(a) Modification strategy of g-C₃N₄. (b) Molecular orbital energies and structures of the g-C₃N₄ and S-g-C₃N₄ as well as the coordination complexes with U(VI) ion [91]. (c) Schematic diagram of the mechanism of g-C₃N₄/TiO₂ photocatalytic reduction of U(VI) and oxidation of As(III). (d) Photoreduction of U(VI) and the oxidation of As(III) by g-C₃N₄/TiO₂ [94]. (e) Schematic diagram of g-C₃N₄-CN agar aerogel seawater uranium extraction device. (f) Performance of g-C₃N₄-CN agar aerogel for uranium extraction from seawater [97]. (g) Mesoporous g-C₃N₄ photocatalytic U(VI) extraction from seawater. (h) Extractability of mesoporous g-C₃N₄ for uranium in deionized water and seawater. (i) The U LIII-edge XANES spectra of U(VI)-loaded mesoporous g-C₃N₄ after irradiation [99].