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Earlier reports have described MoS2 nanotubes with diameters as small as 15 nm. But the tubes reported last week by authors are considerably narrower--they are all just under 1 nm across. Moreover, they are single-walled and produced in yields of up to 15%, which is relatively high for nanotubes. the work demonstrates that subnanometer-diameter nanotubes made of a metal disulfide can be synthesized efficiently. And this suggests that large-scale production of uniform inorganic nanotubes may be feasible--an important consideration if the tubes are found to be commercially useful. Other forms of MoS2 are already used in a number of applications, including catalysis, high-energy-density lithium batteries, and solid lubricants. Authors suggests that the properties of these new MoS2 nanotubes could prove to be a boon to some of these applications.
The nanotubes are grown from MoS2 powder in an evacuated silica ampoule that is placed in a high-temperature gradient. A small amount of C60 is added as a growth promoter. Iodine is used as a transport agent to shuttle atoms of molybdenum and sulfur from the MoS2 powder at the higher temperature end of the ampoule to the nanotubes growing at the lower temperature end. The detailed growth mechanism, including C60's exact role, isn't clear at present. "What is clear is that the synthesis doesn't work without the C60. The nanotubes produced via this process are up to hundreds of micrometers long. They assume a number of different forms, ranging from twisted chiral bundles containing hundreds of thousands of tubes to regularly shaped "furry" forms, according to the paper.The bundles, which contain iodine between the individual nanotubes, can be readily disassembled into individual nanotubes.
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