Figure 2. Synthesis and characterizations of the CDs. (a) Cartoon of the synthesis of the CDs by the one-step hydrothermal method. (b) A typical TEM image of the CDs. Inset shows the particle size distribution of the CDs. Scale bar: 25 nm. (c) Absorption spectrum of the CDs, and the photoluminescence spectra under different excitation conditions. Inset shows the digital photographs of the CD solution under ambient irradiation (left) and a 365 nm-UV irradiation (right). (d) FTIR spectrum of the CDs. (e) XPS spectrum of the CDs.