Tungsten disulfide

Source: Wikipedia, the free encyclopedia.
"Tungsten sulfide" redirects here. Not to be confused with Tungsten trisulfide.
Tungsten disulfide

Left: WS2 film on sapphire. Right: dark exfoliated WS2 film floating on water
Names
IUPAC names
Tungsten sulfur
Bis(sulfanylidene)tungsten
Systematic IUPAC name
Dithioxotungsten
Other names
Tungsten(IV) sulfide
Tungstenite
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
ECHA InfoCard
 100.032.027 Edit this at Wikidata
EC Number
  • 235-243-3
  • InChI=1S/2S.W checkY
    Key: ITRNXVSDJBHYNJ-UHFFFAOYSA-N checkY
  • InChI=1S/2S.W
    Key: ITRNXVSDJBHYNJ-UHFFFAOYSA-N
  • S=[W]=S
Properties
WS2
Molar mass 247.98 g/mol
Appearance Blue-gray powder[1]
Density 7.5 g/cm3, solid[1]
Melting point 1,250 °C (2,280 °F; 1,520 K) decomposes[1]
Slightly soluble
Band gap ~1.35 eV (optical, indirect, bulk)[2][3]
~2.05 eV (optical, direct, monolayer)[4]
+5850·10−6 cm3/mol[5]
Structure
Molybdenite
Trigonal prismatic
(WIV)
Pyramidal (S2−)
Related compounds
Other anions
 Tungsten(IV) oxide
Tungsten diselenide
Tungsten ditelluride
Other cations
Tantalum disulfide
Rhenium disulfide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Tungsten disulfide is an inorganic

hydrodenitrification
.

WS2 adopts a layered structure similar, or isotypic with MoS2, instead with W atoms situated in trigonal prismatic coordination sphere (in place of Mo atoms). Owing to this layered structure, WS2 forms non-carbon nanotubes, which were discovered after heating a thin sample of WS2 in 1992.[6]

Structure and physical properties

Atomic image (top) and model (bottom) of Nb-doped WS2. Blue, red, and yellow spheres indicate W, Nb, and S atoms, respectively. Nb doping allows to reduce the WS2 bandgap.[7]

Bulk WS2 forms dark gray hexagonal crystals with a layered structure. Like the closely related MoS2, it exhibits properties of a dry lubricant.

Although it has long been thought that WS2 is relatively stable in ambient air, recent reports on the ambient air oxidation of monolayer WS2 have found this to not be the case. In the monolayer form, WS2 is converted rather rapidly (over the course of days in ambient light and atmosphere) to tungsten oxide via a photo-oxidation reaction involving visible wavelengths of light readily absorbed by monolayer WS2 (< ~660 nm; > ~1.88 eV).

catalyst for oxidation. The products of the reaction likely include various tungsten oxide species and sulfuric acid. The oxidation of other semiconductor transition metal dichalcogenides (S-TMDs) such as MoS2, has similarly been observed to occur in ambient light and atmospheric conditions.[9]

WS2 is also attacked by a mixture of nitric and hydrofluoric acid. When heated in oxygen-containing atmosphere, WS2 converts to tungsten trioxide. When heated in absence of oxygen, WS2 does not melt but decomposes to tungsten and sulfur, but only at 1250 °C.[1]

Historically monolayer WS2 was isolated using chemical exfoliation via intercalation with lithium from n-butyl lithium (in hexane), followed by exfoliation of the Li intercalated compound by sonication in water.

chlorosulfonic acid[11] and the lithium halides.[12]

Synthesis

WS2 is produced by a number of methods.[1][13] Many of these methods involve treating oxides with sources of sulfide or hydrosulfide, supplied as hydrogen sulfide or generated in situ.

Thin films and monolayers

Widely used techniques for the growth of monolayer WS2 include

metal organic chemical vapor deposition (MOCVD), though most current methods produce sulfur vacancy defects in excess of 1×1013 cm−2.[14] Other routes entail thermolysis of tungsten(VI) sulfides (e.g., (R4N)2WS4) or the equivalent (e.g., WS3).[13]

Freestanding WS2 films can be produced as follows. WS2 is deposited on a hydrophilic substrate, such as sapphire, and then coated with a polymer, such as polystyrene. After dipping the sample in water for a few minutes, the hydrophobic WS2 film spontaneously peels off.[15]

Applications

WS2 is used, in conjunction with other materials, as

hydrotreating of crude oil.[13]
In recent years it has also found applications as a saturable for passively mode locked fibre lasers resulting in femtosecond pulses being produced.

Lamellar tungsten disulphide is used as a dry lubricant for fasteners, bearings, and molds,[16] as well as having significant use in aerospace and military industries.[17][failed verification] WS2 can be applied to a metal surface without binders or curing, via high-velocity air impingement. The most recent official standard for this process is laid out in the SAE International specification AMS2530A.[18]

Research

Like MoS2, nanostructured WS2 is actively studied for potential applications, such as storage of hydrogen and lithium.[11] WS2 also catalyses hydrogenation of carbon dioxide:[11][19][20]

CO2 + H2 → CO + H2O

Nanotubes

Tungsten disulfide is the first material which was found to form

ballistic vests.[23][24]

WS2 nanotubes are hollow and can be filled with another material, to preserve or guide it to a desired location, or to generate new properties in the filler material which is confined within a nanometer-scale diameter. To this goal, non-carbon nanotube hybrids were made by filling WS2 nanotubes with molten lead, antimony or bismuth iodide salt by a capillary wetting process, resulting in PbI2@WS2, SbI3@WS2 or BiI3@WS2 core–shell nanotubes.[25]

Nanosheets

See also: Transition metal dichalcogenide monolayers

WS2 can also exist in the form of atomically thin sheets.[26] Such materials exhibit room-temperature photoluminescence in the monolayer limit.[27]

Transistors

field effect transistors. The approximately 6-layer thick material is created using chemical vapor deposition (CVD).[28]

References

Wikimedia Commons has media related to Tungsten disulfide.
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  16. ^ French LG, ed. (1967). "Dicronite". Machinery. Vol. 73. Machinery Publications Corporation. p. 101.
  17. ^ "Quality Approved Special Processes By Special Process Code". BAE Systems. 2020-07-07.
  18. ^ "AMS2530A: Tungsten Disulfide Coating, Thin Lubricating Film, Binder-Less Impingement Applied". SAE International. Retrieved 2020-07-10.
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  20. ^ Engineer making rechargeable batteries with layered nanomaterials. Science Daily (2013-01-016)
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  22. ^ Zohar, E., et al. (2011). "The Mechanical and Tribological Properties of Epoxy Nanocomposites with WS2 Nanotubes". Sensors & Transducers Journal. 12 (Special Issue): 53–65.
  23. doi:10.1039/C1JM12700D
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  24. ^ Nano-Armor: Protecting the Soldiers of Tomorrow. Physorg.com (2005-12-10). Retrieved on 2016-01-20
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