Reduction Of Gold Precursor Research Articles

Solubility-Driven Isolation of a Metastable Nonagold Cluster with Body-Centered Cubic Structure.

The conventional synthetic methodology for atomically precise gold nanoclusters by using reduction in solution offers only the thermodynamically most stable nanoclusters. Herein, a solubility-driven isolation strategy is reported to access a metastable gold cluster. The cluster, with the composition of [Au9 (PPh3 )8 ]+ (1), displays an unusual, nearly perfect body-centered cubic (bcc) structure. As revealed by ESI-MS and UV/Vis measurements, the cluster is metastable in solution and converts to the well-known [Au11 (PPh3 )8 Cl2 ]+ (2) within just 90 min. DFT calculations revealed that although both 1 and 2 are eight-electron superatoms, there is a driving force to convert 1 to 2 as shown by the increased cohesion and larger HOMO-LUMO energy gap of 2. The isolation and crystallization of the metastable gold cluster were achieved in a biphasic reaction system in which reduction of gold precursors and crystallization of 1 took place concurrently. This synthetic protocol represents a successful strategy for investigations of other metastable species in metal nanocluster chemistry.

Smart colloids containing ensembles of gold nanoparticles conjugated with κ-carrageenan

We study colloids of nanobiocomposites (NBC) containing Au nanoparticles (NP) obtained by reduction of gold precursor with functional groups of κCAR. The AuNPs content was changed from 2.0 to 5.6 w/w %. Hydrolysis of κCAR during reduction of gold ions produced carboxylate groups supporting nanobioconjugation (FT-IR data) and electrostatic stabilization through increased negative ζ-potential. The self-assembly of AuNPs took place after storing NBC, as shown by UV/vis. extinction and transmission electron microscopy. Analysis of the structure-sensitive Rg/Rh ratios obtained by dynamic and static light scattering showed that the colloids have core-shell structure. The macromolecules in the shell exhibited polyelectrolyte expansion at [NaCl] and [KCl] < 0.02 M. Above 0.02 M, the difference between non-specific sodium and specific potassium ions on the shell thickness was registered. The temperature hysteresis of the hydrodynamic radius Rh was similar to that of the pristine κCAR observed previously by optical rotation. Monitoring the equilibration of light scattering intensity at each mini-quenching step of the cooling run allowed further insight into the hysteresis origin. These colloids are interesting for sensing applications because of enhanced scattering of plasmonically coupled AuNPE. Their thermo- and ion-sensitivity can be useful in drug delivery.

Twofold role of Hexadecyltrimethylammonium Bromide in photochemical synthesis of gold nanorods

Abstract Synthesis of gold nanorods by photochemical reduction of gold precursor in cationic surfactant aqueous solution is studied in detail. The effect of concentration of cationic surfactant, Hexadecyltrimethylammonium Bromide, in the nanorods growth solution is examined and the optimum concentration for the synthesis estimated. Increase of the surfactant concentration, from the widely used 80 mM up to 160 mM, leads to considerable enhancement of the gold nanorods aspect ratio. The experimental results couple the improvements on the synthesis achieved increasing the surfactant concentration with the maximization of gold bromide complexes in the precursor solution. On the one hand dissociated bromide ions exchange with chloride stabilizes the gold against disproponation. So obtained strong gold bromide complexes play the role of gold precursor available for the photochemical process. On the other hand dissociated surfactant cations support the anisotropy of the growth through selective Hexadecyltrimethylammonium bilayer formation on AuNRs surfaces where bromide ions are preferentially adsorbed.

Blocking Properties of Superparamagnetic Magnetite Nanoparticles and Gold/Superparamagnetic Magnetite Composite Nanoparticles

The UV and IR block properties of superparamagnetic magnetite nanoparticles (SPMN) and SPMN/gold composite nanoparticles are investigated. The composite nanoparticles were prepared via sonochemical assisted reduction of gold precursor and deposition of gold nanoparticles (GNP) on amine functionalized SPMN. Protective properties of the SPMN and the composite nanoparticles were demonstrated via spectrophotometer measurements. Unlike in the visible and infrared region, there was 0% transmission of radiation through bare SPMN in the UV region. The presence GNP in the composites nanoparticles affects the protecting properties of the SPMN with almost 40% transmission in the UV region. The SPMN/GNP composite nanoparticles were able to block some radiation in the visible region. On the other hand, there was nearly uniform 90% and continuous transmission of infrared rays in naked SPMN and SPMN/GNP composite nanoparticles, respectively.

