Construction of in-situ carbon-doped TiO2 decorated Fe3O4 heterojunction and their enhanced photocatalytic oxidation of As(III) under visible light

• In-situ carbon doping can reduce the band-gap of TiO 2 to 2.41 eV, realizing excitation under visible light. • The constructed Ti–O–Fe and C–O–Ti interfacial chemical bonds can efficiently enhance the carriers separation and photocatalytic rate. • The stable magnetism of photocatalyst is beneficial to recovery and avoid secondary water pollution. This paper is focused on the functional photocatalyst of in-situ carbon-doped TiO 2 decorated Fe 3 O 4 heterojunctions (C/TiO 2 @Fe 3 O 4 ) for the efficient photocatalytic oxidation of As(III). Series of characterizations show that the photocatalytic activity of TiO 2 changes from a single UV wavelength to visible light excitation when carbon atoms are successfully doped in the TiO 2 lattice, expanding the utilization rate of light energy. DFT calculation further confirmed that the C–O–Ti bonds can diminish the theoretical band-gap of TiO 2 . Furthermore, the successful construction of C–O–Ti and Ti–O–Fe interface bonds provide pathways for fast electron transfermation, which can effectively prompt the separation of photo-generated carriers and enhance the photocatalytic oxidation efficiency of As(III). The application results showed that the synthesized C/TiO 2 @Fe 3 O 4 photocatalyst by introducing Fe 3 O 4 with a mass fraction of 1% can complete the transformation of As(III) (10,000 μg/L, 40 mL) to As(Ⅴ) within 12 min under visible light irradiation. In addition, C/TiO 2 @Fe 3 O 4 exhibits excellent reusability, which remains 100% photooxidation efficiency of As(III) without changing crystal structure after 6 cycles and can also be recovered completely with magnet. The remarkable photocatalytic oxidation performances of C/TiO 2 @Fe 3 O 4 can be ascribed to the synergistic effects of OH, O 2 − and h + in the photocatalytic oxidation process and the constructed C–O–Ti and Ti–O–Fe interface bonds.