Preparation Methods of Tungsten Disulfide

Tungsten disulfide does exist in nature, but the quantity is very rare. Therefore, tungsten disulfide is usually prepared by various chemical methods. Preparation methods of tungsten disulfide include hydrothermal method, mechanical stripping method, chemical vapor deposition method and so on.

Tungsten sulfide can be synthesized in a numerous number of methods. Here are the preparation methods of tungsten disulfide as following as:

1. Hydrothermal preparation.

2. Reducing ammonium tetrathiotungstate at -1200°C in presence of hydrogen gas.

3. Gas phase reaction of hydrogen sulfide with tungsten metal in presence of argon atmosphere.

4. Decomposition reaction of various tetraalkylammomum tetrathiotungstate precursors in presence of inert gas.

5. Microwave treatment of a concentrated solution of tungstic acid, elemental sulfur and mono ethanolamine.

6. Heating WS₃ in absence of oxygen atmosphere (otherwise the product will be tungsten trioxide).

7. Melting a proportionate mixture of WO₃, K₂CO₃ and sulfur.

8. Mechanical exfoliation of tungsten sulfide in a liquid phase in presence of chlorosulfonic acid.

Monolayers and stacked few layers of tungsten sulfide can be synthesized by mechanical exfoliation and chemical vapor deposition (CVD) procedure by using WOCI₄, WO(CO)₆, or WCI₆ with HS-(CH₂)₂-SH or HSC(CH₃)₃ as precursors.

2D tungsten disulfide nanosheet crystals having lateral dimensions of less than 100 nm can be synthesized from one-dimensional W₁₈O₄₉ by applying a rolling out method using surfactant-assisted solution process.

Tungsten disulfide nanosheet with less than 10 nm thickness can be prepared from tungsten oxide (WO3) and sulfur powder by a mechanical activation strategy. The total reaction process involves a ball-milling process followed by annealing at 600-700°C in argon atmosphere. The reaction between tungstic acid and thiourea in presence of nitrogen gas at 773 K results uniform graphene-like layered form of tungsten disulfide.

The synthesis of tungsten sulfide nanosheet by the hydrothermal method is still challenging. The prime factor behind the formation of nanosheets is due to the precursor WO_X needed during the formation of tungsten disulfide which does not arise in two dimensional forms. WO_X usually adopt one dimensional or very rarely in zero dimensional nanostructure forms. That is why the sulfurization of the WO_X produces either zero dimensional fullerenes-like or one dimensional nanotube/nanorods like structures.

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