Synthesis of au nanoparticles at "all" pH by H2O2 reduction of HAuCl4

In this article we report the synthesis of Au nanoparticles (NPs), from HAuCl4, in the pH range of 2.9 to 11.2 using H2O2 as the reducing agent. Ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction techniques have been used to characterize the Au NPs. UV-Vis spectral observation showed that the Au NPs synthesized in acidic conditions tend to generate particles with absorption maximum around 540 nm. On the other hand the NPs generated at a pH higher than 8.0 generally have broad absorption with maxima occurring beyond 600 nm. Interestingly, TEM analysis showed that the NPs generated at pH lower than 7.0 tend to be smaller and spherical in shape, whereas the particles generated at a pH beyond 7.0 tend to be non-spherical and larger in sizes or agglomeration of small particles. Also, we speculate on the mechanisms of reduction of HAuCl4 by H2O2 under different pH conditions.     

Langmuir monolayer properties of 4-methylbenzenethiol capped gold nanoparticles

The properties of 4-methylbenzenethiol capped gold nanoparticles have been investigated at the air–water interface. Langmuir isotherms and compression cycles show that a stable monolayer is formed on the water surface. In situ UV-visible spectroscopy confirms that the plasmon absorption band is present which is characteristic of small metallic particles. The monolayer was imaged using real time Brewster Angle Microscopy (BAM). Above surface pressures of 5 mN m^− 1 the monolayer was virtually homogeneous. During decompression, the monolayer fractured into rod-like structures. These rods were initially orientated parallel to the movable barriers containing the monolayer and as the area was increased, their orientation randomized. During subsequent compressions the rods recombined to recreate a homogeneous monolayer.     

Synthesis and characterization of nano-gold composite using Cylindrocladium floridanum and its heterogeneous catalysis in the degradation of 4-nitrophenol

Greener synthesis of nanogold-biocomposite by fungus, Cylindrocladium floridanum was reported in this study. Results revealed that when cultured in static condition for a period of 7d, the fungus accumulated gold nanoparticles on the surface of the mycelia. Bionanocomposites with Au nanocrystals were characterized by UV-Vis spectroscopy, XRD, SEM, EDX and high-resolution TEM. The SPR band of UV-Vis spectrum at 540 nm confirmed the presence of gold nanoparticles on the surface of the fungal mycelia. The fcc (111)-oriented crystalline nature of particles was identified by XRD pattern. The synthesized particles are spherical in shape as evidenced by TEM image. The biocomposites with Au nanoparticles function as an efficient heterogeneous catalyst in the degradation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), in the presence of reducing agent, sodium borohydride which was reflected by UV-Vis spectra of the catalytic reaction kinetics. The reduction of 4-nitrophenol follows pseudo-first-order kinetic model with the reaction rate constant of 2.67 × 10(-2)min(-1) with 5.07 × 10(-6)mol/dm(3) of gold at ca. 25 nm. The rate of the reaction was increased by increasing the concentration of gold nanoparticles from 2.54 × 10(-6) to 12.67 × 10(-6)mol/dm(3) (～ 25 nm) and with reduced size from 53.2 to 18.9 nm respectively. This is the first report on fungal-matrixed gold(0) nanocomposites heterogeneously catalyzing the reduction of the toxic organic pollutant, 4-nitrophenol that enable the recovery and recycling of AuNPs catalysts.     

Synthesis and agglomeration of gold nanoparticles in reverse micelles

Reverse micelles prepared in the system water, sodium bis-(2-ethylhexyl) sulfoccinate (AOT), and isooctane were investigated as a templating system for the production of gold nanoparticles from Au(III) and the reducing agent sulfite. A core-shell Mie model was used to describe the optical properties of gold nanoparticles in the reverse micelles. Dynamic light scattering of gold colloids in aqueous media and in reverse micelle solution indicated agglomeration of micelles containing particles. This was verified theoretically with an analysis of the total interaction energy between pairs of particles as a function of particle size. The analysis indicated that particles larger than about 8?nm in diameter should reversibly flocculate. Transmission electron microscopy measurements of gold nanoparticles produced in our reverse micelles showed diameters of 8-10?nm. Evidence of cluster formation was also observed. Time-correlated UV-vis absorption measurements showed a red shift for the peak wavelength. This was interpreted as the result of multiple scattering and plasmon interaction between particles due to agglomeration of micelles with particles larger than 8?nm.     

