Preparation Method of 1T Phase Single-layer Tungsten Disulfide Nanosheet

Tungsten disulfide (WS₂）has the same structure as molybdenum disulfide. It is a typical sandwich layer structure. Due to its relatively weak van der Waals force between layers, it can also be stripped into single or few layers of nanosheets. It is considered to be another equivalent. An important two-dimensional nanosheet material with unique physical, chemical and electrical properties.

Recently, there have been more and more studies on tungsten disulfide. It is generally believed that there are three phase states of tungsten disulfide, namely 1T, 2H and 3R phases, wherein the 1T phase is WS₂ with one S-W-S monolayer as the minimum repeating unit. Stacked, while the 2H and 3R phases are stacked with two and three SWS monolayers as the smallest repeating unit. Different phase WS₂ materials exhibit different physicochemical properties. For example, a 2H phase material exhibits semiconductor properties, while a 1T phase WS₂ material exhibits metal properties.

Researchers believe that it is difficult to prepare WS₂ nanomaterials with pure single-layer structure by general chemical and physical methods, especially the preparation of single-phase 1T phase monolayer tungsten disulfide nanosheets, most of which are still in the laboratory. Recently, researchers have proposed a method for preparing a 1T phase single-layer tungsten disulfide nanosheet, the preparation process of which includes:

(1) The ammonium tungstate and the lithium salt compound are mixed and ground in a molar ratio of 1:2, and the ground mixture is kept under the protection of an inert gas at 800-1300 ° C for 1-10 h, and cooled to room temperature to obtain a lithium-plated 1T phase. Tungsten sulfide block;

(2) The lithium-plated 1T-phase tungsten sulfide block is directly placed in deionized water, assisted by ultrasonic hydrolysis and stripped for 5-30 min, and the obtained suspension is placed in a centrifuge, and the unpeeled precipitate is removed by centrifugation. Obtaining a 1T phase single layer WS₂ nanosheet suspension;

(3) The 1T phase monolayer tungsten disulfide nanosheet suspension was centrifuged on water and ethanol to remove soluble impurities. Finally, the precipitate 1T phase single layer WS₂ nanosheet was dispersed in a small molecule solvent, and the 1T phase was stored. The thickness of the single layer WS₂ nanosheet is less than 1 nm.

The working principle of the above process is to use lithium thiotungstate and lithium salt compounds as raw materials, heat-treated at a certain temperature to obtain a lithium-ion Li₂WS₂ block of 1T phase, and the lithium Li₂WS₂ block is hydrolyzed in deionized water to form a 1T phase. The layer of tungsten disulfide nanosheets, the target material can be stably existed in small molecular solvents such as water and ethanol, and the thickness is less than 1 nm, and can be applied in the fields of photohydrogen evolution, electrocatalysis and energy storage.

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