Molybdenum disulfide

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Molybdenum disulfide
IUPAC name

Molybdenum disulfide
Other names

Molybdenite
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 MoS2
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 P63/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
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Molybdenum disulfide is the inorganic compound with the formula MoS2. The compound is a di-chalcogenide.

This black crystalline sulfide of molybdenum occurs as the mineral molybdenite. It is the principal ore from which molybdenum metal is extracted. MoS2 is relatively unreactive, being unaffected by dilute acids and oxygen. In its appearance and feel, molybdenum disulfide is similar to graphite. Indeed, like graphite, it is widely used as a solid lubricant because of its low friction properties and robustness.

Contents

Production [edit]

Molybdenite

Molybdenite ore is processed by flotation to give relatively pure MoS2, the main contaminant being carbon. MoS2 also arises by the thermal treatment of virtually all molybdenum compounds with hydrogen sulfide. The natural amorphous form is known as the rarer mineral jordisite.

Molybdenite (MoS2) is the principal ore from which molybdenum metal is extracted.[1]

Structure and physical properties [edit]

In MoS2, each Mo(IV) center occupies a trigonal prismatic coordination sphere, being bound to six sulfide ligands. Each sulfur centre is pyramidal, being 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.[2] Because of the weak van der Waals interactions between the sheets of sulfide atoms, MoS2 has a low coefficient of friction, resulting in 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.[3]

Bulk MoS2 is diamagnetic, indirect bandgap semiconductor similar to silicon, with a gap of 1.2 eV. Because of its anisotropic structure, it exhibits anisotropic conductivity. It has been often investigated as a component of photoelectrochemical (e.g. for photocatalytic hydrogen production) applications and more recently for microelectronics applications.[4] Single layers have proven to have properties differing from the bulk, including a direct 1.8 eV electronic bandgap.[5]

Chemical reactions [edit]

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

2 MoS2 + 9 O2 → 2 MoO3 + 4 SO3

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

2 MoS2 + 7 Cl2 → 2 MoCl5 + 2 S2Cl2

Molybdenum disulfide reacts with alkyl lithium under controlled conditions to form intercalation compounds LixMoS2.[6] With butyl lithium, the product is LiMoS2.[1]

Applications [edit]

Lubricant [edit]

MoS2 with particle sizes in the range of 1–100 µm is a common dry lubricant. Few alternatives exist that can confer the high lubricity and stability up to 350 °C in oxidizing environments. Sliding friction tests of MoS2 using a pin on disc tester at low loads (0.1–2 N) give friction coefficient values of <0.1.[7][8]

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, MoS2 forms a composite with improved strength as well as reduced friction. Polymers that have been filled with MoS2 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 by chemical vapor deposition.

Examples of some diverse applications of MoS2-based lubricants include two-stroke engines (e.g., motorcycle engines), bicycle coaster brakes,automotive CV and universal joints, ski waxes,[9] and even some bullets.[10]

Petroleum refining [edit]

MoS2 is employed as a catalyst for desulfurization in petroleum refineries; e.g., hydrodesulfurization.[11] The effectiveness of the MoS2 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 H2S or an equivalent reagent.

Research trends [edit]

Nanotubes and buckyball-like molecules composed of MoS2 exhibit unusual tribology and electronic properties.[12] Metal di-chalogenides form two-dimensional nanocrystals” layered in sheets of a thickness of 0.7 nanometers or roughly the height of three atoms.[13]

Sheets of MoS2 can be produced using vapor deposition method. Since MoS2 has high melting temperature, directly vaporizing MoS2 is not recommended. However, it can be achieved through chemical reaction. Method 1: Sulfur reacts with thin layer of Mo that's being pre-deposited on the substrate at 750 degree C. Thin, continuous, and uniform MoS2 film is formed directly on the substrate. [14] Method 2: MoS2 thin sheets can also be produced by a two-step thermolysis process. [NH4]2[MoS4]→2NH3+H2S + MoS3 In N2 environment, the temperature requirement is 120-360 degree C MoS3→MoS2 + S Conversion of MoS3 to MoS2 can be achieved at above 800 degree C. [15] however, this transformation process involves too many steps and too many products, and it's hard to control the temperature. Method 3:High quality of MoS2 thin film can be produced by reaction of ammonium thiomolybdates and hydrogen. The involvement of hydrogen not only lowers the reaction temperature to around 423 degree C, but also protects the products against oxidation. [NH4]2[MoS4] + H2 →2NH3+2H2S+MoS2 However, one should be careful with the temperature setting since MoS2 decomposes in H2 once the temperature is higher than 500 degree C. [15]