Copper complexes within the supramolecular solid structure of cyanuric acid and melamine

A complex of copper sulfate was formed by impregnation of the cyanuric acid melamine adduct (CAM) with a solution of copper (II) sulfate. A thermal treatment at 250°C of the dried compound delivered a greenish powder. The UV-Vis spectroscopy showed that an absorption around 700 nm is compatible with a copper (II) sulfate complex coordinated inside the supramolecular structure of CAM. No copper or copper oxide particles were found by means of either transmission or scanning electron microscopy. X-ray photoelectron spectroscopy showed that on the surface there was a considerable amount of Cu(I) (66%) probably coordinated also inside the CAM channels. A brief catalytic test showed the ability of the copper complexes to oxidize sucrose to gluconic acid.     

Preparation of gold nanoparticles in an aqueous medium using 2-mercaptosuccinic acid as both reduction and capping agent

Monolayer protected gold nanoparticles with diameters above 10 nm were prepared by a simple, one step reaction in water. 2-mercaptosuccinic acid (MSA) was used both as reduction agent for hydrogen tetrachloroaurate (HAuCl4) and as stabilizing agent for the gold nanoparticles. Size distribution and surface chemistry were investigated by UV-Vis spectroscopy, scanning electron microscopy and Fourier Transform Infrared Spectroscopy. Particle size can be controlled by adjusting the molar portions of the reactants. The resulting particles are efficiently stabilized against aggregation when MSA is used in a concentration of 40% and above. Below a minimum MSA concentration a long-term particle growth is observed.     

Influence of copper morphology in forming nucleation seeds for graphene growth

We report that highly crystalline graphene can be obtained from well-controlled surface morphology of the copper substrate. Flat copper surface was prepared by using a chemical mechanical polishing method. At early growth stage, the density of graphene nucleation seeds from polished Cu film was much lower and the domain sizes of graphene flakes were larger than those from unpolished Cu film. At later growth stage, these domains were stitched together to form monolayer graphene, where the orientation of each domain crystal was unexpectedly not much different from each other. We also found that grain boundaries and intentionally formed scratched area play an important role for nucleation seeds. Although the best monolayer graphene was grown from polished Cu with a low sheet resistance of 260 Ω/sq, a small portion of multilayers were also formed near the impurity particles or locally protruded parts.     

Microwave-assisted synthesis of Ag nanophases and their optical properties

By microwave-assisted method, silver nanophases were produced with size and morphology control. Silver nanoparticles of controlled size from 10 to 80 nm were obtained. Particle size was controlled by varying reaction conditions, including metal source concentration and molecular weight of protecting agent (PVP). Silver nanowires were produced by releasing the metal source gradually from AgFn(1-n)(n = 1-6) with PVP as the morphology directing agent. UV-Vis spectra showed that Ag nanoparticles have absorption bands around 400 nm and the UV-Vis absorptions slightly blue shifted with decreasing particle size.     

