Molybdenum disulfide

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Molybdenum disulfide
Molybdenum disulfide
Molybdenite-3D-balls.png
Identifiers
CAS number 1317-33-5 YesY
PubChem 14823
ChemSpider 14138 YesY
ChEBI CHEBI:30704 YesY
RTECS number QA4697000
Jmol-3D images Image 1
Properties
Molecular formula MoS
2
Molar mass 160.07 g/mol
Appearance black/lead-gray solid
Density 5.06 g/cm3
Melting point 1185 °C decomp.
Solubility in water insoluble
Solubility decomposed by aqua regia, hot sulfuric acid, nitric acid
insoluble in dilute acids
Structure
Crystal structure Hexagonal, hP6, space group P6
3
/mmc, No 194
Coordination
geometry
Trigonal prismatic (MoIV()
Pyramidal (S2−)
Hazards
MSDS External MSDS
EU Index not listed
Related compounds
Other anions Molybdenum(IV) oxide
Other cations Tungsten disulfide
Related lubricants Graphite
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

Molybdenum disulfide is the inorganic compound with the formula MoS
2
. The compound is classified as a metal dichalcogenide. It is a silvery black solid that occurs as the mineral molybdenite, the principal ore for molybdenum.[1] MoS
2
is relatively unreactive. It is unaffected by dilute acids and oxygen. In appearance and feel, molybdenum disulfide is similar to graphite. It is widely used as a solid lubricant because of its low friction properties and robustness.

Production[edit]

Molybdenite

Molybdenite ore is processed by flotation to give relatively pure MoS
2
, the main contaminant being carbon. MoS
2
also arises by the thermal treatment of virtually all molybdenum compounds with hydrogen sulfide or elemental sulfur. It can also be produced by metathesis reactions from molybdenum pentachloride.[2]

The natural amorphous form is known as the rarer mineral jordisite.

Structure and physical properties[edit]

In MoS
2
, each Mo(IV) center occupies a trigonal prismatic coordination sphere that is bound to six sulfide ligands. Each sulfur centre is pyramidal and is connected to three Mo centres. In this way, the trigonal prisms are interconnected to give a layered structure, wherein molybdenum atoms are sandwiched between layers of sulfur atoms.[3] Because of the weak van der Waals interactions between the sheets of sulfide atoms, MoS
2
has a low coefficient of friction, producing its lubricating properties. Other layered inorganic materials exhibit lubricating properties (collectively known as solid lubricants (or dry lubricants)) including graphite, which requires volatile additives and hexagonal boron nitride.[4]

While bulk material forms a layered structure, nanoparticulate MoS
2
forms fullerene and nanotubular microstructures.[5]

Bulk MoS
2
is a diamagnetic, indirect bandgap semiconductor similar to silicon, with a gap of 1.2 eV.

Chemical reactions[edit]

Molybdenum disulfide is stable in air, consistent with its existence as a common mineral. It reacts with oxygen upon heating forming molybdenum trioxide:

2 MoS
2
+ 9 O
2
→ 2 MoO
3
+ 4 SO
3

Chlorine attacks molybdenum disulfide at elevated temperatures to form molybdenum pentachloride:

2 MoS
2
+ 7 Cl
2
→ 2 MoCl
5
+ 2 S
2
Cl
2

Molybdenum disulfide is a host for formation of intercalation compounds.[6] One example is lithiated material, Li
x
MoS
2
.[7] With butyl lithium, the product is LiMoS
2
.[1]

Applications[edit]

Lubricant[edit]

MoS
2
with particle sizes in the range of 1–100 µm is a common dry lubricant.[8] Few alternatives exist that confer high lubricity and stability at up to 350°C in oxidizing environments. Sliding friction tests of MoS
2
using a pin on disc tester at low loads (0.1–2 N) give friction coefficient values of <0.1.[9][10]

Molybdenum disulfide is often a component of blends and composites where low friction is sought. A variety of oils and greases are used, because they retain their lubricity even in cases of almost complete oil loss, thus finding a use in critical applications such as aircraft engines. When added to plastics, MoS
2
forms a composite with improved strength as well as reduced friction. Polymers filled with MoS
2
include nylon (with the trade name Nylatron), Teflon, and Vespel. Self-lubricating composite coatings for high-temperature applications have been developed consisting of molybdenum disulfide and titanium nitride, using chemical vapor deposition.

Examples of applications of MoS
2
-based lubricants include two-stroke engines (e.g., motorcycle engines), bicycle coaster brakes, automotive CV and universal joints, ski waxes,[11] and even some bullets.[12]

Petroleum refining[edit]

MoS
2
is employed as a cocatalyst for desulfurization in petrochemistry; e.g., hydrodesulfurization.[13] The effectiveness of the MoS
2
catalysts is enhanced by doping with small amounts of cobalt or nickel and the intimate mixture is supported on alumina. Such catalysts are generated in situ by treating molybdate/cobalt or nickel-impregnated alumina with H
2
S
or an equivalent reagent.

