Monolayer 2H Phase Tungsten Disulfide / Graphene Composites

Tungsten disulfide is a typical sandwich layered structure. Because of its relatively weak van der Waals force between layers, it can also be peeled into single or few layers of nanosheets. Tungsten disulfide is considered as another important two-dimensional nanosheet material besides graphene, which has unique physical, chemical and electrical properties.

The preparation of monolayer 2H phase tungsten disulfide/graphene composite material is based on ammonium thiotungstate and lithium salt compounds as raw materials. The 2H phase lithium-intercalated Li₂WS₂ block is obtained by heat treatment at a certain temperature. The lithium-intercalated Li₂WS₂ block is hydrolyzed in deionized water and self-peeled, and then self-assembled with the added graphene oxide to form a monolayer 2H phase tungsten disulfide/graphene composite.

(1)The mixture of ammonium thiotungstate and lithium salts is ground at 1:2 molar ratio. The mixture after grinding is kept in inert gas for 1-10 h at 200-600 ℃ and cooled to room temperature to obtain 2H phase tungsten sulfide block with lithium insertion.

(2)The lithium-intercalated 2H-phase tungsten sulfide block was directly placed in deionized water, assisted by ultrasonic hydrolysis for 5-30 minutes, then the obtained suspension was placed in a centrifuge. After centrifugal separation, the undissolved precipitate was removed and a single layer of 2H-phase WS₂ nanosheet suspension was obtained.

(3)Graphene oxide was added into the suspension of 2H phase monolayer WS₂ nanosheets, and dispersed by ultrasonic for 5-10 minutes. Then, hydrazine hydrate was added to the suspension for 0.5-2 h to obtain monolayer 2H phase WS2/graphene suspension.

(4)The obtained monolayer 2H phase tungsten disulfide/graphene suspension was centrifuged with water and ethanol to remove soluble impurities. Finally, the precipitate monolayer 2H phase tungsten disulfide/graphene composite was dispersed in small molecular solvents and preserved. The thickness of monolayer 2H phase WS₂ nanosheet was less than 1 nm.

Compared with graphene monomer, the composite of tungsten disulfide and graphene has the advantage of greatly improving its conductivity and eliminating the defect of zero bandgap of graphene to a large extent. Therefore, 2H phase tungsten disulfide/graphene composite can be used for the study of single layer tungsten sulfide in the fields of hydrogen photolysis, electrocatalysis and energy storage.

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