Inorganic nanotubes

An inorganic nanotube is a cylindrical molecule often composed of metal oxides, or group III-Nitrides and morphologically similar to a carbon nanotube. Inorganic nanotubes have been observed to occur naturally in some mineral deposits.

A few years after Linus Pauling mentioned the possibility of curved layers in minerals as early as 1930, some minerals such as white asbestos (or chrysotile) and imogolite were actually shown to have a tubular structure. However, the first synthetic inorganic nanotubes did not appear until Reshef Tenne et al. reported the synthesis of nanotubes composed of tungsten disulfide (WS₂) in 1992.

In the intervening years, nanotubes have been synthesised of many inorganic materials, such as vanadium oxide and manganese oxide, and are being researched for such applications as redox catalysts and cathode materials for batteries.

Inorganic nanotubes are morphologically similar to carbon nanotubes and are observed in some mineral deposits of natural origin. Synthetic structures of this type were first reported by the group of Reshef Tenne in 1992.

Typical inorganic nanotube materials are 2D layered solids such as tungsten(IV) sulfide (WS₂), molybdenum disulfide (MoS₂) and tin(IV) sulfide (SnS₂). WS₂ and SnS₂/tin(II) sulfide (SnS) nanotubes have been synthesized in macroscopic amounts. However, traditional ceramics like titanium dioxide (TiO₂), zirconia dioxide (ZrO₂) and zinc oxide (ZnO) also form inorganic nanotubes. More recent nanotube and nanowire materials are transition metal/chalcogen/halogenides (TMCH), described by the formula TM₆C_yH_z, where TM is transition metal (molybdenum, tungsten, tantalum, niobium), C is chalcogen (sulfur, selenium, tellurium), H is halogen (iodine), and the composition is given by 8.2<(y+z)<10. TMCH tubes can have a subnanometer-diameter, lengths tunable from hundreds of nanometers to tens of micrometers and show excellent dispersiveness owing to extremely weak mechanical coupling between the tubes.

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