Abstract
To progress from laboratory research to commercial applications, it is necessary to develop an effective method to prepare large quantities and high-quality of the large-size atomically thin molybdenum dichalcogenides (MoS2). Aqueous-phase processes provide a viable method for producing thin MoS2 sheets using organolithium-assisted exfoliation; unfortunately, this method is hindered by changing pristine semiconducting 2H phase to distorted metallic 1T phase. Recovery of the intrinsic 2H phase typically involves heating of the 1T MoS2 sheets on solid substrates at high temperature. This has restricted and hindered the utilization of 2H phase MoS2 sheets suspensions. Here, we demonstrate that the synergistic effect of the rigid planar structure and charged nature of organic salt such as imidazole (ImH) can be successfully used to produce atomically thin 2H-MoS2 sheets suspension in water. Moreover, lateral size and area of the exfoliated sheet can be up to 50 μm and 1000 μm2, respectively. According to the XPS measurements, nearly 100% of the 2H-MoS2 sheets was successfully prepared. A composite paper supercapacitor using the exfoliated 2H-MoS2 and carbon nanotubes delivered a superior volumetric capacitance of ~410 F/cm3. Therefore, the organic salts-assisted liquid-phase exfoliation has great potential for large-scale production of 2H-MoS2 suspensions for supercapacitor application.
Highlights
The liquid phase exfoliation method is characterized by high scalability and relatively low production costs, and it does not require transfer techniques, making it suitable for producing 2H-MoS2 materials in bulk quantities[6,7]
This study demonstrates that atomically thin MoS2 sheets in the 2H phase can be prepared by organic salts such as imidazole (ImH) or pyridiniumtribromide (PyBr3)
A suspension of the exfoliated 2H-MoS2 sheets was prepared from commercial 2H-MoS2 powder via an ImH or PyBr3 exfoliation process followed by ultrasonication
Summary
The liquid phase exfoliation method is characterized by high scalability and relatively low production costs, and it does not require transfer techniques, making it suitable for producing 2H-MoS2 materials in bulk quantities[6,7]. Coleman et al have demonstrated that liquid-phase exfoliation of MoS2 powder in N-methylpyrrolidone with ultrasonication is a practical route to achieving the preparation of MoS2 sheets. This method yields multi-layered sheets of MoS2, and thin sheets are very rarely observed[10,11]. 1T-MoS2 turns into nanometer-sized flakes after exfoliation along with the occurrence of metal nanoparticle formation and Li2S agglomeration[19] This has dramatically hindered the development of atomically thin MoS2 sheets in most applications that require a pristine structure and large sheets with high concentrations. The 2H-MoS2 suspension allows for the preparation of high electrical conductive composites for energy storage applications
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