Molybdenum Disulfide
Properties
| State | Solid (layered) |
| Color | Dark gray to black with metallic luster |
| Solubility | Insoluble in water and most solvents; dissolves in hot aqua regia and molten alkali |
| Melting Point | 1185 °C (decomposes in air to MoO3 + SO2) |
About Molybdenum Disulfide
MoS2 is the dark-gray, vaguely greasy-feeling powder that gets dusted onto firearm slides, packed into spacecraft bearings, and pressed into the catalyst beds at every petroleum refinery on the planet. The crystal is layered: each Mo atom sits in trigonal-prismatic coordination between two sheets of S atoms, and those S-Mo-S triple slabs are held together only by van der Waals forces. That weak interlayer bonding is what makes the material so useful — the slabs slide past each other under shear with a friction coefficient near 0.05, and the mechanism keeps working in vacuum and at temperatures where any hydrocarbon grease would carbonize. The other big use is hydrodesulfurization. Co- or Ni-promoted MoS2 supported on alumina is the workhorse catalyst that strips sulfur from diesel and jet fuel; without it, low-sulfur fuel standards simply could not be met at scale. Then in 2010, the field of 2D materials caught up: monolayer MoS2 turns out to have a direct 1.8 eV bandgap (versus indirect 1.2 eV in bulk), which kicked off a decade of work on transition-metal-dichalcogenide transistors and photodetectors.
Where you'll encounter it
If you've ever opened a tin of dry lubricant for a bicycle chain or seen the gray-black coating inside a high-end firearm, you've handled MoS2. Machinists know it as the stuff that lets a tap cut threads in stainless steel without seizing, and it shows up in the gear oil for helicopter transmissions because it survives the local temperature spikes where the oil film breaks down. In the catalyst world, anyone who has ever loaded a refinery hydrotreater has shoveled tonnes of CoMo/Al2O3 extrudates that get sulfided in place to MoS2 before going on stream. And in a 2D-materials lab, exfoliating MoS2 onto a SiO2/Si chip with adhesive tape — the same trick that worked for graphene — is one of the standard ways students get their first single-layer device.
Common Uses
- Dry lubricant for spacecraft bearings, firearm slides, and high-temperature greases
- Active phase in Co-Mo/Al2O3 hydrodesulfurization catalysts at every petroleum refinery
- Channel material for monolayer MoS2 transistors and 2D-electronics research devices
- Photocatalyst for visible-light hydrogen evolution from water-splitting cells
- Electrode and intercalation host in lithium and sodium battery research cells
- Friction-modifier additive in helicopter transmission and industrial gear oils
- Anti-seize compound for stainless steel threaded fasteners under high load
Safety Information
GHS classifications: Eye Irritation Category 2A, STOT Single Exposure Category 3 (respiratory tract). The compound itself has low acute toxicity and is biologically inert in bulk form. The hazard is dust inhalation: OSHA PEL is 15 mg/m3 total dust and 5 mg/m3 respirable, with an ACGIH TLV of 10 mg/m3 inhalable Mo and 3 mg/m3 respirable. Use a NIOSH-rated N95 or P100 respirator when weighing or sieving powder. In air above 350 °C, MoS2 oxidizes to MoO3 and SO2 — never burn off lubricant residues in an enclosed space. Standard PPE: safety glasses, nitrile gloves, lab coat. No special storage required.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.