Preparation of few-layer black phosphorus by wet ball milling exfoliation

The wet ball milling (WBM) method is, for the first time, used for the exfoliation of bulk black phosphorus (BP) to obtain few-layer black phosphorus (FBP). Before that, the rational solid–liquid ratio of raw material is determined to be 1:1 (mg/mL) for the popular ultrasound liquid exfoliation (ULE). Obviously, the high proportion of organic solvent used in ULE will lead to serious environmental pollution. Compared with ULE, the solid/liquid ratio for WBM exfoliation is 100:1 (mg/mL) showing its advantage of less demand for organic solvent. In addition, different types of organic solvents are used to determine the proper organic solvent for WBM exfoliation. Ultraviolet–visible–near-infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and laser particle size analyzer are used to comprehensively characterize the layer numbers, morphology size, and phase structure of FBP yielded by WBM exfoliation. The results show that dimethyl sulfoxide (DMSO) is the suitable organic solvent for BP exfoliation; FBP flakes with 3–5 layers and micron size are obtained by WBM exfoliation.