Nanotube oxidation

G. Patzke, F. Krumeich, R. Nesper, Oxidic nanotubes and nanorods - anisotropic modules for a future nanotechnology. Angew. Chem. Int. Ed, 41 (2002) 2462. 

Mohapatra SK, Raja KS, Misra M et al (2007) Synthesis of self-organized mixed oxide nanotubes by sonoelectrochemical anodization of Ti-8Mn alloy. Electrochim Acta 53 590-597... 

We may thus conclude that the availability of titanium oxide nanotubes, and more generally of quasi-ID metal oxides, still opens new possibilities for catalysis, but a more rational effort is required before exploiting their potentiality. 

Thus far, only metal-oxide nanotubes have been synthesized by this process. Whereas crystalline nanotubes were obtained from 2D (layered) oxides, various 3D oxide compounds resulted in semicrystalline or amorphous nanotubes, only. In principle, this kind of process could be extended to the synthesis of nanotubes from chalcogenide and halide compounds in the future. 

In another procedure, carbon nanotubes were used as templates for the deposition of V205 nanotubes the template was subsequently removed by burning the sample in air at 650 °C (40). This strategy can be easily adopted for the synthesis of different oxide nanotubes, as shown by Rao and co-workers (5). 

The double layers of vanadium oxide found in the xerogel have been described in a number of other vanadium oxides by Galy ° and Oka ° they also form the double sheets described above for VeOis. These oxides, in which the vanadium is found in distorted VOe octahedra, show particularly attractive electrochemical capacities " exceeding 200 mAh/g in some cases, as shown in Figure 9. However, at the present time their rate capability appears somewhat limited. More recently vanadium oxide nanotubes have been synthesized, first by Spahr et these compounds also contain double sheets of vanadium oxide and again have interesting but complex... 

Figure 9. Electrochemical behavior of (a) -MnjY205 (reprinted with permission from ref 105, copyright 2000 Elsevier), (b) -NH4V40io, and (c) Mn vanadium oxide nanotubes.

CNTs have been used as templates producing other nanotubes such as gold and zinc oxide nanotubes. These nanotubes are hydrophilic while CNTs are hydrophobic allowing alternative uses where the behavior of the tube can be varied according to its environment. 

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]. 

Metal oxide nanotubes containing bundles of gel fiber... 

Fig. 5.1 Template (organogelator) synthesis of metal oxide nanotubes.

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... 

Tflbk 5. t Preparative methods and surface aiea of metaJ oxides nanotubes... 

Kasuga T, Hiramatsu M, Hoson A, Sekino T, Niihara K (1998) Formation of titanium oxide nanotube. Langmuir 14 3160-3163... 

Gong D, Grimes CA, Varghese OK, Hu W, Singh RS, Chen Z, Dickey EC (2001) Titanium oxide nanotubes array prepared by anodic oxidation. J Mater Res 16 3331-3334... 

Hanabusa K, Numazawa T, Kobayashi S, Suzuki M, Shirai H (2006) Preparation of metal oxide nanotubes using gelators as structure-directing agents. Macromol Symp 235 52-56... 

Satishkumar BC, Govindaraj AG, Vogl EM, Basumallick L, Rao CNR (1997) Oxide nanotubes prepared using carbon nanotubes as templates. J Mater Res 12 604-606... 

Varghese OK, Gong DW, Paulose M, Grimes CA, Dickey EG (2003) Giystallization and high-temperature structural stability of titanium oxide nanotube arrays. J Mater Res 18 156-165... 

As is seen, anode oxidation in sulfuric acid does not corrupt the nanotube structure. After thermal treatment of the anode oxidized nanotubes substantial thinning and loosening of walls was observed. 

Schmuki P. Self-organized oxide nanotube layers on titanium and other transition metals. In Schmuki P, Virtanen S, editors. Electrochemistry at the nanoscale. New York Springer Science 2009. p. 435-66. 

Use of carbon nanotubes as templates for the growth of oxide nanotubes... 

Carbon nanotubes have been successfully used as removable templates for the synthesis of a variety of oxide nanotubes. Ajayan et al.9 reported the preparation of V205 nanotubes by using partially oxidized carbon nanotubes as templates. Apart from coating of CNTs by the oxide phase, metal oxide fillings in the internal cavities and thin oxide layers between the concentric shells of the tubes were also obtained (Fig. 30). A mix-... 

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