Fig. 2. X-ray photoelectron spectroscopy of GQDs. (a) XPS survey scan of GQDs with reaction time of 3 hours, 5 hours, and 7 hours at 200 °C. (b) XPS carbon chemical state of GQDs with reaction time of 3 hours, 5 hours, and 7 hours. (The C–C/C O ratios with various reaction times, respectively, were 2.05, 2.32, and 2.95).
