Noble‐Metal Nanotubes (Pt, Pd, Ag) from Lyotropic Mixed‐Surfactant Liquid‐Crystal Templates

Abstract

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

Lyotropic liquid crystal directed synthesis of nanostructured materials

“…Finally, the Pt species confining to the aqueous region of the molecular assemblies, are reduced to platinum atoms. The mixed surfactant LC template method can be extended to the synthesis of a wide range of 1-D inorganic or organic materials [100].…”

“…Beside the successful synthesis of 1-D nanostructured materials [99,100], Kijima's group also prepared different Pt nanosheets in single or mixed surfactant LLC. In their report, growth of metal particles on the LLC, adsorbed at the solid/solution interface, would be greatly advantageous not only for elucidating the formation mechanism of metal nanotubes but also for producing unknown nanostructured metals.…”

Synthesis and characterization of ZnS nanotubes with crossed-channels

“…There are many investigations on carbon nanotubes, including synthesis, physical properties, application etc. 1 [10][11][12] nitrides (GaN, B 24 N 24 ), [13][14] Si, Te, noble-metal nanotubes (Ag, Au, Pt, Pd), [15][16][17] titanate nanotubes 18 and copolymer nanotubes, 19 but reports on the synthesis of ZnS nanotubes are scarce. 20,21 Most nanotubes that have been synthesized are open-ended linear tubes.…”

Mesoporous Silver Films from Dilute Mixed‐Surfactant Solutions by Using Dip‐Coating

“…A series of further publications reported their advances in the electrochemical synthesis of various mesoporous metal films (Rh, Te, Sn, Se, etc.) in the presence of nonionic surfactant LLCs.[2]Recent work on preparing powders of mesoporous metals includes the work of Kijima et al, [3] who reported that noblemetal (Pt, Pd, Ag) nanotubes (i.e., a mesoporous metal powder) can be synthesized by using chemical reduction in mixedsurfactant LLCs, and that of Yamauchi et al [4] who successfully synthesized mesostructured nickel and nickel-cobalt alloys using electroless deposition in nonionic surfactant LLCs. In the literature many mesoporous metals, synthesized using both chemical and electrochemical templating methods in high-concentration surfactant LLCs, have been reported, however these are generally formed over small areas on microelectrodes or as powders in solution.…”