1T-phase Tungsten Disulfide

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Category: Tungsten Information
Published on Friday, 18 January 2019 00:21
Tungsten Disulfide and molybdenum disulfide have a similar structure------ a typical sandwich structure. Due to its relatively weak van der Waals force between layers, it can also be stripped into nanosheets with single or few layers, which is considered as another important two-dimensional nanosheet material with unique physical, chemical and electrical properties.
Both of them have three phases, including 1T phase, 2H phase and 3R phase. Among these phases, 1T phase is that WS2 uses one S-W-S mono-layer as the smallest repeating unit to stack, while 2H and 3R phase use two and three S-W-S mono-layers respectively as the smallest repeating unit .

 

tungsten disulfide picture

 

Most of WS2 in nature exists in the stable 2H phase, and the 1T and 3R phases are metastable structure which can be converted to the 2H phase under certain conditions. Since the mona-layer 2H-phase WS2 has lost the property of bilayer as the smallest repeating unit, it is also called as the 1H phase. Although the properties of single-layer WS2 nanomaterials in terms of thermodynamics, electricity, optics, mechanics, etc. and their potential applications in the field of optoelectronic devices have attracted wide attention of researchers, it is difficult to prepare a  pure single-layered WS2 nanomaterial by general chemical and physical methods, especially the exfoliation preparation of single-layer tungsten sulfide in different phases.

Some researchers have put forward an approach to prepare the single-layer 1T-phase tungsten disulfide. The major contents are listed below.

Firstly, you should weigh 0.004mol of lithium hydroxide and 0.002mol of ammonium thiotungstate, and mix and grind in an agate mortar for 1h. 

Secondly, the ground mixture should be placed in corundum crucible which will be placed in a tube furnace and be protected by the increasing argon gas. The temperature is up to 800℃, and kept for 10 h. 

Thirdly, you should continue to feed the argon gas and cool down to room temperature. The lithiated 1T-phase Li2WS4 block will be obtained and placed in 50 ml of deionized water. The ultrasonic dispersion will be carried out for 10 min, and the dispersed suspension will be centrifuged to separate the precipitate on a centrifuge rotating at 1000 r/min. 

Fourthly, according to the content of tungsten disulfide in the suspension after removing the precipitation, graphene oxide, of which mass ratio is 1: 0.005, will be added. And then ultrasonic dispersion will be carried out for 10 min. 

Fifthly, 0.25 ml of hydrazine hydrate with a mass fraction of 80% will be added, and ultrasonic dispersion will be running for 0.5 h in order to obtain a single-layer 1T-phase WS2, graphene suspension.

Sixthly, in order to remove soluble contaminants, you should use water and ethanol to wash that graphene suspension three times on the centrifuge rotating at 4000 r/min. 

Finally, the precipitate of single-layer 1T-phase tungsten disulfide will be dispersed in 100 ml of deionized water. That graphene composite material will have a graphene content of about 0.25%, and the 1T-phase single layer of WS2 has a thickness of 0.76 nm.

The method utilizes ammonium thiotungstate and lithium salt compounds as raw materials, and undergoes them through heat treatment at a certain temperature in order to obtain a lithium-ion Li2WS2 block in 1T phase. That block will be hydrolyzed and stripped in deionized water, and will be assembled with the added graphene oxide into a single-layer 1T-phase tungsten disulfide.  That graphene composite material can not only improve the electrical conductivity of the material, but also effectively inhibit the agglomeration of single-layer 1T-phase tungsten disulfide. This method is simple, safe, efficient and suitable for the preparation of large-scale production.

 

 

 

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