Dual-Functional S-Scheme Fe3O4/TiO2/g-C3N4 double-heterostructure bridged by TiO2 for collaborative removal of U(VI) and Sb(III)

Exploiting dual-functional photocatalysts to reduce U(VI) and oxidize Sb(III) is a challenging but efficient way of achieving simultaneous purification. Herein, Fe3O4/TiO2/g-C3N4 (FTC) double-heterostructures with customized stacking order were designed as a dual-functional photocatalyst to collaborative remove U(VI) and Sb(III). When introducing TiO2/g-C3N4 heterojunction and bridging it with Fe3O4/TiO2 using TiO2 as the intermediate layer, FTC showed outstanding photocatalytic activity and can simultaneously achieve 96.5% U(VI) reduction and 88.5% Sb(III) oxidation under sunlight, achieving 90.9% and 85.8% in natural wastewater. The constructed FTC architecture of an S-scheme framework can achieve efficient co-removals of U(VI) and Sb(III) by enhancing the separation and transferal of photoexcited charge carriers with outstanding redox ability employing different reaction sites. TiO2 and g-C3N4 accumulated electrons and holes, respectively, and completed concurrent redox reactions, following the path determined by N(g−C3N4) and O(TiO2), which enhanced the separation of photoexcited carriers. The two-way effect of O2• ⁻ activated by FTC supported positive feedback coupling relationships between the reduction of U(VI) and Sb(III) oxidation. This study not only fulfills the co-removal of U(VI) and Sb (III) for the first time with a capacity of 170.6 and 15.9 mg/g in engineering applications, but also proposes the reaction mechanism of a two-step continuous concerted redox reaction causing high removal determined by the electronic structure, so it lays a foundation for further development of highly efficient and stable heterojunction photocatalysts with concerted effects applied in complex wastewater treatment.