How to Prepare Silver/Tungsten Disulfide Sandwich Composite?

Silver ions can be inserted to tungsten disulfide layers to prepare sandwich composite of silver and tungsten disulfide. The preparation is simple and suitable for large-scale production. And prepared sandwich composite usually has a better conductivity than that of tungsten disulfide.

Tungsten disulfide is a new kind of two-dimensional material. It takes S-W-S sandwich layer as its basic structural unit. And there is weak van der Waals force between layers. Sandwich composites of silver and tungsten disulfide, which is obtained by inserting silver ions into tungsten disulfide layers, can be widely used in conductive materials and lubricating materials.

This kind of sandwich composite can be prepared according to the following experimental principle:

Li_xWS₂ intercalation compounds can be prepared by the reaction of tungsten disulfide with n-BuLi under certain conditions. So monolayer tungsten disulfide can be obtained by the reaction of Li_xWS₂ with water to further prepare the sandwich composite. The equation of the reaction is as follows:

Li_xWS₂+(x-y)H₂O[WS₂Y_-(monolayer)+xLi⁺+(x-y)OH^-]aq+(x-y)/2H₂↑

The above experiment takes an intercalation method of preparing metals under polymer protection. At first, the polymer is mixed with the aqueous solution containing metal ions to form a uniform sol system. Then the sol is inserted into the single layer of tungsten disulfide. Finally, the metal ions are reduced to obtain nanocomposite of tungsten disulfide and polymer.

Sandwich composite of silver and tungsten disulfide can be prepared according to the following steps:

Step One: 0.5 g silver nitrate is dissolved in water to form an aqueous solution with a solvent ratio of 10%. Then silver nitrate is converted into silver oxide by adding equal molar sodium hydroxide solution. The mixture is washed with deionized water several times and dissolved in 15% dilute ammonia water. The mixed solution is continuously reacted with the aqueous solution containing 1 g polyvinyl alcohol. The reaction equation is as follows:

Ag₂O+4NH₃-H₂O→2Ag(NH₃)₂OH+3H₂O

Step Two: The mixed solution was stirred into aqueous solution containing 0.75 g LiWS₂. And then silver is reduced by adding 0.1 M excess formic acid solution drop by drop. The reaction product is centrifugally separated, washed by deionized water and dried in vacuum in turn to successfully prepare sandwich composite of silver and tungsten disulfide.

As metal ions are completely converted into metal elements, prepared sandwich composite usually has a better conductivity than that of tungsten disulfide. The preparation method is simple and suitable for mass production.

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