Distribution Of Au Nanoparticles Research Articles

Assembly of evenly distributed Au nanoparticles on thiolated reduced graphene oxide as an active and robust catalyst for hydrogenation of 4-nitroarenes

Au/SRG nanohybrid with evenly distributed Au nanoparticles anchored on reduced graphene oxide via covalent thiol linkage shows superior catalytic performance for hydrogenation of 4-nitrophenol.

Electroanalytical applications of a graphite–Au nanoparticles composite included in a sonogel matrix

A novel sonogel composite stably including graphite grains studded with Au nanoparticles (AuNPs) has been synthesised with the aim of obtaining an electrode characterised by electrocatalytic activity, reduced surface passivation and simple and reproducible surface renewal. The impregnation of graphite grains with pre-synthesised AuNPs constitutes a valid approach to stably fix a high amount of AuNPs in such an inorganic matrix. As verified by TEM images, AuNPs fixed on carbon grains surface maintain their individual nature, constituting the basic feature for exerting their electrocatalytic and antifouling properties at best. The electrode was characterised through morphological and electrochemical investigations, demonstrating the uniform distribution of AuNPs on the surface and at different depth of the bulk. Finally, electrochemical tests carried out on the cathodic reduction of H2O2 and on the anodic oxidation of glucose demonstrate the electrocatalytic activity of the AuNPs, the high repeatability of the responses obtained and the reproducibility of the electrode systems, simply restored by routine mechanical cleaning procedure. At variance with many non-enzymatic electrode systems developed for glucose determination, the sensor proposed is suitable for the determination of such a species even at the physiologic neutral pH.

Plasmonic Au nanoparticles on 8 nm TiO2 nanotubes for enhanced photocatalytic water splitting

We report here for the first time a successful distribution and attachment of fine Au nanoparticles on ∼8 nm diameter TiO2 nanotubes having significantly increased surface area. Au thin film deposition onto hydrothermally grown TiO2 nanotube arrays followed by thermal annealing breaks up the Au film into desired, uniformly distributed nanoparticles. Visible light absorption spectra of the gold nanoparticles on TiO2 nanotubes indicate that the Au nanoparticles are photo-excited due to plasmon resonance, and charge separation is accomplished by the transfer of photoexcited electrons from the gold particle to the TiO2 conduction band, thereby enhancing photoelectrochemical performance. By virtue of substantially increased surface area with the 8 nm TiO2 nanotube substrate in combination with the plasmonic effect of distributed Au nanoparticles, significantly increased photocurrent density was obtained with extended light absorbance from the UV regime to the visible spectrum region. Such gold nanoparticle decorated, fine TiO2 nanostructures fabricated by a simple and versatile method can be useful for hydrogen generation by water splitting, CO oxidation and various other types of photocatalysts and photovoltaic fuel cells.

Selective deposition of gold nanoparticles on the top or inside a thin conducting polymer film, by combination of electroless deposition and electrochemical reduction

In this paper we present the procedures allowing for synthesis of the composite systems in which Au nanoparticles are located: (i) only on the surface of the polymer film, (ii) only inside the polymer matrix or (iii) both on the polymer surface and in the polymer film. Thin poly(1,8-diaminocarbazole) (PDACz) films were electrodeposited on gold or highly oriented pyrolytic graphite (HOPG) electrodes from acetonitrile solution. Then, Au nanoparticles (NPs) were formed either by electroless deposition on the polymer layer in the solution of HAuCl4 or by electrochemical reduction of AuCl4− incorporated into the polymer matrix, carried out in the solution of HClO4. The amount of deposited Au was determined from electrochemical quartz crystal microbalance measurements and from the reduction charge. The role of protonation of amino groups of the polymer in the process of AuCl4− insertion into the polymer matrix has been discussed. A distribution of Au nanoparticles on the top and inside the polymer film was studied by SEM and TEM images of the polymer cross sections prepared by focused ion beam (FIB) method.

