Black phosphorus quantum dots: synthesis, properties, functionalized modification and applications

Zero-dimensional (0D) black phosphorus quantum dots (BPQDs) are emerging functional nanomaterials. 0D BPQDs are a new form of black phosphorus (BP) nanostructures that were first prepared in 2015; they are different from typical two-dimensional (2D) BP layered nanosheets and one-dimensional (1D) BP nanoribbons. Since 2015, numerous studies have been devoted to exploring various synthetic methods, properties and modifications of BPQDs, which exhibit a broad range of applications. This review systematically summarizes PBQDs for the first time. Different synthetic methods are reviewed, including ultrasonic and electrochemical exfoliation, solvothermal treatment, blender breaking, milling crushing and pulsed laser irradiation. We highlight the physicochemical properties of BPQDs from theoretical models and discuss their experimentally observed properties. The surface modifications and functionalized combination of BPQDs with other substances are summarized by illustrating different hybrid structures, such as BPQDs/nanosheets hybrids, BPQDs-doping films, BPQDs-molecules complexes, polymers-modified BPQDs, and the assembly of BPQDs in devices. The potential applications of BPQDs are demonstrated in current research fields, including bioimaging, fluorescence sensing, nonlinear optical absorbers, cancer therapy, intelligent electronics, photovoltaics, optoelectronics and flexible devices. The current status, challenges and future perspectives of PBQDs are discussed rationally. This timely overall review should be desirable for broad scientists and facilitate the further development of layered nanostructures-derived QDs and other low-dimensional nanomaterials.