Surface-enhanced vibrational spectroscopy of adsorbates on microemulsion synthesized gold nanoparticles

Very small (<10 nm) monodisperse gold nanoparticles (AuNPs) coated with a monolayer of decanethiol were prepared and their surface-enhanced infrared absorption (SEIRA) spectra were measured in the transmission mode. The AuNPs were prepared by the borohydride reduction of HAuCl(4) inside reverse micelles that were made by adding water to a hexane solution of sodium bis(2-ethylhexyl)sulfosuccinate (AOT). The gold nanoparticles were then stabilized by the addition of decanethiol. Subsequent addition of p-nitrothiophenol both facilitated the removal of excess AOT and showed that the gold surface was completely covered by the decanethiol. SEIRA spectra of decanethiol on gold particles prepared in AOT microemulsions were about twelve times more intense than corresponding layers on gold produced by electroless deposition and gave a significantly less noisy spectrum compared to the corresponding surface-enhanced Raman spectrum. The surface-enhanced Raman scattering (SERS) spectra of the same samples showed that the most intense spectrum was obtained from gold nanoparticles with a mean diameter of 2.5 nm. This result is in contrast to previous statements that SERS spectra could only be obtained from particles larger than 10 nm.     

Fabrication of Langmuir-Blodgett film from Polyvinylpyrrolidone stabilized NiCo alloy nanoparticles

The fabrication of monolayer/multilayer films of Polyvinylpyrrolidone (PVP) stabilized NiCo alloy nanoparticles with an average particle size 7 nm via Langmuir-Blodgett method is presented in this paper. The NiCo alloy nanoparticles were synthesized in ethanol using hydrazine hydrate as reducing agent at 60 °C in the presence of PVP and washed with a mixture of chloroform-methanol (1:1) solution to get pure PVP capped alloy nanoparticles. The NiCo alloy suspension was spread to the interface of air/water and transferred to the glass surface. The formation of a Langmuir monolayer/multilayer of PVP stabilized NiCo particles at air/water interface were revealed with the pressure-area isotherm curve. The transfer of nanoparticles on the glass surface was found to be efficient for the first six layers as exhibited by the pressure-area isotherm and increases in absorption intensity in the UV-Vis range. The atomic force microscopy results show that this film has a cubic symmetry in a two dimensional (2D) array.     

Synthesis of uniform and stable silver nanoparticles by a gold seed-mediated growth approach in a buffer system

A seeding growth approach to the preparation of silver nanoparticles with a controllable size was developed. It contained a two-step reaction: the first step was gold seed clusters quickly generated by a chemical reaction using sodium borohydride as a reducing reagent; the second one was controllable silver nanoparticles were grown at the mild condition by using the mixed reducing reagents (hydroxylamine hydrochloride and sodium hydroxide) to form a buffer system. The gold core was beneficial for the crystalline of silver cations to form the nanoparticles and the buffer system which was composed of hydroxylamine hydrochloride and sodium hydroxide, and was helpful for controlling the size and shape of the as-prepared silver nanoparticles. These as-prepared nanoparticles were characterised by X-ray powder diffraction, UV-Vis spectroscopy (UV-Vis) and transmission electron microscopy along with energy dispersive X-ray spectroscopy. The results indicated that the obtained silver nanoparticles are highly crystallised with an average diameter around 10?nm. The content of gold seeds and the mild reaction rate controlled by the buffer system were considered to be key factors in the control of silver nanoparticles’ morphology and size. A possible mechanism of the silver nanoparticles formed was also proposed.     

Facile synthesis of gold nanoflowers with high surface-enhanced Raman scattering activity

Highly branched gold nanoflowers are synthesized in high yield by a simple amino-reducing method, without additional seeds or surfactant agents. We present a systematic investigation of the influence of different parameters on the size, morphology, and monodispersity of gold nanoflowers. The initial concentration of reducing agent, the solvent viscosity, and the reaction temperature play critical roles in the formation of nanoparticles. A lower concentration of reducing agent causes larger particles with sharp and dendritic tips. Moreover, with increasing solvent viscosity, the obtained particles have more and larger tips. Examination of the nanoparticles at different reaction stages with transmission electron microscopy and UV-vis spectroscopy reveals the formation of the gold nanoflowers as a classical growth process in which diffusion-controlled growth gives rise to the highly branched structures. Additionally, these gold nanoflowers have prospects for surface-enhanced Raman scattering (SERS) imaging because of their strong SERS enhancement and clean surface.     