In Situ “Doping” Inverse Silica Opals with Size-Controllable Gold Nanoparticles for Refractive Index Sensing

We report the fabrication of inverse SiO2 opals “doped” with gold (i-Au-SiO2-o) nanoparticles (NPs) via a co-self-assembly method combined with subsequent removal of polystyrene colloidal spheres by calcination. The resulting i-Au-SiO2-o films demonstrate long-range ordering with uniform distribution of ligand-free Au NPs. The size of Au NPs can be tuned from 6 to 30 nm by varying the calcination temperature. The as-prepared i-Au-SiO2-o films preserve both localized surface plasmon resonance (LSPR) and Bragg diffraction peaks simultaneously. Both LSPR and Bragg diffraction peaks are sensitive to the refractive index changes of the surrounding medium—an important feature for sensing applications. The method provides a facile and versatile way to fabricate high-quality Au NP “doped” photonic crystals for applications in sensing and others.

Effect of clustering on ellipsometric spectra of randomly distributed gold nanoparticles on a substrate

We present a theoretical model for describing light scattering from randomly distributed Au nanoparticles on a substrate, including the clustering effect. By using the finite-element Green's function method and spherical harmonic basis functions, we are able to calculate the polarization-dependent reflectivity spectra of the system (modeled by randomly distributed nanoparticles coupled with clusters) efficiently and accurately. The calculated ellipsometric spectra of the system with clusters can adequately describe the experimental data for the whole frequency range. We find that the clustering effect leads to some prominent features in the low frequency range of the ellipsometric spectra, which are attributed to plasmonic resonances associated with the coupling of Au nanoparticles and clusters.

Selective growth of Au nanoparticles on PZT substrates by using a photochemical reaction

We report the surface distribution of Au nanoparticles (NPs) grown on polarity-patterned ferroelectrics by using photochemical-reaction deposition. Polycrystalline lead zirconate titanate (PZT) was used as a ferroelectric substrate. The local polarization orientation on the surface was patterned by using atomic force microscopy (AFM). The Au NPs were grown by ultraviolet (UV) light exposure of the polarity-patterned PZT substrates while immersed in Au salt solutions. The wavelength dependence of the deposition of the NPs was investigated using UV band pass filters. The dimensions and the surface distribution of the NPs were measured by using AFM. For UV light without a filter, more NPs were formed on the +z polarity region than on the other regions. However, for UV light with wavelengths of 315 nm and 365 nm, we observed the selective deposition of NPs on +z polar domains. The NPs on the +z polar domains were denser and larger than those on the other non-polar regions. The average size of the NPs was ∼30 nm and the number density was ∼22/µm2. In addition, the electron affinity of the PZT was found to be ∼3.0 eV from scanning Kelvin probe microscopy measurements of the PZT film surface with the deposition of Au NPs. This study suggests the possibility of controlling the sizes and the positions of Au NPs on a surface by optimizing the UV wavelength and polarity patterning of the ferroelectrics.

Digital simulation for 3D reconstruction of coherent x-ray diffractive imaging

In coherent x-ray diffractive imaging, the oversampled far-field diffraction pattern for phase retrieval iterative algorithm is used in order to reconstruct the information about the real space. The support constraint is one of the most important steps of the 3D phase retrieval process. Here we use a small nonperiodic 2D digital image as an object for studying the algorithm of pursuing support constraint automatically and noise correction for different types of noises in the diffraction pattern. We find an efficient method of noise correction while the traditional methods do not work well in the high noise condition. The result shows that this method can be used to reduce the effect effectively for the reconstruction. We also study the 3D reconstruction for the electron density distribution of Au nano-particles. We achieve a good reconstruction separately with and without noise effect in the diffraction pattern and we find that the signal-to-noise ratio should be bigger than 27 for successful 3D reconstruction.

Preparation and high-temperature properties of Au nano-particles doped α-Al2O3 composite coating on TiAl-based alloy

Au nano-particles doped α-Al2O3 composite coatings were successfully prepared on TiAl-based alloy by electrodeposition, using the Al2O3 sols with minor addition of HAuCl4 solution. The even distribution of Au nano-particles (<2.0wt.%) in the α-Al2O3 matrix has been observed. Isothermal oxidation tests of the samples coated with the as-prepared novel coatings at 900°C in static air for 200h shown that the oxygen inward diffusion can be effectively suppressed to a low level. The results of high-temperature cyclic oxidation test at 900°C in air revealed that the oxidation and spallation resistance of TiAl-based alloy were improved significantly under thermal cycling. In the as-prepared coatings, cracks were shielded by means of crack bridging and the fracture resistance of the formed scales can be improved by toughening effects of the composite structure. Surface scratching tests after the cyclic oxidation exhibited that the adhesion of the formed composite scale on TiAl-based alloy was remarkably improved by the Au nano-particles doped α-Al2O3 composite coating.

