Step-addition Method for Enhancing the Yield of Gold Nanoparticles in Block Copolymer Solution

Triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) has been used to synthesize gold nanoparticles from hydrogen tetrachloroaureate (III) hydrate (HAuCl₄·3H₂O) salt in aqueous solution at room temperature. Measurements were performed using the triblock copolymer Pluronic P85 (EO₂₆PO₃₉EO₂₆) at a fixed concentration (1 wt%) mixed with varying HAuCl₄·3H₂O concentration in the range of 0.001 to 0.1 wt%. The surface plasmon resonance (SPR) band in UV-visible absorption spectra confirmed the formation of the gold nanoparticles. The maximum yield of the nanoparticles was found at 0.005 wt% of the salt solution. Small-angle neutron scattering (SANS) does not show any significant change in the scattering profile in these suspensions of the nanoparticles. A similar behavior was also observed in dynamic light scattering (DLS) experiments where autocorrelation function was found to be independent of the salt concentration. This can be understood since a high-block copolymer-to-gold ion ratio (r ～ 22) is required in the reduction reaction to produce gold particles. As a result, a very small fraction of the block copolymers were associated with the gold nanoparticles, and hence lead to a very low yield. Both SANS and DLS basically see the micelles of most of these block copolymers, which are not associated with nanoparticles. Based on this explanation, a step-addition method was used to enhance the yield of gold nanoparticles by manifold, where the gold salt is added in small steps to maintain higher value of r (>22), and therefore continuous formation of nanoparticles.     

A novel synthesis route for a gold–polymer soft composite material

We report on the synthesis of a metal–polymer composite material using an interfacial polymerization approach. The advantage of this approach is to form an intimate contact be‐tween the metal and polymer, which is an important param‐ eter for the synthesis of a nanocomposite material. It was found that polymerization of o‐phenylenediamine (PDA) us‐ing HAuCl₄ as an oxidizing agent leads to the formation of poly‐PDA with a fiber‐like morphology, while the reduction of HAuCl₄ results in the formation of well dispersed and sta‐bilized gold nanoparticles within the polymer matrix. The synthesis was carried out at the organic–aqueous interface. The resultant composite material was purely hydrophilic in nature and deposited at the aqueous fraction of the reaction medium. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

General approach for fabricating nanoparticle arrays via patterned block copolymer nanoreactors

A general approach to fabricate nanoparticle arrays of different kinds of materials is demonstrated in this paper. It was found that the center-to-center distance of the nanoparticles or the nanoclusters can be controlled using patterned block copolymer nanoreactors by adding polystyrene (PS) homopolymer to poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) diblock copolymer thin film. The number of the nanoparticles formed in the P4VP nanodomains can also be adjusted by addition of polystyrene (PS) homopolymer to poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) diblock copolymer. In fabrication of Au nanoparticle arrays, HAuCl₄ precursor was directly loaded into P4VP nanodomains of the diblock copolymer thin film by using a methanol solvent, which is a good solvent for P4VP but non-solvent for PS. The Au nanoparticle arrays were then obtained by reducing HAuCl₄ with sodium citrate dihydrate, and then in situ transferred to silicon substrate by a two-step calcination method. ZnO and Fe _x O _y nanoparticle arrays were also synthesized by this approach with thermal decomposition and double decomposition reactions, respectively. Additionally, the advantage of using two-step calcination method over the air plasma method was discussed.     

Peptide-induced patterning of gold nanoparticle thin films

In this work, the use of patterned proteins and peptides for the deposition of gold nanoparticles on several substrates with different surface chemistries is presented. The patterned biomolecule on the surface acts as a catalyst to precipitate gold nanoparticles from a precursor solution of HAuCl₄ onto the substrate. The peptide patterning on the surfaces was accomplished by physical adsorption or covalent attachment. It was shown that by using covalent attachment with a linker molecule, the influence of the surface properties from the different substrates on the biomolecule adsorption and subsequent nanoparticle deposition could be avoided. By adjusting the reaction conditions such as pH or HAuCl₄ concentration, the sizes and morphologies of deposited gold nanoparticle agglomerates could be controlled. Two biomolecules were used for this experiment, 3XFLAG peptide and bovine serum albumin (BSA). A micro-transfer molding technique was used to pattern the peptides on the substrates, in which a pre-patterned poly(dimethylsiloxane) (PDMS) mold was used to deposit a lift-off pattern of polypropylmethacrylate (PPMA) on the various substrates. The proteins were either physically adsorbed or covalently attached to the substrates, and an aqueous HAuCl₄ solution was applied on the substrates with the protein micropatterns, causing the precipitation of gold nanoparticles onto the patterns. SEM, AFM, and Electron Beam Induced Current (EBIC) were used for characterization.     

Nanostructured Materials with Conducting and Magnetic Properties: Preparation of Magnetite/Conducting Copolymer Hybrid Nanocomposites by Ultrasonic Irradiation

Conducting copolymer poly(aniline-co-p-phenylenediamine) [poly(Ani-co-pPD)] and surface-modified magnetite (Fe₃O₄) composites were synthesized by ultrasonically-assisted chemical oxidative polymerization. Fe₃O₄ nanoparticles were surface-modified with silane coupling agent methacryloxypropyltrimethoxysilane (MPTMS) in order that they would be well dispersed for the reaction process. It was also found that the aggregation of Fe₃O₄ nanoparticles could be reduced under ultrasonic irradiation. TEM analysis confirmed that the resulting poly(Ani-co-pPD)/Fe₃O₄ nanocomposite showed core–shell morphology, in which Fe₃O₄ nanoparticles were well dispersed. The incorporation of Fe₃O₄ in the nanocomposites was endorsed by FT-IR. The nanocomposites were also confirmed by UV-visible, TGA and XRD. Conductivity of the nanocomposites was found to be in the range of 7.02 × 10^?4–6.54 × 10^?6 S/cm. Higher saturated magnetization of 12 emu/g was observed for composite with 20% Fe₃O₄.     

