Scalable Synthesis of High-Quality Graphene Quantum Dots by Reductive Intercalation/Exfoliation of Coal.

Abstract

Coal, historically a low-cost and abundant energy resource, is emerging as a promising carbon-rich precursor for advanced nanomaterials. In this work, we introduce a reductive intercalation strategy to synthesize reduced (electron-rich) graphene quantum dots (GQDs) directly from anthracite coal. Potassium intercalation transforms the rigid graphenic framework of anthracite coal into a stage-I polyelectrolyte salt that spontaneously dissolves in <i>N</i>-methyl-2-pyrrolidone (NMP), yielding uniform (2.5-3.5 nm), reduced GQDs without the need for sonication or oxidative processing. The method achieves an isolated yield of <28% based on the starting mass of anthracite coal. Practically, this means that 3.6 kg of coal can yield up to 1 kg of graphene quantum dots, highlighting the scalability and efficiency of this approach. The resulting GQDs exhibit a direct bandgap of 3.4 eV and strong excitation-dependent photoluminescence. Thermo-optical characterization of GQDs in NMP reveals a thermal diffusivity of (6.4 ± 0.3) × 10^-8 m²/s and a nonlinear refractive index of -4.69 × 10^-9 cm²/W, demonstrating their potential for photothermal conversion and nonlinear optical applications. Notably, the GQDs can be precipitated and collected as slurries or powders that are readily dispersible in a variety of other solvents, including water, ethanol, isopropanol, facilitating their integration into diverse solution-processable systems. This scalable, oxidation-free approach positions coal as a viable feedstock for high-performance quantum nanomaterials with potential applications in sustainable sensing, and thermal management technologies.