Figure 4.

(A) Fabrication of GQDs by the hydrothermal exfoliation of GO with the assistance of potassium superoxide (KO₂); reproduced from Zhao et al. (2017) with permission from Elsevier. (B) Hydrothermal cutting of starch to synthesize GQDs; reproduced from Chen et al. (2018) with permission from the Royal Society of Chemistry. (C,D) Acid-free solvothermal exfoliation of different carbon-based precursors to fabricate GQDs; reproduced from Shin et al. (2015) and Tian et al. (2016) with permission from the Royal Society of Chemistry and Elsevier.