Efficient Preparation and Optoelectronic Properties of Coal Liquefaction Asphalt-Based Carbon Quantum Dots

Coal liquefaction pitch is a by-product of the direct coal liquefaction process. In this paper, it was used as a high-quality carbon source to prepare fluorescent carbon quantum dots (CQDs) by sulfuric acid oxidative depolymerization, and the preparation process was optimized by response surface methodology (RSM). The key technical parameters such as reaction temperature (58 °C), duration (2.1 h) and liquid-solid ratio (ratio of the volume of 98% concentrated sulfuric acid to the mass of liquefaction pitch) (17.5∶1) were obtained, and blue fluorescent CQDs with uniform particle size (2~8 nm), high yield and high fluorescence yield were successfully synthesized.The CQDs have a graphitized core-shell structure, which is mainly composed of 3 aromatic ring aggregates, and the surface is rich in oxygen-containing functional groups such as −OH, −COOH and −SO₃H. Optical performance tests show that the CQDs exhibit wavelength-dependent fluorescence emission characteristics under 340 nm ultraviolet excitation, show a maximum emission peak at 394 nm, and have a relatively high quantum yield (32.5%). In addition, CQDs exhibit excellent photoelectric conversion ability, which destroys bacterial structures by generating reactive oxygen species (ROS) such as ·O₂⁻ and ·OH under light, with an average bactericidal efficiency of 97.27%. This study provides a new idea for the high-value utilization of coal pitch.