Figure 1

Four synthesis techniques are employed to produce graphene quantum dot (GQD) substrates of varying oxidation level. (a) Schematic illustration of synthesis techniques to produce no-oxidation GQDs (no-ox-GQDs), low-oxidation GQDs (low-ox-GQDs), medium-oxidation GQDs (med-ox-GQDs), and high-oxidation GQDs (high-ox-GQDs). (b) Normalized X-ray photoelectron spectroscopy (XPS) data of no-, low-, med-, and high-ox-GQDs. Arrows indicate the center of the C1s carbon-carbon (C-C) bond at 284.5 eV and increasing oxidation via contributions of various carbon-oxygen bonds (see Fig. S1 for deconvolutions and peak ratios). (c) Normalized absorbance (dashed) and fluorescence emission (solid) spectra of no-ox-GQDs in hexane solution and low-, med-, and high-ox-GQDs in water. All GQDs were excited at 320 nm.