Blue light-emitting carbon dots from victorian brown coal

Carbon dots (CDs) are innovative fluorescent carbon nanomaterials with sizes smaller than 10 nm. However, the practical applications of CDs have been hindered by the relatively high cost of precursors, which limits their large-scale production. Coal is known to be the most abundant with low cost and broadly distributed natural resource on the Earth. It is an organic matter mainly composed of carbon, hydrogen, and oxygen. Thus, coal is an attractive precursor for synthesizing CDs with a large-scaled production. In this study, we demonstrate a one-step extraction method for obtaining blue light-emitting CDs from Victorian brown coal in Australia, which is low cost and has an abundant reserve over the world. The extraction of certain substances from the brown coal was achieved using ethanol as a solvent. Subsequently, the solution of the extracted substances exhibited blue luminescence when exposed to ultraviolet irradiation. Transmission electron microscopy images revealed nanoparticles with an average size of 4.0 nm. The photoluminescence spectrum displayed a broad peak with a full width at half maximum of 116 nm, centered around 448 nm, when excited at 360 nm. Remarkably, these characteristic features closely resemble those observed in fluorescent CDs obtained from high-cost precursors using multi-step procedures such as pyrolysis decomposition, chemical oxidation, microwave-assisted synthesis, ultrasonic synthesis, and laser ablation synthesis. These results demonstrate the successful extraction of fluorescent substances or CDs from the brown coal using a simple one step extraction method. Furthermore, we suggest that fluorescent substances or CDs may naturally be present in Victorian brown coals.