Synthesis of Core-Shell (Pd-Au) Bimetallic Nanoparticles in Microemulsions

Palladium-gold core-shell nanoparticles were synthesized in the aqueous domains of water in oil microemulsions by the sequential reduction of H₂PdCl₄ and HAuCl₄. The nanoparticles were characterized by ultraviolet-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). The UV-vis spectra confirm the presence of palladium nanoparticles after reducing H₂PdCl₄. These particles have been used as seeds for the core-shell particles. UV-vis spectra show that, after reducing HAuCl₄, the surface plasmon absorption of the nanoparticles is dominated by gold, revealing the encapsulation of the palladium seeds. These results agree with crystallographic analysis performed with high-resolution TEM pictures, as well as with selected area electron diffraction. The TEM pictures show the core-shell nanoparticles with an average diameter of 9.1 nm, as compared with 5 nm for the palladium seeds, in good agreement with the used Pd:Au molar ratio.     

A facile approach to synthesize poly(4-vinylpyridine)/multi-walled carbon nanotubes nanocomposites: highly water-dispersible carbon nanotubes decorated with gold nanoparticles

A facile approach to attach high-density and uniform gold nanoparticles on individual multi-walled carbon nanotubes (MWNTs) is achieved. By simple grinding, water-soluble linear polymers poly(4-vinylpyridine) (PVP)-wrapped around nanotubes and thus rendered them reversibly soluble in water, ethanol, and DMF. Individual tubes are clearly observed after PVP-wrapped nanotubes were spin-coated onto a silicon wafer. Subsequently, Au nanoparticles were densely decorated on the individual MWNTs by in situ reduction of HAuCl₄ in the homogeneous aqueous solution of MWNTs–PVP to form stable water-dispersible Au/PVP/MWNTs hybrid. Morphology of Au nanoparticles was determined by scanning electron microscope and atomic force microscope. The diameter of the Au nanoparticles is controlled in the range of 3.5 to 13.5 nm. The presence of gold nanoparticles with decreased particle size was also detected by UV–Vis spectroscopy.     

Water‐Soluble Gold Nanoparticles: From Catalytic Selective Nitroarene Reduction in Water to Refractive Index Sensing

Water‐soluble gold nanoparticles (Au NPs) stabilized by a nitrogen‐rich poly(ethylene glycol) (PEG)‐tagged substrate have been prepared by reduction of HAuCl₄ with NaBH₄ in water at room temperature. The morphology and size of the nanoparticles can be controlled by simply varying the gold/stabilizer ratio. The nanoparticles have been fully characterized by TEM, high‐resolution (HR) TEM, electron diffraction (ED), energy‐dispersive X‐ray spectroscopy (EDS), UV/Vis, powder XRD, and elemental analysis. The material is efficient as a recyclable catalyst for the selective reduction of nitroarenes with NaBH₄ to yield the corresponding anilines in water at room temperature. Furthermore, the potential ability of the Au NPs as a refractive index sensor owing to their localized surface plasmon resonance (LSPR) effect has also been assessed.     

Regioselective Bridging Calix[6]arenes: Synthesis and X-ray Structure of Trisbridged Calix[6]arene

The preparation and characterization of gold nanoparticles (～6 nm in diameter) modified with mono-6-thio-β-cyclodextrin (II) is described. The resulting monolayer-protected gold nanoparticles are water-soluble and more stable. The concentration of II plays a crucial role for the distribution of the modified nanoparticles. When the ratio of concentration of II to HAuCl₄,[II]/[HAuCl₄] ≥ 0.93, a stable gold nanoparticle with uniform distribution and diameter of 6.0 ± 0.9 nm will be obtained. The recognition of modified gold nanoparticles to organic guest molecule is researched. The modified gold nanoparticles can make the electrochemical reduction current of nitrobenzene decrease and can be self-assembled in three-dimensional to form spherical clusters with ligand of methylene green.     

Formation of gold nanoparticles in the system constituted by chloroauric acid and ED-20 epoxy oligomer

Possibility of obtaining gold nanoparticles in interaction of HAuCl₄·4H₂O with ED-20 epoxy oligomer under heating was examined. Conditions for control over the size of Au nanoparticles in the course of their formation are suggested.     

