A lot of attention is currently focused on nanosized tubular materials because of their unique physical properties and potential applications as gas and fluid paths or reservoirs in catalysis, fuel cells, sensors, and separation systems. [1] Since the discovery of carbon nanotubes, [2] there have been reports on a variety of inorganic nanotubes based on boron nitride, [3] metal sulfides, [4] metal borates [5] and metal oxides. [6] Besides high-temperature processes, [2][3][4][5] another approach that makes use of solid or molecular templates [6] has been developed for the synthesis of such nanotubular materials. For metals important in catalysis and other nanotechnological fields, synthesis by using nanoporous polymer and anodic aluminum films as templates led to gold, [7a] nickel, [7b] and palladium [7c] nanotubes, but with inner diameters as large as 10-100 nm. Furthermore, no report has appeared on the fabrication of metal nanotubes by using a surfactant or other molecular templates, although mesoporous platinum was obtained by using the lyotropic liquid crystals (LCs) of nonionic surfactants. [8] In brief, the previous templating approaches to metals yielded only nanoporous materials or thick-walled tubular structures. This fact seems to suggest that thin-walled metal nanotubes with diameters below 10 nm might be unobtainable because of their extremely high surface energies, in spite of their potentially attractive functionalities, as expected by analogy with the magnetically and catalytically unique properties of platinum nanowires. [9] The previous surfactant templating process that was first applied to the synthesis of mesoporous silica MCM-4, [10] used almost exclusively a single ionic or nonionic surfactant. In contrast, our recent study revealed that the lyotropic nematic media of nonionic-cationic mixed surfactant are effective for the preparation of tin oxide microwires. [11] This motivated us to apply such a mixed surfactant template to the fabrication of nanostructured metals. Herein we demonstrate the first synthesis of platinum, palladium, and silver nanotubes, with inner diameters of
Nanohole‐structured single‐crystalline Pt nanosheets have been synthesized by the borohydride reduction of Na2PtCl6 confined to the lyotropic liquid crystals (LLCs) of polyoxyethylene (20) sorbitan monooleate (Tween 80) with or without nonaethylene‐glycol (C12EO9). The Pt nanosheets of around 4–10 nm in central thickness and up to 500 nm or above in diameter have a number of hexagonal‐shaped nanoholes ∼1.8 nm wide. High‐resolution electron microscope images of the nanosheets showed atomic fringes with a spacing of 0.22 nm indicating that the nanosheets are crystallographically continuous through the nanoholed and non‐holed areas. The inner‐angle distributions for the hexagonal nanoholes indicate that the six sides of the nanoholes are walled with each two Pt (111), Pt (1${\bar {1}}$1) and Pt (010) planes. The formation mechanism of nanoholed Pt nanosheets is discussed on the basis of structural and compositional data for the resulting solids and their precursory LLCs, with the aid of similar nanohole growth observed for a Tween 80 free but oleic acid‐incorporated system. It is also demonstrated that the nanoholed Pt nanostructures loaded on carbon exhibit fairly high electrocatalytic activity for oxygen reduction reaction and a high performance as a cathode material for polymer‐electrolyte fuel cells, along with their extremely high thermostability revealed through the effect of electron‐irradiation.
Platin‐, Palladium‐ und Silber‐Nanoröhren mit 6–7 nm Außendurchmesser wurden in einer Templatsynthese durch Reduktion der Metallsalze erhalten (siehe Bild). Die als Templat fungierenden Flüssigkristalle wurden durch 1:1‐Kombination von mittleren und großen Tensidmolekülen zu hexagonal angeordneten zylindrischen Micellen hergestellt.
Single‐crystalline Pt nanosheets with a nanogroove‐network structure (see figure) are reported. A method of loading the nanogrooved Pt nanosheets on a carbon support is also described and the resulting nanogroove‐networked Pt on a carbon support (Pt/C) is demonstrated to exhibit fairly high electrocatalytic activity for oxygen reduction, which is of interest for fuel cells.
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