Spontaneous deposition of gold nanoparticle nanocomposite on polymer surfaces through sol-gel chemistry

A aminosilica nanocomposite layer containing a monolayer of gold nanoparticles (d = 18-22 nm) with a well-defined spacing was spontaneously deposited on an unmodified polystyrene surface via a sol-gel reaction when the reduction reaction was carried out under 1:8 molar ratio (gold(III):aminosilane). The amount of aminosilica and spacing between gold nanoparticles were found to be a function of the aminosilane:water molar ratio, which contributes to the plasmonic property of the films with its absorption wavelength ranging between 701 and 548 nm. Furthermore, the nanocomposite film that consists of a monolayer of nanoparticles in aminosilica has also been deposited on the surface of polystyrene beads. This core-shell structure was found capable of storing electrostatic charges and forming a well-separated 2D array.     

One-step synthesis and luminescent properties of nanocrystalline YVO4:Eu3+ powders

In this paper, nanocrystalline YVO4:Eu3+ powders have been successfully synthesized via high-temperature solution-phase synthesis process. The nanocrystalline YVO4:Eu3+ particles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV/Nis absorption spectra and luminescence spectra, luminescence decay curve and Fourier transform infrared (FT-IR), X-ray photoelectron spectra (XPS) respectively. The as-prepared nanocrystalline YVO4:Eu3+ particles are well crystallized with ellipsoidal morphology. The emission of YVO4:Eu3+ particles show emission originating from the 5D0 level, with 5D0-7F2 at 616 nm as the most prominent group. The excitation spectrum fits basically with the absorption spectrum from the vanadate ions. FT-IR and XPS spectra indicate that the surface ligands of nanocrystalline particles were oleic acid and oleylamine. The lifetime for the luminescence of Eu3+ in the as-prepared YVO4:Eu3+ samples are shorter than that of the bulk material due to the absorption of organic ligands on the nanoparticle surface.     

Size-tunable near-infrared PbS nanoparticles synthesized from lead carboxylate and sulfur with oleylamine as stabilizer

High quality PbS nanocrystals are synthesized reproducibly through lead stearate and sulfur stabilized by oleylamine in a non-coordinating solvent. The morphology, crystalline form and phase composition of PbS nanocrystals are examined by transmission electron microscopy (TEM), high-resolution TEM, x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS). The as-synthesized PbS nanocrystals have strong absorption and photoluminescence emissions in the near-infrared region. The size of PbS nanocrystals from 5 to 13?nm can be adjusted through the optimization of the synthesis conditions. The smaller PbS nanoparticles are obtained at the lower reaction temperature, lower precursor concentration, larger oleylamine quantity and larger lead precursor/sulfur ratio. The basic oleylamine enhances the reactivity of both lead stearate precursor and sulfur precursor in the reaction.     

Controlling binding site densities on glass surfaces

The density of surface-immobilized ligands or binding sites is an important issue for the development of sensors, array- or chip-based assays, and single-molecule detection methods. The goal of this research is to control the binding site density of reactive ligands on surfaces by diluting surface amine groups in self-assembled and cross-linked monolayers on glass prepared from solutions containing very low concentrations of (3-aminopropyl)triethoxysilane (APTES) and much higher concentrations of (2-cyanoethyl)triethoxysilane. The surface amine sites are suitable for attaching labels and ligands by reaction with succinimidyl ester reagents. Labeling the amine sites with fluorescent molecules and imaging the single molecules with fluorescence microscopy provides a means of determining the density of amine sites on the surface, which were incorporated into the self-assembled monolayer with micrometer spacings in proportion to the concentration of APTES in the synthesis. Biotin ligands were also bound to these surface amine sites using a succinimidyl ester linker, and the immobilized biotin was then reacted with either streptavidin-conjugated gold colloid particles or fluorescently labeled neutravidin. Imaging of these samples yields consistent amine and biotin site coverages, indicating that quantitative control and chemical conversion of binding sites can be achieved at very low (<10(-7)) fractions of a monolayer.     

