relation to the self-assembled behavior of Au NPs. TEM studies were used to have a direct insight into the morphology of micelle templates and their shape and size for self-assembled NPs. L121 along with DPS (C12 carbon chain) produced well-defined micelles loaded with tiny NPs of 3-6 nm in the L121-rich region of the mixture, while large flower-like compound micelles with a clear core-shell morphology were produced in the DPS-rich region. TPS and HPS (C14 and C16 hydrocarbon chains, respectively) with stronger hydrophobicity than DPS also produced almost similar micelles loaded with tiny NPs in the L121-rich region, but they disappear in the surfactant-rich region. Replacement of zwitterionic with ionic surfactants did not yield micelle templates for self-assembled NPs. Results conclude that well-defined micelles of L121 are the fine templates for self-assembled NPs that can only be achieved in the presence of a neutral surfactant with low concentration and low hydrophobicity.

Facile Synthesis of Gold (Au) Nanoparticles Using <i>Cassia auriculata</i> Flower Extract

The green synthesis is the versatile tool to produce the nano scale materials. The present study deals with the synthesis of gold nanoparticles using the Cassia auriculata flower extract. The complete reduction of gold ions was observed after 45 min of reaction under stirrer condition. The colour changes in reaction mixture (dark red colour) was observed during the reaction period because of the formation of gold nanoparticles in the reaction mixture enables to produce particular colour due to their specific properties (Surface Plasmon Resonance). The formation of gold nanoparticles was confirmed using UV visible spectroscopy, the size of the nanoparticles measured by using particle size analyzer. The morphology of the poly dispersed gold nanoparticles was studied using TEM, This green synthesis method is cost effective; and eco friendly technique to produce large scale production of Nanomaterials

Micromolar Hg(ii) induced the morphology of gold nanoparticles: a novel luminescent sensor for femtomolar Hg(ii) using triazole capped gold nanoparticles as a fluorophore

In this paper, we report the morphological changes of gold nanoparticles induced by micromolar Hg(II) and the determination of femtomolar Hg(II) by a luminescent method. 3,5-Diamino-1,2,4-triazole capped gold nanoparticles (DAT-AuNPs) were synthesized by a wet chemical method. The HR-TEM images show that the spherical structure of DAT-AuNPs was changed into a chain-like structure after the addition of micromolar Hg(II) due to the strong coordination of DAT-AuNPs with Hg(II). The binding of Hg(II) with DAT-AuNPs was confirmed by XPS. The XPS of Hg5p shows two peaks at 69.3 eV for 5p1 and 74.35 eV for 5p3, suggesting that mercury was present as Hg(II), coordinated with DAT-AuNPs. The DAT-AuNPs show the emission maximum at 776 nm while exciting at 520 nm and the emission intensity was enhanced after the addition of even nanomolar Hg(II). The quantum yield estimated for DAT-AuNPs in the presence of Hg(II) was 1.5-fold higher than that of free DAT-AuNPs. This suggests that Hg(II) induced the fluorescence properties of DAT-AuNPs due to photoinduced electron transfer and metal binding-induced conformational restriction upon complexation. Based on the enhancement of emission intensity, the concentration of Hg(II) was determined. Further, the DAT-AuNPs showed an extreme selectivity towards the determination of 10 nM Hg(II) in the presence of a 50 000-fold higher concentration of common interferents. The emission intensity increases linearly in the concentration range of 1 × 10−7 to 5 × 10−13 M Hg(II) and the detection limit was found to be 0.75 fM L−1 Hg(II) (S/N = 3). This method was successfully utilized for the determination of Hg(II) in environmental samples.

Block copolymer-mediated synthesis of gold nanoparticles in aqueous solutions: Segment effect on gold ion reduction, stabilization, and particle morphology