Localized synthesis of gold nanoparticles in anisotropic alginate structures

We present a method to create alginate nanocomposite objects having two regions with distinct chemical composition by spatially confining the synthesis of gold nanoparticles (Au NPs) in the polysaccharide matrix. Controlling the floating of sodium alginate drops on calcium chloride solution containing specific concentrations of gold ions, we demonstrate the formation of bicolour structures with a mushroom-like shape. Their immersed portion (the cap) was exclusively involved in the uptake and reduction of gold precursor, acquiring the typical purple colour of Au NPs; whereas, the emerged portion (the stem) did not participate in the in situ synthesis and retained the white colour of calcium alginate. Moreover, we noted that the localized growth of Au NPs was strongly related to the initial amount of gold precursor. In fact for high concentrations, the gold ions were just encapsulated inside the gel matrix and no reduction was observed in the wet structures neither in the cap nor in the stem. The reported procedure is simple and capable of directing the synthesis of Au NPs into selected areas of the alginate matrix, making possible the fabrication of a novel class of alginate structures with an anisotropic character and potential applications in the area of drug delivery and biosensors.

Synthesis of anisotropic gold shell on carbon nanotube

This paper reports a simple procedure to synthesize gold-coated carbon nanotubes. The method involves the reduction of gold precursor on oxidized carbon nanotubes. UV–Visible absorption spectroscopy and electron microscopy were used to study the gold precursor reduction on the carbon nanotubes. Scanning and transmission electron microscopy analysis showed the formation of an irregular gold layer around the CNT surface. The resulting nanoparticles show an anisotropic shape with dimensions between 100 and 200 nm. This hybrid material displays an intense absorption in the near infrared range with an absorption maximum at 840 nm.

Au/Au@Polythiophene Core/Shell Nanospheres for Heterogeneous Catalysis of Nitroarenes

Monodisperse Au/Au@polythiophene core/shell nanospheres were facilely prepared through the reduction of gold precursor, AuCl₄⁻, by 2-thiopheneacetonitrile in an aqueous solution. Concomitantly, 2-thiopheneacetonitrile polymerized during this redox process. As a result, Au nanoparticle was encapsulated by conductive polymer shell to afford novel core/shell nanospheres. Interestingly, the shell was composed of very tiny Au nanoparticles surrounded with thiophene polymers. Thus, the new material is best described as Au/Au@polythiophene core/shell nanospheres. FT-IR spectroscopy revealed that the Au nanoparticles were coordinated by the C≡N groups of the polythiophene shell. Some of the C≡N groups were partially hydrolyzed into COOH groups during the redox process because of the acidic reaction condition. The shell was conductive based on the typical ohmic behavior found in electrical measurement. The Au/Au@polythiophene core/shell nanospheres were found to be very active catalysts for the hydrogenation of various nitroarene compounds into corresponding aminoarene compounds in the presence of NaBH₄. Both hydrophilic and hydrophobic nitroarenes were efficiently hydrogenated under mild conditions.

Synthesis of highly fluorescent and thio-linkers stabilize gold quantum dots and nano clusters in DMF for bio-labeling

