Unraveling the role of defect types in Fe3O4 for efficient NIR-driven photocatalytic inactivation

Defect engineering is of great importance to tailor photocatalytic activity, which is uncertain in determining the antibacterial performance relationship with defect types. In this study, Fe3O4 nanoparticles with different va-cancies were successfully prepared to investigate their distinct effects on the near-infrared (NIR) driven pho-tocatalytic bacterial inactivation activity. Compared to the Fe3O4-1 with Fe-O vacancies, Fe3O4-2 with Fe-O-Fe vacancies contained improved photogenerated electron-hole separation efficiency and stronger adsorption ability to O-2, and thus greatly facilitated the generation of reactive oxygen species (O-2(-) and OH). Meanwhile, Fe3O4-2 with a narrow band gap can enhance NIR light absorption and the generation of heat. Moreover, Fe3O4-2 with Fe-O-Fe vacancies possessed enhanced bacteria-binding ability, thereby decreasing the diffusion distance of the released reactive oxygen species and heat, which could significantly accelerate bacterial killing. Owing to these tendencies, Fe3O4-2 fully inactivated 99% Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) within 10 min NIR irradiation, displaying better inactivation efficiency than Fe3O4 -1. This study reveals the defect type-dependent photocatalytic behaviors, providing new insights into the antibacterial mechanisms of Fe3O4.