Controlled Synthesis of Tungsten Disulfide Nanomaterials

1T-WS₂ structure and 2H-WS₂ structure of tungsten disulfide nanomaterials controlled synthesis is important. The 1T-WS₂ structure is considered an efficient co-catalyst for hydrogen evolution due to the increased density of catalytic active sites and the metal conductivity, while the 2H-WS₂ structure can be used as a visible photosensitizer. Therefore, various synthetic methods for the crystalline phase modulation of WS₂ have received much attention. Since the conversion from 1T-WS₂ to stable 2H-WS₂ can be easily achieved by annealing, the study of feasible methods to achieve the opposite conversion has received much attention.

The lithium intercalation hydrothermal method is an important wet chemical method to achieve the conversion of the 2H phase to the 1T phase. This method uses alkali metal (lithium) to enter the bulk 2H-WS₂ layer and then reacts with water to form a large amount of hydrogen gas to achieve WS₂ stripping, producing 1T-WS₂ in the process.

The researchers found that products prepared at room temperature had a low lithium-ion content, resulting in insufficient peeling. Heating can increase the lithium-ion content and thus the stripping efficiency. However, most such exfoliated WS₂ showed low stability (complete conversion of lithium-ion exfoliated 1T-WS₂ to 2H-WS₂ was observed after one and a half months) and a mixture of 1T and 2H phases.

To solve the above problems, Liu et al. reported stable metal 1T-WS₂ nanoribbons intercalated with ammonia ions, and the samples did not change for more than six months, indicating good stability. Another wet chemical method to solve the above two problems is the colloidal controlled synthesis method, which can achieve the controlled fabrication of a stable crystalline phase of WS₂.

For example, Mahler et al. prepared colloidally stable WS₂ monolayers with distorted 1T structures by controlling the reactivity and reaction time of tungsten precursors. So far, much attention has been focused only on liquid-based approaches to achieve crystalline phase modulation, and some other strategies should also be explored.

Due to the anisotropic nature of WS₂ nanostructures, the effect of different morphologies on the properties is significant. The use of different strategies to synthesize WS₂ with specific morphologies and to investigate the growth mechanisms controlling the WS₂ morphology have gained much attention. Three main morphologies, including nanosheets, intermediate frequency WS₂, and NT-WS₂, have been widely studied due to their good physical and chemical properties.

Article Source: Sun, CB., Zhong, YW., Fu, WJ. et al. Tungsten disulfide nanomaterials for energy conversion and storage. Tungsten 2, 109–133 (2020).

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