Synthesis, characterization and preliminary toxicity assays of NIR-active Au-silicate nanoparticles through a sol-gel processing

Monodisperse Au-silicate nanoparticles (10.7±1.6 nm in diameter) were prepared by reduction of aqueous solution containing 2 mM HAuCl₄ with sodium citrate (1 wt.%) in a hydrosol, in which small clusters of silicate formed by hydrolysis and polymerization of 3-aminopropyltrimethoxysilane (APTMS). APTMS covalently linked to reduced gold particles through its -NH₂ end-group. UV-vis spectra of the obtained Au-silicate nanoparticles showed a peak at ∼690 nm due to the interface effects between the Au and the silicate matrix. The Au-silicate nanoparticles exhibited near-IR (NIR) sensitivity. Cytotoxicity and limited hemocompatibility in vitro for the prepared Au-silicate nanoparticles were also investigated. It was shown that at lower concentration (<1 μg/ml), the Au-silicate nanoparticles were biocompatible without causing any cytotoxicity and hemolysis.     

Synthesis of Au nanoparticles with Bi adlayers using glucose as dispersant

Well-dispersed Au/Bi nanoparticles with average size below 10 nm were prepared by using NaBH₄ to reduce HAuCl₄ with glucose as dispersant. The obtained Au/Bi NPs were well characterized by UV-Vis spectra, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and electrochemical measurements. The electrochemical study found that Bi adlayers on the surface of Au nanoparticles owns two kinds of surface structures, including a low coverage (2 × 2)-Bi adlayer and a close-packed (p × √3)-2 Bi adlayer due to the strong interaction between the two Bi layers and the below Au atoms, which is same with that bulk on Au surface.     

Preparation of poly(styrene‐b‐N‐isopropylacrylamide) micelles surface‐linked with gold nanoparticles and thermo‐responsive ultraviolet–visible absorbance

Poly(styrene‐b‐N‐isopropylacrylamide) (PSt‐b‐PNIPAM) with dithiobenzoate terminal group was synthesized by reversible addition‐fragmentation‐transfer polymerization. The dithiobenzoate terminal group was converted into thiol terminal group with NaBH₄, resulting thiol‐terminated PSt‐b‐PNIPAM‐SH. After PSt‐b‐PNIPAM‐SH assembled into core‐shell micelles in aqueous solution, gold nanoparticles were in situ surface‐linked onto the micelles through the reduction of gold precursor anions with NaBH₄. Thus, temperature responsive core/shell micelles of PSt‐b‐PNIPAM surface‐linked with gold nanoparticles (PSt‐b‐PNIPAM‐Au micelles) were obtained. Transmission Electron Microscopy revealed the successful linkage of gold nanoparticles and the dependence of the number of gold nanoparticles per micelle on the molar ratio of HAuCl₄ to thiol group of PSt‐b‐PNIPAM. Dynamic Light Scattering analysis demonstrated thermo‐responsive behavior of PSt‐b‐PNIPAM‐Au micelles. Changing the temperature of PSt‐b‐PNIPAM‐Au micelles led to the shrinkage of PNIPAM shell and allowed to tune the distance between gold nanoparticles. Ultraviolet–visible (UV–vis) spectroscopy clearly showed the reversible modulation of UV–vis absorbance of PSt‐b‐PNIPAM‐Au micelles upon heating and cooling. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5156–5163, 2007     

Selective detection and recovery of gold at tannin-immobilized non-conducting electrode

A tannin-immobilized glassy carbon electrode (TIGC) was prepared via electrochemical oxidation of the naturally occurring polyphenolic mimosa tannin, which generated a non-conducting polymeric film (NCPF) on the electrode surface. The fouling of the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferricyanide ions as a redox marker. The NCPF was permselective to HAuCl₄, and the electrochemical reduction of HAuCl₄ to metallic gold at the TIGC electrode was evaluated by recording the reduction current during cyclic voltammetry measurement. In the mixed electrolyte containing HAuCl₄ along with FeCl₃ and/or CuCl₂, the NCPF remained selective toward the electrochemical reduction of HAuCl₄ into the metallic state. The chemical reduction of HAuCl₄ into metallic gold was also observed when the NCPF was inserted into an acidic gold solution overnight. The adsorption capacity of Au(III) on tannin-immobilized carbon fiber was 29 ± 1.45 mg g⁻¹ at 60 °C. In the presence of excess Cu(II) and Fe(III), tannin-immobilized NCPF proved to be an excellent candidate for the selective detection and recovery of gold through both electrochemical and chemical processes.     