We report here on the segment effects of poly(ethylene oxide)-containing block copolymers (PEO-BCP) on the reduction activity for tetrachloride gold(III) ([AuCl4]−), interfacial activity for gold surface, colloidal stability, and morphology of gold nanoparticles formed in aqueous solutions. In particular, the effects of poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), polyethylene (PE) segments and amino group (NH2) on the rate of [AuCl4]− reduction, adsorption of PEO-BCP onto gold surface, colloidal stability, and morphology of gold nanoparticles formed in aqueous solutions were examined using a poly(ethylene oxide)–poly(propylene oxide) triblock copolymer (PEO–PPO–PEO, Pluronic L44), an amino-terminated poly(ethylene oxide)-poly(propylene oxide) block copolymer (PEO–PPO–NH2, SURFONAMINE® L-207), a poly(ethylene oxide) homopolymer (PEO, poly(ethylene glycol)2000), and a polyethylene–poly(ethylene oxide) block copolymer (PE–PEO). We found that the reduction activity of PEO-BCP for [AuCl4]− became higher with the order of PEO–PPO–NH2<PE–PEO<PEO<PEO–PPO–PEO. The interfacial activity (affinity) of PEO-BCP for gold surface increased with the order of PEO<PE–PEO<PEO–PPO–PEO≪PEO–PPO–NH2. Consequently, the colloidal stability of gold nanoparticles formed in aqueous PEO–PPO–NH2 solutions was extremely high compared with that in PEO, PEO–PPO–PEO, and PE-PEO solutions. In addition, the size of gold nanoparticles formed in aqueous PEO–PPO–NH2 solutions was much smaller than that in aqueous solutions of PEO–PPO–PEO, PEO or PE–PEO.

Au(III)–CTAB reduction by ascorbic acid: Preparation and characterization of gold nanoparticles

Upon addition of tetrachloroauric(III) (HAuCl4) to a solution of cetyltrimethylammonium bromide (CTAB), a perfect transparent yellow colored and yellowish-precipitate appears within the time of mixing, indicating the formation of a complex between HAuCl4 and CTAB. Morphology of gold nanoparticles in situ via chemical reduction of title reaction has been determined by using conventional techniques. The position and shape of the surface plasmon resonance (SRP) band strongly depends on the [ascorbic acid], [HAuCl4], [CTAB] and mixing ratio of the reactants. Sub-, post- and dilution-micellar effects are accountable to the aggregation and/or adsorption of gold nanoparticles onto the surface of CTAB. The morphology of particles was altered by changing the [reactants] as well as [CTAB]. A mechanism of nanoparticle formation has been proposed comprising different steps of particle growth.

Controlling the morphology of gold nanoparticles synthesized photochemically in a polymer matrix through photonic parameters

A facile method for the preparation of gold nanoparticles (AuNPs) with various morphologies, including triangles, cubes and nanospheres into a urethane methacrylate polymer matrix, has been developed. The hybrid nanocomposites have been obtained by photoreduction of a gold precursor in the presence of a 30 wt% urethane methacrylate containing quaternary ammonium structure and 70 wt% functional monomer, carboxyl oligo-urethane dimethacrylate. The final materials contain gold nanoparticles with a morphology dependant on the reaction conditions. The influence of photonic and chemical parameters on the shape of the nanoparticles has been examined. Specific interactions between the macromolecular network and the nascent particles play an important role insofar as they control the access of metal atoms to the different crystalline planes of the growing nanoparticles, which is necessary to obtain anisotropic objects. A common mechanism for the formation of the various types of AuNPs is proposed. Coupling the intrinsic characteristics of metal nanoparticles with those of the copolymer substrate could result in materials with innovative properties.

Large Scale Fabrication of Gold Nano-Structured Substrates Via High Temperature Annealing and Their Direct Use for the LSPR Detection of Atrazine

The present work is reporting on the fabrication of localized surface plasmonic resonant (LSPR) gold nano-structures on glass substrate by using different high annealing temperatures (500 °C, 550 °C, 600 °C) of initially created semi-continue gold films (2 nm and 5 nm) by the electron beam evaporation technique. Interestingly, well-defined gold nano-structures were also obtained from continuous 8 nm evaporated gold film - known as the value above gold percolated thickness - once exposed to high temperatures. The surface morphology and plasmonic spectroscopy of “annealed” nano-structures were controlled by key experimental parameters such as evaporated film thickness and annealing temperature. By using scanning electron microscopy (SEM) characterization of annealed surface it was noticed that the size and inter-particle distance between nano-structures were highly dependent on the evaporated thin film thickness, while the nanoparticle shape evolution was mainly affected by the employed annealing temperature. Due to the well-controlled morphology of gold nano-particles, prominent and stable LSPR spectra were observed with good plasmon resonance tunability from 546 nm to 780 nm that recommend the developed protocol as a robust alternative to fabricate large scale LSPR surface. An example of a LSPR-immunosensor is reported. Thus, the monoclonal anti-atrazine antibodies immobilizion on the “annealed” gold nano-structures, as well as the specific antigen (atrazine) recognition were monitored as variations of the resonance wavelength shifts and optical density changes in the extinction measurements.

