The morphology of g-C3N4 and CNCD-2 were characterized by TEM. As shown in Fig. 1a, the g-C3N4 has a typical layered porous structure. The microstructure of g-C3N4 was well maintained after CDs modification (Fig. 1b), and some CDs nanoparticles with a diameter of about 1 nm were observed on the surface of CNCD-2 (Fig. 1c) [42]. Next, the TEM elemental mapping of CNCD-2-U (CNCD-2 after photoreduction of uranium) was shown in Fig. 1e-1i. The main elemental constituent of CNCD-2-U was C, N, O and
