A review on the preparation and applications of coal-based fluorescent carbon dots

Deep processing and functional applications of coal are important strategies to overcome the bottleneck of current coal applications. In recent years, the fluorescent carbon dots (CDs), a new member of the carbon nanomaterials family, have shown great application prospects in biological imaging, chemical sensing and photocatalysis owing to their excellent biocompatibility, non-toxicity, tunable fluorescence emission, outstanding energy storage performance and other unique properties. Coal and coal-derived materials contain large amounts of crystallite structure and condensed aromatic ring clusters, which are connected by the densely distributed carbon-oxygen bonds. The linkage can be broken by chemical, electrochemical or physical methods to obtain fluorescent CDs. Therefore, the coal and coal-derived materials with wide distribution, large reserves and low price are ideal source materials for preparation of CDs. Herein, we summarize the preparation methods of CDs from coal together with their merits and demerits. Meanwhile, the effects of the type of coal and coal-derived materials and preparation conditions on the properties of fluorescent CDs are analyzed. Furthermore, the properties and applications of coal-based CDs and their nanocomposites in chemical detection, biological imaging, photocatalysis are outlined with emphasis on the formation of heterogeneous structures in nanocomposites based on CDs. Finally, the future development of coal-based CDs is prospected. It is expected that this review will provide key information for the preparation and applications of coal-based CDs, thus providing an economical and sustainable choice for the comprehensive utilization of coal.