| Summary: | A bifunctional magnetic Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>@TiO<sub>2</sub> or MS-TiO<sub>2</sub> antimicrobial nanocomposite was prepared based on simple sol-gel methods with common equipment and chemicals. Reaction pH was found to influence the TiO<sub>2</sub> upload in the nanocomposite. The alkaline condition produced the greatest TiO<sub>2</sub> upload, while the acidic condition the least. Annealing at 300 °C turned the as-synthesized amorphous TiO<sub>2</sub> into one with high content of anatase, the most photoactive form of TiO<sub>2</sub>. Irradiated by 365 nm UV light, a sample of 30 mg/mL of annealed nanocomposite containing 12.6 wt.% Ti was shown to be able to completely eradicate 10<sup>4</sup> CFU/mL of the laboratory-grown <i>E. coli</i> within 25 min, 25 min faster than the control when the 365 nm UV light was employed alone. The nanocomposite demonstrated consistent antimicrobial performance over repeated uses and was easily recoverable magnetically due to its high magnetization value (33 emu/g). Additionally, it was shown to reduce the bacterial count in a real surface water sample containing 500–5000 CFU/mL of different microbes by 62 ± 3% within 30 min. The irradiating 365 nm UV light alone was found to have generated little biocidal effect on this surface water sample. The nanocomposite is promising to serve as an effective, safe, and eco-friendly antimicrobial agent, especially for surface water disinfection.
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