Synthesis of Upconverting Hydrogel Nanocomposites Using Thiol‐Ene Click Chemistry: Template for the Formation of Dendrimer‐Like Gold Nanoparticle Assemblies

The synthesis of upconverting hydrogel nanocomposites by base‐catalyzed thiol‐ene click reaction between 10‐undecenoic acid capped Yb³⁺/Er³⁺‐doped NaYF₄ nanoparticles and pentaerythritol tetrakis(3‐mercaptopropionate) (PETMP) as tetrathiol monomer is reported. This synthetic strategy for nanocomposite gels is quite different from works where usually the preformed gels are mixed with the nanoparticles. Developing nanocomposites by surface modification of capping ligands would allow tuning and controlling of the separation of the nanoparticles inside the gel network. The hydrogel nanocomposites prepared by thiol‐ene click reaction show strong enhancement in luminescence intensity compared to 10‐undecenoic acid‐capped Yb³⁺/Er³⁺‐doped NaYF₄ nanoparticles through the upconversion process (under 980 nm laser excitation). The hydrogel nanocomposites display strong swelling characteristics in water resulting in porous structures. Interestingly, the resulting nanocomposite gels act as templates for the synthesis of dendrimer‐like Au nanostructures when HAuCl₄ is reduced in the presence of the nanocomposite gels.     

Synthesis of hollow and nanoporous gold/platinum alloy nanoparticles and their electrocatalytic activity for formic acid oxidation

In this work, hollow Au/Pt alloy nanoparticles (NPs) with porous surfaces were synthesized in a two-step procedure. In the first step, tri-component Ag/Au/Pt alloy NPs were synthesized through the galvanic replacement reaction between Ag NPs and aqueous solutions containing a mixture of HAuCl₄ and H₂PtCl₄. In the second step, the Ag component was selectively dealloyed with nitric acid (HNO₃), resulting in hollow di-component Au/Pt alloy NPs with a porous surface morphology. The atomic ratio of Au to Pt in the NPs was easily tunable by controlling the molar ratio of the precursor solution (HAuCl₄ and H₂PtCl₆). Hollow, porous Au/Pt alloy NPs showed enhanced catalytic activity toward formic acid electrooxidation compared to the analogous pure Pt NPs. This improved activity can be attributable to the suppression of CO poisoning via the “ensemble” effect.     

Synthesis of P(MBA-co-MAA) microsphere-grafted PAMAM dendrimers and their application as supporters for gold nanoparticles

Poly(N,N′-methylenebisacrylamide-co-acrylic acid) microsphere-supported polyamidoamine (PAMAM) dendrimers up to third generation (G) were grown onto the surface as well as the gel-layer of P(MBA-co-MAA) microspheres by a divergent method. The P(MBA-co-MAA) supported PAMAM dendrimers were used as heterogeneous stabilizers for the gold nanoparticles by an in situ reduction of HAuCl₄ via the efficient coordination interaction between the amino groups of the supported PAMAM dendrimers and the gold atoms. The effects of the generations of the P(MBA-co-MAA) supported PAMAM dendrimer on the loadings and the catalytic activity of the heterogeneous Au nanoparticles were systematically investigated with the reduction of 4-nitrophenol to 4-aminophenol as a model reaction.     

Controllable synthesis and catalysis application of hierarchical PS/Au core-shell nanocomposites

Polystyrene (PS)/gold (Au) core-shell nanocomposites with tunable size, high stability, and excellent catalytic activity have been synthesized by a facile method that combines the ionic self-assembly with the in situ reduction. The composition and stoichiometry, as well as its morphology and optical properties of these nanocomposites have been examined and verified by various characterization techniques. The size and the coverage of gold nanoparticles (NPs) can be simply tailored by changing the amount of 3-aminopropyltrimethoxysilane (APTES), the functionalization time, the protonation time, and the amount of chloroauric acid (HAuCl₄). The continuous red shifts of the localized surface plasmon resonance absorption of the Au NPs on the PS spheres are observed. Importantly, the obtained Au NPs with controllable and uniform size on the surfaces of amino-functionalized PS spheres exhibit excellent size-dependent catalytic properties for the reduction of 4-nitrophenol (4-NP) by NaBH₄.     

