Reaction route, mechanism, and procedure of the photoredox of U(Ⅵ) and Sb(Ⅲ) using a Fe 3 O 4 /TiO 2 /g-C 3 N 4 heterojunction nano- photocatalyst under visible sunlight

Abstract Magnetic Fe3O4/TiO2/g-C3N4, as a stable and recyclable ternary two-layer heterojunction nano-photocatalyst, has been synthesized to integrate the merits of each which can remove U(Ⅵ) and Sb(Ⅲ) through responding to almost full-wave band of visible of sunlight. Meanwhile through the combination of actual tests (free radical trapping tests), characterization (XRD, FT-IR, Raman, XPS, EXAFS and EPR) and theoretical calculations structure optimization, band structures, TDOS, electrostatic potential, charge density difference and Bader charge analysis) revealed reaction route, catalytic mechanism and reaction procedure of this photocatalytic reaction. It was found that the adsorption process took place between TiO2/ g-C3N4 heterostructure in the form of (C3)–N–U(Ⅵ)–O2c–Ti and N…Sb(Ⅲ)–O2c–Ti where N(g-C3N4) and O(TiO 2) played decisive roles. The built-in electric field and electronic structure motivated TiO2 and g-C3N4 to accumulate a large amount of e- to reduce U(Ⅵ) and h+ to oxidize Sb(Ⅲ) respectively, and completed the light-induced redox reaction by making full use of the e-, •OH and O2• ⁻ produced by photoexcited carriers which were difficult to recombine, finally, heterojunction complexes of (C3)–N–U(Ⅳ)–O2c–Ti, C=N–U(Ⅳ)–O2c–Ti and N…Sb(Ⅴ)–O2c–Ti were formed. Moreover, the two-way effect of O2• ⁻ proved that the redox of U(Ⅵ) and Sb(Ⅲ) had a coupling relationship. In addition, Fe3O4/TiO2/g-C3N4 prevented the damage of Fe3O4's photodissolution to its structure while Fe3O4 provided a new and interrelated path for the redox of U(Ⅵ) and Sb(Ⅲ).