Evaluation of a modified carbon micromesh electrode as a new substrate for electrochemical immunosensing

Here we report a novel immunosensor platform technology based on self-assembled monolayer (SAM) of electrodeposited gold (Au) nanostructures with subsequent antibody attachment. Carbon cloth micro-fibres were employed for the first time as a working electrode in an immunosensor device. Uniform distribution of Au nanoparticles was achieved on the surface of microfibers with regulation of particle size and shape made possible via controlled scan rate during deposition from aqueous AuCl4. The electrodes were successfully characterised using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA). Chemiluminescence detection confirmed successful attachment of anti-actin antibodies onto the modified conducting surface, allowing detection of various concentrations of the actin antigen (0.1–1 µg ml−1). The binding of antigen to antibody was successfully measured using EIS in 1 mM K3Fe(CN)6/K4Fe(CN)6 as a redox probe, which allowed determination of charge transfer resistance (Rct) changes upon binding. A linear increase in Rct was observed with increasing concentration of antigen (actin). Therefore, we have clearly demonstrated that this new electrochemical immunosensor design is effective, and can be applied to the analysis of a clinically significant protein.

Zinc Phthalocyanine and Silver/Gold Nanoparticles Incorporated MCM-41 Type Materials as Electrode Modifiers

Mercaptopropyl functionalized ordered mesoporous silica spheres were prepared (MPS). Ag or Au nanoparticles (NPs) were anchored onto the MPS materials (Ag-MPS or Au-MPS). Further, zinc phthalocyanine (ZnPc) was adsorbed into the channels and surface (MPS-ZnPc, Ag-MPS-ZnPc, Au-MPS-ZnPc). Diffuse reflectance studies revealed the successful incorporation of Ag or Au NPs inside the silica spheres with and without ZnPc. TEM images showed the uniform distribution of Ag or Au NPs in the silica spheres of different size ranging from 4 to 22 nm or 6 to 31 nm, respectively. XRD pattern showed average crystallite particle size of 18 or 28 nm for Ag or Au NPs respectively which were reduced to 14 or 16 nm on introduction of ZnPc which oxidizes the metal NPs partially. Chemically modified electrodes were prepared by coating the colloidal solutions of the silica materials on the glassy carbon (GC) electrodes. Electrocatalytic reductions of O(2) and CO(2) at the modified electrodes were studied. The presence of Ag or Au NPs was found to increase the electrocatalytic efficiency of ZnPc toward O(2) reduction by 290% or 70% based on the current density measured at -0.35 V and toward CO(2) reduction by 150% or 120% based on the current density measured at -0.60 V respectively. Catalytic rate constants were increased 2-fold for O(2) reduction and 8-fold for CO(2) reduction due to Ag or Au NPs, respectively, which act as nanoelectrode ensembles. The synergic effect of ZnPc and metal NPs on the electrocatalytic reduction of O(2) is presented.

Formation of ultrafine uniform gold nanoparticles by sputtering and redeposition

Uniformly distributed Au nanoparticles with controllable size were fabricated by focused ion beam bombardment of thin gold films. In situ scanning electron microscopy and ex situ transmission electron microscopy were used to characterize the nanoparticles. Results show that a dual particle size distribution was generated at low ion fluence, while highly uniform Au particles with diameters around 2 nm formed at high fluence. The balance between sputtering and redeposition is responsible for the formation and size control of the nanoparticles. Optical absorption measurement revealed strong size dependant resonances that are attributed to the surface plasmon resonance of the Au particles.

Determination of the size distribution of metallic nanoparticles by optical extinction spectroscopy

A method is proposed to estimate the size distribution of nearly spherical metallic nanoparticles (NPs) from optical extinction spectroscopy (OES) measurements based on Mie's theory and an optimization algorithm. The described method is compared against two of the most widely used techniques for the task: transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS). The size distribution of Au and Cu NPs, obtained by ion implantation in silica and a subsequent thermal annealing in air, was determined by TEM, grazing-incidence SAXS (GISAXS) geometry, and our method, and the average radius obtained by all the three techniques was almost the same for the two studied metals. Concerning the radius dispersion (RD), OES and GISAXS give very similar results, while TEM considerably underestimates the RD of the distribution.