Synthesis of chitosan-stabilized gold nanoparticles by atmospheric plasma

We report a facile method to prepare gold nanoparticles by atmospheric plasma. Chitosan, was used as a stabilizing agent and gold precursor. In chitosan solution was reduced by atmospheric plasma at room temperature. We find the plasma treatment is effective for reducing the gold precursor and the process only takes minutes. The obtained gold nanoparticles were characterized with UV–vis spectroscopy and transmission electron microscopy. The results indicated that the morphology and size distribution of gold nanoparticles prepared varied with treatment time and the ratio of chitosan to precursor metal salts. Additionally, a preliminary study on air component analysis indicated that the moisture in air plays an important role in producing the active ingredient for the production of gold nanoparticles.

Fractal of Gold Nanoparticles Controlled by Ambient Dielectricity: Synthesis by Laser Ablation as a Function of Permittivity

The nanosecond pulsed laser ablation of a gold plate at the excitation wavelength of 532 nm was conducted in the supercritical fluid of dipolar trifluoromethane (CHF3). The generation of gold nanoparticles was investigated as a function of the fluid density that corresponded to changes in the permittivity and thermal properties over the wide ranges. The analysis of data from electron microscopy and small-angle X-ray scattering (SAXS) revealed that the principal product is a gold nanonetwork with length up to a few 10 μm and a branched structure. The gold nanonetwork consisted of gold nanospheres with an average diameter of 20 nm and a mass fractal structure. The mass fractal dimension of the nanonetwork changed by the fluid density, and its dimension was attributed to the number of the nanospheres. It was clarified that not the fluid thermal properties but the ambient dielectricity and polarization energy during the ablation are responsible for the morphology and number of gold nanoparticles. This is the ...

Production of aqueous spherical gold nanoparticles using conventional ultrasonic bath

A conventional ultrasonic bath was used to examine the feasibility of forming aqueous spherical gold nanoparticles (GNPs) under atmospheric conditions. The effects of ultrasonic energy on the size and morphology of GNPs were also investigated. Highly monodispersed spherical GNPs were successfully synthesised by sodium citrate reduction in a conventional ultrasonic bath, without an additional heater or magnetic stirrer, as evidenced by ultraviolet–visible spectra and transmission electron microscopy. Ultrasonic energy was shown to be a key parameter for producing spherical GNPs of tunable sizes (20 to 50 nm). A proposed scheme for understanding the role of ultrasonic energy in the formation and growth of GNPs was discussed. The simple single-step method using just a conventional ultrasonic bath as demonstrated in this study offers new opportunities in the production of aqueous suspensions of monodispersed spherical GNPs.

Generation of diversiform gold nanostructures inspired by honey’s components: Growth mechanism, characterization, and shape separation by the centrifugation-assisted sedimentation

The green synthesis of irregular-shaped nanomaterials used for various applications in nanoplasmonics, medicine, and biotechnology creates an economical and environmental challenge. We describe the rapid wet-chemical approach to synthesis of stable and water-soluble gold nanostructues at room temperature. In addition to spherical and road-like nanoparticles, gold decahedra and triangular plates were grown using the one-step synthesis process of HAuCl4 in the presence of honey, in which main components act as reducing (glucose) and stabilizing (fructose) agents; the mechanism of the process is discussed in details. The requirements for anisotropic phase boundaries for generation of polyhedral gold nanocrystals in solutions are highlighted. The synthesis, morphology, and separation procedure of gold nanoparticles are examined using the techniques of optical spectroscopy, transmission electron microscopy, and atomic force microscopy. We demonstrate that centrifugation can be used for efficient separation of nanoparticles with different shapes from a mixture. It was found that while centrifuging, the spheres sediment at the bottom of the tube, segregating from rods that form a deposit on the side wall, whereas polygons remain in the solution.

