Research progress on preparation and physicochemical properties of coal-based graphene quantum dots

Graphene quantum dots (GQDs) have attracted great research interest due to their remarkable quantum confinement and edge effects. In addition to exhibiting stable photoluminescence, it also has many advantages such as low cytotoxicity, good solubility and chemical inertness, making it widely used in bioimaging, photocatalysts and sensors. The industrial development of GQDs has been seriously hampered by the expensive raw materials and tedious operation of traditional preparation methods. Coal and its derivatives not only possess the characteristics of low price and abundant reserves, but also show greater advantages than graphite, graphene, graphite oxide and other carbon materials in the preparation of GQDs due to its inherent internal disorder structure and small crystal domain. GQDs can be prepared by simply stripping the aromatic ring clusters inside the coal and its derivatives through physical, chemical or electrochemical methods. This review first summarizes the “top-down” synthesis method of coal-based graphene quantum dots (C-GQDs) and its pros and cons. Then the structural morphology, chemical composition, fluorescence properties of C-GQDs and their influencing factors are analyzed. Further, we describe the progress in applications of C-GQDs in fields such as sensors, bioimaging and energy Finally, the future development of C-GQDs is discussed from the perspectives of preparation methods, carbon source selection and research directions, and the following experimental schemes are proposed: (1) Experiment with H₂O₂ as oxidizer and thermally altered coals as carbon sources;  (2) Experiments other than oxidation with sulfuric acid and nitric acid using superhigh organic sulfur coals as carbon sources;  (3) Experiment on coal macerals as a carbon sources. In addition, the combination of experimentally derived basic data and computer simulation technology can solve the problems of current research such as single fluorescence color and low quantum yield. The goals of clean utilization of coal resources and green development of GQDs have been achieved.