Formation of gold nanoparticles on multiwalled carbon nanotubes by thermal evaporation

Multiwalled carbon nanotubes (MWCNTs) were grown on W substrates by chemical vapor deposition and modified with Au nanoparticles by thermal evaporation. The resulting hybrid structures were investigated by TEM to determine the effects of evaporation rate, nominal film thickness, and substrate temperature on the nanoparticle size and distribution. The results demonstrate that as-grown MWCNTs can be used as a support for well distributed Au nanoparticles, with the size and distribution on the carbon nanotubes being primarily influenced by the nominal film thickness. The observed structures ranged from small 4 nm diameter spherical particles to 150 nm long wire-like structures. Depositions with substrates at 25 °C and 400 °C resulted in similar particle structures, except for the highest amount of deposited Au.

Synthesis of Gold Nanoparticles Supported by Aggregated Assemblies of Triblock Copolymers in Aqueous Phase : Effect of Temperature

The effect of temperature on the self-assembled behavior of polymers P103 and P84, and their subsequent use as soft templates for the synthesis of gold (Au) nanoparticles (NP) have been studied with the help of SEM, TEM, and UV-vis spectral measurements. Both the triblock copolymers (TBP) exist in the form of liquid crystalline thread like assemblies. P103 being more hydrophobic shows a structural transition from liquid crystal (LC) threads to sheets at 50°C and bear uniformly distributed Au NP, the size of which increases with the increase in temperature. P84 being more hydrophilic shows only LC threads and no sheets, but the LC threads bearing running groove at 50°C, act as wonderful nucleation sites for the growth of large cubic Au NP. The presence of surface cavities constituted by polyethylene oxide (PEO) and polypropylene oxide (PPO) blocks on LC phase of both TBPs are considered to be the nucleation sites for Au NP. The greater hydrophobicity of P103 in comparison to P84 favors the uniform distribution of NP throughout the LC phase while an increase in the temperature facilitates this process.

SEC Characterization of Au Nanoparticles Prepared through Seed-Assisted Synthesis

In this paper we report the use of size-exclusion chromatography (SEC) for rapid determination of the sizes and size distributions of Au nanoparticles (NPs) prepared by seed-assisted synthesis. Analytical separation of Au NPs was performed in a polymer-based column of pore size 400 nm. We characterized the sizes and size distributions of the Au NPs by using 10 mM sodium dodecyl sulfate (SDS) as mobile phase and obtained a linear relationship (R 2 = 0.986) between retention time and size of Au NPs within the range 9.8–79.1 nm; the relative standard deviations of these retention times were less than 0.3%. These separation conditions were used to characterize the sizes and size distributions of Au NPs prepared by seed-assisted synthesis. In addition to observing the elution times of the Au NPs we also simultaneously characterized their size-dependent optical properties by spectral measurement of the eluting peaks by use of an on-line diode-array detector (DAD), i.e., monitoring of the stability of the Au NP products. By using this approach we found the presence of SDS was beneficial in stabilizing the synthesized Au NPs. We also found that the volume of Au metal ions used affected the sizes of the final products. SEC seems an efficient tool for characterizing the sizes of NPs fabricated by seed-assisted synthesis.

Electrochemical determination of dopamine and ascorbic acid at a novel gold nanoparticles distributed poly(4-aminothiophenol) modified electrode

A modified electrode is fabricated by embedding gold nanoparticles into a layer of electroactive polymer, poly(4-aminothiophenol) (PAT) on the surface of glassy carbon (GC) electrode. Cyclic voltammetry (CV) is performed to deposit PAT and concomitantly deposit Au nanoparticles. Field emission transmission electron microscopic image of the modified electrode, PAT-Au(nano)-ME, indicates the presence of uniformly distributed Au nanoparticles having the sizes of 8-10nm. Electrochemical behavior of the PAT-Au(nano)-ME towards detection of ascorbic acid (AA) and dopamine (DA) is studied using CV. Electrocatalytic determination of DA in the presence of fixed concentration of AA and vice versa, are studied using differential pulse voltammetry (DPV). PAT-Au(nano)-ME exhibits two well defined anodic peaks at the potential of 75 and 400mV for the oxidation of AA and DA, respectively with a potential difference of 325mV. Further, the simultaneous determination of AA and DA is studied by varying the concentration of AA and DA. PAT-Au(nano)-ME exhibits selectivity and sensitivity for the simultaneous determination of AA and DA without fouling by the oxidation products of AA or DA. PAT and Au nanoparticles provide synergic influence on the accurate electrochemical determination of AA or DA from a mixture having any one of the component (AA or DA) in excess. The practical analytical utilities of the PAT-Au(nano)-ME are demonstrated by the determination of DA and AA in dopamine hydrochloride injection and human blood serum samples.

