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Mechanical exfoliation from bulk layered crystal is widely used for preparing two-dimensional (2D) layered materials, which involves not only out-of-plane interlayer cleavage but also in-plane fracture. Through a statistical analysis on the exfoliated 2D flakes, we reveal the in-plane cleavage behaviors of six representative layered materials, including graphene, h-BN, 2H phase MoS2, 1T phase PtS2, FePS3, and black phosphorus. In addition to the well-known interlayer cleavage, these 2D layered materials show a distinctive tendency to fracture along certain in-plane crystallography orientations. With theoretical modeling and analysis, these distinct in-plane cleavage behaviors can be understood as a result of the competition between the release of the elastic energy and the increase of the surface energy during the fracture process. More importantly, these in-plane cleavage behaviors provide a fast and noninvasive method using optical microscopy to identify the lattice direction of mechanical exfoliated 2D layered materials.

The aim of this work was to synthesize a silver-chitosan composite to enhance the antibacterial properties of the composite by using as small an amount of silver as possible. The silver-chitosan composite was prepared using a facile method. The structure character of the silver-chitosan composite was characterized by X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FT-IR). Its antibacterial activities were evaluated by measurements of the minimal inhibition concentration (MIC), inhibition zone diameter and the kinetics of antibacterial activity. The results indicated that silver was connected with the chitosan homogeneously and stably after initiation by potassium persulfate. The composite exhibited high antibacterial activity to Candida albicans with low MIC and relatively low optical density; it also had good antibacterial activity to Escherichia coli with larger inhibition zone diameter.