Tungsten(IV) sulfide

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Tungsten(IV) sulfide
Molybdenite-3D-balls.png
Identifiers
CAS number 12138-09-9 YesY
PubChem 82938
ChemSpider 74837 YesY
EC number 235-243-3
ChEBI CHEBI:30521 YesY
Jmol-3D images Image 1
Properties
Molecular formula WS2
Molar mass 247.98 g/mol
Appearance blue-gray powder[1]
Density 7.5 g/cm3, solid[1]
Melting point 1250 °C decomp.[1]
Solubility in water slightly soluble
Structure
Crystal structure Molybdenite
Coordination
geometry
Trigonal prismatic (WIV)
Pyramidal (S2−)
Hazards
EU Index Not listed
Related compounds
Other anions Tungsten(IV) oxide, Tungsten diselenide
Other cations Molybdenum disulfide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Tungsten(IV) sulfide is the chemical compound with the formula WS2. It occurs naturally as the rare mineral called tungstenite. This material is a component of certain catalysts used for hydrodesulfurization and hydrodenitrification.

WS2 adopts a layered structure related to MoS2, with W atoms situated in trigonal prismatic coordination sphere. Owing to this layered structure, WS2 forms inorganic nanotubes, which were discovered on example of WS2 in 1992.[2]

Properties[edit]

Bulk WS2 forms dark gray hexagonal crystals with a layered structure. They are not chemically active and can only be dissolved by a mixture of nitric and hydrofluoric acids. When burned 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 at 1250 °C.[1]

Synthesis[edit]

WS2 is produced by a number of methods:

  • Hydrothermal synthesis[3]
  • Gas phase reaction of H2S or H2S/Ar mixture with tungsten metal[3]
  • Reduction of ammonium tetrathiotungstate ((NH4)2WS4) at ~1300 °C in a flow of hydrogen gas[3][4]
  • Direct decomposition of various tetraalkylammonium tetrathiotungstate precursors in inert gas atmosphere.[3]
  • Microwave treatment of a solution of tungstic acid, elemental sulfur and monoethanolamine.[3]
  • Heating WS3 in absence of oxygen (otherwise the product is tungsten trioxide).[1]
  • Melting a mixture of tungsten trioxide, potassium carbonate and sulfur.[1]
  • Liquid phase exfoliation of bulk WS2 in chlorosulfonic acid.[5]

Uses[edit]

Nanostructured WS2 finds application as hydrogen and lithium storage material,[6] as material for solid-state secondary lithium battery cathodes; as a component of batteries and other electrochemical devices; as a dry lubricant; and as catalyst in hydrodesulfurization of crude oil.[3] WS2 also catalyses production of carbon monoxide:

CO2 + H2 → CO + H2O

bringing the reaction yield to the level above 99.9%.[4]

Nanotubes[edit]

Scanning electron microscopy image of WS2 nanotube bundles.
Transmission electron microscopy image of individual WS2 multi-wall nanotube.
Illustration of PbI2/WS2 core–shell nanostructure.

Tungsten disulfide is the first material which was found to form inorganic nanotubes, in 1992.[2] This ability is related to the layered structure of WS2, and macroscopic amounts of WS2 have been produced by the methods mentioned above.[3]

Apart from scientific interest, these nanotubes are studied for potential applications. WS2 nanotubes have been investigated as reinforcing agents to improve the mechanical properties of polymeric nanocomposites. In a study, WS2 nanotubes reinforced biodegradable polymeric nanocomposites of polypropylene fumarate (PPF) showed significant increases in the Young's modulus, compression yield strength, flexural modulus and flexural yield strength, compared to single- and multi-walled carbon nanotubes reinforced PPF nanocomposites, suggesting that WS2 nanotubes may be better reinforcing agents than carbon nanotubes.[7] The addition of WS2 nanotubes to epoxy resin improves adhesion, fracture toughness and strain energy release rate. The wear of the nanotubes-reinforced epoxy is eight times lower than that of pure epoxy.[8] WS2 nanotubes were embedded into a poly(methyl methacrylate) (PMMA) nanofiber matrix via electrospinning. The nanotubes were well dispersed and aligned along fiber axis. The enhanced stiffness and toughness of PMMA fiber meshes by means of inorganic nanotubes addition may have potential uses as impact-absorbing materials, e.g. for ballistic vests.[9][10]

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, inorganic nanotube hybrids were made by filling WS2 nanotubes with molten lead, antimony or bithmuth iodide salt by a capillary wetting process, resulting in PbI2@WS2, SbI3@WS2 or BiI3@WS2 core–shell nanotubes.[11]

Nanosheets[edit]

WS2 can also exist in the form of atomically thin sheets.[12][13] Interesting properties such as Room-Temperature Photoluminescence [13] and anode material in Li-ion battery have been reported in recent studies.[6][14]

References[edit]

  1. ^ a b c d e f Mary Eagleson (1994). Concise encyclopedia chemistry. Walter de Gruyter. p. 1129. ISBN 978-3-11-011451-5. Retrieved 6 November 2011. 
  2. ^ a b Tenne R, Margulis L, Genut M, Hodes G (1992). "Polyhedral and cylindrical structures of tungsten disulphide". Nature 360 (6403): 444–446. doi:10.1038/360444a0. 
  3. ^ a b c d e f g Panigrahi, Pravas Kumar; Pathak, Amita (2008). "Microwave-assisted synthesis of WS2 nanowires through tetrathiotungstate precursors". Sci. Technol. Adv. Mater. (free download) 9 (4): 045008. doi:10.1088/1468-6996/9/4/045008. 
  4. ^ a b Erik Lassner; Wolf-Dieter Schubert (1999). Tungsten: properties, chemistry, technology of the element, alloys, and chemical compounds. Springer. pp. 374–. ISBN 978-0-306-45053-2. Retrieved 6 November 2011. 
  5. ^ http://pubs.acs.org/doi/abs/10.1021/jz300480w
  6. ^ a b http://pubs.acs.org/doi/full/10.1021/jz300480w
  7. ^ Lalwani, Gaurav (September 2013). "Tungsten disulfide nanotubes reinforced biodegradable polymers for bone tissue engineering". Acta Biomaterialia 9 (9): 8365–8373. doi:10.1016/j.actbio.2013.05.018. PMID 23727293. 
  8. ^ E. Zohar, S. Baruch, M. Shneider, H. Dodiu, S. Kenig, D.H. Wagner, A. Zak, A. Moshkovith, L. Rapoport and R. Tenne (2011). "The Mechanical and Tribological Properties of Epoxy Nanocomposites with WS2 Nanotubes". Sensors & Transducers Journal 12 (Special Issue): 53–65. 
  9. ^ C. S. Reddy, A. Zak and E. Zussman (2011). "WS2 nanotubes embedded in PMMA nanofibers as energy absorptive material". J. Mater. Chem. 21 (40): 16086–16093. doi:10.1039/C1JM12700D. 
  10. ^ Physorg.news – Nano-Armor: Protecting the Soldiers of Tomorrow
  11. ^ R. Kreizman, A. N. Enyashin, F. L. Deepak, A. Albu-Yaron, R. Popovitz-Biro, G. Seifert and R. Tenne (2010). "Synthesis of Core-Shell Inorganic Nanotubes". Adv. Funct. Mater. 20 (15): 2459–2468. doi:10.1002/adfm.201000490. 
  12. ^ http://www.sciencemag.org/content/331/6017/568.abstract
  13. ^ a b http://pubs.acs.org/doi/abs/10.1021/nl3026357
  14. ^ http://www.sciencedaily.com/releases/2013/01/130116102018.htm