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, Fe 3 O 4 nanoparticles with different vacancies were successfully prepared to investigate their distinct effects on the near-infrared (NIR) driven photocatalytic bacterial inactivation activity. Compared to the Fe 3 O 4 -1 with Fe-O vacancies, Fe 3 O 4 -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, Fe 3 O 4 -2 with a narrow band gap can enhance NIR light absorption and the generation of heat. Moreover, Fe 3 O 4 -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, Fe 3 O 4 -2 fully inactivated 99% Escherichia coli ( E. coli ) and Bacillus subtilis ( B. subtilis ) within 10 min NIR irradiation, displaying better inactivation efficiency than Fe 3 O 4 -1. This study reveals the defect type-dependent photocatalytic behaviors, providing new insights into the antibacterial mechanisms of Fe 3 O 4 .