between the layers in the VO x nanotubes can be controlled by the length of the
aCH 2 a chain in the amine template.
Most of the VO x nanotubes obtained by the hydrothermal method are openended. Very few closed tubes had flat or pointed conical tips. Cross-sectional TEM
images of the nanotubular phases show that instead of concentric cylinders, (i.e.
layers that fold and close within themselves), the tubes are made up of single or
double layer scrolls providing a serpentine-like morphology [248, 249]. The scrolls
are seen in the images as circles that do not close (Figure 8.27(c)). Non-symmetric
fringe patterns in the tube walls exemplify that most of the nanotubes are not
rotationally symmetric and carry depressions and holes in the walls. Diamineintercalated VO x nanotubes are multilayer scrolls with narrow cores and thick
walls, composed of packs of several vanadium oxide layers (Figure 8.27(d)). Many
of the nanotubes formed by layered materials show various types of defects. They
also exhibit unusual tip structures. The tips are not always spherical in these
nanotubes. These aspects are discussed at length by Rao and Nath [22].
8.3.4
Useful Properties of Inorganic Nanotubes
The properties and applications of the inorganic nanotubes have not been investigated as extensively as would be desirable. The electronic structures of MoS 2 and
WS 2 have been examined briefly and the semiconducting nature of the nanotubes
confirmed [250, 251a]. It is necessary to investigate the optical, electrical and other
properties of the various chalcogenide nanotubes. This is especially true of nanotubes of NbS 2 and such materials which are predicted to be metallic [251b]. NbSe 2
nanotubes have been found to be metallic at ordinary temperatures, becoming superconducting at lower temperatures [252]. Electronic and optical properties of the
BN nanotubes have not yet been investigated in detail. Theoretical calculations
suggest BN tubes to be insulating with a wide band gap of 5.5 eV [221].
Like carbon nanotubes, it would be worthwhile to look into the H 2 storage ability
of some of the inorganic nanotubes [253]. The chalcogenide nanotubes with an
@6 A ˚ van der Waals gap between the layers, are potential candidates for storage
capacity. It has been shown recently that BN nanotubes can store a reasonable
quantity of H 2 [254]. Multi-walled BN nanotubes have been shown to possess
a capacity of 1.8–2.6 wt% of H 2 uptake under @10 MPa at room temperature.
This value, though smaller than that reported for CNTs, nevertheless suggests the
possible use of BN nanotubes as a hydrogen storage system. MoS 2 nanotubes could be electrochemically charged and discharged with a capacity of 260
mA h g
À1 at 20
C, corresponding to a formula of H 1:24 MoS 2 [255]. The high storage capacity is believed to be due to the enhanced electrochemical–catalytic activity
of the highly nanoporous structure. This may find wide applications in high energy batteries.
Mechanical properties of BN nanotubes would be worthy of exploration. Unlike
carbon nanotubes, BN nanotubes are predicted to have stable insulating properties
8.3 Inorganic Nanotubes 253
aCH 2 a chain in the amine template.
Most of the VO x nanotubes obtained by the hydrothermal method are openended. Very few closed tubes had flat or pointed conical tips. Cross-sectional TEM
images of the nanotubular phases show that instead of concentric cylinders, (i.e.
layers that fold and close within themselves), the tubes are made up of single or
double layer scrolls providing a serpentine-like morphology [248, 249]. The scrolls
are seen in the images as circles that do not close (Figure 8.27(c)). Non-symmetric
fringe patterns in the tube walls exemplify that most of the nanotubes are not
rotationally symmetric and carry depressions and holes in the walls. Diamineintercalated VO x nanotubes are multilayer scrolls with narrow cores and thick
walls, composed of packs of several vanadium oxide layers (Figure 8.27(d)). Many
of the nanotubes formed by layered materials show various types of defects. They
also exhibit unusual tip structures. The tips are not always spherical in these
nanotubes. These aspects are discussed at length by Rao and Nath [22].
8.3.4
Useful Properties of Inorganic Nanotubes
The properties and applications of the inorganic nanotubes have not been investigated as extensively as would be desirable. The electronic structures of MoS 2 and
WS 2 have been examined briefly and the semiconducting nature of the nanotubes
confirmed [250, 251a]. It is necessary to investigate the optical, electrical and other
properties of the various chalcogenide nanotubes. This is especially true of nanotubes of NbS 2 and such materials which are predicted to be metallic [251b]. NbSe 2
nanotubes have been found to be metallic at ordinary temperatures, becoming superconducting at lower temperatures [252]. Electronic and optical properties of the
BN nanotubes have not yet been investigated in detail. Theoretical calculations
suggest BN tubes to be insulating with a wide band gap of 5.5 eV [221].
Like carbon nanotubes, it would be worthwhile to look into the H 2 storage ability
of some of the inorganic nanotubes [253]. The chalcogenide nanotubes with an
@6 A ˚ van der Waals gap between the layers, are potential candidates for storage
capacity. It has been shown recently that BN nanotubes can store a reasonable
quantity of H 2 [254]. Multi-walled BN nanotubes have been shown to possess
a capacity of 1.8–2.6 wt% of H 2 uptake under @10 MPa at room temperature.
This value, though smaller than that reported for CNTs, nevertheless suggests the
possible use of BN nanotubes as a hydrogen storage system. MoS 2 nanotubes could be electrochemically charged and discharged with a capacity of 260
mA h g
À1 at 20
C, corresponding to a formula of H 1:24 MoS 2 [255]. The high storage capacity is believed to be due to the enhanced electrochemical–catalytic activity
of the highly nanoporous structure. This may find wide applications in high energy batteries.
Mechanical properties of BN nanotubes would be worthy of exploration. Unlike
carbon nanotubes, BN nanotubes are predicted to have stable insulating properties
8.3 Inorganic Nanotubes 253