Useful Properties of Inorganic Nanotubes

Mechanical properties of BN nanotubes would be worthy of exploration. Unlike carbon nanotubes, BN nanotubes are predicted to have stable insulating properties 

Electrochemical studies have been performed with the alkylammonium intercalated YOx nanotubes [256] as well as Mn intercalated VO, nanotubes [257]. Cyclic voltammetry studies of alkylammonium-VO nanotubes showed a single reduction peak, which broadened, on replacing the amine with Na, with an additional peak. Li ion reactivity has also been tested with Mn-VO nanotubes by reacting with n-butyllithium, and it was found that - 2 lithiums per V ion are consumed. Electrochemical Li intercalation of Mn-VO nanotubes shows that 0.5 Li ions per V atom were intercalated above 2 V [257]. This observation may be relevant to battery applications. 

CNTs have been used as AFM tips and there appears to be every likelihood that extremely narrow structures can be probed [179]. WS2 could be mounted on the ultrasharp Si tip following a similar methodology. These tips were tested in an AFM microscope by imaging a replica of high aspect ratio, and it was observed that these WS2 nanotube tips provide a considerable improvement in the image quality compared to the conventional ultrasharp Si tips [258]. 

The most likely application of the chalcogenide nanotubes is as solid lubricants. Mo and W chalcogenides are widely used as solid lubricants. It has been observed that the hollow nanoparticles of WS2 show better tribological properties and act as a better lubricant compared to the bulk phase in every respect (friction, wear and life-time of the lubricant) [259]. Tribological properties of 2H-M0S2 and WS2 powder can be attributed to the weak van der Waals forces between the layers, which allow easy shear of the films with respect to each other. The mechanism in the WS2 nanostructures is somewhat different and the better tribological properties may arise from the rolling friction allowed by the round shape of the nanostructures. 

Recently, open-tipped M0S2 nanotubes were prepared by the decomposition of ball-milled ammonium thiomolybdate powder under a H2-thiophene atmosphere, and used as catalyst for the methanation of CO with H2 [260]. The conversion of CO to CH4 was achieved at a much lower temperature compared to polycrystalline M0S2 particles, and there was no deterioration even after 50 h of consecutive catalysis cycles. This observation is of importance in the context of energy conversion of global CO2. 

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