Fig. 4. Characterization of the surface composition and chemical state of the CDs. (a–c) FT-IR characterization of the CDs washed for two times, six times and further reduced by hydrogen, respectively; (d–i) XPS survey; high-resolution XPS were de-convoluted following the literature: (d and g) for H-CDs, (e and h) for P-CDs and (f and i) for R-CDs.