'Ex-Situ' Annealing and Structural Transformations in Gold Nanoparticles

The atomic structure and morphology of gold nanoparticles have been studied using High-Resolution Transmission Electron Microscopy (HRTEM). The structural transformations of these particles have been probed through ex-situ annealing experiments, yielding population statistics on structure as a function of particle size and annealing temperature. The results show that for an original structurally heterogeneous particle population, there is a rise in the percentage of particles with the decahedral morphology as annealing temperature is increased. This can be correlated with a reduction in the number of icosahedral particles as a function of annealing temperature. HRTEM imaging following low temperature annealing reveals a range of modified and distorted decahedral particles, giving insight into the temperature threshold of the solid state transformation and the microstructural processes occurring.

Influence of ion irradiation on the morphology, structure, and optical properties of gold nanoparticles synthesized in SiO2 and Al2O3 dielectric matrices

Irradiation of fused quartz (SiO2) and sapphire (Al2O3) by Ne+ and F+ ions with medium energies and their subsequent annealing enables us to control the intensity and frequency of surface plasmon resonance in Au nanoparticles (NPs) synthesized in oxide matrices. The control process can be implemented because NPs dissolve during irradiation and undergo partial reconstruction at annealing. The degree of reconstruction depends on the matrix material and the type and dose of ions. It has been found that the difference in the results obtained by means of irradiation with ions with similar masses is substantially affected by the chemical nature of the ions. The composition, morphology, and structure of the unirradiated and irradiated layers are investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry.

Direct Comparison of Kinetic and Thermodynamic Influences on Gold Nanomorphology

Under a given set of conditions, nanomaterials can crystallize into structures that are entirely inconsistent with the bulk material and may adopt a range of faceted morphologies that depend on the particle size. A size-dependent phase diagram, a graphical representation of the chemical equilibrium, offers a convenient way to describe this relationship among the size, morphology, and thermodynamic environment. Although creating such a diagram from conventional experiments is extremely challenging (and costly), theory and simulation allow us to use virtual experiments to control the temperature, pressure, size, structure and composition independently. Although the stability and morphology of gold nanoparticles has been add-ressed numerous times in recent years, a critical examination of the literature reveals a number of glaring contradictions. Typically gold nanoparticles present as multiply-twinned structures, such as icosahedra and decahedra, or faceted monocrystalline (fcc) shapes, such as truncated octahedra and cuboctahedra. All of these shapes are dominated by various fractions of {111} and {100} facets, which have different surface atom densities, electronic structure, bonding, chemical reactivities, and thermodynamic properties. Although many of the computational (and theoretical) studies agree on the energetic order of the different motifs and shapes, they do not necessarily agree with experimental observations. When discrepancies arise between experimental observations and thermodynamic modeling, they are often attributed to kinetics. But only recently could researchers analytically compare the kinetics and thermodynamics of faceted nanoparticles. In this Account, we follow a theoretical study of the size, shape, and structure of nanogold. We systematically explore why certain shapes are expected at different sizes and (more importantly) why others are actually observed. Icosahedra are only thermodynamically preferred at small sizes, but we find that they are the most frequently observed structures at larger sizes because they are kinetically stable (and coarsen more rapidly). In contrast, although the phase diagram correctly predicts that other motifs will emerge at larger sizes, it overestimates the frequency of those observations. These results suggest either a competition or collaboration between the kinetic and thermodynamic influences. We can understand this interaction between influences if we consider the change in shape and the change in size over time. We then use the outputs of the kinetic model as inputs for the thermodynamic model to plot the thermodynamic stability as a function of time. This comparison confirms that decahedra emerge through a combination of kinetics and thermodynamics, and that the fcc shapes are repressed due to an energetic penalty associated with the significant departure from the thermodynamically preferred shape. The infrequent observation of the fcc structures is governed by thermodynamics alone.

Growth and dewetting of gold on Si(1 1 1) investigated in situ by grazing incidence small angle x-ray scattering

The most accessible way to grow semiconductor nanowires remains so far the use of gold nanoclusters on a (111) semiconductor surface, for instance Si(111). Precise knowledge of the morphology of gold nanoparticles obtained by growth or dewetting on Si(111) is essential to better control the growth of nanowires. Both formation routes were investigated in situ by grazing incidence small-angle x-ray scattering. During the growth at 300°C, Au atoms first nucleate on the wetting layer and give rise to islands having the shape of truncated spheres with an average contact angle of 38° for deposits of 1.4 and 2 monolayers. Dewetting is obtained by annealing of a 2 monolayer room temperature deposit, leading to the formation of particles. The average contact angle increases from 53° to 73° from 270°C to 360°C. Moreover, an analysis of the island height suggests that an AuSi alloy with a thickness of approximately 1.5nm could be present at the top of the monocrystalline islands in the solid state before the eutectic temperature. The liquid–solid interface tension of the AuSi alloy droplet (1.0Jm−2) and the work of adhesion (1.1Jm−2) are deduced at the eutectic temperature.