Phyllanthin-assisted biosynthesis of silver and gold nanoparticles: a novel biological approach

Abstract  The anisotropic gold and spherical–quasi-spherical silver nanoparticles (NPs) were synthesized by reducing aqueous chloroauric acid (HAuCl₄) and silver nitrate (AgNO₃) solution with the extract of phyllanthin at room temperature. The rate of reduction of HAuCl₄ is greater than the AgNO₃ at constant amount of phyllanthin extract. The size and shape of the NPs can be controlled by varying the concentration of phyllanthin extract and thereby to tune their optical properties in the near-infrared region of the electromagnetic spectrum. The case of low concentration of extract with HAuCl₄ offers slow reduction rate along with the aid of electron-donating group containing extract leads to formation of hexagonal- or triangular-shaped gold NPs. Transmission electron microscopy (TEM) analysis revealed that the shape changes on the gold NPs from hexagonal to spherical particles with increasing initial concentration of phyllanthin extract. The Fourier transform infrared spectroscopy and thermogravimetric analyses reveal that the interaction between NPs and phyllanthin extract. The cyclic voltammograms of silver and gold NPs confirms the conversion of higher oxidation state to zero oxidation state. Graphical abstract  Anisotropic gold and silver nanoparticles were synthesized by a simple procedure using phyllanthin extract as reducing agent. The rate of bioreduction of AgNO₃ is lower than the HAuCl₄ at constant concentration of phyllanthin extract. The required size of the nanoparticles can be prepared by varying the concentration of phyllanthin with AgNO₃ and HAuCl₄.      

Formation and encapsulation of gold nanoparticles using a polymeric amine reducing agent

We report on the use of poly(allylamine) hydrochloride (PAH) as a reducing agent for the controlled formation of gold nanoparticles (AuNPs) in the size range of 5–50 nm. The formation of AuNPs using this polymer matrix allows for the AuNPs to be imbedded in the polymer matrix, once formed. The kinetics of AuNP formation are shown to be pseudo first-order in [HAuCl₄] at room temperature. The kinetics of AuNP formation are controlled by the ratio of reducing agent to HAuCl₄ as well as the overall concentration of the PAH and HAuCl₄. Additionally, at low PAH:HAuCl₄ mole ratios, the plasmon resonance wavelength can be controlled through the ratio of the reactants. This plamson resonance shift is shown to be related to AuNP size by means of TEM imaging data on the AuNPs.     

Experimental investigations of the formation kinetics of gold nanoparticles in polymeric media

The kinetics of UV-induced formation of gold nanoparticles in polymethylmethacrylate films doped with chloroauric acid HAuCl₄ is studied. The films are investigated by the absorption spectroscopy and smallangle X-ray scattering methods. The changing size and polydispersity of gold nanoparticles are analyzed during their formation. The growth of gold nanoparticles is determined by the properties of a polymeric matrix and the rate of diffusion fluxes of matter.     

Novel fabrication and catalytic application of poly(ethylenimine)-stabilized gold–silver alloy nanoparticles

Novel synthesis of amine-stabilized Au–Ag alloy nanoparticles with controlled composition has been devised using poly(ethylenimine) (PEI) as a reducing and a stabilizing agent simultaneously. The composition of Au–Ag alloy nanoparticles was readily controlled by varying the initial relative amount of HAuCl₄ and AgNO₃. Due to the presence of abundant amine functional groups in PEI, which could act as the dissolving ligand for AgCl, the precipitation problem of Ag⁺ in the presence of Cl⁻ from the gold salt was avoided. On this basis, the relatively high concentrations of HAuCl₄ and AgNO₃ salts were used for the fabrication of Au–Ag alloy nanoparticles. The PEI thus plays triple roles in this study that include the co-reducing agents for HAuCl₄ and AgNO₃, the stabilizing agents for Au–Ag alloy nanoparticles, and even the dissolving agents for AgCl. As a novel material for use in catalysis, the Au–Ag alloy nanoparticles including pure Au and Ag samples were exploited as catalysts for the reduction of 4-nitrophenol in the presence of NaBH₄. As the Au content was increased in the Au–Ag alloy nanoparticles, the rate constant of the reduction was exponentially increased from pure Ag to pure Au.     

Fabrication of a nanostructured gold-polymer composite material

A facile synthesis route is described for the preparation of a poly-(o-aminophenol)-gold nanoparticle composite material by polymerization of o-aminophenol (AP) monomer using HAuCl₄ as the oxidant. The synthesis was carried out in a methanol medium so that it could serve a dual solvent role, a solvent for both the AP and the water solution of HAuCl₄. It was found that oxidative polymerization of AP leads to the formation of poly-AP with a diameter of 50±10nm, while the reduction of AuCl₄ ^- results in the formation of gold nanoparticles (∼ 2nm). The gold nanoparticles were uniformly dispersed and highly stabilized throughout the macromolecular chain that formed a uniform metal-polymer composite material. The resultant composite material was characterized by means of different techniques, such as UV-vis, IR and Raman spectroscopy, which offered the information about the chemical structure of polymer, whereas electron microscopy images provided information regarding the morphology of the composite material and the distribution of the metal particles in the composite material.