Research[edit]

Nanotubes and buckyball-like molecules composed of MoS
2
exhibit unusual tribological and electronic properties.[14] MoS
2
has been investigated as a component of photoelectrochemical (e.g. for photocatalytic hydrogen production) applications and for microelectronics applications.[15] MoS
2
and other transition metal dichalcogenides form bulk crystals composed of two-dimensional layers stacked in the vertical direction. Such two-dimensional layers are similar in form to graphene and express diverse electronic and optical properties[16] that can differ from those in bulk. Whereas bulk MoS
2
has an indirect band gap of 1.2 eV, single layers of MoS
2
have a direct 1.8 eV electronic bandgap[17] allowing the production of switchable transistors[15] and sensitive photodetectors.[18] The sulfur group on MoS
2
's surface interacts with noble metals, including gold. The bond between MoS
2
and gold nanostructures was found to act as a highly coupled gate capacitor with a reduced carrier-transport thermal-barrier and increased thermal conductivity.[19][20]

Calculations indicate that MoS
2
transistors would consume on the order of less power than silicon transistors while in the "off" state. For molybdenum disulfide sheets, Raman spectra cannot be fully explained as phenomena involving certain characteristic vibrations of the crystal network.[21]

See also[edit]

References[edit]

  1. ^ a b Roger F. Sebenik et al. "Molybdenum and Molybdenum Compounds" in Ullmann's Encyclopedia of Chemical Technology 2005; Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_655
  2. ^ "Metathetical Precursor Route to Molybdenum Disulfide" Inorganic Syntheses, 1995, vol. 30, 33-37. doi:10.1002/9780470132616.ch8
  3. ^ Wells, A.F. (1984). Structural Inorganic Chemistry. Oxford: Clarendon Press. ISBN 0-19-855370-6. 
  4. ^ Thorsten Bartels et al. (2002). "Lubricants and Lubrication". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley VCH. doi:10.1002/14356007.a15_423. 
  5. ^ Reshef Tenne, Meir Redlich "Recent progress in the research of inorganic fullerene-like nanoparticles and inorganic nanotubes" Chemical Society reviews (2010), 39(5), 1423-34. doi:10.1039/B901466G
  6. ^ Benavente, E.; Santa Ana, M. A.; Mendizabal, F.; Gonzalez, G. "Intercalation chemistry of molybdenum disulfide" Coordination Chemistry Reviews 2002, 224, 87-109. doi:10.1016/S0010-8545(01)00392-7
  7. ^ W. Müller-Warmuth, R. Schöllhorn (1994). Progress in intercalation research. Springer. ISBN 0-7923-2357-2. 
  8. ^ F. L. Claus, "Solid Lubricants and Self-Lubricating Solids", Academic Press, New York, 1972.
  9. ^ G. L. Miessler and D. A. Tarr (2004). Inorganic Chemistry, 3rd Ed. Pearson/Prentice Hall publisher. ISBN 0-13-035471-6. 
  10. ^ Shriver, D. F.; Atkins, P. W.; Overton, T. L.; Rourke, J. P.; Weller, M. T.; Armstrong, F. A. (2006). Inorganic Chemistry. New York: W. H. Freeman. ISBN 0-7167-4878-9. 
  11. ^ "On dry lubricants in ski waxes". Swix Sport AX. Retrieved 2011-01-06. 
  12. ^ "Barrels retain accuracy longer with Diamond Line". Norma. Retrieved 2009-06-06. 
  13. ^ Topsøe, H.; Clausen, B. S.; Massoth, F. E. (1996). Hydrotreating Catalysis, Science and Technology. Berlin: Springer-Verlag. 
  14. ^ Y. Feldman, E. Wasserman, D. J. Srolovitz, and R. Tenne "High-Rate, Gas-Phase Growth of MoS2 Nested Inorganic Fullerenes and Nanotubes" Science 267, 222-225 (1995).
  15. ^ a b Radisavljevic, B.; Radenovic, A.; Brivio, J.; Giacometti, V.; Kis, A. (2011). "Single-layer MoS2 transistors". Nature Nanotechnology 6 (3): 147–150. Bibcode:2011NatNa...6..147R. doi:10.1038/nnano.2010.279. PMID 21278752. 
  16. ^ Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S. (2012). "Electronics and optoelectronics of two-dimensional transition metal dichalcogenides". Nature Nanotechnology 7 (11): 699–712. doi:10.1038/nnano.2012.193. PMID 23132225.  edit
  17. ^ Splendiani, A.; Sun, L.; Zhang, Y.; Li, T.; Kim, J.; Chim, J.; F.; Wang, Feng (2010). "Emerging Photoluminescence in Monolayer MoS2". Nano Letters 10 (4): 1271–1275. Bibcode:2010NanoL..10.1271S. doi:10.1021/nl903868w. PMID 20229981. 
  18. ^ O. Lopez-Sanchez, D. Lembke, M. Kayci, A. Radenovic, and A. Kis (2013) "Ultrasensitive photodetectors based on monolayer MoS2". Nature Nanotechnology 8, 497, 2013. doi:10.1038/nnano.2013.100
  19. ^ Sreeprasad, T. S.; Nguyen, P.; Kim, N.; Berry, V. (2013). "Controlled, Defect-Guided, Metal-Nanoparticle Incorporation onto MoS2via Chemical and Microwave Routes: Electrical, Thermal, and Structural Properties". Nano Letters: 130813110201000. doi:10.1021/nl402278y.  edit
  20. ^ "Another breakthrough in replacing silicon in transistors". KurzweilAI. Retrieved 2013-09-11. 
  21. ^ Wed, 03/12/2014 - 1:52pm. "Material rivaling graphene may one day be mined from rocks". Rdmag.com. Retrieved 2014-04-06.