A facile method for synthesis of silver and Fe₃O₄ reusable hierarchical nanocomposite for antibacterial applications

Silver (Ag) nanoparticles are effective disinfectants that offer a broad-spectrum of antibacterial activities. However, concerns about releasing Ag-based disinfectants into environment have significantly limited their large-scale applications. In this study, a facile and environmentally benign method was developed to grow Ag nanoparticles on polydopamine-functionalized Fe₃O₄ particles, forming a hierarchical Fe₃O₄-polydopamine-Ag nanocomposite. The polydopamine layer was coated on the surface of the Fe₃O₄ particles via self-polymerization under ambient conditions; it subsequently facilitated the formation of Ag nanoparticles from [Ag(NH₃)₂]⁺ and provided anchoring sites for the immobilization of the Ag nanoparticles. The nanocomposite presented excellent antibacterial activities against both Gram-negative (Escherichia coli) and Gram-positive(Staphylococcus aureus) bacteria, with respective minimum inhibitory concentration as 40 and 60 μg/mL, respectively. Furthermore, the nanocomposite can be separated and recovered magnetically, avoiding environmental contamination and enabling particle reuse. Recycling tests showed that over 60% of the original antibacterial activity of the particles was retained after 6 cycles of reuse.