Prof. Alla Zak
HIT – Holon Institute of technology
The discovery of inorganic nanotubes (INT) of layered transition metal dichalcogenides of MoS2 and WS2 more than two decades ago by Tenne group opened new research field in a solid state chemistry and in nanomaterials science. Since, the synthesis of micro- and nanotubes of these and related materials attracts a great attention of research community, because of their novel uniquely promising mechanical and electronic properties.
Recently we developed the route for synthesis of pure INT-WS2 phase in significant quantities, which allows wide investigation of their properties and applications. These INT demonstrate excellent behavior as fillers in polymer composites, for preparation of field-effect transistors, for hydrogen evolution and storage, for optoelectronic devices, phototransistors and hydro desulfurization catalysts.
Oppositely to WS2, mutual attempts to recur the synthesis of MoS2 nanotubes by solid–gas reaction from corresponding oxide failed because of the instability of the Mo oxide phases at high temperature reaction conditions.
Here I will report on our last advances in synthesis of multiwall nanotubes of WS2 and MoS2 by solid–gas reaction, which are reproducible and allow some control over nanotubes aspect ratio. Moreover, single- to five-layers inorganic nanotubes of WS2 were recently successfully synthesized. Highly exergonic conditions, required for folding of relatively rigid three-atomic S-W-S layers into nanotubes of 5-7 nm in diameter, were supported by high power plasma irradiation and precursor properties. We found out that plasma parameters are responsible for the length and amount of layers of these INTs.
I will present also our last results on Raman investigation of individual WS2 nanotubes under tensile stress. The nanotubes were embedded into electrospun polymer fibers, while load was transferred to the nanotubes from the stretched fibers. This experiment demonstrated the effective load transfer from polymer to nanotubes indicative on strong adhesion between two materials. The surface of WS2 nanotubes was untreated (not functionalized). The properties of the nanotubes during elongation were elucidated.