Electrochemical synthesis of gold nanoparticles onto indium tin oxide glass and application in biosensors

A simple one-step method for the electrochemical deposition of gold nanoparticles (GNPs) onto bare indium tin oxide film coated glass substrate without any template or surfactant was investigated. The effect of electrolysis conditions such as potential range, temperature, concentration and deposition cycles were examined. The connectivity of GNPs was analyzed by UV-Vis absorption spectroscopy and scanning electron microscopy. The nanoparticles were found to connect in pairs or to coalesce in larger numbers. The twin GNPs display a transverse and a longitudinal localized surface plasmon resonance (LSPR) band, which is similar to that of gold nanorods. The presence of longitudinal LSPR band correlates with high refractive index sensitivity. Conjugation of the twin-linked GNPs with albumin bovine serum-biotin was employed for the detection of streptavidin as a model based on the specific binding affinity in biotin/streptavidin pairs. The spectrophotometric sensor showed concentration-dependent binding for streptavidin.     

Growth of anisotropic platinum nanostructures catalyzed by gold seed nanoparticles

This paper reports an effective method for the synthesis of platinum nanostructures with anisotropic morphologies by decomposition of platinum dichloride in oleylamine at intermediate temperatures catalyzed by gold seed nanoparticles. A small quantity of spherical gold nanoparticles formed in situ was used to trigger the nucleation and anisotropic growth of the Pt nanocrystals. By varying the amount of gold seed nanoparticles, porous flower-like, irregular polyhedron-shaped, multi-branched rod shaped, and caterpillar-like Pt nanostructures were produced in high yields at 190–240 °C in reaction times of a few minutes. Control of morphology under different conditions has been systematically studied and a kinetically controlled induced growth mechanism has been proposed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Synthesis of relatively monodisperse ZnO nanocrystals from a precursor zinc 2,4-pentanedionate

Monodisperse ZnO nanoparticles were successfully prepared through the decomposition of zinc acetylacetonate precursor in oleylamine. The samples were characterized by transmission electron microscope, X-ray diffraction and infrared spectroscopy. The particle size and morphology could be modified through tuning the reaction temperature, reaction period and concentration of zinc acetylacetonate. The grain size of monodisperse ZnO could be obtained at 205 and 300 °C for 1 h with 1:100 molar ratio of acetylacetonate and oleylamine, respectively. The average grain size of ZnO nanoparticles increased and the shape of ZnO particles varied with the reaction period prolonging or reaction temperature increasing. Some ZnO particles had self-aggregated into a belt using a solution of 1:10 molar ratio of zinc acetylacetonate and oleylamine at 250 °C for 1 h. The oleylamine plays an important role in preventing aggregation of ZnO nanoparticles.     

Anisotropic growth of gold clusters to gold nanocubes under UV irradiation

A chiral reagent, 2-naphthol, has been introduced under alkaline solution as a reductant for HAuCl(4) in CTAB micelle to produce exclusively cubic gold nanoparticles under UV photoactivation. Prolonged irradiation helped the digestion of the primarily evolved spherical particles into smaller gold nanocubes, which then act as tiny cubic seeds, leading to the formation of larger nanocubes. The smaller cubes take the assistance of CTAB under alkaline condition to serve as the seed in directing the transformation of all the spherical colloids into cubic shapes under continuous irradiation via Ostwald ripening. The shape transformation of the nanoparticles has been monitored by repetitive TEM imaging and absorption spectral analysis. The FTIR analysis proves that the gold nanocubes are capped by CTAB. The XRD pattern authenticates the formation of the fcc gold nanocubes. GCMS studies in turn confirmed the presence of hydroxylation of 2-naphthol in the course of the reaction, leaving exclusively cubic gold nanoparticles at the final stage of the photoactivation reaction.