Alumina nanotubes

Alumina nanotubes have been prepared by the anodic oxidation of aluminum [41] the resulting tubes have one-dimensional channels with uniform diameters of 5nm and lengths of 50-100 nm. An alumina membrane with a highly ordered nanohole array in 50-100 nm diameter has also been synthesized by long-period anodization thus these local alumina nanotubes have been tried as a template for metal nanowire formation. 

Interrante and coworkers40 have also produced silicon carbide nanotubes by the deposition of cyclic carbosilanes inside alumina nanotubes, followed by pyrolysis and removal of the alumina in hydrofluoric acid. 

Kamalakaran, R., Lupo, F., Grobert, N., Lozano-Castello, D., Jin-Phillipp, N. Y. and Ruhle, M., In-situ formation of carbon nanotubes in an alumina-nanotube composite by spray pyrolysis , Carbon, 2003, 41, 2737-2741. 

A1203. Alumina nanotubes have been prepared by electrochemical means.12 Two different preparation methods designated as normal stepwise anodization (NSA) and lateral stepwise anodization (LSA) have been employed for the purpose. The major difference between the two methods is the way the potential was applied. An aluminium film deposited on a p-type Si substrate was anodized in dilute H2SO<. In NSA, the potential was applied to the bottom surface of the Si substrate, while in LSA, it was applied to the top surface of the alumina film. The nanotubes formed were attached to the anodic porous alumina film (Fig. 34a). The NSA tubes were smaller than the LSA tubes. In addition to straight alumina nanotubes, branched alumina nanotubes were also obtained in the same synthesis (Fig. 34b).12,98... 

Fig. 34 TEM images of alumina nanotubes (a and b) NSA tubes (c) LSA tubes (d) side-view of the branched alumina tubes attached to the APA film, (Y indicates Y-shaped branched cells, S indicates the stem of such branched cells). (Reproduced with permission from refs. 12 and 98). 

Figure 3. Porous alumina formed by anodizing in meniscal region (Uf=70 V) a) tilted cells at the angle of 7 deg b) a changing inclination of pores c) top view after pore etching for 10 min d) alumina nanotubes obtained after pore etching for 20 min.

Lu et al. [31] synthesized alumina nanotubes via the hydrothermal technique. For a typical synthesis, AKNOsjs and camphor sulfonic acid, as surfactant, were dissolved in water. An ammonia aqueous solution was added to adjust the pH value to 5.4. A Teflon-lined stainless steel autoclave heated to 160 °C was used to grow the nanotubes for 24 h. A solid precipitate was collected by centrifugation, washed with ethanol and dried in air at room temperature followed by grinding. The product of this synthesis exhibits a one-dimensional morphology with a length of 500 nm and a diameter of 50 nm, and a boehmite phase. 

MicheU RM, Lorenzo AT, Miiller AJ, Lin MC, Chen HL, Blaszczyk-Lezak I, Martin J, Mijangos C. The crystallization of confined polymers and block copolymers infiltrated within alumina nanotube templates. Macromolecules 2012 45 1517-1528. 

Nanowires or Nanorods TiOi nanorods have been prepared using alumina nanotube templates, The templates are prepared by anodisation of aluminium films on FTO. The SEM images of templates prepared by Bwana are shown in Figure 3.36. ... 

Xi D, Pei Q (2007) In situ preparation of free-standing nanoporous alumina template for polybithiophene nanotube arrays with a concourse base. Nanotechnology 18 095602... 

Piao, L. et al., Methane decomposition to carbon nanotubes and hydrogen on an alumina supported nickel aerogel catalyst, Catal. Today, 74,145, 2002. 

A similar approach for the production of hydrothermal carbon nanotubes is the hydrothermal carbonization of glucose in the macrochannels of anodic alumina membranes [16]. Depending on the pore size of the membrane different hollow hydrother-... 

The Pt current collector was first used to deposit short ( 2 pm) Pt nanoposts [37,73] into the template membrane (Fig. 21A). These Pt nanoposts anchor the alumina membrane to the Pt surface and will serve to make electrical contact to the LiMu204 nanotubes. After Pt deposition, the pores in the membrane were filled with an aqueous solution that was 0.5 M in LiNOs and 1 M in Mn(N03)2 (Fig. 21B). The excess solution was wiped from the membrane surface, and the solvent (water) was removed by heating (50°C) in vacuum for 1 hour. The assembly was then heated at 500°C in air for 5 hours. This burns away the plastic tape and also causes tubules of LiMu204 to form within the pores (Figs. 21C, 22). 

Metal oxide nanotubes have been synthesized by a diverse variety of fabrication routes. For example titania nanotubes, and nanotube arrays, have been produced by deposition into a nanoporous alumina template [48-51], sol-gel transcription using organo-gelators as templates [52,53], seeded growth [54], hydrothermal processes [55-57] and anodic oxidation [58-65]. 

The advantage of template synthesis is that organo or hydrogelator templates can direct the shape-controlled synthesis of oxide nanotubes. Recent reports describe the use of carbon nanofibers as a template for the shape-controlled synthesis of zirconia, alumina and silica nanotubes [78]. The shape of vapor grown carbon nanofiber... 

Imai H, Takei Y, Shimizu K, Matsuda M, Hirashima H (1999) Direct preparation of anatase Ti02 nanotubes in porous alumina membranes. J Mater Chem 9 2971-2972 Michailowski A, A1 Mawlawi D, Cheng GS, Moskovits M (2001) Highly regular anatase nanotubule arrays fabricated in porous anodic templates. Chem Phys Lett 349 1-5 Jung JH, Kobayashi H, van Bommel KJC, Shinkai S, Shimizu T (2002) Creation of novel helical ribbon and double-layered nanotube Ti02 structures using an... 

Imai H, Take Y, Shimizu K, Matsuda M, Hirashima H (1999) Direct preparation of anatase Ti02 nanotubes in porous alumina membranes. J Mater Chem 9 2971-2975... 

It should be mentioned that alternative possibilities to prepare similar membranes include the use of a porous alumina membrane as matrix, with the titania nanotubes grown in the channels. Nanoporous alumina membranes are commercial products, also synthesized by anodic oxidation. The commercial Whatman Corporation anodic membrane has holes of about 20-nm diameter at the top of the membrane and about 200-nm diameter at the bottom of membrane. Within these pores Ti02 nanotubes fabricated by template synthesis and water vapour hydrolysis could be grown, but non-uniform membrane characteristics are obtained due to the non-uniform pores of the commercial alumina... 

By applying the template technique, Kyotani et al. and Che et al. succeeded in preparing Pt and Pt/Ru metal-filled uniform carbon nanotubes in which the metal is present as either nanorods or nanoparticles. It should be noted that no metal was observed on the outside wall of the tubes. This is due to the preparation procedure, in which the metal precursor was loaded into the carbon-deposited alumina film before the dissolution of alumina by HF (see Fig. 10.1.9). Thus, there is no other space for metal to be loaded except in the channels. 

---