Enhanced photocatalytic activity of liquid phase exfoliated WS2 nanosheets

Due to their large surface area and novel electronic properties, tungsten disulfide (WS2) nanosheets are promising materials for potential photocatalysis applications. The fabrication of large-scale WS2 nanosheets is a fundamentally important step to realize their applications. The liquid phase exfoliation method, which involves the mechanical exfoliation of layered materials in a solvent, has proven to be a feasible technique for fabricating nanosheets with high yields. Here, we systematically examine the optimization of the fabrication of WS2 nanosheets by exfoliating the WS2 powder in isopropyl alcohol, a low boiling point solvent, using a low-power probe sonicator and ball milling method. We show that prolonged sonication produces a concentration as high as 0.64 mg/ml, and the same concentration can be fabricated in less than half the time if the bulk powder is ball milled prior to the sonication. An atomic force microscopy study reveals that the proportions of monolayers and bilayers can be significantly increased if the nanosheet dispersions are centrifuged at a higher speed or sonicated for a long time. The photodegradation measurements reveal that the decomposition rate of methyl orange with nanosheets is at least 10% higher than that with WS2 powder, suggesting that the photocatalytic activity of WS2 can be enhanced if it is reduced to nanosheets.