Structure and Morphology of Gold Nanoparticles in Solution Studied by TEM, SAXS and UV-Vis

Gold nanoparticles have a great number of applications, among others in material sciences, biology and medicine. A method for the synthesis of gold nanoparticles in solution with the use of gemini surfactant was proposed and the nanoparticles obtained were subjected to thorough characterisation. The method proposed is a modi cation of the Turkevich method, based on reduction of tetrachloroauric acid in the presence of trisodium citrate and a dicationic (gemini) surfactant 1,1′-(1,4-butan)bis(3-dodecyloxymethylimidazolium) di-propionate. Morphology and size distribution of gold nanoparticles obtained were examined by the transmission electron microscopy (TEM), UV Vis spectroscopy and small angle scattering of synchrotron radiation (SAXS). The plasmon resonance of the nanoparticles obtained was observed in the wavelength range corresponding to the presence of gold nanoparticles with sizes ranging from 5 to 100 nm. TEM images con rmed that the spherical shape of nanoparticles was dominated in reference solutions prepared of sodium citrate and tetrachloroauric acid. In the solutions prepared with addition of gemini surfactant, the gold nanoparticles of triangular morphology were observed.

Synthesis and characterizations of iso‐luminol‐functionalized, tadpole‐shaped, gold nanomaterials

Iso-luminol functionalized gold nanomaterials were synthesized in high yield by a simple seeding approach, using the chemiluminescent reagent iso-luminol as reductant in the presence of HAuCl(4), AgNO(3) and cetyltrimethylammonium bromide (CTAB). The morphology of as-prepared gold nanoparticles was characterized by transmission electron microscopy and UV-vis spectroscopy, showing that gold nanotadpoles (AuNTps) were obtained. Subsequent experiments revealed that the amounts of seed colloids and AgNO(3) and the concentrations of iso-luminol and CTAB in the growth solution play critical roles in the formation of well-shaped AuNTps. The surface state of AuNTps was characterized by UV-vis spectroscopy and fluorescence spectroscopy, indicating that iso-luminol and its oxidation product, 4-aminophthalate, coexisted on the surface of AuNTps. The CL behaviour was studied by static injection CL experiments, demonstrating that AuNTps were of CL activity. Finally, the growth mechanism of AuNTps was also discussed.

Influence of Single Use and Combination of Reductants on the Size, Morphology and Growth Steps of Gold Nanoparticles in Colloidal Mixture

A comprehensive investigation on the formation mechanism of gold nanoparticles (AuNPs) in colloidal mixture obtained from the reduction of chloroauric acid (HAuCl4) solution using a single reducing agent (sodium citrate; process-I), (tannic acid; process-II), and a combination of two reducing agents (sodium citrate plus tannic acid; process-III) is reported. The growth steps at different time intervals during synthesis of colloidal AuNPs were monitored in situ and ex situ using various methods for all the three processes. The measurement of changes in the surface plasmon band position of colloidal AuNPs, along with dynamic light scattering results gave important information for the first assessing of particle size, shape and distribution. Besides, the size and morphological changes at different stages during different processes were also analyzed by transmission electron microscopy. The final Au particles of processes-I & II exhibited different shapes (spherical and nanowires) with particle size and nano wire diameter of 12 nm and 17 nm, respectively. Nevertheless, combination of two reductants (process-III) surprisingly leads to drastically reduced size (ca. 3 nm) with spherical morphology compared to their parent solutions with either of single reducing agent. This result clearly indicates that the combination of reductants has a significant influence on the particle size, morphology and formation mechanism.

Dynamic control of gold nanoparticle morphology in a microchannel flow reactor by glucose reduction in aqueous sodium hydroxide solution

Continuous flow synthesis of gold nanoparticles was demonstrated using a microchannel reactor with glucose reduction in aqueous alkaline medium. Particle size, morphology, and visual/optical properties of the dispersion liquid were controlled dynamically by tuning of the rate of NaOH addition. Characteristic star-like nanoparticles formed spontaneously as a quasi-stable state, but they changed the morphology to round shape and showed spectral change over time.