Evolution of large-area reduced graphene oxide nanosheets from carbon dots via thermal treatment

Herein, we reveal a novel and facile pathway for the synthesis of reduced graphene oxide (rGO) from annealed carbon dots (CDs). The CDs (~ 2.5 nm) were synthesized from L-ascorbic acid via microwave synthesis at 180°C, after which formation of rGO nanosheets (≥ 40% yield) was achieved through 10 min annealing of CDs under N2 from 250-700°C. The TEM images showed that the CDs are initially transformed into an accreted sphere-like turbostratic carbon (d = 0.3390 nm) after annealing at 250°C, and finally to a layered ‘graphene-like’ nanomaterial (length ≈ 0.2-2.6 µm) at thermal treatment temperatures ≥ 500°C. The transformation into rGO was evidenced by the decrease in the oxygenated functional group content and removal of the oxygen functional groups facilitated the growth of rGO nanosheets through the interconnection of the C-C bonds at the defected CD edges. The FTIR, PL, PDF, and 13C NMR spectra confirmed the loss of functional groups after annealing at 700°C. Raman, and in particular PDF data, confirmed and rationalised the growth and evolution of the structured carbon domains with increasing annealing temperature. A mechanism to rationalize the data is proposed.