Size-controlled MoS2 nanosheet through ball milling exfoliation: parameter optimization, structural characterization and electrocatalytic application

Unique properties and potential applications of 2D materials draw much attention for mass production of thin-layer 2D materials. Ball milling exfoliation of 2D materials has been rarely used, in spite of a promising dry phase production method, because of the superficial information in the mechanism and the effect of the operating parameters on the yield, size and thickness. Here, we investigate systematically the ball milling operating parameters in the exfoliation of bulk MoS2 in the presence of sodium cholate (SC) as an exfoliant. The yield and dimensions of the exfoliated MoS2 nanosheet were monitored by changing the parameters such as the weight ratio of bulk MoS2 and SC (SC/MoS2), the filling ratio in the volume of milling ball and container (?), milling ball size (d(B)), milling revolution speed (n(R)), and initial mass of bulk MoS2 (mMoS2<i). The yield of exfoliation is found to be 95% at the optimum ball milling conditions (SC/MoS(2)50%, mMoS2<i =;0.20 g). In addition, yield and size of the exfoliated MoS2 were controlled by the conditions of the ball milling. As for the evaluation of the exfoliated MoS2, we developed a novel method by use of the XRD profile to determine the size and thickness of the ball-milled MoS2 powder with less than 30% difference from those determined by the well-known absorption method. Finally, the size and thickness of the MoS2 nanosheets prepared by ball milling exfoliation were correlated with their electrocatalytic and photoelectrocatalytic activities.