Influence of organic solvents on the production of graphene quantum dots via liquid-phase exfoliation

Graphene quantum dots (GQDs) exhibit pronounced quantum confinement and edge effects, resulting in tunable band gaps, high photostability, and chemical robustness, which make them promising candidates for optoelectronic applications. In this work, GQDs were probe sonicated using three organic solvents, N–methyl–2–pyrrolidone (NMP), dimethylformamide (DMF), and dichloromethane (DCM) to elucidate the role of solvent properties on exfoliation efficiency and resulting structure property relationships. Structural and morphological analysis revealed pronounced solvent–dependent differences. GQDs produced in NMP exhibited the smallest lateral dimensions (∼2–10 nm), narrow thickness distribution (∼1.6–6.1 nm), and improved structural ordering, as evidenced by a relatively sharp (002) diffraction feature and the lowest Raman I_D/I_G ratio (0.34), indicating reduced defect density. UV–visible absorption spectra showed a blue–shifted absorption edge for NMP–derived GQDs, while optical band gaps estimated from Tauc plots yielded values of 2.75 eV (NMP), 2.53 eV (DMF), and 2.35 eV (DCM). Consistently, photoluminescence measurements revealed the strongest and most blue–shifted emission for NMP–exfoliated GQDs, confirming enhanced quantum confinement and suppressed non–radiative recombination. These results demonstrate that solvent selection critically governs the structural and optical quality of GQDs, with NMP enabling the formation of highly uniform and optically superior GQDs suitable for scalable optoelectronic applications.