Highly efficient and continuous production of few-layer black phosphorus nanosheets and quantum dots via acoustic-microfluidic process

Few-layer black phosphorus (BP) with tunable band gap and excellent electronic properties is an emerging two dimensional semiconductor that has been demonstrated to be useful in many applications. Here we introduce an acoustic-microfluidic (AM) process for exfoliation of BP powder to produce few-layer BP flakes and BP quantum dots (BPQDs) in a continuous-flow process. The AM process yielded a 45 wt% exfoliation efficiency in 6 min, and produced few-layer BP flakes of stripe shape with a lateral size of 434 ± 135 nm and a thickness of 2.5 ± 1.2 nm, corresponding to 2-4 layers of phosphorene, at a production rate of 9.8 mg hr−1. In contrast, the conventional batch process yielded an exfoliation efficiency of only 14 wt% even after 6 hrs, and produced larger and thicker BP flakes. Furthermore, prolonging the AM process to additional 12 min resulted in efficient fragmentation of the flakes into a few nanometer BPQDs (diameter 2.6 ± 1.0, thickness 1.7 ± 0.6 nm). The efficiency in the exfoliation and subsequent fragmentation can be attributed to the cavity activities maximized by flow rate. The AM-exfoliated BP nanosheets and BPQDs is found to be stable in 8 months aging as long as their exposure to air and water is avoided.