Carbon-supported growth of cross-linked platinum nanowires by surfactant templating and their elecrochemical characterization.

Platinum/carbon (Pt/C) composite materials were prepared by the hydrazine reduction of H2PtCl6 confined to a mixed surfactant lytropic liquid crystal (LC)/C mixture with varying amounts of water. The reaction at relatively low water contents successfully yielded cross-linked Pt nanowires with wire-widths of 2-5 nm. The novel Pt nanostructure is believed to be from poorly hydrated hexagonal domains formed together with layered domains by the phase separation of the precursory LC mixture in the presence of carbon. Electrochemical measurements using cyclic volutammetry and membrane electrode assemblies revealed that the cross-linked nanowired Pt/C composite exhibits fairly high electrocatalytic activity for oxygen reduction reaction, as well as a high performance as the cathode material for polymer electrolyte fuel cells.

Antibacterial properties of nanostructured silver titanate thin films formed on a titanium plate.

Antibacterial activity of various surfaces against methicillin-resistant Staphylococcus aureus (MRSA) was studied. Sodium titanate thin film with a porous network structure and sodium titanate nanotube thin film were formed on titanium surfaces through the reaction of titanium plates with NaOH solutions. Through a silver ion-exchange treatment, Na(+) ions in sodium titanate were exchanged with Ag(+) ions in silver acetate solution, along with the loading of silver nanoparticles on the titanate surfaces. Results of silver ion elution tests of the thin films in fetal bovine serum solution indicate that the release period and the number of silver ions released from the silver titanate thin films can be controlled by altering the crystal structure, nanostructure, and thickness of the titanate phase. The silver ion-exchanged titanate thin films showed high antibacterial activity against MRSA. It was also revealed that although the crystal structure of titanate itself has no large antibacterial effect, higher antibacterial activity mainly arises from the silver ions held in the interlayer spacing of the titanate. The obtained results should aid the development of more convenient and inexpensive antibacterial implants.

Self-organization of surfactant-metal-ion complex nanofibers on graphite surfaces and their application to fibrously concentrated platinum nanoparticle formation.

We report the fabrication of self-organized surfactant nanofibers containing platinum ions on a highly oriented pyrolytic graphite (HOPG) surface from mixed solutions of hexadecyltrimethylammonium hydroxide (C16TAOH) and hydrogen hexachloroplatinate (IV) (H2PtCl6). The fibrous surfactant self-assembly was stable in air, even after being soaked in water, in contrast to surfactant hemicylindrical micelles, which are stable only at graphite/solution interfaces. The results show that the graphite surface served as an essential template for the specific formation of fibrous surfactant self-assemblies. In addition, when surfactant nanofibers containing metal ions were treated with hydrazine, platinum nanoparticles concentrated in the nanofibers formed on the HOPG surface. We also prepared surfactant nanofibers containing gold ions on HOPG surfaces and formed gold nanoparticles in the nanofibers.

Plate, wire, mesh, microsphere, and microtube composed of sodium titanate nanotubes on a titanium metal template.

Sodium titanate nanotube/titanium metal composites were synthesized by hydrothermal treatment of titanium metals with various morphologies such as plate, wire, mesh, microsphere, and microtube at 160 degrees C in aqueous NaOH solution and by the subsequent fixation treatment by calcination at 300 degrees C. The surface of the composite was covered with sodium titanate nanotubes with a diameter of approximately 7 nm, and the core part of the composite was titanium metal phase. The raw titanium metal acts as a template or a morphology-directing agent of micrometer size or more to arrange the nanotubes as well as a titanium source for the formation of nanotubes. The concentration of titanium species increases in the reaction solution as the dissolution of titanium metal is accelerated by the reaction between titanium and OH-. Furthermore, with an increase in concentration of titanium species in the reaction solution, the titanium species are re-precipitated as sodium titanate nanotubes onto the titanium metal. Titanium metal with a large surface area and volume can form sodium titanate nanotubes on the surface of the titanium metal, though titanium metal with a small volume and surface area tends to dissolve with the hydrothermal treatment. Even in the synthesis using titanium metal with a small volume and surface area, sodium titanate nanotubes are formed and cover the surface of the titanium metal by adding another titanium metal as a source of titanium species in the reaction solution.