Molecular Ordering and 2D Conductivity in Ultrathin Poly(3-hexylthiophene)/Gold Nanoparticle Composite Films

This paper reports the first comparison of the structure and electrical conductivity properties of spin cast (SC) and Langmuir-Schaeffer (LS) films of regioregular poly(3-hexylthiophene) (P3HT). In addition, the effect of incorporating highly monodisperse Au nanoparticles (NPs), with a core diameter of approximately 5 nm, into SC and LS P3HT films is described. A detailed picture of molecular organization in the films has been obtained using ultraviolet-visible absorption spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. Film morphology was correlated with pseudo-two-dimensional conductivity measured using scanning electrochemical microscopy, with P3HT in the semiconducting regime. It was found that SC films, which were slightly thicker than those formed with the LS technique, exhibited greater organization. This resulted in an order of magnitude higher lateral conductivity for the SC films. Inclusion of Au NPs (50 wt %) into both SC and LS films resulted in the formation of uniform and relatively flat (rms roughness approximately 1 nm) composite films. Surprisingly, the addition of NPs did not disrupt the characteristic crystal structure found for the native P3HT films. The effect of Au NPs on film lateral conductivity was found to be determined by the distribution of Au NPs within the polymer, which varied significantly between SC and LS films. Whereas Au NPs aggregated into hexagonally packed clusters in SC films, NPs in LS films were predominantly uniformly distributed between the lamella bilayer. It was found that, while the inclusion of Au NPs caused the lateral conductivity to decrease in SC films, in LS films, the lateral conductivity increased by a factor of 2.

TEM characterization of Au nano-particles in TiO2 single crystals by ion implantation

Nano-particles of Au embedded in TiO2 (rutile) single crystals have been synthesized by 260keV Au ion implantation up to a fluence of 5×1016ions/cm2. Cross-sectional and high resolution transmission electron microscopy (TEM) has been utilized to characterize the size and depth distribution as well as the microstructure of Au nano-particles. The size of Au nano-particles varies 1–20nm in the TiO2 matrix and the maximum particle size increased with the increasing implantation fluence. These large particles gradually moved toward the surface as implantation fluence increases. Most of Au nano-particles have a specific orientation relationship with the original TiO2 matrix in both as-implanted and post-implantation annealed samples, which is: [110]Au∥[110]TiO2 and (002)Au∥(2¯2¯0)TiO2, although the implanted regions of TiO2 were entirely amorphized. The influences of dose rate and annealing on the size and distribution of Au nano-particles are also discussed.

The dispersion of Au nanoparticles in SiO 2/TiO 2 layered films by the liquid phase deposition (LPD) method

Au nanoparticles dispersed SiO 2/TiO 2 layered films were prepared by a novel wet process known as the liquid phase deposition method. Their structure, surface morphology, chemical states, particle size and optical properties were investigated by using X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy and ultraviolet–visible absorption spectroscopy. Au nanoparticles were obtained in the both oxide matrices by the thermal reduction. The XPS studies showed that Au III and Au I ionic species were co-deposited in the SiO 2/TiO 2 layered films. TEM observation revealed that the most of Au nanoparticles were transferred into the crystalline anatase TiO 2 matrix after the heat treatment. It was found that, the distributed Au nanoparticles were more stable in the crystalline TiO 2 than amorphous SiO 2 matrix. The mean size of Au in SiO 2 (∼ 15 nm) is larger than that of TiO 2 (∼ 5 nm) matrix. An absorption peak of Au particles was observed at the wavelength of ca. 570 nm which could be assigned to the surface plasmon absorption band of Au nanoparticles.