Unlike graphene, MoS2 has a large intrinsic bandgap, essential for making transistors. A switchable transistor based on single- and multi-layer MoS2 have been described. Transistors made from mechanically exfoliated MoS2 exhibit a high current on/off ratio of 1×10^8 and have electron mobility of 200 cm^2/(V·S). Recently, the chemical vapor deposition growth of MoS2 thin films are in use since they can be transferred easily from one substrate to the other. In addition, MoS2 electric double-layer transistors formed with an ionic liquid have succeeded, and ambipolar transport was observed. [16] Sensors have also been made from monolayers of MoS2.[4]

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. ^ Wells, A.F. (1984). Structural Inorganic Chemistry. Oxford: Clarendon Press. ISBN 0-19-855370-6. 
  3. ^ Thorsten Bartels et al. (2002). "Lubricants and Lubrication". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley VCH. doi:10.1002/14356007.a15_423. 
  4. ^ a b Radisavljevic, B.; Radenovic, A.; Brivio, J.; Giacometti, V.; Kis, A. (2011). "Single-layer MoS2 transistors". Nature Nanotechnology 6 (3): 147–150. doi:10.1038/nnano.2010.279. 
  5. ^ Splendiani, A.; Sun, L.; Zhang, Y.; Li, T.; Kim, J.; Chim, J.; F. (2010). "Emerging Photoluminescence in Monolayer MoS2". Nano Letters 10 (4): 1271–1275. doi:10.1021/nl903868w. 
  6. ^ W. Müller-Warmuth, R. Schöllhorn (1994). Progress in intercalation research. Springer. p. 50. ISBN 0-7923-2357-2. 
  7. ^ G. L. Miessler and D. A. Tarr (2004). Inorganic Chemistry, 3rd Ed. Pearson/Prentice Hall publisher. ISBN 0-13-035471-6. 
  8. ^ 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. 
  9. ^ "On dry lubricants in ski waxes". Swix Sport AX. Retrieved 2011-01-06. 
  10. ^ "Barrels retain accuracy longer with Diamond Line". Norma. Retrieved 2009-06-06. 
  11. ^ Topsøe, H.; Clausen, B. S.; Massoth, F. E. (1996). Hydrotreating Catalysis, Science and Technology. Berlin: Springer-Verlag. 
  12. ^ 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).
  13. ^ Wang, Q.H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J.; Strano, M. (2012). "Electronics and optoelectronics of two-dimensional transition metal dichalcogenides". Nature Nanotechnology 7 (11): 699–712. doi:10.1038/nnano.2012.193. 
  14. ^ Zhan, Yongjie; Liu, Zheng; Najmaei, Sina; Ajayan, Pulickel; Lou, Jun (2012). "Large-Area Vapor-Phase Growth and Characterization of MoS2 Atomic Layers on a SiO2 Substrate". Small Journal 7: 966–971. 
  15. ^ a b Liu, Keng-Ku; Zhang, Wenjing; Lee, Yi-Hsien; Lin, Yu-Chuan; Chang, Mu-Tung; Su, Ching-Yuan; Chang, Chia-Seng; Li, Hai; Shi, umeng; Zhang, Hua; Lai, Chao-Sung; Li, Lain-Jong (2012). "Growth of Large-Area and Highly Crystalline MoS2 Thin Layers on Insulating Substrates". American Chemical Society 12: 1538–1544. 
  16. ^ Pu, Jiang; Yomogida, Yohei; Liu, Keng-ku; Li, Lain-Jong; Iwasa, Yoshihiro; Takenobu, Taishi. "Highly Flexible MoS2 Thin-Film Transistors with Ion Gel Dielectrics". American Chemical Society 12: 4013–4017. 
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