One-dimensional assemblies of platinum nanoparticles on a graphite surface using nonionic/ionized mixed hemicylindrical micelle templates.

One-dimensional (1-D) self-assemblies of Pt nanoparticles on a graphite surface have been synthesized via a template-directed sintering process of individual nanoparticles, using nonionic/cationic mixed hemicylindrical micelle templates of dodecyldimethylamine oxide surfactant at graphite/solution interfaces. The dimension and morphology of Pt nanoparticles can be widely controlled by the concentration of Pt ions equivalent to the mixing ratio of nonionic and cationic species in the surfactant micelle. This approach could be extended to fabricate a wide range of self-assembling metallic nanostructures on surfaces using various nonionic/cationic mixed micelle-like self-assemblies carrying metal ions at interfaces, while providing a fundamental insight into a 1-D self-assembly from individual nanoparticles.

Single-crystalline platinum nanosheets from nonionic surfactant 2-D self-assemblies at solid/aqueous solution interfaces.

Single-crystalline platinum nanosheets have been prepared via a new methodology based on the chemical reduction of a platinum salt (H2PtCl6) with hydrazine at a graphite/solution interface, using polyoxyethylene (20) sorbitan monostearate (Tween 60) based self-assembly (hemicylindrical micelle) templates. The platinum nanosheets with a uniform thickness of as thin as 3.5 +/- 1 nm are surface-smooth and continuous over relatively large length scales of micrometer sizes. In striking contrast to the Tween 60 based system, no Pt nanosheets are obtained with nonaethylene glycol monododecyl ether (C12EO9) and polyoxyethylene (23) dodecyl ether (C12EO23). No Pt nanosheets are also obtainable with a laterally homogeneous layer of Tween 60 formed at the silica/solution interface. These results indicate that surfactant Tween 60 molecules with a triple polyoxyethylene structure, as well as their hemicylindrical micelle templates, play an essential role for the formation of the Pt nanosheets. It is also suggested that the interfacially directed growth of Pt metals within the aqueous shells of the Tween 60 hemicylindrical micelles induces the thin Pt crystals as thick as the aqueous shells. The present approach could be extended to prepare a wide range of novel nanostructures of noble metals, using various micelle-like self-assemblies at interfaces.

Synthesis of high surface area hydroxyapatite nanoparticles by mixed surfactant-mediated approach.

A new surfactant-mediated approach was developed to synthesize hydroxyapatite (HAp) nanoparticles with high surface areas by calcination of their precursors encapsulated with calcium stearate using mixed surfactant-containing reaction mixtures. Acidic aqueous solution of calcium phosphate was mixed with both or either nonaoxyethylene dodecyl ether (C12EO9) and polyoxyethylene(20) sorbitan monostearate (Tween 60) and then was treated with aqueous ammonium at 25 degrees C. The C12EO9-based single surfactant system yielded an aggregate of platy HAp nanoparticles 20-40 nm in size, whereas the Tween 60-based single and mixed systems led to lath-shaped HAp nanoparticles 2-8 nm wide and encapsulated with calcium stearate. On calcination at 500 degrees C, the stearate-encapsulated HAp nanoparticles in the latter two systems were deorganized into high surface area HAp nanoparticles. Particularly, the HAp nanoparticles in the mixed system exhibited a specific surface area as high as 364 m2 g(-1) that is roughly 3 times larger than 160 m2 g(-1) for those in the single system. The significantly high surface area for the former is attributed to much less adhesion of decapsulated HAp nanoparticles, which originated from the particle-separating effect of the C12EO9 molecules adsorbed on the outer surface of the stearate-encapsulated HAp nanoparticles to inhibit their agglomeration or interfacial coordination. The present results demonstrate that the mixed use of two different surfactants as a source of encapsulating and templating agent and a particle-separating agent is specifically effective for the synthesis of high surface area HAp nanoparticles.