Preparation and Characterization of Polymer‐Protected Pt@Pt/Au Core‐Shell Nanoparticles

Poly(N‐vinyl‐2‐pyrolidone) protected Pt‐core bimetallic Pt/Au‐shell (Pt@Pt/Au) nanoparticles were prepared by multi‐step reduction of HAuCl₄ and H₂PtCl₆ alternately by hydrogen adsorbed on platinum atom. Transmission electronic microscopy (TEM) and x‐ray diffraction (XRD) were used to characterize Pt@Pt/Au nanoparticles. The structure of the shell of the nanoparticles seems to be the Au‐Pt solid solution.     

Ternary Ag/Polyaniline/Au nanocomposites: Preparation,characterization and electrochemical properties

Ternary Ag/Polyaniline/Au nanocomposites were synthesized successfully by immobilizing of Au nanoparticles (NPs) on the surface of Ag/Polyaniline (PANI) nanocomposites. Ag/PANI nanocomposites were prepared via in situ chemical polymerization of aniline in the presence of 4-aminothiophenol (4-ATP) capped silver colloidal NPs. Then, uniform gold (Au) NPs were assembled on the surface of resulted Ag/PANI nanocomposites through electrostatic interaction to get Ag/Polyaniline/Au nanocomposites. The nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), ultraviolet visible spectroscopy (UV-Vis), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). Moreover, Ag/PANI/Au nanocomposites were immobilized on the surface of a glassy carbon electrode and showed enhanced electrocatalytic activity for the reduction of H₂O₂ compared with Ag/PANI.     

Fe3O4磁性纳米粒子的超声包金及其表征

超声条件下, 在乙醇分散的3-氨丙基三乙氧基硅烷(APTES)功能化的磁性Fe₃O₄纳米粒子和四氯合金酸的混合溶液中滴加柠檬酸钠, 成功地制备了磁性Fe₃O₄/Au复合纳米粒子. 采用X射线粉末衍射仪(XRD)、紫外吸收可见光谱(UV-Vis)、带有电子能谱仪(EDS)的扫描电子显微镜(SEM)、透射电子显微镜(TEM)、光电子能谱(XPS)、超导量子干涉仪(SQUID)等方法, 对复合粒子的形态、结构、组成以及磁学性质进行了表征. 结果表明: 在此条件下制得的复合粒子粒径在30 nm左右, 室温下磁化强度可达63 emu/g.     

Biomimetic synthesis of gold nanoparticles and their aggregates using a polypeptide sequence

The polypeptide sequence MS14 (MHGKTQATSGTIQS) was used to explore a new method for biomimetic preparation of gold nanoparticles and their aggregates. Self‐congregation of gold nanoparticles into aggregates in MS14 aqueous solution and self‐assembly of gold crystallites onto the designed complex of MS14‐PET film [protonated poly(ethylene terephthalate)] proved the specific gold‐binding characteristic of the single‐copy peptide MS14 in vitro. In aqueous solution MS14 could recover Au(III) to Au(0), tested by means of TEM, EDX and XPS. Further research suggested that the pH of the solution and the concentration of Au(III) influenced the morphology and size of the gold nanoparticles formed. In addition, extra reducing agent, sodium citrate, was introduced into the HAuCl₄–MS14 system and uniformly dispersed nanoparticles under neutral condition were obtained. Finally, we discuss the possible mechanism of this biomimetic synthesis. Copyright © 2007 John Wiley & Sons, Ltd.     

