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 (similar to 2.5 nm) were synthesized from L-ascorbic acid via microwave synthesis at 180 degrees C, after which formation of rGO nanosheets (>= 40% yield) was achieved through 10 min annealing of CDs under N-2 from 250-700 degrees 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 degrees C, and finally to a layered 'graphene-like' nanomaterial (length approximate to 0.2-2.6 mu m) at thermal treatment temperatures >= 500 degrees 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 C-13 NMR spectra confirmed the loss of functional groups after annealing at 700 degrees 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. (c) 2021 University of the Witwatersrand. Published by Elsevier Ltd.