This study demonstrates a one versus two-step synthesis of fluorescent gold quantum dots (F-AuQDs) and nano clusters (F-AuNCs) functionalized with thiolated organic linkers using reduction of gold precursor in N,N′-dimethylformamide in 1 h of reaction. The F-AuQDs and F-AuNCs show fluorescence emission at 425 ± 5 nm upon excitation at 345 ± 5 nm of wavelength, with good water solubility and stability. Five different thiolated organic binary linkers consisting of various functional groups including: carboxylic acid, hydroxyl, and aromatic amine, were conjugated with the F-AuQDs and F-AuNCs. The formation mechanism and functionalization of the F-AuQDs and F-AuNCs was characterized using UV–vis absorption spectra, UV–vis light, fluorescent emission spectra, pH, TEM, and FTIR. The fluorescence emission of the F-AuQDs and F-AuNCs is greatly dependent on the thio-linker. This novel one-step approach provides facile and fast synthesis of F-AuQDs and F-AuNCs over the two-step method, with less than 5 h of reaction and workup compared to more than 28 h of reaction for the two-step approach. These thio-linker functionalized F-AuQDs and F-AuNCs have a wide application in fluorescent labeling of biomolecules, optical devices, imaging, energy transfer, and biosensing.

Chemical Kinetics of Gold Nanorod Growth in Aqueous CTAB Solutions

The chemical kinetics of the silver-mediated growth of gold nanorods prepared by the reduction of gold precursor in aqueous cetyltrimethylammonium bromide (CTAB) solution has been systematically studied using spectroscopic monitoring and electron microscopy. The rate of monomer depletion −d[Aun+]/dt has a linear dependence on both [Aun+] and seed nuclei concentration at 30 °C. Particle growth is significantly retarded by hexadecyltrimethylammonium bromide (CTAB) and KBr, with the order ca. −1 for [Br–]. The rate of nanoparticle growth is dependent on the reducing ascorbate monoanion concentration and is consequently highly pH dependent around the pKa1 of ascorbic acid, while AgNO3 retards the observed kinetics for both the growth of nanorods from ca. 2 nm seed nuclei and the overgrowth of Au nanorods.

Gold Nanoshells on Polystyrene Cores for Control of Surface Plasmon Resonance

A method is presented for synthesizing core-shell structures consisting of monodisperse polystyrene latex nanospheres as cores and gold nanoparticles as shells. Use of polystyrene spheres as the core in these structures is advantageous because they are readily available commercially in a wide range of sizes, and with dyes or other molecules doped into them. Gold nanoparticles, ranging in size from 1 to 20 nm, are prepared by reduction of a gold precursor with sodium citrate or tetrakis(hydroxymethyl)phosphonium chloride (THPC). Carboxylate-terminated polystyrene spheres are functionalized with 2-aminoethanethiol hydrochloride (AET), which forms a peptide bond with carboxylic acid groups on their surface, resulting in a thiol-terminated surface. Gold nanoparticles then bind to the thiol groups to provide up to about 50% coverage of the surface. These nanoparticles serve as seeds for growth of a continuous gold shell by reduction of additional gold precursor. The shell thickness and roughness can be controlled by the size of the nanoparticle seeds as well as by the process of their growth into a continuous shell. By variation of the relative sizes of the latex core and the thickness of the gold overlayer, the plasmon resonance of the nanoshell can be tuned to specific wavelengths across the visible and infrared range of the electromagnetic spectrum, for applications ranging from the construction of photonic crystals to biophotonics. The position and width of the plasmon resonance extinction peak are well-predicted by extended Mie scattering theory.

Iron Oxide Composite Nanoparticles and Sensing Properties

ABSTRACTThis paper reports findings of an investigation of the synthesis of monolayer-capped iron oxide and core (iron oxide)-shell (gold) nanocomposite and their assembly towards thin films as sensing materials. Pre-synthesized and size-defined iron oxide nanoparticles were used as seeding materials for the reduction of gold precursors, which was shown to be effective for coating the iron oxide cores with gold shells (Fe oxide@Au). The unique aspect of our synthesis is the formation of Fe oxide@Au core-shell nanoparticles with controllable surface properties. By controlling the reaction temperatures and manipulating the capping agent properties and solution compositions, the size, shape, composition, and monodispersity can be tailored. The core-shell nanoparticles were shown to form molecularly-mediated thin film assemblies using molecular mediators. The sensing properties of the nanostructures on piezoelectric devices were examined for the detection of volatile organic compounds. The preliminary results have provided important insights into the design of core-shell nanocomposites as sensing materials.