Superparamagnetic POT/Fe3O4 nanoparticle composites with supported Au nanoparticles as recyclable high-performance nanocatalysts

A novel method has been developed to successfully synthesize Fe₃O₄ nanoparticles with tunable size and morphology supported on shells of poly(o-Toluidine)(POT) hollow microspheres. The as-prepared POT/Fe₃O₄ nanoparticle composites can be used as novel and magnetic-responsive catalyst supports to produce highly efficient and recyclable noble metal catalysts. The size of Fe₃O₄ nanoparticles supported on shells of POT hollow microspheres can be tuned from 4 to 12 nm by changing the concentration of Fe ions. The roles of the doping acid of POT and Zeta potentials of Fe₃O₄ nanoparticles and POT in the formation of the POT/Fe₃O₄ nanoparticle composites were discussed. Furthermore, gold nanoparticles that were supported on the as-synthesized POT/Fe₃O₄ nanoparticle composites have been achieved by utilizing the reactivity of POT towards Au ions. The size of gold nanoparticles can be tuned by altering the concentration of HAuCl₄. Finally, the catalytic activity of the obtained POT/Fe₃O₄/Au composites for 4-nitrophenol (4NP) reduction is investigated. The results demonstrate that such magnetic-responsive polymer-supported gold nanoparticles can be easily recovered and reused five times still remains high catalytic performance, which indicate their potential applications in the field of catalysis.     

Biosynthesis of gold nanoparticles using Allium noeanum Reut. ex Regel leaves aqueous extract; characterization and analysis of their cytotoxicity,antioxidant, and antibacterial properties

Gold nanoparticles have unique and excellent medical and nonmedical properties and application compared with other metallic nanoparticles. Recently, they have been used for the prevention, control, and treatment of bacterial and fungal diseases. In the recent study, fresh and clean leaves of Allium noeanum Reut. ex Regel leaves have been used for the synthesis of gold nanoparticles. Also, we evaluated the cytotoxicity, antioxidant, and antibacterial properties of HAuCl₄, A. noeanum, and the synthesized nanoparticles (Au NPs). These nanoparticles were analyzed by FT‐IR, UV, XRD, EDS, FE‐SEM, and TEM tests. FTIR results offered antioxidant compounds in the plant were the sources of reducing power, reducing gold ions to Au NPs. In TEM images revealed an average diameter of 10‐30 nm. At the beginning of biological experiments, DPPH free radical scavenging test was carried out to examine the antioxidant property. Also, in the bacterial part of this study, the concentration of HAuCl₄, A. noeanum, and AuNPs with minimum dilution and no turbidity was considered MIC. To determine MBC, 60 μL of MIC and three preceding chambers were cultured on Muller Hinton Agar. The minimum concentration with no bacterial growth was considered MBC. Au NPs revealed excellent antioxidant potential against DPPH, non‐toxicity property against human umbilical vein endothelial cells, and antibacterial activities against Streptococcus pneumonia, Bacillus subtilis, Staphylococcus aureus, Staphylococcus saprophyticus, Salmonella typhimurium, Pseudomonas aeruginosa, Shigella flexneri, and Escherichia coli O157:H7. These findings show that the inclusion of A. noeanum extract improves the solubility of Au NPs, which led to a notable enhancement in the antioxidant and antibacterial effects.     

Synthesis of gold/polydopamine composite surfaces on glass substrates for localized surface plasmon resonance and catalysis

Composite materials of polydopamine (PDA) and gold nanoparticles on glass substrates (Au/PDA@slide) were obtained via a simple chemical process. First, PDA films (PDA@slide) were formed by immersing slides in 20 mg ml⁻¹ dopamine aqueous solution at pH = 8.5 for 1 h. Then, PDA@slide was dipped in 0.02 M chloroauric acid (HAuCl₄) aqueous solution for a certain time, Au/PDA@slide being formed. Gold nanoparticles were obtained by the reductive properties of PDA. The morphology and chemical composition of the composite material were characterized using scanning electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy. The catalytic properties of Au/PDA@slide were evaluated using the reduction of 4‐nitrophenol (4‐NP) in the presence of sodium borohydride (NaBH₄) aqueous solution at room temperature. The catalytic activity of the optimal Au/PDA@slide was so satisfactory that the reduction of 4‐NP was completed within 10 min. Moreover, the Au/PDA@slide composite material was stable up to five cycles without significant loss of its catalytic activity. In addition, Au/PDA@slide also exhibited photocatalytic ability, photodegrading 2.5 ml of 17.5 mg l⁻¹ methyl orange in 100 min. By measuring the UV–visible absorption bands of Au/PDA@slide, it was proved that the condition of the strongest surface plasmon resonance of Au/PDA@slide was the optimal condition for catalytic reduction of 4‐NP.