WS 2 Nanotubes Synthesized for Lithium Storage
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reversibly modified the interband transition (S11) intensities in semiconducting SWNTs—by light-induced refilling and depletion of the valence band—and in spiropyran-functionalized SWNTs (SPSWNTs) by photoinduced changes in the dye’s polarity. It is well-known that spiropyran molecules exhibit photochromic effects under UV-excitation, undergoing a transition to the merocyanine form. In this work, the researchers showed that the S11 modulation of SP-SWNTs corresponds to the UV-induced, reversible conversion of spiropyran by a ring-opening reaction to its merocyanine form. However, they also observed an absorption band at 440 nm that they indicate is due to the merocyanine aggregation by the functionalized SWNTs. Absorption-band shifts observed for merocyanine-SWNTs indicated to the researchers that the dye’s π -electron system strongly interacts with the SWNT. In addition, the researchers interpreted other spectral features as evidence that spiropyrans/merocyanines are either bonded to the sidewalls or to the ends of the SWNTs. They used atomic force microscopy to show that SP-SWNTs exist in solution both as individual nanotubes and bundles of 2–5 nanotubes with lengths in the range of 0.4–2 µm. The researchers said that discovering the nature of SWNT-substrate interactions will lead to further advances in SWNTbased chemical sensors. Furthermore, they believe that their work “presents an impetus for an exploration of a new type of chemical sensors based on the interaction of an analyte with a host molecule.” STEVEN TROHALAKI
ic devices. Wang’s research team has focused on how lithium is stored in WS2 nanotubes, which represents an important process in using these materials as electrodes or anodes in rechargeable batteries. The researchers synthesized WS2 nanotubes from amorphous WS3 at high temperature in a hydrogen atmosphere. They report a very high yield of ~80%. Characterization of the material by transmission electron microscopy with field
emission indicated that the nanotubes have a length of a few hundred nanometers, have open tips, a diameter between 30 nm and 40 nm, with wall thicknesses of ~15 nm. The hollow core measured roughly 4.6 nm. Electrochemical properties were assessed based on coin cell testing. Wang and co-workers identified electrochemical properties of the WS2 nanotubes that differ significantly from WS2 as a powder material. The WS2 nanotube electrode
WS2 Nanotubes Synthesized for Lithium Storage The discovery of fullerenes and carbon nanotubes has led to extensive research aimed toward the synthesis of similar one-dimensional nanostructures to carbon nanotubes, but based on different materials. These novel nanomaterials could find applications in diverse fields such as quantum computing, sensing and biomedical devices, and energy needs such as hydrogen storage. An example for such one-dimensional nanomaterials is WS2 nanotubes discovered by R. Tenne and co-workers in the early 1990s. In the October issue of Electrochemical and Solid-State Letters (p. A321), G.X. Wang, S. Bewlay, J. Yao, H
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