Tuning Size and Defect Chemistry of TiO2 via Flash Nanoprecipitation for Enhanced Photocatalytic Antibacterial Activity

Titanium dioxide (TiO2) has been extensively studied as an inorganic photocatalyst for antibacterial applications. Its activity depends strongly on structural features, particularly particle size and defect state, yet these are challenging to control reproducibly under mild conditions using conventional sol-gel or hydrothermal methods. This difficulty possibly arises from the hydrolysis-condensation process, which is highly sensitive to local composition and mixing and readily trigger aggregation. Herein, we report a flash nanoprecipitation (FNP) approach to fabricate anatase TiO2 with a tunable hydrodynamic diameter of 190-850 nm and a higher defect density than a conventional product (Ti3+ /Ti: FNP 34.9% vs conventional 23.5%). Notably, even at a comparable size (~400 nm), FNP-TiO2 retains a higher Ti 3+ /Ti of 31.0%, suggesting a process contribution beyond the pure size effect. Meanwhile, the defect-enriched TiO 2 shows a band-gap narrowing (FNP: 3.22 eV vs conventional: 3.32 eV) together with improved charge separation and, more importantly, the FNP-TiO2 achieve an inactivation rate of 100% against both S. aureus and E. coli under UV irradiation, higher than conventional TiO2 and commercial P25. This work provides a simple, mild and easy-to-operate strategy that is compatible with continuous operation for the practical preparation of inorganic photocatalysts for disinfection.