Synthesis of high crystallinity g-C3N4 hollow spheres for efficient photocatalytic removal of U(VI) under visible light

Here, we report the preparation of hollow g-C3N4 nanospheres with different crystallinity (HCN-R, R=Air, N2, NH3) by adjusting the calcination atmosphere. The hollow sphere structure is conducive to fully exposing the surface active site, shortening the electron transmission distance, and the incident light can be reflected and refracted multiple times in the hollow sphere to improve the light utilization efficiency·NH3 atmosphere can improve the crystallinity of hollow spherical g-C3N4. The increase of crystallinity is helpful to eliminate the electron capture center and promote the charge transfer in the two-dimensional π-conjugate plane. HCN-NH3 has the fastest photocatalytic removal rate of U(VI) (0.0286 min−1). The photocatalytic mechanism indicates that e– and •O2– radicals promote the removal process of U(VI), and U(VI) is deposited in the form of (UO2)O2·2H2O under air.