Flat gold nanostructures by the reduction of chloroaurate ions constrained to a monolayer at the air-water interface

Formation of flat gold nanostructures occurs by the reduction of a Langmuir monolayer of hydrophobized chloroaurate ions using anthranilic acid as a reducing agent present in the subphase. Vigorous shaking of the aqueous chloroauric acid solution with a solution of surfactant, such as octadecylamine (ODA) or benzyldimethylstearylammonium chloride (BDSAC) in chloroform results in rapid transfer of chloroaurate ions (AuCl4−) from the aqueous phase to the chloroform phase. Strong electrostatic interactions between negatively charged chloroaurate ions and cationic head groups of ODA and BDSAC molecules, making the gold ions sufficiently hydrophobic, are believed to be responsible for the transfer of AuCl4− ions from the aqueous to the organic phase. Surface pressure-area (Π-A) isotherm measurements reveal that these hydrophobized chloroaurate ions behave as amphiphilic molecules and form stable Langmuir monolayers on the acidic aqueous subphase. Spreading of hydrophobized chloroaurate ions on the surface of aqueous anthranilic acid solution results in the immobilization of AuCl4− ions strictly at the two dimensional surface. Hence, further reduction of these AuCl4− ions by anthranilic acid molecules from the subphase leads to the formation of highly anisotropic, flat gold nanostructures at the air-water interface. The capping of gold nanoparticles formed at the air-water interface by ODA and BDSAC enables their facile transfer as multilayers onto suitable solid substrates by the Langmuir-Blodgett (LB) technique. Multilayer Langmuir-Blodgett films were characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), electron diffraction and X-ray photoelectron spectroscopy

Silver nanoparticles of variable morphology synthesized in aqueous foams as novel templates

In this paper, we describe the synthesis of silver nanocrystals within aqueous foams as a template. More specifically, we show that aqueous Ag+ions may be electrostatically complexed with the anionic surfactants aerosol OT (sodium bis-2-ethylhexyl-sulfosuccinate, (AOT) and sodium dodecyl sulphate (SDS)) in a highly stable liquid foam. After drainage of the foam, the silver ions are reducedin situby introducing sodium borohydride into the foam by capillary flow. This leads to the formation of silver nanoparticles of spherical, tape-and sheet-like morphology in the foam. The structure of the foam is extremely complex and presents reaction sites of different spatial extent. The differences in foam reaction-site geometry are believed to be responsible for the morphology variation in the silver nanoparticles observed. The silver nanoparticles are observed to be extremely stable in solution suggesting that the AOT or SDS molecules stabilize them. This approach appears promising for application in large-scale synthesis of nanoparticles and may be readily extended to other chemical compositions

Variation in morphology of gold nanoparticles synthesized by the spontaneous reduction of aqueous chloroaurate ions by alkylated tyrosine at a liquid-liquid and air-water interface

We demonstrate the formation of gold nanocrystals of different morphologies using alkylated tyrosine (AT) as a reducing agent at a liquid-liquid and air-water interface. The reduction of aqueous chloroaurate ions occurs in a single step wherein the AT molecule plays the multifunctional role of a phase transfer, reducing and capping agent. Gold nanoparticles formed at the air-water interface are very thin, flat sheet or ribbon-like nanostructures, which are highly oriented in the (111) direction. On the other hand, reduction of aqueous chloroaurate ions at a liquid-liquid interface by AT molecules present in the organic phase yielded nanoparticles having predominantly spherical morphology but with no specific crystallographic orientation. The difference in morphology of the nanoparticles may be due to the different orientational and translational degrees of freedom of the AT molecules and gold ions at these two interfaces. The AT-capped gold nanoparticles were characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and nuclear magnetic resonance spectroscopy (1H NMR), while the LB films of flat gold sheets were also studied by X-ray photoemission spectroscopy (XPS)

Synthesis of a stable gold hydrosol by the reduction of chloroaurate ions by the amino acid, aspartic acid

Development of reliable protocols for the synthesis of nanoparticles of well-defined sizes and good monodispersity is an important aspect of nanotechnology. In this paper, we present details of the synthesis of gold nanoparticles of good monodispersity by the reduction of aqueous chloroaurate ions by the amino acid, aspartic acid. The colloidal gold solution thus formed is extremely stable in time, indicating electrostatic stabilization via nanoparticle surface-bound amino acid molecules. This observation has been used to modulate the size of the gold nanoparticles in solution by varying the molar ratio of chloroaurate ions to aspartic acid in the reaction medium. Characterization of the aspartic acid-reduced gold nanoparticles was carried out by UV-visible spectroscopy, thermogravimetric analysis and transmission electron microscopy. The use of amino acids in the synthesis and stabilization of gold nanoparticle in water has important implications in the development of new protocols for generation of bioconjugate materials

One-step synthesis of hydrophobized gold nanoparticles of controllable size by the reduction of aqueous chloroaurate ions by hexadecylaniline at the liquid-liquid interface

Vigorous stirring of a biphasic mixture containing hexadecylaniline in chloroform and aqueous chloroauric acid results in the formation of gold nanoparticles of controllable size in the organic phase

Use of aqueous foams for the synthesis of gold nanoparticles of variable morphology

In this paper we describe the facile synthesis of gold nanocrystals of variable morphology using aqueous foam as a template. The aqueous foams are formed by bubbling an aqueous solution of AuCl−4 ions electrostatically complexed with the surfactant cetyltrimethylammonium bromide (CTAB). The gold ions in the stable foam are then reduced by hydrazine vapours, this process leading to the formation of gold nanoparticles of spherical, flat plate and flake-like structures. The variation in morphology of the gold nanoparticles derived from the foam is believed to arise from the complex spatial structure of reaction sites in the foam. The foam-derived gold nanoparticles were analysed by UV-vis spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy

Foam-based synthesis of cobalt nanoparticles and their subsequent conversion to Co<SUB>core</SUB>Ag<SUB>shell</SUB> nanoparticles by a simple transmetallation reaction

Cobalt nanoparticles have been synthesized via a novel, foam-based protocol. The foam is formed from an aqueous mixture of Co2+ ions, an anionic surfactant and oleic acid where the cobalt ions are electrostatically entrapped by the surfactant at the thin borders between the foam bubbles and their junctions. The entrapped cobalt ions may be reduced in-situ by a moderately strong reducing agent resulting in the formation of nanoparticles with the foam playing the role of a template. The nanoparticles are immediately capped and stabilized against oxidation by oleic acid present in the foam matrix. The oleic acid-capped Co nanoparticles can be redispersed either in an aqueous or organic medium making this procedure very attractive. The cobalt nanoparticles are readily converted to CocoreAgshell nanoparticles by simple addition of a silver salt to the Co nanoparticle solution, the cobalt atoms on the nanoparticle surface acting as localized reducing agents for the silver ions